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【单选题】
Methods of studying vary; what works__1__ for some students doesn ’ t work at all for others. The only thing you can do is experiment __2__ you find a system that does work for you. But two things are sure: __3__ else can do your studying for you, and u nless you do find a system that works, you won' t although college. Meantime, there are a few rules that__4__ for everybody. The hint is "don't get ___5___ ". The problem of studying, __6__ enough to start with, becomes almost__7__ when you are trying to do __8__ in one weekend. __9__ the fastest readers have trouble __10__ that. And if you are behind in written work that must be __11__, the teacher who accepts it __12 _late will probably not give you good credit. Perhaps he may not accept it__13__ . Getting behind in one class because you are spending so much time on another is really no __ 1 4__. Feeling pretty virtuous about the seven hours you 'spend on chemistry won' t __ 1 5__one bit if the history teacher pops a quiz. And many freshmen do get into trouble by spending too much time on one class at the __ 1 6__of the others, either because they like one class much better or because they find it so much harder that they think, they should __ 1 7__all their time to it. __ 1 8__the reason, going the whole work for one class and neglecting the rest of them is a mistake, if you face this __ 1 9__, begin with the shortest and easiest __ 2 0__. Get them out of the way and then go to the more difficult, time consuming work.
A.
to do
B.
doing
C.
at doing
D.
with doing
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【单选题】何为无源逆变?
A.
逆变电路交流侧接电网。
B.
逆变电路交流侧接负载。
C.
逆变电路没有直流电源。
D.
逆变电路没有交流电源。
【简答题】简述电子线路系统设计步骤
【简答题】冬小麦是我市重要的粮食作物之一,栽培历史悠久,品质优良.请根据研究冬小麦过程中所遇到的有关问题作答: (1)冬小麦茎的高矮、产量高低、成熟早晚等都是性状,生物性状的遗传一般是由DNA上的______控制的. (2)冬小麦的高茎(A)和矮茎(a)是一对______,将两株高茎冬小麦杂交,收集全部种子共672粒种植,后代出现部分矮茎冬小麦.则子代中高茎冬小麦的基因组成是______,矮茎冬小麦的基因组...
【单选题】“士为知己者活”体现有效的领导来源于:
A.
上级了解下级的需求
B.
上下级之间友情牢固
C.
上级不顾下级利益
D.
上为下级设定崇高友情
【多选题】当UPS交流输入中断时,逆变器无法逆变,应如何查找缺陷()?
A.
检查旁路电源是否正常
B.
测量直流输入电压,因为若直流输入电压过低,控制电路检测到直流电压过低信号后,就会中断逆变电路工作
C.
检查辅助电源是否正常,逆变管及驱动管有无损坏
D.
检查输出保护电路
【简答题】如图5-6所示的有源逆变电路,为了加快电动机的制动过程,增大电枢电源,应如何调节口角?为什么?电枢电流增大后,换相重叠角是否会加大?这是否会造成逆变失败?
【简答题】三相全控桥式有源逆变电路,为加快电动机的制动过程、增大电枢电流,应如何调节卢角?对于电枢电流为10A的电动机制动系统,当U 2 =220V、L B =5mH时,考虑安全裕量,为防止逆变失败,求β的最小值β min 。
【判断题】硅稳压管稳压是利用了硅二极管的反向截止区特性。
A.
正确
B.
错误
【简答题】画出频率开环、电压源(SPWM)逆变器—异步电机变频调速系统原理图(包括详细的主电路、控制电路),说明 主功率开关器件旁为何必须反并联续流二极管?
【单选题】在Altium Designer 的电路板编辑区里,每按一下“空白键”,浮动的零件将逆时针旋转90度。试问如何设定才能改变为逆时针旋转45度?
A.
在操控设定的对话盒里的PCB Editor/Display页,将旋转角度栏位设定为45即可。
B.
在操控设定对话盒里的PCB Editor/General页,将旋转角度栏位设定为45即可。
C.
按住“Ctrl”健,再按“空白键”。浮动的零件将逆时针旋转45度。
D.
不可改变。
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