On the "persistency" of scientific publications: introducing an h-index for journals

What do we really mean by a "good" scientific journal? Do we care more about the short-time impact of our papers, or about the chance that they will still be read and cited on the long run? Here I show that, by regarding a journal as a "virtual scientist" that can be attributed a time-dependent Hirsch h-index, we can introduce a parameter that, arguably, better captures the "persistency" of a scientific publication. Curiously, however, this parameter seems to depend above all on the "thickness" of a journal.