More than just medical literature, PubMed Central was developed by the National Center for Biotechnology Information (NCBI) and publishers of life sciences literature. PubMed allows access to nearly 2 million full text journal articles.
Web of Science indexes over 11,000 scholarly journals in the sciences (1975 - present). Web of Science's strength is in its interdisciplinary focus and its ability to perform citation searching. It also works seamlessly with EndNote & EndNote Online citation management software.
Google Scholar provides an easy way to search broadly for scholarly literature across a range of disciplins and topics. As with a general Google search, Google Scholar attempts to bring the more relevant results to the top of the results list.
Drawbacks to Google Scholar include: