I read this book in the early 90s:

http://www.amazon.com/Library-Research-Models-Classification...

The gist of it was that the "value" of a scholarly article could be measured by the number of citations, weighted by the number of citations each of the articles that cited it got, and so on.

Basically PageRank (though without the actual mathematics that to calculate the number).

In addition there's long standing research in the field of Library Science about the importance of citations. It seems like a natural progression from judging the quality of a paper by the number and quality of papers citing it, to PageRank.

This book basically described something very similar to PageRank in 1993 (5 years before Google): http://www.amazon.com/Library-Research-Models-Classification...