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【判断题】
D-H方法是为每个关节处的杆件坐标系建立3*3变换矩阵A.
正确
B.
错误
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参考解析：
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【简答题】实验室可由苯甲醛和乙酐在无水碳酸钾的作用下,控制温度在160~180°C制备肉桂酸,该反应成为Perkin反应,已知肉桂酸的pKa=4,mp=133°C,难溶于冷水,可溶于热水。请回答: (1)请写出该反应的反应机理。 (2)分离提纯过程中,水蒸气蒸馏的目的是什么?蒸馏前为什么需向出产物溶液中加入碳酸钠? (3)如何进一步提纯肉桂酸,用什么简便方法可以判断其纯度? (4)肉桂酸的红外光谱中应该有哪...
【单选题】You __ go and see a doctor at once because you have got a fever.
A.
can
B.
must
C.
dare
D.
would
【单选题】You go and see a doctor right now. Because you got a fever.
A.
can
B.
must
C.
dare
D.
would
【判断题】If you want to go and see a doctor, it's a good idea to make an appointment before you go.
A.
正确
B.
错误
【简答题】同相比例电路属____负反馈电路,而反相比例电路属 负反馈电路。
【单选题】You'd better go and see a doctor if you ______.
A.
see a sleepwalker in action
B.
never sleepwalk
C.
sleepwalk frequently
D.
sleepwalk occasionally
【单选题】You’d better go and see a doctor if you
A.
see a sleepwalker in action．
B.
never sleepwalk．
C.
sleepwalk occasionally．
D.
sleepwalk frequently．
【判断题】When you feel ill and want to go and see a doctor, it is a good idea to make an appointment before you go.
A.
正确
B.
错误
【单选题】When you feel ill and want to go and see a doctor, it is a good idea to make an appointment before you go .
A.
Appropriate.
B.
Inappropriate.
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