| Most of the pioneers of low-temperature
physics expected gases to liquefy, but none of them predicted superconductivity.
This phenomenon was discovered in 1911 by Onnes while he was studying frozen
mercury. More than 40 years passed before physicists were able to offer an explanation for superconductivity. The accepted theory, developed in the 1950s, holds that the fundamental behavior of electrons changes at very low temperatures because of the effects of quantum mechanics. Electrons are tiny particles that make up the outer part of an atom, circling rapidly around the nucleus of the atom. In a regular conductor—a metal that conducts an electric current—the outermost electrons are not bound tightly to the atoms, and so they move around relatively freely. The flow of these electrons is an electric current. At normal temper A. electrons do not move freely through the metal B. electrons are crowded together C. paired electrons move uninterruptedly D. paired electron dance together to and fro 热门试题:[单选题]Passage 1
Plants and animals that have been studied carefully seem to have built-in clocks. These biological clocks, as they are called, usually are not quite exact in measuring time. However, they work pretty well because they are "reset" each day, when the sun comes up.
Do pigeons use their biological clocks to help them find directions from the sun? We can keep pigeons in a room lit only by lamps. And we can program the lighting to produce artificial "days",different from the day outside. After a while we have shifted their clocks. Now we take them far away from home and let them go on a sunny day. Most of thegn start out as if they know just which way to go, but choose a wrong direction. They have picked a direction that would be correct for the position of the sun and the time of day according to their shifted clocks.
It is known and experimented that homing pigeons can tell directions by the sun. But what happens when the sky is darkly overcast by clouds and no one can see where the sun is? Then the pigeons still find their way home. The salne experiment has been repeated many times on sunny days and the result was always the same. But on very overcast days clock-shifted pigeons are just as good as normal pigeons in starting out in the right directions. So it seems that pigeons also have some extra sense of direction to use when they cannot see the sun.
Naturally, people have wondered whether pigeons might have a built-in compass—something that would tell them about the directions of the earth's magnetic field. One way to test that idea would be to see if a pigeon's sense of direction can be fooled by a magnet attached to its back.
With a strong magnet close by, a compass can no longer tell direction.
To test the idea, a group of ten pigeons had strong little magnet bars attached to their backs.
Another group carried brass bars instead which were not magnetic. In a number of experiments,both groups were taken away from home and let go. On sunny days none of the magnet-pigeons was fooled. They were just as good as the brass-pigeons in starting out in the right direction toward home. On cloudy, overcast days, however, with no sun the brass-pigeons chose the right direction,but the magnet-pigeons were in trouble. They later started out in different directions and acted completely lost.
What does the author want to say by citing the last experiment?
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A.On heavily cloudy days, pigeons that are not well trained do not fly. B.Pigeons use different sources to find directions on different weather. C.Magnetic field is an important source in helping pigeons to find directions. D.The little magnet bars make it easier for pigeons to find directions. [单选题]下列哪个因素对多轴航拍效果影响最大
A.风速 B.负载体积 C.负载类型 [判断题]节肢动物的消化管与体壁之间有很大的混合体腔，所以它不是真体腔动物。（）
[判断题]电子对账单可由客户通过个人网上银行获取。
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A.1 B.2 C.3 D.4 [填空题]未列入月度设备停电计划的项目一般不得列入周计划。对于新增重点工程、临时消缺等项目，相关部门应提供必要说明，并通过调控机构安全校核后方可列入周设备停电计划，但均统计为（）。
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conversation. At the end of the conversation, you will be given 15 seconds to
answer the questions.
Now listen to the conversation. What is the proper description of the saucepans A. Imitation wood, dark brown color, country-style. B. Imitation wood, light brown color, country-style. C. Imitation wood, dark brown color, city-style. D. Imitation wood, light brown color, city-style. [单项选择]大便时和便后肛门剧痛并带少量鲜血的病有
A. 肛管直肠周围脓肿 B. 直肠息肉 C. 肛裂 D. 混合痔 E. 血栓性外痔 [判断题]>连铸工艺的特点是不经轧制从钢液间接得到钢坯。 ( )
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A.5～10mm； B.10～15mm； C.15～20mm； D.20～30mm。 [单项选择]属足太阴脾经的腧穴是（）。
A. 血海 B. 少海 C. 小海 D. 照海 E. 气海 [多项选择]项目融资大致上可以分为( )等几个阶段。
A. 投资研究阶段 B. 投资决策阶段 C. 融资决策分析阶段 D. 融资结构分析阶段 E. 融资谈判和执行阶段 [单项选择]世界上第一家自助式餐厅开设于美国的（）。
A. 芝加哥 B. 休斯敦 C. 洛杉矶 D. 华盛顿 [多选题]《关于加强反洗钱客户身份识别有关工作的通知》（【2017】235号文）要求加强对特定自然人客户的身份识别，特定自然人包括哪些（ ）
A.外国政要 B.国际组织的高级管理人员 C.上述A、B的特定关系人 D.中国局级以上官员 [单选题]地下降水施工时：对于降水、截水和回灌等方法的应用，应严格遵守《建筑基坑支护技术规程》JGJ120相关要求，地下水应降至开挖基坑底面（）以下，防止水泡导致基坑塌方。
A.0.3m B.0.5m C.0.7m D.0.9m [单选题]AC/A值是指每使用1D的调节所引起的（ ）
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A.利用消防水池供水。 B.利用移动消防装备与固定消防设施相结合供水 C.利用固定消防设施供水 D.利用移动消防装备直接供水 [单选题]坚决反对和防止腐败是全党一项重大的政治任务。不坚决惩治腐败.党同人民群众的血肉联系就会受到严重损害.就有丧失( )的危险.就有可能走向自我毁灭。
A.党的领导地位 B.党的执政基础 C.党的执政地位 D.党的核心地位 [单选题]一环形跑道上画了100个标记点，已知相邻任意两个标记点之间的跑道距离相等。某人在环形跑道上跑了半圈，问他最多能经过几个标记点？（ ）
A.49 B.50 C.51 D.100 [判断题]隔离开关操作人员须经过培训并取得由供电设备管理单位颁发的安全操作证后，才能担任工作。
A.正确 B.错误 [单选题] ()沿建筑物外围从地面搭起,用于外墙砌筑和装修。
A.外脚手架 B.里脚手架 C.上脚手架 D.下脚手架 [单选题]225.挂有超限货物车辆的列车，由于车站值班员错误办理，造成该列车进入非固定线路，未发生冲突脱轨事故，属于( )铁路交通事故。
A.一般A类事故 B.一般B类事故 C.一般C类事故 D.一般D类事故 [单选题]塔式起重机安装前安装单位应对所用的螺栓和销轴进行检查,其高强螺栓使用次数不得超过( )次, 不得严重锈蚀。
A.1 B.2 C.3 D.5 [单选题]属于战略管理核心环节的是（）
A.战略分析 B.战略实施 C.战略制定 D.战略控制 [单选题]发票人一般应在作业（ ）小时之前将工作票交给工作领导人，使之有足够的时间熟悉工作票中的内容并做好准备工作。
A.4 B.6 C.10 D.12 [简答题]研究植物营养与肥料的目的是什么？
[单项选择]病人看到房屋倾斜，汽车变得扭曲，电线杆像筷子一样细，这种现象是
A. 非真实感 B. 视物变形 C. 错觉 D. 幻视 E. 人格解体 [填空题]数据的逻辑结构可用一个二元组B＝(K，R)来表示，其中K是 【1】 ，R是 【2】 。
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