发表于2025-06-10
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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新东方·新托福考试专项进阶:高级阅读 下载 mobi pdf epub txt 电子书 格式 2025
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评分考托福的筒子们,加油啊,托福书在手,好红红火火恍恍惚惚哈哈哈哈哈哈哈
评分京东的包装真的超级放心!一点都没有损坏!以后买书也要认准京东了(?????????)新东方自营店嘻嘻当然放心是正版(?????????)
评分书本已经收到了质量很好啊!
评分本系列丛书从托福考试所考查的听、说、读、写四项技能入手,为考生提供详尽的考试指导,并将各技能分为初、中、高三级,通过独特的“进阶训练”方式,再辅以大量练习,帮助考生逐步掌握托福实考的技巧,同时切实提高英语实际运用能力,从而在短期内轻松取得托福高分。本丛书内容编排由易到难,循序渐进,实战性强,是不可多得的托福备考资料。
评分看着不错呢,好好学英语。封皮儿色差好大。
评分“托福”译自TOEFL,中国人称为考“托福”。
评分包装很好,发货也很快。
评分书很不错,还在看初级,等着最后用高级提高自己了
新东方·新托福考试专项进阶:高级阅读 mobi epub pdf txt 电子书 格式下载 2025