http://www.loc.gov/mods/v3 http://www.loc.gov/standards/mods/v3/mods-3-2.xsd
pt. A. Carbocyclic and metallorganic rings.--pt. B. Heterocyclic rings.
[by] Robert J. Cotter and Markus Matzner.
Organic chemistry (New York, N.Y.) ; v. 13