On the result page of the SISSA Discovery Service at the bottom of each entry displayed there is a link to a tool called PlumX Metrix.
This tool collects metrics about the impact of the resource that you are searching. It provides a more complete picture and answers questions about scientific impact for a large part of journal articles and books (including e-books).
PlumX, named Library Journal’s most ambitious database in 2013, gathers metrics across five categories—usage, mentions, captures, social media and citations.
Metrics are gathered around what Plum Analytics calls artifacts—providing more information than journals. PlumX Metrix gives explicit information about where the citations come from.