I. Introduction
The last decade has been characterized by an enormous growth of the amount of scientific information available on-line; recent estimates reported that a new paper is published every 20 seconds [1]. PubMed includes almost 27M papers with a growth rate of about 1,370 new articles per day. Elsevier Scopus and Thomson Reuthers ISI Web of Knowledge respectively index more than 57 and 90 million papers. The Cornell University Library arXiv initiative provides access to over 1M e-prints from various scientific domains. At the same time, an increasing percentage of papers is published on-line as Open Access content [2] and thus can be freely read: the full text of more in four PubMed publications and more than 17% of the articles indexed by Scopus and ISI Web of Knowledge is available on-line for free and this percentages are considerably growing. The Directory of Open Access Journals, one of the most authoritative indexes of high quality, Open Access, peer-reviewed publications, lists more than 9,400 journals and almost 2.5M papers. Sometimes between 2017 and 2021, more than half of the global papers are expected to be published as Open Access content [3]. Moreover, several top conferences are making their articles freely available through dedicated archives even before the conference takes place. Social networks are experimenting a rapid adoption in scientific communities [4], [5]: research networks like ResearchGate, Academia.edu or Mendeley are rapidly expanding, facilitating scientific information sharing [6].