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[单选题]
一段直径不变管道的流速从2m/s增加到4m/s时，在水流都处于层流区时，沿程水损失是原来的（)倍。
A.2
B.4
C.6
D.8
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（请给出正确答案）
A.2
B.4
C.6
D.8
答案
更多“一段直径不变管道的流速从2m/s增加到4m/s时，在水流都处于层流区时，沿程水损失是原来的()倍。”相关的问题
第1题
拟建一座用于出租的房屋，获得土地的费用为30万元。房屋有4种备选高度，不同建筑高度的建造费用和房屋建成后的租金收入及经营费用如下表。
| 层数(层) | 3 | 4 | 5 | 6 |
| 初始建造费用(万元) | 200 | 250 | 310 | 380 |
| 年运行费用(万元) | 15 | 25 | 30 | 40 |
| 年收入(万元) | 40 | 60 | 90 | 110 |
第4题
A、在固定成本不变的情况下，经营杠杆系数说明了销售量增长(减少)所引起息税前利润增长(减少)的幅度
B、在固定成本不变的情况下，销售量越大，经营杠杆系数越小，经营风险也就越小
C、其他因素不变，固定成本越大，经营杠杆系数越大
D、当固定成本趋于0时，经营杠杆系数趋于无穷大
第6题
建筑材料期末试题：混凝土中掺入适量的木质素磺酸钙后，若保持拌合料流动性和硬化后强度不变时，可以获得节省 的效果。
第8题
1. “The Nobel Prize in Physiology or Medicine 2004”Press Release(15分)
4 October 2004
The Nobel Assemblyat Karolinska Institutet has today decided to award The Nobel Prize in Physiology or Medicine for 2004 jointly toRichard Axel and Linda B. Buckfor their discoveries of "odorant receptors and the organization of the olfactory system"
Summary
The sense of smell long remained the most enigmatic of our senses. The basic principles for recognizing and remembering about 10,000 different odours were not understood. This year's Nobel Laureates in Physiology or Medicine have solved this problem and in a series of pioneering studies clarified how our olfactory system works. They discovered a large gene family, comprised of some 1,000 different genes (three per cent of our genes) that give rise to an equivalent number of olfactory receptor types. These receptors are located on the olfactory receptor cells, which occupy a small area in the upper part of the nasal epithelium and detect the inhaled odorant molecules.
Each olfactory receptor cell possesses only one type of odorant receptor, and each receptor can detect a limited number of odorant substances. Our olfactory receptor cells are therefore highly specialized for a few odours. The cells send thin nerve processes directly to distinct micro domains, glomeruli, in the olfactory bulb, the primary olfactory area of the brain. Receptor cells carrying the same type of receptor send their nerve processes to the same glomerulus. From these micro domains in the olfactory bulb the information is relayed further to other parts of the brain, where the information from several olfactory receptors is combined, forming a pattern. Therefore, we can consciously experience the smell of a lilac flower in the spring and recall this olfactory memory at other times.
Richard Axel, New York, USA, and Linda Buck, Seattle, USA, published the fundamental paper jointly in 1991, in which they described the very large family of about one thousand genes for odorant receptors. Axel and Buck have since worked independent of each other, and they have in several elegant, often parallel, studies clarified the olfactory system, from the molecular level to the organization of the cells.
第9题
T.对
F.错
第10题
A.生产量等于销售量，统称为产销量
B.把生产总成本按其性态区分为固定成本和变动成本
C.单位变动成本可变
D.产品销售收入和生产总成本均为产销量的线性函数
E.单位产品销售税率不变
第11题
将英语短文译为中文
3 Self-Powered Nanotech (10分)
Nanosize machines need still tinier power plants
By Zhong Lin Wang
The watchmaker in the 1920s who devised the self-winding wristwatch was on to a great idea: mechanically harvesting energy from the wearer’s moving arm and putting it to work rewinding the watch spring.
Today we are beginning to create extremely small energy harvesters that can supply electrical power to the tiny world of nanoscale devices, where things are measured in billionths of a meter. We call these power plants nanogenerators. The ability to make power on a minuscule scale allows us to think of implantable biosensors that can continuously monitor a patient’s blood glucose level, or autonomous strain sensors for structures such as bridges, or environmental sensors for detecting toxins — all running without the need for replacement batteries. Energy sources are desperately needed for nanorobotics, microelectromechanical systems (MEMS), homeland security and even portable personal electronics. It is hard to imagine all the uses such infinitesimal generators may eventually find.
In Brief
★Nanotechnology has huge potential — but those minuscule devices will need a power source that is better than a battery.
★ Waste energy, in the form. of vibrations or even the human pulse, could provide sufficient power to run such tiny gadgets.
★ Arrays of piezoelectric nanowires could capture and transmit that waste energy to nanodevices.
★ Medical devices will likely be a major application. A pacemaker’s battery could be charged so it would not need replacing, or implanted wireless nanosensors could monitor blood glucose for diabetics.
