A two-sided academic landscape : snapshot of highly-cited documents in Google Scholar ( 1950-2013 )

The main objective of this paper is to identify and define the core characteristics of the set of highly-cited documents in Google Scholar (document types, language, free availability, sources, and number of versions), on the hypothesis that the wide coverage of this search engine may provide a different portrait of these documents with respect to that offered by traditional bibliographic databases. To do this, a query per year was carried out from 1950 to 2013 identifying the top 1,000 documents retrieved from Google Scholar and obtaining a final sample of 64,000 documents, of which 40% provided a free link to full-text. The results obtained show that the average highly-cited document is a journal or book article (62% of the top 1% most cited documents of the sample), written in English (92.5% of all documents) and available online in PDF format (86.0% of all documents). Yet, the existence of errors should be noted, especially when detecting duplicates and linking citations properly. Nonetheless, the fact that the study focused on highly cited papers minimizes the effects of these limitations. Given the high presence of books and, to a lesser extent, of other document types (such as proceedings or reports), the present research concludes that the Google Scholar data offer an original and different vision of the most influential academic documents (measured from the perspective of their citation count), a set composed not only of strictly scientific material (journal articles) but also of academic material in its broadest sense.