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