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【简答题】
有一个电子管,其真空度(即电子管内气体压强)为 1.0×10 -5 mmHg,则27 °C 内单位体积的分子数为_____×10 17 /m 3 .(玻尔兹曼常量k=1.38×10 -23 J/K , 1 atm=1.013×10 5 Pa =76 cmHg ) (填2个数字+小数点)
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举一反三
【单选题】Laser light beamed onto glass fibers casts a characteristic pattern.
A.
projects
B.
molds
C.
cuts
【单选题】The word 'laser' was coined as an acronym for Light Amplification by the Stimulated Emission of Radiation. Ordinary light, from the Sun of a light bulb, is emitted spontaneously, when atoms or molecul...
A.
need
B.
device
C.
influence
D.
reproduction
【单选题】Why do the American doctors think of using laser light to treat heart disease?
A.
Beeause laser light is quite powerful．
B.
Because laser light is penetrating．
C.
Because laser light can destroy the blocking materials in human’s artery．
D.
Because laser light can travel through the human body．
【单选题】What’S the main idea of the passage7
A.
Laser light treatment of heart disease should take the place of the traditional operatlon．
B.
Laser light treatment has been proved better and more effective than the traditional operation．
C.
More advanced technology should be encouraged to try on．
D.
Laser light treatment of heart disease still needs’more research．
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