蔬菜作物缺(),首先表现为顶端生长点停止生长,幼叶畸形,邹缩。叶脉间不规则褪绿。

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问题:

蔬菜作物缺(),首先表现为顶端生长点停止生长,幼叶畸形,邹缩。叶脉间不规则褪绿。

考点:农艺师考试蔬菜栽培蔬菜栽培题库
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如图所示为一磁流体发电机示意图,A、B是平行正对的金属板,等离子体(电离的气体,由自由电子和阳离子构成,整体呈电中性)从左侧进入,在t时间内有n个自由电子落在B板上,则关于R中的电流大小及方向判断正确的是(  )

A.I= ,从上向下

B.I= ,从上向下

C.I= ,从下向上

D.I= ,从下向上

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如图所示,水平面上有两电阻不计的光滑金属导轨平行固定放置,间距d=0.5m,左端通过导线与阻值为2Ω的电阻R连接,右端通过导线与阻值为4Ω的小灯泡L连接;在CDEF矩形区域内有竖直向上的匀强磁场,CE长为2mCDEF区域内磁场的磁感应强度B如图所示随时间t变化;在t=0s时,一阻值为2Ω的金属棒在恒力F作用下由静止从AB位置沿导轨向右运动,当金属棒从AB位置运动到EF位置的全过程中,小灯泡的亮度都没有变化。求:⑴通过小灯泡的电流强度;⑵恒力F的大小;⑶金属棒的质量。

题型:填空题

Have you seen the film Star Wars? If you have, you’ll know what an energy–gun is, and a light–sword too. The gigantic space ship in Star Wars can destroy a whole planet in a second or two, and it does so. Fortunately, it isn’t our planet; it belongs to a distant system, far out in space.

The great empty spaces of the universe are no problem in star Wars. The fighters know how to fold space over, like a sheet of paper, so that very distant stars are brought close together; they call it “hyperspace”. This means, of course, that their ships don’t have to creep along at the speed of light. If they did that, they would take years, even centuries, to reach the battlefield. Hyperspace allows them to travel as “supralight” speed and get there in a couple of hours. It’s good clean fun (健康无害的娱乐) though.

We certainly don’t know all about physics yet, but we do have the work of Albert Einstein. He asked us to believe that nothing could travel faster than light through an empty space --- but don’t let that miserable idea spoil the film for you, even though all our observations up to now have shown that Einstein was dead right --- forget it. Sit back and watch those energy–shells blow up the hated enemy. The Star Wars princess is extremely beautiful.

The more we “discover”, the more we must admire Einstein. He knew it all before us --- by about 1910 in fact. We observe certain very high speed particles (微粒), and they behave exactly as Einstein predicted they would. We can give them a speed almost equal to light, but they never quite reach light speed. He predicted that a very fast–moving object, as it flashed by a stationary observer(静止的参照物), would seem to have much greater weight than usual. And that, too, was proved correct.

So far as scientific theory or evidence is concerned, there is no such thing as hyperspace, no such speed as supralight. Space is as we know it, and light speed is the highest possible speed. “But,” say the story-writers, “that’s only true at present. We don’t know all about physics yet. Who knows --- who knows if there isn’t another set of facts just waiting to be discovered; another universe perhaps, just round the corner?”

Einstein seems to have been prepared for that too. In his theories he emphasized the word “relative”. Everything --- speed, weight, time, etc. --- is relative to something else. Nothing, by itself is real or absolute. So if there is another universe somewhere, we shall only know about it relative to ourselves. So far there’s no sign of it. But for the future, well, who knows?

51.What is the purpose of science – fiction stories and films?

They point out the way ahead, and scientists are grateful.

They encourage us in our searching for the truth.

They show us what the future universe will be like.

They are written and made to entertain us.

52.If you see Star Wars, what might spoil it for you, according to the passage?

A.Einstein’s theories.          

B.The uncomfortable surroundings of the theatre.

       C.The ugly actress and actors.   

D.The rude audience.

53.Einstein predicted that the increase in weight          .

applies only to big things, like huge space–ships

is apparent only to the stationary observer

is a real increase       

remains even after the objective has stopped moving

54.Einstein’s theories emphasized          .

A.everything is relative to something else         B.the universe is infinite (无限的)

C.light speed is the highest possible speed     D.there is another universe somewhere

55.Although Einstein did not observe the behavior of high–speed objects,         .

his theories predicted they travels at light speed

his theories predicted them with great accuracy

he knew they would be discovered       

he predicted them in the year 1910

题型:填空题

下列对于久期公式的理解,不正确的是( )。

A.收益率与价格反向变动

B.价格变动的程度与久期的长短有关

C.久期越长,价格的变动幅度越大

D.久期公式中的D为修正久期

题型:填空题

下列不属于电路作用的是()。

A.连接电气器件

B.转换其他形式能为电能

C.处理

D.电能转换其他形式能

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