Web of Science To find open access articles in Web of Science, when you have your search results displayed, scroll down to the bottom of the Refine Results column, select Open Access and YES to limit your results to OA works.
If you have an article and are looking for an open access version of it, try one of the options below. Neither of these services has 100% coverage of OA scholarship, but both are easy to use and provide access to a high percentage of materials in institutional repositories and on preprint servers.
Open Access Button - Enter an article's URL, DOI, citation, title, PMC ID, or PubMed ID to search for an OA version of the article - You can also search for datasets with the Open Access Button - A browser extension is also available - click on "Get the Extension" from the Open Access Button's homepage - If your article is not found, Open Access Button will give you an option to request the article from the author
Unpaywall - A browser extension for Chrome and Firefox that searches for open access versions of an articles
Federal Agencies (info from the University of Minnesota Libraries) Policies vary somewhat from agency to agency; many allow for a 12-month embargo period before being made publicly available in an open access repository.