  The main objective of this paper is to identify the set of highly-cited
documents in Google Scholar and to define their core characteristics (document
types, language, free availability, source providers, and number of versions),
under the hypothesis that the wide coverage of this search engine may provide a
different portrait about this document set respect to that offered by the
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 full-text link. The results obtained show that the average highly-cited
document is a journal article or a book (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
especially when detecting duplicates and linking cites properly must be pointed
out. The fact of managing with highly cited papers, however, minimizes the
effects of these limitations. Given the high presence of books, and to a lesser
extend of other document types (such as proceedings or reports), the research
concludes that 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 by strictly scientific material
(journal articles) but academic in its broad sense
