Including cited non-source items in a large-scale map of science: What difference does it make?
A direct citation map containing a combination of 43 million source and non-source documents has been created. Over half of the documents in the map are non-source documents. The social sciences are much more heavily represented by non-source items, and assume a more central position in the map. Over 500,000 books appear in the map; these are much more highly cited on average than articles.
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