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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特彆有用的教輔,還是618價格公道,買全瞭
評分還不錯吧還好不錯可以用,比較官方權威的參考書
評分很不錯,希望有幫助
評分這係列的人復習資料還是不錯的,推薦英語基礎弱的人先做這個再刷原題!
評分嗬嗬江湖救急近近景近景近近景近景
評分挺好的,物流也很快,書也不錯。??(?•?ω•? ?)?
評分閱讀(Reading):有三篇文章
評分還沒拆,目前隻做瞭初級閱讀,感覺得從易到難,不然自信心得受挫摺。加油?
評分聽力中級很適閤提高聽力的朋友,沒事練習聽力,還是挺喜歡的,雖然不會去靠托福,但是學習英語聽聽英語本身也是一種享受。
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