IsisCB Explore is a public bibliographic search tool, from the History of Science Society and the University of Oklahoma…
“Nearly 200,000 interlinked bibliographic citations to books, chapters, articles, dissertations, and reviews from the Isis Bibliography of the History of Science 1974 to present. Annually updated.”
Rather annoyingly it misleadingly touts itself as “An open access discovery service”, when what that headline claim actually means is simply that “it’s public”.
On testing, it lacks an OA search facet on the sidebar.
On a search for electric light I tested four random articles from 54 results. One was in India, only a link to a journal home page. One was in a paywalled Taylor and Francis journal (£30 to “rent” the article for 24 hours!). Another was in a paywalled Cambridge UP Press journal (£20 access). The fourth was in a Taiwanese journal which declared “You do not currently have access to this content”.
I’m not sure how fresh the DOI Web links are, either. The first three DOI links I tried all proved to be broken.