(edit)
ChemSpider NIST Chemistry Web Book NIST Atomic Spectra Database ATcT Active Thermochemical Tables NIST Basic Atomic Spectroscopy Database NIST Chemical Kinetics Database GAPHYOR A Database on Properties of Atoms, Molecules, Gases and Plasmas, including Chemical Reactions CODATA - Fundamental Physical Constants Conversion of Units (German website) WebElements Periodic Table ChemFinder Free database form CambridgeSoft Sheffield Chemdex A directory of chemistry on the WWW US Patent and Trademark Office
Biblioteca di Ateneo - Università di Trento