You can search open access resources in Helka database by choosing 'Open Access' under Availability.
In Helda you can find theses, dissertations, research articles and institutional series, as well as teaching and research material produced by the departments and faculties of the University.
The Helda Open Books collection contains open access books produced by researchers and teachers of the University of Helsinki. The collection can be found in Helda, the University of Helsinki digital repository.
DOAB (Directory of Open Access Books) is the most extensive critical directory of scientific Open Access books. For those interested in Open Access publishing, DOAB website contains a useful listing of subject areas including information about the publishers.
OAPEN-database contains freely available scientific monographs, mainly in the humanities and social sciences. Open Access eBooks on JSTOR contains openly available academic monographs, mainly in the field of humanities and social sciences.
You can install a browser extension or a plug-in to facilitate finding articles which are open access.