PLOS ONE: “The Number of Scholarly Documents on the Public Web”

“Our estimates show that at least 114 million English-language scholarly documents are accessible on the web, of which Google Scholar has nearly 100 million. Of these, we estimate that at least 27 million (24%) are freely available since they do not require a subscription or payment of any kind.”

I’d say that 27m is probably a large underestimate, given that the two engines used for the study (Google Scholar and Microsoft Academic Search) are proven to be poor at indexing open repositories and open access journals. Given a few hours of work I could probably winkle out from JURN a list of 100 “big” URLs, which together would put JURN at 25m (primarily in English) — before even starting to tally all the other URLs.