Sciences
"...the Centre for Science and Technology Studies (CWTS) of Leiden University developed for Elsevier Scopus an indicator called the source normalized impact per paper (SNIP, see Moed, 2009). This indicator can be seen as an important alternative to the impact factor.
SNIP, produced by CWTS and powered by Scopus, "measures contextual citation impact by weighting citations based on the total number of citations in a subject field. The impact of a single citation is given higher value in subject areas where citations are less likely, and vice versa.