Name Info Provider Link
subscription/membership/fee required Ovid Technologies, Inc. http://ovidsp.ovid.com/ovidweb.cgi?T=JS&PAGE=linkout&SEARCH=17942416.ui
free resource PubMed Central https://www.ncbi.nlm.nih.gov/pmc/articles/pmid/17942416/
subscription/membership/fee required Silverchair Information Systems https://academic.oup.com/nar/article-lookup/doi/10.1093/nar/gkm746