The chemical constituents of Bai-Hua-Qian-Hu, the root of Peucedanum praeruptorum Dunn (Umbelliferae) - four new coumarins - Chen,Z.X.; Huang,B.S.; She,Q.L.; Zeng,G.F. (Yao Xue Xue Bao (Acta Pharmaceutica Sinica), 1979)