Open access and sources of full-text articles in Google Scholar in different subject fields

Google Scholar, a widely used academic search engine, plays a major role in finding free full-text versions of articles. But little is known about the sources of full-text files in Google Scholar. The aim of the study was to find out about the sources of full-text items and to look at subject differences in terms of number of versions, times cited, rate of open access availability and sources of full-text files. Three queries were created for each of 277 minor subject categories of Scopus. The queries were searched in Google Scholar and the first ten hits for each query were analyzed. Citations and patents were excluded from the results and the time frame was limited to 2004-2014. Results showed that 61.1 % of articles were accessible in full-text in Google Scholar; 80.8 % of full-text articles were publisher versions and 69.2 % of full-text articles were PDF. There was a significant difference between the means of times cited of full text items and non-full-text items. The highest rate of full text availability for articles belonged to life science (66.9 %). Publishers' websites were the main source of bibliographic information for non-full-text articles. For full-text articles, educational (edu, ac.xx etc.) and org domains were top two sources of full text files. ResearchGate was the top single website providing full-text files (10.5 % of full-text articles).