null ①零，零的 ②无效的，无价值的 ③类光[的]†
null 零的；零
数据库 数据库管理系统及其实现技术 释文 null 空值
- electric flux density
- electric force line
- electric free enthalpy
- electric furnace bottom tapping
- electric furnaces
- electric generator
- electric gravity analysis
- electric heated roll
- electric heating
- electric heating digestion apparatus
- electric heating floor
- electric heating oil gathering process
- electric heating radiator
- electric hoist
- electric hydraulic control system
- electric hysteresis effect
- electric hysteresis loop
- electric ignition technology
- electric image
- electric image method
- electric incubator
- electric induction
- electric initiation
- electric instruments components
- electric instruments system