Determination of two stilbene glycoside in five processed products ofRheum palamatum Identification and comparison of constituents in HPLC fingerprint of five Chinese herbal pieces from Rheum palamatum Anthraquinone contents in five processed products from Rheum palamatum Simultaneous determination of two anthraquinone-O-glucosides in five processed pieces from Rheum palamatum Simultaneous determination of two anthraquinone-O-glucosides in five processed pieces from Rheum palamatum