The following are the most commonly used physics databases. For other physics related databases, see here.

arXiv.org e-Print Archive
arXiv provides open access to electronic pre-prints in Astrophysics, Physics, Mathematics, Computer Science, Quantitative Biology, Quantitative Finance and Statistics.

INSPEC
Coverage: 1969-present. INSPEC indexes and abstracts serials, conference proceedings, standards and reports in the physical sciences, electrical engineering & computer science.

Web of Science
Web of Science is a multidisciplinary citation database that provides access to the journals and conference proceedings in the sciences, social sciences, arts, and humanities, with coverage to 1900.

inSPIRE (Stanford Public Information Retrieval System (SPIRES) High Energy Physics (HEP) Database
INSPIRE was developed by a collaboration of the physics labs at CERN, DESY, Fermilab and SLAC. Focused on the High Energy Physics (HEP) information, INSPIRE combines the successful SPIRES database content, curated at DESY, Fermilab and SLAC, with the Invenio digital library technology developed at CERN. INSPIRE provides several options for searching high-energy physics related articles, including journal papers, preprints, e-prints, technical reports, conference papers and theses, comprehensively indexed by the SLAC and DESY libraries since 1974.

SPIE digital library
The SPIE Digital Library is the most extensive resource available on optics and photonics, providing unprecedented access to more than 230,000 technical papers from SPIE Journals and Conference Proceedings from 1990 to the present. More than 17,000 new research papers are added annually.

SpringerMaterials
SpringerMaterials is based on the Landolt-Bèornstein New Series, the unique, fully evaluated data collection in all areas of physical sciences and engineering. SpringerMaterials also comprises the Dortmund Data Bank Software & Separation Technology, a Database on Thermophysical Properties and the Linus Pauling Files, a Database on Inorganic Solid Phases and chemical safety data.

techXtra
Provides a way to search across databases for articles, books, websites, industry news, job announcements, technical reports, technical data, full text eprints, current research, teaching and learning resources and more in engineering, mathematics and computing.