The Impact Factor List is published annually by Thomson Reuters in the Journal Citation Reports, which requires an institutional subscription. SCImago Journal Rank is a freely-accessible alternative of the quality of a scientific journal.
Thomson Reuters annually provides a list of the impact factor of the journals indexed in the Science Citation Index Expanded and the Social Science Citation Index, also owned by Thomson Reuters. Accessing to the Journal Citation Reports requires an institutional subscription.
SCImago Journal Rank provides an alternative for the scientific journals' citation impact and is freely accessible, called SCImago Journal Rank indicator. Like Thomson's Impact Factor, this depends on the number of citations of the average article of each journal.