List of major search engines in the academic Open Access world:
CORE – COnnecting REpositories: the largest aggregator of Open Access scientific publications from around the world.
Dart Europe: portal founded in 2005 as a partnership of national and university libraries and consortia to improve global access to European research theses.
DOAJ – Directory of Open Access Journals: indexes diamond and gold Open Access and peer-reviewed scientific journals.
DOAB – Directory of Open Access Books: indexes more than 80,000 peer-reviewed open access academic books published by some 780 publishers.
Lens: open-access platform that collects patent data from different repositories worldwide and integrates it with bibliographies and search data (from PubMed, CrossRef, Microsoft Academic).
OpenAIRE: provides access to publicly funded European Commission Open Access scientific literature by indexing metadata or full-text of contributions registered in institutional or thematic repositories, Open Access journals and publishers, dataset repositories, service aggregators such as DataCite, BASE, DOAJ.
OpenAlex: open source database developed by the non-profit organisation OurResearch and distributed under a CC0 open domain licence. It indexes academic works based on open data with the goal of inclusiveness.
Open Knowledge Maps: it graphically displays scientific works by grouping them into maps based on the research area. Open Knowledge Maps only considers scientific works provided with abstracts, because this is the element that allows automatic analysis of contents. Another requirement is the indexing of contributions in BASE, PubMed or OpenAire, while both open access contributions and those in publications that require a subscription are included.
Science open: is a platform that provides access to Open Access publications together with a range of services (e.g. usage metrics).