发表于2025-01-22
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.
……
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
新东方·新托福考试专项进阶:高级阅读 下载 mobi epub pdf 电子书孩子要的,学托福必备吧,大家都在用。
评分为了自学准备托福考试买的~包装很好京东快递优秀~
评分 评分还没拆,目前只做了初级阅读,感觉得从易到难,不然自信心得受挫折。加油?
评分很不错,希望有帮助
评分很有用的书,很有针对性,帮助很大
评分2005年9月,美国教育考试服务中心ETS在全球推出了一种全新的综合英语测试方法,即能够反映在一流大专院校教学和校园生活中对语言实际需求的新托福考试,即TOEFL iBT(Internet Based Test)。
评分新东方·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