SLAC SPIRES database
SPIRES plot
LANL e-print archives,
arXiv.org
KEK KISS database
CERN Document Server
American Physical Society
American Institute of Physics
Links to some journals
MZ-TH publications,
Top-cited MZ-TH papers
MATH database
MathSciNet
Physics Direct (Elsevier)
Particle Data Group
Eric Weisstein's World of Mathematics
Handbook of Differential Equations
Scientific.ru