A 2013 European Commission report found that, among new papers being published, perhaps half are now free. Further, a 2014 study published in PLoS One, “The Number of Scholarly Documents on the Public Web,” has used computer science techniques to estimate the total amount of research knowledge available on the Web.
As of 2013, when the scientists used algorithms to make their estimates, there were at least 114 million English-language studies available on the Web.
Of these 114 million, 27 million were open access — meaning that about one-quarter of online research knowledge in the English-speaking world is now free to the public on the Web.
There were significant differences in the availability of papers across disciplines. Some of the disciplines connected with the most profitable industries had the highest percentages of open papers: 50% for computer science; 42% for business and economics; 35% each for geosciences and physics.
It is also true that material and agricultural sciences and engineering all were estimated to have only 12% of their papers open to the public.
By contrast, only 19% of social science studies were found to be open access.
The authors note that academic research, open access or not, is not uniformly available on all search engines. For example, at the time of the study, Google Scholar indexed approximately 100 million of the 114 million studies available on the Web — 87%, therefore it would be useful for researchers to consider as a standard practice querying multiple databases and academic search engines.
Source: Massive and growing volume of free research on the Web: 27 million documents and counting / Journalist’s Resource (Harvard Kennedy School, Shorenstein Center)