MEDLINE/PubMed, Scopus, EMBASE, Chemical Abstracts Service/SciFinder, ChemWeb, Google Scholar, EMCare, Genamics JournalSeek, MediaFinder®-Standard Periodical, Directory, PubsHub, J-Gate, CNKI Scholar, Suweco CZ, TOC Premier, EBSCO, Ulrich's Periodicals Directory, JournalTOCs and Dimensions.