Name	Info	Provider	Link
	subscription/membership/fee required	Ovid Technologies, Inc.	http://ovidsp.ovid.com/ovidweb.cgi?T=JS&PAGE=linkout&SEARCH=8403482.ui
	subscription/membership/fee required	Wiley	https://onlinelibrary.wiley.com/resolve/openurl?genre=article&sid=nlm:pubmed&issn=0307-6938&date=1993&volume=18&issue=4&spage=375
	subscription/membership/fee required	Silverchair Information Systems	https://academic.oup.com/ced/article-lookup/doi/10.1111/j.1365-2230.1993.tb02223.x