CRC Handbook of Chemistry and Physics
– Provides broad coverage of all types of physical science data--melting points, boiling points, heat capacity, vapor pressure, etc.--commonly encountered by scientists and engineers.
Google Scholar
– Journal articles, books, and other resources across many subjects. Provides a "cited by" feature to indicate other papers containing a source paper as a reference.
PubMed
– Journal articles covering biomedical research and the clinical sciences including nursing, dentistry, veterinary medicine, pharmacy, allied health, and pre-clinical sciences. Also good coverage of literature in cellular and molecular biology and biochemistry. Mid 1960's to present.
Royal Society of Chemistry
– Full text of over 45 journals published by the Royal Society of Chemistry. The journals cover all aspects of chemistry. 1841 to 1996.