The National Library of Medicine free article search engine, containing article references from MEDLINE, PreMEDLINE, OLDMEDLINE, plus some publisher-supplied and out of scope citations from certain general science and chemistry journals. To run a cited reference search on an article found in PubMed, copy and paste the PMID article Identifier here.
JSTOR is a full-text database consisting of the Arts and Sciences I, II, III, IV, Complement, Ecology & Botany and General Science Collections which provide access to the back files of over 300 scholarly journals from the sciences, social sciences and arts and humanities.
Environment Complete covers agriculture, ecosystem ecology, energy, natural resources, marine & freshwater science, geography, environmental technology & law, urban planning and more. It includes full-text from over 920 journals and 190 monographs.
Zoological Record indexes and abstracts worldwide zoological literature. All major areas of zoology are represented, including: behavior, ecology, evolution, habitat, nutrition, parasitology, reproduction, taxonomy, and zoogeography.
SciFinder Scholar contains a comprehensive database of chemical and chemical engineering literature including patents (1907 - date, with selected coverage back to 1878) and the CAS Registry with information on 18 million substances. Also useful for biotechnology, toxicology, environmental science, medicine, food science and nuclear science.