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【单选题】
完成下列各题 Young Marconi had the teachers to give him lessons at home in Italy.He loved books,especially 21 on science.He had curious mind and always wanted to prove for himself 22 he read. 23 day,when he was sitting by an open window,it seemed that a thousand 24 filled his ears.“Where are they all 25 ?”he asked himself.“And where will they go? What happens to all the words that people say?Do they 26 in the air around the earth, 27 waiting for someone to pick them up?” At once Marconi went to work.Sounds cal3 be made t0 28 ,he thought,if they are given a push by electricity.If I call push a piece of wood across the waves of water.I can also 29 sounds through the air waves by electrical power. A few weeks 30 he called his mother and father up to his workroom for a 31 .He touched a little machine,and two floors below there was the sound of a buzz(嗡嗡声).“How did you do it?”they asked.“Your machine is 32 far from the sound.” “That’s right,”he said happily.“I have just found a 33 to carry sound without wires.’’ Although Marconi’S father did not think the wireless sound would 34 be important,he gave his son some money to 35 his work.“Father,with this money I am going to send messages round the world one day.’’
A.
that
B.
those
C.
ones
D.
one
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【单选题】桥式整流电容滤波电路输出电压平均值U0(AV)= ( )
A.
0.45U2
B.
0.9U2
C.
1.1U2
D.
1.2U2
【简答题】滚珠丝杠副进行预紧的目的是什么?常见的预紧方法有哪几种?
【单选题】国际建设是( )为保卫主权、领土完整和安全,防御外来侵略和颠覆,在军事、政治、经济、科技、文化等方面所进行的国家防务建设。
A.
民族
B.
国家
C.
阶级
D.
个人
【简答题】在用有机溶剂(三氯甲烷、乙醚等)从碱水溶液中萃取生物碱时,为何先加入有机溶剂再碱化较好。
【单选题】下列哪一项不属于工厂化育苗所选择三大类型的温室( )
A.
塑料管棚
B.
智能温室
C.
日光温室
D.
现代温室
【多选题】9 1989年救助公约关于适用范围作了哪些扩大:
A.
“可航水域或任何其他水域”,不再仅指海上救助
B.
任何关于救助的案件都可适用本公约
C.
“可航水域或任何其他水域”不包括内陆水域
D.
本公约适用在公约成员国境内提起的有关本公约所辖事项的诉讼或仲裁
【多选题】滚珠丝杠预紧的目的有( )。
A.
增加阻尼比,提高抗振性
B.
提高传动刚度
C.
消除轴向间隙
D.
加大摩擦力,使系统能自锁
E.
防止丝杠变形
【判断题】(    )换刀点是数控加工中刀架转位换刀时的位置。
A.
正确
B.
错误
【单选题】单相桥式整流电容滤波电路输出电压平均值U0=( )UZ
A.
0.45
B.
0.9
C.
1.1
D.
1.2
【多选题】下列对甲烷气体的描述正确的有?()
A.
甲烷能间接引起气候变化
B.
甲烷的主要人为释放源是工业生产
C.
甲烷分子对全球变暖的贡献是二氧化碳分子的20多倍
D.
自然条件下,甲烷浓度的季节变化主要受氢氧自由基控制
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