Timothy Hall,毕业于美国哥伦比亚大学,英语语言学专业硕士。
Arthur H. Milch,美国新泽西学院TESOL专业教育学硕士。
Denise McCormack,美国新泽西学院TESOL专业教育学硕士。
The principles making radio possible were developed throughout the nineteenth century. The first breakthrough was by the British physicist Michael Faraday in 1831. He discovered that when an electric current passes through one wire, it produces a current in another wire even though the wires do not touch each other. In 1864, James Maxwell showed that this current——composed of electromagnetic waves——travels at the speed of light. Heinrich Hertz proved that the waves pass through solid objects. With these discoveries in place, the race was on to develop a system of wireless radio.
Among the contenders was Reginald Fessenden, a Canadian inventor. Fessenden began experimenting with radio detectors in order to explore the possibility of voice transmission. In 1900, he was the first person to transmit his voice, but the sound was unrecognizable because the waves were not continuous. He invented a barreter detector, taking its name from the French word exchanger, to receive AM (amplitude modulated) signals, but it was not sensitive enough. One day in 1901, he accidentally left a filament of wire in acid for too long until only a tip of the wire was in contact with the acid. Fessenden noticed that, with the wire in the acid, the barreter was very sensitive to nearby continuous radio waves.
Fessenden called his invention a liquid barreter, but it became known as an electrolytic detector. The detector consisted of several connected parts forming an electric circuit. A silver-coated platinum wire was dipped into a small platinum cup filled with nitric or sulfuric acid and connected to the ground. A battery was connected between the wire and the acid, prompting a current to flow in the detector. Someone wearing headphones that were hooked up to the detector could hear a hissing noise, which could be adjusted by turning a dial until the hissing noise stopped. At that point, the detector was highly sensitive to incoming radio waves.
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不错不错不错不错不错不错
评分超级品类日买的书,价钱还是很划算的,买了好多书,希望下次还有类似活动,继续囤书
评分考试用的,很好,纸张质量很好,印刷也很清晰
评分书很不错,还在看初级,等着最后用高级提高自己了
评分2005年9月,美国教育考试服务中心ETS在全球推出了一种全新的综合英语测试方法,即能够反映在一流大专院校教学和校园生活中对语言实际需求的新托福考试,即TOEFL iBT(Internet Based Test)。
评分符合预期,值得购买.
评分不错不错,对于英语学习很有帮助,整本书的框架循序渐进
评分 评分新托福由四部分组成,分别是阅读(Reading)、听力(Listening)、口试(Speaking)、写作(Writing)。每部分满分30分,整个试题满分120分。
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