In case you are interested in searching the medical literature, AnatomyLens is a free search engine on IBM Alphaworks services (not to be confused with the IBM Alphaworks technology download site which offers not-free software). IBM Alphaworks services requires registration purely for tracking usage statistics.
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AnatomyLens provides a search over annotations of PubMed articles and GOA annotations using the GO (gene ontology) and FMA (Foundational Model of Anatomy) ontologies. Here's a brief description:
Anatomy Lens is a search engine that helps scientists hone in on PubMed articles most relevant to their research. Users enter anatomy terms, MeSH terms, and biological processes as search keywords. Anatomy Lens is more precise and has better recall than text search. For example, for the query Alzheimer's, brain, neuron development, Anatomy Lens will match Alzheimer's articles that discuss dendrite development in the hippocampus, whereas a standard text search will only find articles containing the queried keywords explicitly and might also find articles that are unrelated (such as articles about neuron development in the spine).
Any feedback/comments are welcome. Thanks!
Kavitha Srinivas
IBM Research, SHER OWL reasoning project.