About  Citation Tools:
Google Scholar

Google Scholar also includes citation data.  It is interdisciplinary and covers journal articles plus many other types of publications, including books, reports, theses and dissertations, and patents.  Google does not publish information about what subjects, resources, journals, publishers, years, etc. are covered by the database. 

It is possible to search by subject or author, and limit by year or publication.  Google Scholar searches the full text of publications where it is available.
The interface is much less sophisticated than Web of Science and it does not show article bibliographies, although it is possible to open a list of articles that cite a given publication.  Options for sorting, manipulating, and downloading data are not very well developed. 

Google Scholar is freely available, whereas both Web of Science and Scopus require a paid subscription.  However, to be able to access full-text of articles that are part of the library subscription, you need to access Google Scholar through the library web site.

NEXT: Citation Data for Education