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Lesson2

Scanning

1、单选题：
‎Read the passage "The Discovery of X-rays" quickly and choose the paragraph(s) which contain(s) the answer(s). You may choose more than one answer for question 3. ‌‎‌The Discovery of X-rays‌‎ ‌Par. 1 Except for a brief description of the Compton effect, and a few other remarks, we have postponed the discussion of X-rays until the present chapter because it is particularly convenient to treat X-ray spectra after treating optical spectra. Although this ordering may have given the reader a distorted impression of the historical importance of X-rays, this impression will be corrected shortly as we describe the crucial role played by X-rays in the development of modern physics.‌Par. 2 X-rays were discovered in 1895 by Roentgen while studying the phenomena of gaseous discharge. Using a cathode ray tube with a high voltage of several tens of kilovolts, he noticed that salts of barium would fluoresce when brought near the tube, although nothing visible was emitted by the tube. This effect persisted when the tube was wrapped with a layer of black cardboard. Roentgen soon established that the agency responsible for the fluorescence originated at the point at which the stream of energetic electrons struck the glass wall of the tube. Because of its unknown nature, he gave this agency the name X-rays. He found that X-rays could manifest themselves by darkening wrapped photographic plates, discharging charged electroscopes, as well as by causing fluorescence in a number of different substances. He also found that X-rays can penetrate considerable thicknesses of materials of low atomic number, whereas substances of high atomic number are relatively opaque. Roentgen took the first steps in identifying the nature of X-rays by using a system of slits to show that (1) they travel in straight lines, and that (2) they are uncharged, because they are not deflected by electric or magnetic fields.‌Par. 3 The discovery of X-rays aroused the interest of all physicists, and many joined in the investigation of their properties. In 1899 Haga and Wind performed a single slit diffraction experiment with X-rays which showed that (3) X-rays are a wave motion phenomenon, and, from the size of the diffraction pattern, their wavelength could be estimated to be 10-8 cm. In 1906 Barkla proved that (4) the waves are transverse by showing that they can be polarized by scattering from many materials.‌Par. 4 There is, of course, no longer anything unknown about the nature of X-rays. They are electromagnetic radiation of exactly the same nature as visible light, except that their wavelength is several orders of magnitude shorter. This conclusion follows from comparing properties 1 through 4 with the similar properties of visible light, but it was actually postulated by Thomson several years before all these properties were known. Thomson argued that X-rays are electromagnetic radiation because such radiation would be expected to be emitted from the point at which the electrons strike the wall of a cathode ray tube. At this point, the electrons suffer very violent accelerations in coming to a stop and, according to classical electromagnetic theory, all accelerated charged particles emit electromagnetic radiations. We shall see later that this explanation of the production of X-rays is at least partially correct.‌Par. 5 In common with other electromagnetic radiations, X-rays exhibit particle-like aspects as well as wave-like aspects. The reader will recall that the Compton effect, which is one of the most convincing demonstrations of the existence of quanta, was originally observed with electromagnetic radiation in the X-ray region of wavelengths.‌‎‌‎When were X-rays discovered?‌
选项：
A: Par. 1
B: Par. 2
C: Par. 3
D: Par. 4
E: Par. 5
答案: 【 Par. 2】点我阅读全文

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01 绪论

单元测试（一）

1、单选题：
‏（   ）已成为纺织工业中发展最快的一个行业。‏
选项：
A: 非织造材料与工程
B: 服装工程
C: 染整技术
D: 轻工技术
答案: 【 非织造材料与工程】点我阅读全文

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期中测验

期中测验卷

1、单选题：
( )是指保险人将其承担的保险业务，部分或全部转移给其他保险人的一种保险。
选项：
A: 分保
B: 原保险
C: 共同保险
D: 重复保险
答案: 【 分保】点我阅读全文

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第一周 急诊常见症状的病情评估及分层救治（一）

第一周单元测验

1、单选题：
‍患者75岁，男性，胸骨后疼痛4小时，向左肩放射，伴恶心、呕吐，首先应进行的检查是​
选项：
A: 心电图
B: 胸部X线
C: 胸部CT
D: 超声心动图
答案: 【 心电图】点我阅读全文

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第3周 R数据管理

第3周 小测

1、单选题：
class(sqrt((1:4)%*%(1:4))) 返回结果是
选项：
A: matrix
B: numeric
C: integer
D: array
答案: 【 matrix】点我阅读全文

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第三单元 生产与服务管理

第三单元测试

1、单选题：
‍生产系统是由输入、转化、输出和反馈控制四个部分构成的，核心功能是（）‍
选项：
A: 转化
B: 输入
C: 反馈
D: 输出
答案: 【 转化】点我阅读全文

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第五章 系统评价方法

第五章单元测验

1、单选题：
‎下列哪项不是系统评价的要素？‏
选项：
A: 评价对象
B: 评价主体
C: 评价时期
D: 评价结果
答案: 【 评价结果】点我阅读全文

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第一章导论

测试一

1、填空题：
‍黄侃的龙学代表作​
答案: 【 《文心雕龙札记》】点我阅读全文

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第1讲初始VisualBasic

第1讲单元测验

1、单选题：
​属于VB6.0特点的是 __________。‍
选项：
A: 事件驱动的编程机制
B: 没有数据类型的程序设计语言
C: 基于对象、不支持结构化
D: 没有可视化设计工具
E: 只能通过文本编辑工具编写程序
F: 具有丰富的数据类型、类库
答案: 【 事件驱动的编程机制;
具有丰富的数据类型、类库】点我阅读全文

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