mass number

同根派生

Chemical element is the general term for the same type of atoms with the same mass number.
化学元素是具有相同核电荷数的同一类原子的总称。
Any of two or more nuclei with the same mass number and atomic number that have different radioactive properties and can exist in any of several energy states for a measurable period of time.
同质异能素两种或更多种具有相同的质子数和原子数，但有不同的辐射特性并能在几种能量状态中的任一种里存在一段可测量时间的原子核中
A cloud is a mass of vapor in the sky.
云是天空中的水汽团。
The mass rally was a total fiasco.
那次群众集会彻底失败。
He thumbed through the directory to look for her number.
他翻阅电话号码簿找寻她的号码。