An Improved HPLC-DAD Method for Quantitative Comparisons of Triterpenes in Ganoderma lucidum and Its Five Related Species Originating from Vietnam oleh Do Thi Ha, Le Thi Loan, Tran Manh Hung, Le Vu Ngoc Han, Nguyen Minh Khoi, Le Viet Dung, Byung Sun Min, Nguyen Phuong Dai Nguyen