arXiv, an open-access e-print service for the sciences, offers more than 100,000 articles in physics. Owned by Cornell University, arXiv is partially funded by the National Science Foundation.

Maintained by the National Radio Astronomy Observatory and others of the AstroWeb Consortium, AstroWeb provides a rich index of links and resources: telescopes and other "observing" resources, data resources, publication resources, organizations, research areas, software resources.

The collection of databases at the website of the Harvard-Smithsonian Center for Astrophysics includes the Chanda X-Ray Center atomic database for X-ray plasma spectral modeling, HITRAN molecular spectroscopy database, and others.

This site, derived from books by astrophysicist Eric Chaisson, divides the history of the universe into 8 periods: from particulate and galactic to biological and future. Each section has fully developed text plus links. Good resource for undergraduate cosmology.

DOAJ is a fast-growing collection of "free, full-text, quality-controlled scientific and scholarly journals" in a broad range of subjects and languages. See the Institute of Physics' New Journal of Physics which has one of the highest impact factors in physics.

EurekAlert!, an online news service of AAAS, the science society, provides searchable research and awards news from universities, journals, government agencies, corporations, and other organizations.

The successor to Spires, inSpire offers articles, news, citation statistics, plus new features such as personal author pages, fulltext search, a blog, and the ability to claim your papers. The site is run by CERN, DESY, Fermilab, and SLAC (Stanford Linear Accelerator Center).

Entrée to Berkeley Lab's six physics sections: Electroweak Symmetry Breaking, Dark Matter - Dark Energy, International Linear Collider Physics, Theoretical Physics, Quark and Lepton Flavor Physics, Particle Physics [see PDG Review of Particle Physics below].

Lawrence Livermore pursues nuclear energy research as well as research in nanotechnologies and in a broad range of other focused and interdisciplinary areas. Also at the site: the journal Science & Technology.

National Institute of Standards and Technology's (NIST) Physical Reference Data has eight sections: 1. physical constants, 2. atomic spectroscopic data, 3. molecular spectroscopic data, 4. ionization data, 5. X-ray and gamma-ray data, 6. nuclear physics data, 7. condensed matter physics data, 8. other NIST data.

NIST's Physics Laboratory provides measurements and standards nominally aimed at U.S. industry, but also useful to academic researchers. The Physics Laboratory has a number of divisions: from Quantum Physics to Biomolecular Physics. Also check the physics portal.

Particle Data Group (PDG), an international collaboration, reviews particle physics and related areas of astrophysics. PDG also compiles and analyzes data. The site includes tables, conservation laws, educational sites and tools, and reviews.

Includes physics news, jobs, a blog, products, symposia and other events, plus selected articles from the site's proprietary online PhysicsWorld. From IOP (Institute of Physics).

PhysLink.com includes physics and astronomy resources for education, research, and reference. Aimed more at undergraduates and physics newcomers, the site includes news from national laboratories, NASA, NIST; tables of physical constants; HEP databases; links to professional societies and institutes; and educational resources.

These well-organized resource links from NASA's High Energy Astrophysics Science Archive Research Center (HEASARC) include information on astronomy, astrobiology, astronomical images, space programs, organizations, and educational resources.

The WWW Virtual Library: Physics includes the following subject areas: space physics, biophysics, beam physics, nuclear, laser, optical, acoustics and signal processing, and plasmas. Links lead to resources in research, glossaries, FAQs, conferences, etc.