Google and Google Scholar - Google Scholar indexes open access articles, identifying them within a results list with a green arrow. While not all articles found on Google or Google Scholar include free full text, Google searches many open access repositories in addition to proprietary content.
BASE - Bielefeld Academic Search Engine indexes academically relevant web resources from over 2000 sources. It was created and developed by Bielefeld University Library.
CORE - Find Open Access research papers from data providers from all over the world including institutional repositories, subject-repositories and journal publishers.
Open Access Theses and Dissertations (OATD) - OATD is a discovery service intended to improve the ability to put researchers and scholars in touch with the valuable and unique Open Access content. OATD does not index or redistribute any document's full text.
OpenAire - Search repositories and OA journals from across Europe and the world.
IDEAS/RePEc - Internet Documents in Economics Access Service (IDEAS) for Research Papers in Economics (RePEc) includes open access working papers, book chapters and software components. The service has been made possible through the collaborative effort of volunteers worldwide.
