| Astrophysics (Index) | About |
The Astrophysics Data System (ADS, aka the SAO/NASA Astrophysics Data System) is an online, searchable bibliography of astrophysics, plus an archive of astronomy/astrophysics papers that includes papers back to 1900 and before. ADS is run by the Center for Astrophysics (CfA), essentially the Harvard College Observatory (HCO) and the Smithsonian Astrophysical Observatory (SAO) merged. NASA is a major funder of ADS, as part of NASA's effort to make astronomy/astrophysics data available.
I've seen the phrase Astrophysics Data Service referring to the same system: possibly it is an older name for it.