热门试题
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1.
儿童早期的知识、技能的获得，多半由潜移默化得来，这是( )
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2.
下列各项中，属于所有者权益的有
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3.
3.Friction is a force which opposes motion. Much of the energy supplied to a complicated machine with many moving parts is wasted in overcoming this opposition. The energy is converted into useless heat. The amount thus lost can be considerably reduced and the life of the machine prolonged by careful lubrication. This reduction improves the efficiency of the machine. Another way in which friction is reduced is to substitute roller or ball bearings for the earlier type of bearing, in which the surfaces in contact move by sliding. Bearings of these later types are used very extensively in many kinds of modern machinery.It must not be assumed, however, that friction is always a disadvantage. In many instances it is highly important. Belts are often used in conveying power from one machine to another. In the absence of friction, this could not be done. The driving wheel would not run the belt, neither would the belt run the wheel to driver. Without friction, then, belted machinery could not be used. Again in the case of all motor vehicles, friction is essential in the operation of the brake. Were there no friction, there could be no brake. But even this illustration does not give an adequate picture of the importance of friction. The vehicle could not even be started if it were not for the friction exerted between the tires and the road. Nails hold in wood, and screws hold in either wood or metal by reason of friction, without which they would be useless. Walking is difficult enough on an icy pavement, but it would be wholly impossible if there were no friction at all between the shoe and the pavement.(5分)3.1Friction arises when____.(1分)A. an opposing force of motion existsB. the energy is wastedC. everything is motionlessD. a complicated machine is supplied with energy
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4.
全辐射式温度传感器利用物体在全光谱范围内总辐射能量与温度的关系测量温度。全辐射式温度传感器测得的温度与物体的实际温度相比总是（）
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5.
查看材料作者说七斤在鲁镇“的确已经是一名出场人物”是何意思?有无讽刺成分?(4分)
