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)‬.‎