①画出三相交流异步电动机降低电源电压(UN、0.8U、0.5U)时的人为机械特性曲线

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问题:

①画出三相交流异步电动机降低电源电压(UN、0.8U、0.5U)时的人为机械特性曲线(n-T、n-S曲线),说明特性变化的特点。

②并说明在电动机负载不变时,电网电压下降对电动机的影响。

考点:机械工程机电传动控制机电传动控制题库
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短文填空 先读下面的短文,掌握其大意,然后根据短文内容和所给首字母,在空格内填入一个适当的词,使短文意思完整。所填单词在题后横线上必须完整写出。

(本大题5分,每格0.5分)

True friends are hard to find. Often you thought you could believe in someone, b     1 later he or she may let you down.

A true friend is someone who will always be there for you. T  2 good times or bad times, they will stand by your side. They will not l 3 you alone when things get difficult. They will a 4 you without trying to change you. A friend will b 5 new and exciting things into your life and make it richer.

True friends will keep your worst secrets as you will keep t 6 . They will be honest and you can always believe in them. If you talk to someone who you believe in, you don’t have to worry about what you may say. We can enjoy this freedom only with friends.

Friendship is a two-way street. To find a true friend and keep the friendship between you, you must do the same thing as w 7 . Be there for your friends when they are in need and share the good times with them .O 8 them the same things they give to you. Friendship will break quickly if only one person is giving and p 9 effort(努力) into it.

You will find there is nothing more v 10 than having a true friend by your side to share life with, just as someone says, “There is nothing on this earth more to be prized(珍惜) than true friendship.”

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在窗体上画一个名称为Text1的文本框和一个名称为Commandl的命令按钮,然后编写如下事件过程: Private Sub Commandl Click()Dim arrayl(10,10)As IntegerDim i As Integer,j As IntegerFor i=1 To 3 For j=2 To 4array l(i,j)=i+j Next jNext iText1.Text=arrayl(2,3)+arrayl(3,4) End Sub 程序运行后,单击命令按钮,在文本框中显示的值是______。

A.12

B.13

C.14

D.15

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毛细管色谱柱的柱容量小、出峰快,因此要求()。

A.瞬间注入大量样品

B.瞬间注入极小量样品

C.缓慢注入极小量样品

D.缓慢注入大量样品

E.进样速度

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假定某投资者按1000元的价格购买了年利息收入为80元的债券,并持有2年后以1060元的价格卖出,那么该投资者的持有期收益率为()。

A.6%

B.8%

C.11%

D.14%

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社区卫生服务是以______为基础的照顾。

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