MEDLINE (Medical Literature Analysis and Retrieval System Online) is a bibliographic database of life sciences and biomedical information. It includes bibliographic information for articles from academic journals covering medicine, nursing, pharmacy, dentistry, veterinary medicine, and health care. MEDLINE also covers much of the literature in biology and biochemistry, as well as fields such as molecular evolution.
Compiled by the United States National Library of Medicine (NLM), MEDLINE is freely available on the Internet and searchable via PubMed and NLM's National Center for Biotechnology Information's Entrez system.
The database 
The database contains more than 21.6 million records from 5,582 selected publications covering biomedicine and health from 1950 to the present. Originally the database covered articles starting from 1965, but this has been enhanced, and records as far back as 1950/51 are now available within the main index. The database is freely accessible on the Internet via the PubMed interface and new citations are added Tuesday through Saturday. For citations added during 1995-2003: about 48% are for cited articles published in the U.S., about 88% are published in English, and about 76% have English abstracts written by authors of the articles.
MEDLINE uses Medical Subject Headings (MeSH) for information retrieval. Engines designed to search MEDLINE (such as Entrez and PubMed) generally use a Boolean expression combining MeSH terms, words in abstract and title of the article, author names, date of publication, etc. Entrez and PubMed can also find articles similar to a given one based on a mathematical scoring system that takes into account the similarity of word content of the abstracts and titles of two articles.
MEDLINE functions as an important resource for biomedical researchers and journal clubs from all over the world. Along with the Cochrane Library and a number of other databases, MEDLINE facilitates evidence-based medicine. Most systematic review articles published presently build on extensive searches of MEDLINE to identify articles that might be useful in the review. MEDLINE influences researchers in their choice of journals in which to publish: few biomedical researchers today consider publishing in a journal not indexed by MEDLINE, because other researchers would not find (or cite) their work.
Inclusion of journals 
More than 5,500 biomedical journals are indexed in MEDLINE. New journals are not included automatically or immediately. Selection is based on the recommendations of a panel, the Literature Selection Technical Review Committee, based on scientific scope and quality of a journal. The Journals Database (one of the Entrez databases) contains information, such as its name abbreviation and publisher, about all journals included in Entrez, including PubMed.
PubMed usage has been on the rise since 2008. In 2011, PubMed/MEDLINE was searched 1.8 billion times, up from 1.6 billion searches in the previous year.
Searching MEDLINE effectively is a learned skill; untrained users are sometimes frustrated with the large numbers of articles returned by simple searches. Counterintuitively, a search that returns thousands of articles is not guaranteed to be comprehensive.
Unlike using a typical Internet search engine, PubMed searching of MEDLINE requires a little investment of time. Using the MeSH database to define the subject of interest is one of the most useful ways to improve the quality of a search. Using MeSH terms in conjunction with limits (such as publication date or publication type), qualifiers (such as adverse effects or prevention and control), and text-word searching is another. Finding one article on the subject and clicking on the "Related Articles" link to get a collection of similarly classified articles can expand a search that yields few results.
Online access 
- GoPubMed - explore PubMed/MEDLINE with Gene Ontology
- HubMed - an alternative interface to the PubMed medical literature database.
- eTBLAST - a natural language text similarity engine for MEDLINE and other text databases.
- Twease - an open-source biomedical search engine
See also 
- "Data, News and Update Information". NLM Systems. 2009-03-30. Retrieved 2009-04-13.
- "Number of Titles Currently Indexed for Index Medicus® and MEDLINE® on PubMed®". NLM. 2011-11-15. Retrieved 2012-03-20.
- "PubMed related articles: a probabilistic topic-based model for content similarity". BMC Bioinformatics (2007) 8:423. 2007-10-30. Retrieved 2011-05-30.
- "MEDLINE Journal Selection Fact Sheet". LSTRC. Retrieved 2009-04-13.
- "PubMed Tutorial - Building the Search - Search Tools - Journals Database". Retrieved 2009-09-06.
- "Key MEDLINE® Indicators". NLM. 2012-02-06. Retrieved 2012-03-20.
- iPubMed Search MEDLINE/PubMed through interactive and fuzzy search
- PubMed Tutorials
- MEDLINE Journal Selection