在直流调速系统中,对直流电动机运行速度进行控制从而实现运动机构的调速。()
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Our school-run factory _____ various kinds of chemical devices last year.
A. turned into
B. turned up
C. turned out
D. turned off
Smoking is not good _____ you because it can affect your health.
A. for
B. at
C. to
D. on
在标准双极工艺中,发射区电阻常用做()和()。在单层金属工艺中广泛用做隧道。