Name	Info	Provider	Link
	subscription/membership/fee required	Ovid Technologies, Inc.	http://ovidsp.ovid.com/ovidweb.cgi?T=JS&PAGE=linkout&SEARCH=9676677.ui
	subscription/membership/fee required	Silverchair Information Systems	https://jamanetwork.com/journals/jama/fullarticle/vol/280/pg/267