CORE: CORE is a multidisciplinary aggregator of OA research. CORE has the largest collection of OA articles available. It allows users to search more than 219 million OA articles. While most of these link to the full-text article on the original publisher's site, or to a PDF available for download, five million records are hosted directly on CORE.
Directory of Open Access Journal: A multidisciplinary, community-curated directory, the Directory of Open Access Journals (DOAJ) gives researchers access to high-quality peer-reviewed journals. It has archived more than two million articles from 17,193 journals, allowing you to either browse by subject or search by keyword.
arXiv e-Print Archive : The arXiv e-Print Archive is run by Cornell University Library and curated by volunteer moderators, and it now offers OA to more than one million e-prints. There are advisory committees for all eight subjects available on the database.
JURN: A multidisciplinary search engine, JURN provides links to various scholarly websites, articles, and journals that are free to access or OA. Covering the fields of the arts, humanities, business, law, nature, science, and medicine,
EBSCO Open Dissertations : EBSCO Open Dissertations is a collaboration between EBSCO and BiblioLabs to increase traffic and discoverability of ETD research.
Google Scholar: Google Scholar is a search engine for academic work. Not everything listed on Google Scholar will be freely available in full. But it is a good place to start if you’re looking for a specific paper; many papers can be downloaded for free.
UC Santa Barbara databases