發表於2024-11-22
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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還有來得及打開,以後要努力學習英語
評分京東圖書很方便,速度很快,價格便宜
評分托福備考經典教材,助力衝百一次成功。
評分自己復習托福還可以
評分托福在中國大陸一共有133個考場,編號從STN80000到STN80132,按照考場開放的順序排序,第一個開放的托福考場是STN80000 北京工商大學,其中北京、四川、陝西、河南、上海等地的考場最為緊張。
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。
評分京東買書又快又好 辛苦快遞小哥瞭
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評分新東方·新托福考試專項進階:高級閱讀 pdf epub mobi txt 電子書 下載