USA UMLS is used for query expansion A longer list of gateways is at the OMNI Launch Pad . These are more selective and more organised than the indexing engines, but less selective than subject gateways. All these services usually index at the level of an entire web site. Name Location Features Yahoo USA Search or browse through hierarchical categories. NISS UK Especially good for UK Higher Education BUBL Link UK A browsable and searchable directory of resources.
Indexing engines Powerful indexing engines index millions of documents on the network.
They are very comprehensive but do not discriminate by subject or quality and do not organise the documents. You can search but not browse. These search services index at the level of a web page rather than an entire document. Name Location Features Alta Vista USA Search for documents or Usenet postings. Alta Vista Europe Sweden European mirror of Alta Vista Lycos USA Search for documents, people, sound and image files.