PubMed, a service of the U.S. National Library of Medicine, contains over 17 million citations from MEDLINE and other life science journals. Coverage goes back to the 1950s. PubMed also includes links to full-text articles and MeSH subject headings.
A large research database for nursing and allied health literature. Lots of full text, cited reference lists, author affiliation info, evidence-based care sheets, and more.