药物的生物活性可以认作与药物的化学结构的某种函数有关。如药物的生物活性 A 与药物化学结构相关联的特定理化性质 X_1、X_2、X_3……存在着某种函数关系,那么:A=f(X_1,X_2,X_3,X_4……)(1)如果这些理化特性彼此间相互独立,没有强烈的依赖关系,按数学中的变分法原理,上式函数可分离为这些理化特性各自函数的乘积。 The biological activity of a drug can be considered as a function of the chemical structure of the drug. For example, there is a certain functional relationship between the biological activity A of a drug and the specific physico-chemical properties X_1, X_2, X_3 ... associated with the chemical structure of the drug. Then: A = f (X_1, X_2, X_3, X_4 ...) These physical and chemical properties are independent of each other, there is no strong dependence, according to mathematical variational principle, the above function can be separated into the product of these physical and chemical properties of the product.