These pages are based on an appendix from Katcher
BS. MEDLINE: a guide to effective searching in PubMed and
other interfaces. 2nd ed. San Francisco: Ashbury Press; 2006.
They contain links (not possible from the printed pages -- see
sample book pages) and are continually updated.
MEDLINE is a bibliographic database that is produced by the National
Library of Medicine. Because MEDLINE is so large (more than 13
million records) and so exquisitely organized, it is generally
considered to be the premiere index to the world's medical literature
of biomedical journal articles. PubMed
is the most frequently used version of MEDLINE.
These pages describe a number of MEDLINE-related resources on
the Web. Some of these are within the National
Library of Medicine’s Web site, which is among the most
important health sites on the Web.
The text below has also been chunked into smaller pages, with
navigation on the left.
MEDLINE from the National Library of Medicine
Library of Medicine, which produces MEDLINE and licenses it
to other vendors, provides free access on its Web site:
If you are not already using MEDLINE, PubMed
is the best place to start (unless you are starting out at an
academic institution that uses Ovid).
is very fast, easy to use, and has excellent on-line MeSH help.
PubMed provides context-specific links to other Entrez
databases and to resources beyond the National Library of
Medicine. Among experienced searchers not using a particular university-based
MEDLINE interface such as Ovid, PubMed has become the de facto
PubMed is MEDLINE with additional citations that have not yet
been indexed for MEDLINE or are beyond its scope, as well as citations
from OLDMEDLINE (pre-1966 citations). An NLM Fact Sheet explains
between MEDLINE and PubMed.
For serious searches in any MEDLINE interface, you will want
to give some thought to the MeSH that best describe the concepts
you are researching, and PubMed's MeSH
Database is particularly helpful in this regard. In fact,
you can even construct your search strategy from within this well-designed
MeSH Database, which can be reached from a link on the PubMed
Late in 2009, a new PubMed interface was rolled out. This new
interface allows easier access to the features described in my
book. In particular, the page that displays your search results
includes a box (search details) that shows how your query was
processed. For more information about each element, see PubMed
Help or NLM's more detailed MEDLINE/PubMed
Data Element Descriptions information page. (And, yes, I'm
glad the interface-specific text in my book was limited to Appendix
PubMed's Clinical Queries and Topic-Specific Queries filters
(linked from PubMed's home page) provide a handy means for starting
a search. After an initial search, you will probably want to construct
additional search strategies based on what you have learned.
To get the most out of this interface, take a look at PubMed’s
Tutorials (linked from the PubMed home page).
is intended for users who come to the National Library of Medicine
without knowing what is there or how best to search for it. NLM
Gateway provides a single interface for searching in a number
of the Library’s resources, including PubMed, MedlinePlus
(described below, under “Health Information on the Web”),
the NLM Catalog, ClinicalTrials.gov, DIRLINE (Directory of Health
Organizations), and others. NLM Gateway's most remarkable feature
is that it searches simultaneously within multiple retrieval systems.
Its Find Terms button leads you to information about the Medical
Subject Headings (MeSH) that might encompass the terms you enter.
If you know that what you are looking for is in MEDLINE, then
PubMed is a more appropriate interface, because its limits feature
is specific to MEDLINE. (The limits button in the NLM Gateway
is for categories, such as journal articles, consumer health,
books/serials/AV, or databanks.) However, NLM Gateway provides
access to much more information than can be found in MEDLINE.
A full description of what's available from NLM Gateway can be
found on its "About" page.
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Other Interfaces to MEDLINE
(public site) and Ovid
(many institutions) are the most widely used, but there are other
interfaces to MEDLINE on the Web. Some are free, some are free
with registration, and some are fee-based. A sampling: Medscape
(a Web site for clinicians), BioMedSearch.com
(combines PubMed with other sources), Infotrieve
(specializes in document delivery), and PaperChase.
If you are affiliated with a major teaching institution, you
can probably apply for a remote access account that will make
your home or office computer screen look like the one in the library.
Such libraries generally use either the Ovid interface to MEDLINE
or a customized version of PubMed that has been tailored to best
serve the library's patrons. In addition, many university libraries
offer full-text access to a growing number of on-line journals
for which they have paid subscriptions. (See Journals on the Web.)
