Evidence of open access of scientific publications in Google Scholar: A large-scale analysis - ScienceDirect

"Highlights   • 55% of the documents covered by Web of Science from 2009 and 2014 are freely available in some form from Google Scholar. • 23% of documents are available from the publisher, 17% from repositories, and 40% from other sources, mainly ResearchGate. • Many publishers still do not declare a clear user license in CrossRef, difficulting the identification of OA types. • OA levels are higher in the Natural and Health sciences, and lower in Social Sciences, Engineering, and Arts & Humanities. • OA levels are higher for publications produced in Europe, USA, and Brazil (36–50%), than in Asian countries (18–36%)...."