ScienceDirect
http://www.sciencedirect.com/
SpringerLink
http://link.springer.com/
Academic Search Premier
http://www.ebscohost.com/academic/academic-search-premier
ProQuest Central
http://www.proquest.com
Web of Science
http://www.thomsonreuters.com
Free Medical Journals
http://www.freemedicaljournals.com/