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primary system
avia.	〔客〕主要系统
el.	主系统【核】; 一回路系统
hydroel.st.	一次系统
mil., air.def.	保密系统; 一次雷达系统
space	主系统
tech.	一次回路; 主要系统
primary slip system
met.	初始滑移系统

primary system: 131 phrases in 20 subjects

Agriculture	1
Air defense	3
Automobiles	1
Aviation	28
China	2
Construction	1
Earth sciences	3
Economy	1
Electric machinery	1
Electronics	44
General	2
Hydroelectric power stations	2
Information technology	2
Nautical	1
Nuclear and fusion power	1
Refrigeration	2
Skydiving	1
Space	12
Technology	22
Telecommunications	1