Name	Info	Provider	Link
	subscription/membership/fee required	International Union of Crystallography	http://scripts.iucr.org/cgi-bin/paper?tk2728
	free resource	PubMed Central	https://www.ncbi.nlm.nih.gov/pmc/articles/pmid/21753998/
	free resource	Europe PubMed Central	https://europepmc.org/abstract/MED/21753998