周期元素 meaning in English

period element
periodic element

Orders of periodic elements of general linear group over any field
任意域上一般线性群周期元素的阶
Calculation of scattering cross section of the electron and the second period element atom
低能电子与第二周期元素原子碰撞截面的理论计算
Through analysis on the structure of valence electron shell , the atom radius , the bonding orbital and other important parameters , this paper discusses the irregularity in the second circle of nonmetal elements and the irregular courses
摘要本文通过对第二周期元素价电子层结构、原子半径、成键轨道及其重要参数的分析，讨论了第二周期非金属元素的不规则现象，并且分析了产生这些不规则性的原因。