For copyright reasons, remote access is limited to those with
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Medical Subject Headings (MeSH)
Deliberate and careful use of Medical Subject Headings (MeSH)--the
National Library of Medicine's controlled vocabulary for health-related
concepts--is a major contributor to complete and precise MEDLINE
An excellent publicly available resource for using MeSH is the
Database. A link to this MeSH Database can be found on the
search screen. The MeSH Database home page includes links to three
excellent tutorials. (And there's more
MeSH information on the NLM Distance Education Web site.)
Use the MeSH
Database to determine what concepts from this controlled vocabulary
best describe your search topic. PubMed search strategies can
be constructed from within this database.
When you find an interesting article in PubMed,
use the Citation display to see the MeSH terms that were used
to index it. Each of these MeSH terms (some of them with subheadings,
some of them as Major MeSH) will appear as a hyperlink. You can
use these links to learn more about these MeSH. You can also use
them as the basis for a new search (selected MeSH terms will be
searched exactly as they were applied to the citation, with subheadings,
etc). You may see additional Entrez database search links options
for some terms. If there are substances in the Citation display,
they may include links to PubChem
Other MeSH resources from the National Library of Medicine include
what might be called a Medical Subject Headings Home
Page, with links to a number of other MeSH-related resources,
including a Fact
Sheet with detailed information about MeSH and a MeSH
Browser. (For most users, the MeSH
Database will be more useful.)
The National Library of Medicine's Unified
Medical Language System (UMLS) links other controlled vocabularies
to MeSH. Among these are RxNorm
(standard names for clinical drugs, which can be searched with
a downloadable browser called RxNav),
CT (the College of American Pathologists' Systematized Nomenclature
of Medicine--Clinical Terms), and more than 100 other source vocabularies.
PubMed and the Entrez MeSH Database use the Unified Medical Language
System to link entry terms to MeSH.
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The National Library of Medicine's PubMed
Tutorial (a page with links to animated tutorials) will provide
you with an excellent overview of PubMed and the MeSH vocabulary.
This frequently updated page now includes more than a dozen animated
quick tours. Check out this wonderful resource.
Whether you normally use PubMed or another source of MEDLINE,
the MeSH Vocabulary portion is worth reviewing. The three MeSH
tutorials can also be accessed from PubMed's MeSH
Many institutional libraries use Ovid MEDLINE and have created
their own web-based tutorials (also of value for users of PubMed
and other interfaces to MEDLINE).
If your institutional library offers MEDLINE classes, take one.
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In-Process Citations in PubMed
It takes some time for articles to be indexed for MEDLINE. High-profile
journals like JAMA or the New England Journal of
Medicine are indexed within days, but other journals take
weeks to months. As citations are received from publishers, before
they are indexed for MEDLINE, they are placed in PubMed
and are available from the default query box. These citations
are based on the electronic files received from the publisher
and are marked with one of two tags: "PubMed - as supplied
by publisher" (as they are added) or, more commonly, "PubMed
- in process" (accuracy of bibliographic data being reviewed
and MeSH vocabulary being assigned, if the article is within the
scope of MEDLINE).
If you search by author, journal, or unqualified words, these
in-process citations will appear at the top of your search results.
Further down you will see citations whose Medical Subject Headings
(MeSH), Publication Types, Substance Names, and other indexing
elements have been added. These are tagged as "PubMed - indexed
While it is generally preferable to use all of the indexing features
that are built into MEDLINE, you may wish to augment your searches
with in-process citations.
There are several ways to keep track of in-process citations.
If you are interested in a particular journal, you can see its
articles as they are added to PubMed. Just enter the full name
or its official abbreviation (for help see the Journals
Database). If you subscribe to a journal, you may be able
to have the table of contents e-mailed to you upon publication.
Most journals publish the table of contents of the most recent
issue on their Web site (see Journals
on the Web). You can also store a pre-constructed search strategy
NCBI" (a PubMed service) and have the results sent to
you by e-mail.
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Journals on the Web
Many journals are available on the Web in full text, but free
access is often limited to subscribers. Most academic medical
center libraries maintain online subscriptions for students and
faculty (Links to full-text journal articles can be found within
Ovid or PubMed searches, depending on the institution).
When you see the
icon (green banner) in the Summary display of your PubMed search
results, it means you can see the full text article for free.
An increasing number of journals provide free full text access
to all or some of their articles, sometimes within six months
or a year after initial publication. Here are some additional
sources of free full text articles:
The National Library of Medicine's PubMed
Central is an archive of free full-text articles. Articles
in PubMed Central are sometimes also available from the publishers'
Web sites, but those in PubMed Central are published in a standard
format to insure their permanence on the Web.
