ISI maintained citation databases covering thousands of academic journals, including a continuation of its longtime print-based indexing service the Science Citation Index (SCI), as well as the Social Sciences Citation Index (SSCI) and the Arts and Humanities Citation Index (AHCI). All of these were available via ISI's Web of Knowledge database service. This database allows a researcher to identify which articles have been cited most frequently, and who has cited them. The database provides some measure of the academic impact of the papers indexed in it, and may increase their impact by making them more visible and providing them with a quality label. Some anecdotal evidence suggests that appearing in this database can double the number of citations received by a given paper. The company's main product was Current Contents, which gathers the tables of contents for recent academic journals. For several years this also included Citation Classics, personal commentaries on highly cited papers.
The ISI also published the annual Journal Citation Reports which list an impact factor for each of the journals that it tracked. Within the scientific community, journal impact factors continue to play a large but controversial role in determining the kudos attached to a scientist's published research record.
A list of over 14,000 journals was maintained by the ISI. The list included some 1,100 arts and humanities journals as well as scientific journals. Listings were based on published selection criteria and are an indicator of journal quality and impact.
ISI published Science Watch, a newsletter which every two months identified one paper published in the previous two years as a "fast-breaking paper" in each of 22 broad fields of science, such as Mathematics (including Statistics), Engineering, Biology, Chemistry, and Physics. The designations were based on the number of citations and the largest increase from one bimonthly update to the next. Articles about the papers often included comments by the authors.
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The ISI also published a list of "ISI Highly Cited Researchers", one of the factors included in the Academic Ranking of World Universities published by Shanghai Jiao Tong University. This continues under Clarivate.
