High Quality Content by WIKIPEDIA articles! The Astrophysics Data System (usually referred to as ADS), developed by the National Aeronautics and Space Administration (NASA), is an online database of over eight million astronomy and physics papers from both peer reviewed and non-peer reviewed sources. Abstracts are available free online for almost all articles, and full scanned articles are available in Graphics Interchange Format (GIF) and Portable Document Format (PDF) for older articles. New articles have links to electronic versions hosted at the journal`s webpage, but these are typically available only by subscription (which most astronomy research facilities have). It is managed by the Harvard–Smithsonian Center for Astrophysics.