Dean Giustini, UBC Google Scholar Blogger writes an interesting post in which he directs our attention to a study comparing WoS and Google Scholar by Drs. Pauly and Stergiou. Pauly and Stergiou compared WoS and Google Scholar using 114 papers from 11 disciplines from 1925 to 2004.

"It's axiomatic that databases bought by university libraries - like ISI's Web of Science (WoS) - outperform free search tools like Google Scholar. Or is it? A recent study co-authored by Daniel Pauly, director of the UBC Fisheries Centre suggests otherwise; the study compared WoS with Google Scholar, with some surprising results."