The following articles on for citation metrics are freely available via Google Scholar:

1. Bakkalbasi N, Bauer K, Glover J, Wang L. Three options for citation tracking: Google Scholar, Scopus and Web of Science. Biomedical digital libraries. 2006;3(1):7.
2. Harzing AW, van der Wal R. Google Scholar: the democratization of citation analysis. Ethics in Science and Environmental Politics. 2008;8(1):61-73.
3. Harzing AWK, van der Wai R. Google Scholar as a new source for citation analysis. Ethics in Science and Environmental Politics(ESEP). 2008;8(1):61-73.
4. Hirsch JE. An index to quantify an individual's scientific research output. Proceedings of the National Academy of Sciences. 2005;102(46):16569-72.
5. Meho LI, Yang K. A new era in citation and bibliometric analyses: Web of Science, Scopus, and Google Scholar. Arxiv preprint cs/0612132. 2006.
6. Meho LI, Yang K. Impact of data sources on citation counts and rankings of LIS faculty: Web of Science versus Scopus and Google Scholar. Journal of the American Society for Information Science and Technology. 2007;58(13):2105-25.
7. van Aalst J. Using Google Scholar to Estimate the Impact of Journal Articles in Education. Educational Researcher. 2010;39(5):387-400.
8. Yang K, Meho LI. Citation analysis: A comparison of google scholar, scopus, and web of science. Proceedings of the American Society for Information Science and Technology. 2006;43(1):1-15.