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Global Change Master Directory
http://gcmd.gsfc.nasa.gov/
Guided directory search.
Global Information Locator Service (GILS)
http://www.gils.net/index.html
the GILS home page.
Z39.50 Maintenance Agency
http://lcweb.loc.gov/z3950/agency/
the ANSI/NISO Z39.50 (ISO 23950) information retrieval protocol standard, maintained at the Library of Congress.