何为剪应力?连接件不被剪断的条件是什么?许用剪应力与许用正应力的关系怎样?

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问题:

何为剪应力?连接件不被剪断的条件是什么?许用剪应力与许用正应力的关系怎样?

考点:线路运行与检修专业考试送电线路高级工送电线路高级工题库
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山地迎风坡降水______,背风坡降水______.在温带地区,沿海和内陆相比较是______的降水多.赤道向两极年降水量是逐渐______的.亚洲季风气候显著的原因是______.

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阅读理解。

     The hole in the Earth's ozone layer (臭氧层) has until now protected Antarctica from the worst effects of

global warming. But scientists have warned that as the hole closes up in the next few decades, temperatures

on the continent could rise by around 3oC on average, with melting ice contributing to a global sea level

increase of up to 1.4 metres.

     In the past decades the western Antarctic has seen rapid ice loss as the world has warmed, but the other

parts of the continent have, paradoxically, been cooling, resulting in a 10% increase in ice in the seas around

the region. This is because the hole in the ozone layer has increased cold winds in Antarctica, making much

of the continent surface colder than usual.

     But now that the gasses that cause the ozone hole have been banned, scientists expect the hole to repair

itself within the next 50 to 60 years. By then the cooling effect will have faded out and the Antarctic will face

the full impact of global warming. This means an increase in average air temperatures of around 3OC and a

reduction in sea ice by around a third.

     The biggest threat to the continent comes from warming seas. Robert Johnson, a scientist who monitors

Antarctica ice sheets, said, "The ice sheets in Antarctica are hundreds of metres thick. But once warm ocean

waters start flowing underneath, the ice will begin thinning and could break up very quickly." Thinning ice

sheets cause ice to break away from the continent and to melt even faster. Escaping ice from western

Antarctica has already resulted in a 10% rise in global sea level in recent decades.

     Johnson believes that international action to reduce global warming is required immediately or it may be too

late. "Everything is connected-Antarctica may be a long way away but it is an important part of the Earth's

system," said Johnson. "It contains 90% of the world's ice, 70% of the world's fresh water and that is enough,

if it melts completely, to raise sea levels by 63 metres."

     Even in a worse-case situation scientists don't expect the ice to entirely disappear, but predict that, because

of the melting ice sheets, average sea level rise will be around 1.4 metres higher by the end of the century.

1. The underlined word "paradoxically" (in Paragraph 2) most probably means "_____". [ ]

A. rapidly

B. approximately

C. contradictorily

D. apparently

2. What is the effect of the hole in the ozone layer on Antarctica? [ ]

A. It is causing the ice to melt faster.

B. It is making much of the continent colder.

C. It is making the effects of global warming in the region worse.

D. It is reducing the amount of water in Antarctica.

3. What do scientists think is the biggest danger facing Antarctica? [ ]

A. Rising sea levels.

B. Warming sea water temperature.

C. Water pollution.

D. Growing ice sheets.

4. Which of the following is true according to the passage? [ ]

A. Antarctica is currently experiencing the full effects of global warming.

B. The average temperature has increased by 3OC in recent decades.

C. Antarctica contains most of the world's fresh water.

D. Ten percent of Antarctica's ice has already been lost.

5. The best title for the passage is _____. [ ]

A. Our planet in danger

B. Antarctica melting away

C. Action plan to save Antarctica

D. Let's save the ozone layer

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某投资项目总投资为5000万元,其中自有资金为2500万元,借款年利率8%,若项目的全投资内部收益率为12%,则该项目的自有资金内部收益率将( )。

A.小于8%
B.等于12%
C.大于12%
D.等于8%

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以下关于DFD与IDEFO比较错误的是______。

A.在模型规范方面,DFD方法更加规范,更加适合初学者
B.DFD图用箭头也叫做数据流来描述数据移动的方向
C.IDEFO还可以表示出控制流和说明处理或活动实施方式的一些约束
D.这两种方法都是基于结构化分析思想

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亚音速气流在光滑扩张形管道内流动时,气流参数的变化规律是().

A.速度下降,压力升高

B.速度下降,压力下降

C.速度上升,压力下降

D.速度上升,压力升高

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