發表於2024-09-21
新東方·新托福考試專項進階:高級閱讀 pdf epub mobi txt 電子書 下載
Timothy Hall,畢業於美國哥倫比亞大學,英語語言學專業碩士。
Arthur H. Milch,美國新澤西學院TESOL專業教育學碩士。
Denise McCormack,美國新澤西學院TESOL專業教育學碩士。
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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買瞭一個係列很多本,最近一本一本買的……趕緊看啊
評分趕著京東搞活動,把剩下的GRE和托福的書都買瞭,蠻劃算的!這麼多書,盡全力去看!希望自己在10個月內順利攻下托福GRE,然後把科研也搞好,再發一篇好的paper,等畢業以後去美帝讀個博士。加油咯??
評分書不錯,活動也劃算,下次再來……
評分報名瞭今年的考試,打算打個醬油。
評分托福從這裏開始,看見這本書就有學托福的欲望,印刷好。
評分很好很好很好很好很好,沒問題沒問題沒問題沒問題沒問題。
評分孩子精心挑選,看效果吧
評分喜歡在jd買買買,因為方便快捷,質量也挺好的。小到生活日用品、食品,大到手機數碼大傢電都在jd買買買。每天逛京東就像逛市場?由於經常買,訂單多,就不一一評價瞭,好評都統一用此評語……?
評分報名瞭今年的考試,打算打個醬油。
新東方·新托福考試專項進階:高級閱讀 pdf epub mobi txt 電子書 下載