發表於2025-03-04
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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還不錯,用過之後再來評價
評分書買瞭好多,300-180,但還是比不上去年,隔壁都不怎麼逛瞭,60元損失心疼
評分其實不是今年考托福,但是看有活動就買瞭,希望考好
評分好書。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。
評分書很不錯,專業用書,非常好
評分京東的東西非常有保證,送貨也很及時,非常喜歡!
評分還行吧,質量還不錯,手感也不錯
評分經典的英語教材,質量不錯!
評分考試 學習用書,比較有價值。
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