The journal Science reports on a study carried out by the Google Scholar team. According to this research:
In 1995, only 27% of citations pointed to articles published in nonelite journals. That portion grew to 47% by 2013. And the nonelite journals published an increasing share of the most highly cited papers within each field as well, growing from 14% to 24%.
John Bohanon: Uprising: Less prestigious journal publishing greater share of high-impact papers. (at news.sciencemag.org)
Anurag Acharya et al: Rise of the Rest: The Growing Impact of Non-Elite Journals. (at arxiv.org)