When you see the
icon (orange and green banner) in the Summary display of your
results, it means that the article can be found in PubMed
Central. If you like, you can use the "limits" tab
in PubMed and, under "subsets," limit your searches
to PubMed Central.
Open Access Journals
An increasing number of journals are developing publishing models
that facilitate free access to full text articles. Some institutions,
such as the University of California at San Francisco, encourage
researchers to consider publishing their work in open
access or reasonably priced journals as means of protecting
scholarly communication. Here are some resources:
Open Access Journals (DOAJ)
of Science (PLoS)
essay in the New England Journal of Medicine (April 13,
2006), discusses the issue of open access journals.
Finding Journal Names
If you need help in finding the name of a journal, try the Entrez
Journals Database. The opening page also provides the means
to find information about Entrez journals that have links
to full-text web sites.
Articles Not Available on the Web
Much of what you find in MEDLINE will not be available on the
Web as a full-text document, but you can still obtain a copy if
you do not have convenient access to a medical library. The National
Library of Medicine's Loansome Doc allows you to order documents
after first establishing an agreement with a nearby medical library.
Detailed information about Loansome
Doc is available on the National Library of Medicine’s
Web Site, in the Fact Sheets section. Links to Loansome Doc are
built into PubMed and NLM Gateway. Documents are available in
a variety of forms (mail, fax, pickup, or internet), depending
on the capacity of the local library. Charges vary, also depending
on the local library.
If you have an My
NCBI account (a free PubMed service), you can configure it
for other document delivery services (Loansome Doc is the default).
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Library of Medicine offers a wide array of web-based resources
in addition to PubMed/MEDLINE, as can be seen from their home
page and from their list of NLM
Databases & Electronic Resources. At this writing, there
are 70 such resources -- everything from accurate and clearly
written health information for consumers (MedlinePlus,
which is also
available for mobile devices) to the NLM
Catalog (books, audiovisuals, journals, and electronic resources,
all indexed with MeSH) to the Visible
Human Project to a collection of online books (Bookshelf)
to the original
Index Catalog of the Library of the Surgeon General's Office
from the History of Medicine to the National Center for Biotechnology
Information (NCBI)'s Entrez
You can save your PubMed search strategies by creating a free
NCBI" account (a PubMed service). You can even schedule
regular repeat searches and receive the results via e-mail.
Technical Bulletin publishes information about changes as
they occur, and back issues are well indexed. For example, a recent
issue announced the release of RxNav,
a downloadable browser for RxNorm,
the NLM repository of standard names for clinical drugs.
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Health Information on the Web
There's a tremendous amount of health information on the Web,
but most of it suffers from two basic problems:
1. It varies widely in quality. When you find a new site, look
to see who sponsors it, and determine its intended audience.
Is it current? What is its evidence base? The Medical Library
Association has a similar
list of questions on its site. MedlinePlus has a useful
page of links, entitled Evaluating
2. Unlike MEDLINE and other structured databases, most of the
Web is completely unorganized. Search engines look at all the
words on a Web page, as well as the links to and from the Web
page (and, in some cases, additional criteria) for determining
its ranking in response to a query. The ranking of "hits"
from a search may or may not be suitable to your needs. Sometimes
it's helpful to start elsewhere than Google.
Here is a sampling of useful places to go:
Interesting Search Tools
In addition to its well-known main search page, Google offers
a variety of specialized search pages. Google
Scholar uses Google's search algorithm, but its results are
limited to articles and books of scholarly interest. According
to Google, you can use it "to find articles from a wide variety
of academic publishers, professional societies, preprint repositories
and universities, as well as scholarly articles available across
the web." You can set Scholar's Preferences
to show links within your affiliated medical library.
Searches for health information in Scholar will often point to
abstracts. When you find useful articles in Scholar, determine
how they were indexed for PubMed (MeSH
terms), and do another search in PubMed using these terms.
Why? Because of the way that Scholar ranks hits, it is likely
to miss the latest papers, and -- more importantly -- it lacks
PubMed's ability to conduct Boolean searches based on the concepts
that are represented by MeSH terms. You can see the MeSH terms
for an article by displaying it in the "citation" format.
Google Scholar, still in beta at this writing, is attracting
a lot of attention from medical librarians (see Banks
2005 and Henderson
limits its results to scientific information. Its default mode
searches both journals and the web, and its results page provides
a link to each search. Less well known than Google Scholar, this
is a powerful tool. Highly recommended.
