The original citation service in the USA is provided by the Institute of Scientific Information (ISI), which publishes the Science Citation Index (SCI) and the Social Science Citation Index (SSCI). These are both online at DIALOG, and can be searched using the RANK command to identify the top 10, 20, 100 authors based on a specified topic and how many times others have cited them. Generally it is useful to also note the number of articles each author has published, and to create a visualization of the citation clusters that quickly identify both centers of excellence and citation “clubs” a form of citation incest. Acquired by Thomson Reuters, and losing Eugene Garfield and Henry Small (the latter to Maps of Science, see below), this is still the primary service but not growing to its fullest potential. We exploit this via specialist information brokers; Mary Ellen Bates in particular has pioneered use of the RANK command–someone who does not know what they are doing can run up a huge bill that is not necessary.
Elsevier, late to the game, publishes an online service, Scopus.
China has adapted the idea to its own publications, and this is an extraordinary resource, one that a multinational Open Source Agency would strive to rapidly extend to all nations and all languages. This is not to be confused with the effort by Thompson Reuters to expand into Chinese citation analytics as described by Philip Purnell in “Citation Analysis in China,” Beijing, May 2011.
Maps of Science, founded by Dick Klavans, who is unique for having complete access to all ISA data for his company, recently confirmed by a court when ISI balked at honoring its original deal, is the best exploitation scientist and artist we know of, using citation to find clusters of excellence and to identify gaps at the national, industrial, or company level.