Journal Citation Report

aka JCR is a resource that gives information and impact factors about academic journals, from the science and social science fields. It is powered by Thomson Reuters and is connected to ISI Web of Knowledge. 
The main information you can access from this website is the following:

• the basic bibliographic information of publisher, title abbreviation, language, ISSN

• the subject categories (there are 171 such categories in the sciences and 54 in the social sciences)*

More information can be obtained from the Thomson Reuters webpage:

http://thomsonreuters.com/products_services/science/science_products/a-z/journal_citation_reports/

* http://en.wikipedia.org/wiki/Journal_Citation_Reports