  Bibliometric indexes are customary used in evaluating the impact of
scientific research, even though it is very well known that in different
research areas they may range in very different intervals. Sometimes, this is
evident even within a single given field of investigation making very difficult
(and inaccurate) the assessment of scientific papers. On the other hand, the
problem can be recast in the same framework which has allowed to efficiently
cope with the ordering of web-pages, i.e., to formulate the PageRank of Google.
For this reason, we call such problem the PaperRank problem, here solved by
using a similar approach to that employed by PageRank. The obtained solution,
which is mathematically grounded, will be used to compare the usual heuristics
of the number of citations with a new one here proposed. Some numerical tests
show that the new heuristics is much more reliable than the currently used
ones, based on the bare number of citations. Moreover, we show that our model
improves on recently proposed ones.
