Chronicle of Higher Education:  Access to Online Journals Reduces Breadth of Citations, Study Finds, by Lila Guterman:

Scholars’ access to more and more journal articles online may have had the perverse effect of slowing the steady increase in the number of citations of discrete articles, according to a study published today in Science [Electronic Publication and the Narrowing of Science and Scholarship]. The unfortunate result may be to tamp down debate among researchers.

When journals began posting their archived issues online, the study suggests, that may have had an effect opposite to what many publishers and librarians had anticipated. In the study, James A. Evans, an assistant professor of sociology at the University of Chicago, looked at 34 million articles published from 1945 to 2005. He found, if he controlled for the prevailing trend of widening citations, that as more articles appeared online, scholars’ citations tended toward more-recent and less-diverse articles.