SAO/NASA Astrophysics Data System
external page NASA Astrophysics Data System (ADS) is a virtual library portal for researchers in the fields of Astronomy and Physics, which is maintained at the Harvard-Smithsonian Astrophysical Observatory (SAO) on behalf of NASA.
Altogether, the bibliographical databases for astronomy and physics contain about 13,5 million entries (as of 2020) with about 250 000 new entries every year.
Aside from literature searches, the database can be queried for bibliometry and analytics.
Note
In many cases the astronomical literature has been scanned in back to the first volume of the journal. The results are accessible in full-text versions. The physics literature goes back for varying periods depending on the collaborative partnerships (for example, with CrossRef since 2008).
Access
Using ADS services is free of charge; however, access to the full texts depends on whether the search location has (where applicable) appropriate licences for the publications in question.
Tutorials
You can learn the basic principles from the resources maintained at:
