Astrophysics Data System (ADS):
> http://esoads.eso.org
Astrophysics Source Code Library (ASCL):
> http://ascl.net/
arXiv (E-print service in the fields of physics, mathematics, etc. astro-ph can be found here.):
> http://arxiv.org/
NASA/IPAC Extragalactic Database (NED):
> http://nedwww.ipac.caltech.edu/
Strasbourg astronomical Data Center (CDS):
> http://cds.u-strasbg.fr/
The Extrasolar Planets Encyclopaedia:
> http://exoplanet.eu/