IOPscience is an online service for all journal content published by the Institute of Physics. It contains more than 300,000 articles, from 1874 to the present day. Also includes pre-prints from eprintweb.org (a free service, based on the arXiv.org at Cornell University), and editorial and news from IOP community websites.
CRC Handbook of Chemistry and Physics is a major source of chemical and physical property data. It includes information on elements, inorganic compounds, organic compounds, physical constants, units and conversion factors, symbols, and nomenclature.