"Counting citations" sounds simple; however, citation analysis tools count citations from different sets of publications. When you perform a citation analysis, you may wish to use several resources to count citations in order to fully capture an article's impact.
Web of Science counts citations, and only counting citations from articles indexed by ThomsonISI, the company that owns Web of Science. It consists of seven databases containing information gathered from thousands of scholarly journals, books, book series, reports, conferences, and more. We subscribe to three databases.
Science Citation Index Expanded - It fully indexes over 6,650 major journals across 150 scientific disciplines and includes all cited references captured from indexed articles.
Social Sciences Citation Index - It fully indexes over 1,950 journals across 50 social sciences disciplines. It also indexes individually selected, relevant items from over 3,300 of the world's leading scientific and technical journals.
Arts & Humanities Citation Index - It fully covers 1,160 of the world's leading arts and humanities journals. It also indexes individually selected, relevant items from over 6,800 major science and social science journals.
Thomson Reuters introduced ResearcherID for authors/researchers. It provides a solution to the author’s ambiguity problem within the scholarly research community. It assigns a unique identifier to enable researchers manage their publication lists, track their times cited counts and h-index, identify potential collaborators and avoid author misidentification. And it is fully integrated with Web of Knowledge. To access ResearcherID.com, you must first sign in or register with the Web of Knowledge
Scopus counts citations, also only counting citations from articles included in the Scopus database. As the largest abstract and citation database of research literature and quality web sources Scopus covers nearly 18,000 titles from more than 5,000 publishers.
Google Scholar is likely to produce more cited references than either Web of Science or Scopus, but it also produces duplicates. In addition, Google does not provide a complete list of all the publications it indexes, so it is difficult to know if Google Scholar provides comprehensive citation counts. For authors, Google Scholar Citations provide a simple way to keep track of citations to their articles. They can check who is citing their publications, graph citations over time, and compute several citation metrics.