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About grey literature in medical systematic reviews

GreyNet:  The Grey Literature Network Service

Science.gov is a gateway to over 50 million pages of authoritative selected science information provided by U.S. government agencies, including research and development results.

https://web.archive.org/web/20140514171345/http://www.scienceaccelerator.gov/ Science Accelerator searches science, including R&D results, project descriptions, accomplishments, and more, via resources made available by the Office of Scientific and Technical Information (OSTI), U.S. Department of Energy

The GrayLIT network: A science portal of technical reports. From the Office of Scientific & Technical Information at the United States Department of Energy.

Grey Literature Library for UK Archaeology

The International Journal on Grey Literature published one volume in 2000.  The content may be limited to subscribers.