SCImago is a research group from the Consejo Superior de Investigaciones Científicas (CSIC), University of Granada, Extremadura, Carlos III (Madrid) and Alcalá de Henares, dedicated to information analysis, representation and retrieval by means of visualisation techniques. The group has developed the SJR Portal and the SCImago Journal Rank (SJR) indicator.
The SJR indicator is a size-independent metric aimed at measuring the current average prestige per paper of journals. A citation from a journal with a relatively high SJR is worth more than a citation from a journal with a lower SJR.
The SJR scores for journals are available at http://www.scimagojr.com/. Scopus Journal Analyzer publishes SJR values for journals from 1999 and later.
Details of the calculation of the SJR indicator are available at http://www.scimagojr.com/SCImagoJournalRank.pdf and http://arxiv.org/ftp/arxiv/papers/0912/0912.4141.pdf.