doai.io, oadoi.org und Open Access Button sind drei DOI-Suchdienste, die nach Open Access abgelegten Volltexten eines Artikels suchen (via Alexandria Blog bzw. bjoern.brembs.net):
«You can copy and paste the digital object identifier (DOI) of any article into services which locate a freely available version for you. DOAI and oaDOI search preprint archives, researchgate or institutional repositories for accessible versions. (…)
The latest version of the Open Access Button also retrieves publicly available versions of paywalled articles, much like DOAI or oaDOI. However, it comes with a critical improvement over these two services: it allows you to send a request for any articles that isn’t already covered and the OAButton team will try to make it available. In that way, the OAButton not only provides you with the articled, but also expands the coverage of publicly accessible research.»