Here are three useful tools to help you discover Open Access content online:
Kopernio: Automatically search the Library's subscriptions, pre-print servers, institutional repositories and private blogs for free PDFs. Works with Web of Science, Pubmed, Google Scholar and 1000s of other academic platfroms including ScienceDirect and JSTOR.
UnPaywall: Add the Unpaywall app to Chrome. Search for content that you can use legally. Sources include repositories run by universities, governments, and scholarly societies, as well as open content hosted by publishers.