题目内容
() are used to tune radios to particular frequencies in the resonant circuits .
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() is an electronic component made of semiconductor material.
A small current flowing from the () to the emitter can control a much larger current between the collector and emitter terminals.
When reverse-biased, an ideal () would block all current. A real one lets perhaps 10 microamperes through–not a lot, but still not perfect.
电梯的有齿曳引机通过与蜗杆相连，涡轮与曳引轮同装在同一根轴上，曳引绳挂在曳引轮上。
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