某井内有密度为1.20g/cm3的钻井液200m3,欲将其密度提高到1.25g/cm3,需密度为4.2g/cm3的重晶石()吨。 ["A、16.95","B、15.95","C、15.95","D、14.24"]
电动机拖动系统由哪些部分组成?
世界上最大的导弹快艇“纳努契卡”号是哪国在1971年建造的() ["A、日本","B、英国","C、美国","D、前苏联"]
变频器主电路中安装的断路器有什么作用?
航迹舵对指标航向修正量小数点位的处理方法为:() ["0.1~0.5取0,0.6~0.9取1.0","0.1~0.5取0.5,0.6~0.9取1.0","0.1~0.5取0,0.6~0.9取0.5","0.1~0.5取0.5,0.6~0.9取0.5"]
为什么变频器的通、断电控制一般均采用接触器控制?