MEDLINE is the U.S. National Library of Medicine’s (NLM) premier bibliographic database covering the fields of medicine, nursing, dentistry, veterinary medicine, the health care system, and preclinical sciences. MEDLINE contains citations and abstracts from more than 5,000 international biomedical journals. There are over 15 million records in the database, dating back to the mid-1950s. MEDLINE can be accessed through the PubMed interface.
PubMed was developed by the National Center for Biotechnology Information at the National Library of Medicine. PubMed provides free access to MEDLINE. Other PubMed services include: links to other related sources, links to related articles, and the ability to store collections of citations, and save and automatically update searches.
Also, the National Library of Medicine offers an extensive PubMed Tutorial.