periodic c law周期律
roof periodic caving law顶板周期垮落规律
periodic law of elemen元素周期律
Periodic law culture teaching元素周期表
On Periodic Law论周期律
element periodic law元素周期律
the periodic law化学元素周期律
elemental periodic law元素周期律
Periodic law constant周期律常数
N（名词） the principle that the chemical properties of the elements are periodic functions of their atomic weights or, more accurately, of their atomic numbers (元素)周期律 (Also called Mendeleev's law)