PubMed
"PubMed, a service of the National Library of Medicine, includes over 15 million citations for biomedical articles back to the 1950's. These citations are from MEDLINE and additional life science journals. PubMed includes links to many sites providing full text articles and other related resources."
The link address is: http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed