Medline and PubMed

http://medline.cos.com/
Comprehensive source for life sciences and biomedical bibliographic information. Free access to abstracts, but full text requires registration.  Yearly registration cost.C

http://www.nlm.nih.gov/databases/freemedl.html
NLM offers PubMed and Internet Grateful Med, two free systems to search MEDLINE

                                                                 http://www.nlm.nih.gov/pubs/web_based.html
                                                                   PubMed and Internet Grateful Med Training Manuals

                                                                 http://www.nlm.nih.gov/pubs/factsheets/netresources.html
                                                                 National Library of Medicine Internet-Accessible Resources