Name	Info	Provider	Link
	subscription/membership/fee required	Ovid Technologies, Inc.	http://ovidsp.ovid.com/ovidweb.cgi?T=JS&PAGE=linkout&SEARCH=38330498.ui
	subscription/membership/fee required	Silverchair Information Systems	https://academic.oup.com/pmj/article-lookup/doi/10.1093/postmj/qgae012