Study of character stability and increase-rate of bio-active constituents in chosen clones of Eucommia ulmoides Research of Chinese medicine pairs (Ⅷ) —— Salviae Miltiorrhizae Radix et Rhizoma-Carthami Flos Research on Chinese medicine pairs (Ⅶ) —— Angelicae Sinensis Radix-Chuanxiong Rhizoma Research on Chinese medicine pairs (Ⅵ) —— Coptidis Rhizoma-Euodiae Fructus