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【单选题】
螺旋副在摩擦系数一定时,螺纹的牙型半角越大,则( )。A.
当量摩擦系数越小，自锁性能越好
B.
当量摩擦系数越小，自锁性能越差
C.
当量摩擦系数越大，自锁性能越差
D.
当量摩擦系数越大，自锁性能越好
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【单选题】某交流发电机正常工作时的电动势为e=Emsinωt,如果发电机转子转速提高一倍,线圈匝数也同时增加一倍,其他条件不变,则发电机的电动势为
A.
e=4Emsin2ωt
B.
e=4Emsinωt
C.
e=2Emsin2ωt
D.
e=2Emsinωt
【简答题】That is the day of the ceremony. We have been invited to it.
【简答题】We have two daughters: Kristen is seven years old and Kelly is four. Last Sunday evening, we invited some people home for dinner. I dressed them nicely for the party, and told them that their job was ...
【单选题】I was invited to have ____good breakfast and _____ restaurant we went to was excellent. [ ]
A.
a ; the
B.
不填 ; the
C.
the ; a
D.
the ; the
【单选题】Im supposed to go to the meeting, but I have an out—Sam invited me first to come to his wedding. The underlined word means ______.
A.
plan
B.
problem
C.
trouble
D.
excuse
【单选题】We've invited Mr and Mrs Brown to dinner. But we'll have to________ because of the baby's sickness. [ ]
A.
take up
B.
make up
C.
give up
D.
put off
【单选题】交流发电机工作时电动势为e=E m sin ωt,若将发电机的转速提高一倍,同时将电枢所围面积减小一半,其他条件不变,则其电动势变为( )
A.
e′=E m sin
B.
e′=2E m sin
C.
e′=E m sin 2ωt
D.
e′= sin 2ωt
【单选题】交流发电机工作时的电动势为 e = E m sin ωt 。若将其电枢的转速提高 1 倍,其他条件不变,则其电动势变为( )
A.
E m sin
B.
2 E m sin
C.
E m sin2 ωt
D.
2 E m sin2 ωt
【简答题】We have two daughters: Kristen is seven years old and Kelly is four．Last Sunday evening, we invited some people home for dinner．I dressed them nicely for the party, and told them that their job was to...
【简答题】All we invited have arrived, ______________?
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