Cochrane Reviews section of this database contains systematic iterature reviews in health care. The Cochrane Central Register of Controlled Trials reports randomised and quasi-randomised controlled trials.
U.S. National Library of Medicine search engine that searches HSDB (Hazardous Substances Data Bnak), Toxline, ChemIDplus, LactMed, DART (Developmental and Reproductive Toxicology Database), TOXMAP, TRI (toxics Relsease Inventory), CTD (comparative Toxicogenomics Database, Household Products Database, Haz-Map, IRIS (integrated Risk Information System), ITER (International Toxicity Estimates for Risk), ALTBIB (resources on Alternatives to the Use of Liver Vertebrates in Biomedical Research and Testing).
NDLTD - The Networked Digital Library of Theses and DIssertations is an International organization promoting the adoption, creation, use, dissemination, and preservation of electronic theses and dissertations. The Global ETD search engine is where you can search these resources.