OAIster (find the pearls...). OAIster
is the University of Michigan Digital Library's attempt at creating
a collection of freely available, previously difficult-to-access,
academically-oriented digital resources.
Of course you can search for specific practice guidelines within
MEDLINE/PubMed by limiting your search to Publication Type "Practice
Guideline" and following the links, but there are other resources
for practice guidelines:
Guideline Clearing House is the Agency for Healthcare Research
and Quality's (AHRQ) public archive for evidence-based clinical
practice guidelines. AHRQ guidelines can also be accessed from
(Health Services/Technology Assessment Text),
which is an electronic book on the National Center for Biotechnology
These are all free full text resources.
Evidence Based Medicine
Some evidence based medicine resources require a subscription,
but here is a sampling of free resources:
These sites are also useful for health professionals. The Medical
Library Association (MLA) has produced a User's
Guide to Finding and Evaluating Health Information on the Web,
which includes a list of their "top ten" most useful
consumer web sites. My own favorite is MedlinePlus,
which has links to carefully vetted health
topic pages, a serviceable medical
dictionary, links to patient drug
information sheets, and links to all the current
health news, in reverse chronological order (organized by
day). Health-related stories are a staple of the media, and we
often are questioned about them. This is a good way to find enough
information to locate the study itself.
Librarians are experts in the organization of intellectual resources
(historically, this has been books), so it is not surprising that
medical librarians have made significant attempts at organizing
medical information on the Web. Here is a sampling:
a collaborative project of health science libraries in the Greater
Midwest Region of the US and the National Library of Medicine
- The Recommended
Core Collection of Web Sites for Hospital Libraries, created
by the Camden Campus Library of the University of Medicine &
Dentistry of New Jersey, is another useful list of links.
MD is a directory of directories, organized by topic areas.
Links to more links. Compiled by Eric Rumsey at the Hardin Library
for the Health Sciences at the University of Iowa -- a very
- The National Library of Medicine (NLM) - see NLM
Resources on this Web site.
- There are many such directories, but a different approach
to using the Web is Jan's
Search Tips, which takes the form of a well-written blog.
Quite a few MEDLINE-related tips can be found in its archives.
Academic medical center libraries subscribe to a variety of Web-based
resources that can be accessed from the library (or remotely by
affiliates of the library). A sampling:
- EMBASE - a bibliographic
database with a somewhat different scope than MEDLINE. Offers
extensive coverage of the drug and biomedical literature.
- Web of Science
- A bibliographic database with excellent search capabilities
for cited reference searching.
- Cochrane Database of Systematic
Reviews - Evidence-based reviews of the clinical
of the Cochrane Reviews are free-of-charge).
- Drug Information Fulltext
- Full text access to American
Hospital Formulary Service Drug Information.
- Harrison's Online
- Full text access to Harrison's Principles of Internal Medicine.
Librarians themselves are the best resource; visit your library.
Institutes of Health (NIH) is the premier institution for
biomedical research. As you might expect, its Web site is huge.
Each of its many institutes
and centers has its own Web site. (The National Library of
Medicine (NLM), which produces MEDLINE/PubMed, is part of NIH.)
of Health and Human Services is the overall government agency
for health. Its Web site is designed for the general public. However,
it also contains links to the various NIH
institutes and centers, the Food
and Drug Administration (FDA), the Centers
for Disease Control and Prevention (CDC), the Agency
for Healthcare Research and Quality (AHRQ), and other U.S.
Government health agency Web sites.
The U.S. Government's role in biomedical research, public health,
and health care delivery has been the subject of a great deal
of literature, and it is all well indexed in MEDLINE. There are
MeSH for each of the above-named agencies. To use these in your
MEDLINE searches, go to the Entrez
MeSH Database and take a look. Here is a link to United
States Dept. of Health and Human Services within the MeSH
Public Health Sites
If you are working in public health, take advantage of Partners
in Information Access for the Public Health workforce.
Other useful public health sites:
A great deal of highly specialized health-related information
on the Web is managed by specific professional associations. Become
a member of the organizations that represent what you do.
Google's wonderfully spare search page provides a link to Google
Image Search, where you can find images to spruce up your
presentations. Less well known but more powerful for serious educational
purposes is HEAL
(Health Education Assets Library). HEAL describes itself as
"a digital library that provides freely accessible digital
teaching resources of the highest quality that meet the needs
of today's health sciences educators and learners." HEAL
is peer reviewed, and its images are organized by MeSH. The CDC
maintains a Public
Health Image Library. The National Library of Medicine maintains
from the History of Medicine.
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