什麼是自行車
bicycle
Lightweight, two-wheeled, steerable machine that is propelled by the rider. The wheels are mounted in a metal frame, and the front wheel is held in a movable fork. The rider sits on a saddle and steers by handlebars attached to the fork, propelling the bicycle by two pedals attached to cranks that turn a driving sprocket. An endless chain transmits power from the driving sprocket to a back-wheel sprocket. A heavy pedalless form built in 1818 was propelled simply by the rider paddling his feet against the ground. In 1839 the Scottish blacksmith Kirkpatrick Macmillan (1813-1878) built a bicycle propelled by pedals, cranks, and drive rods; he is widely credited with inventing the bicycle. Important innovations were introduced by Pierre and Ernest Michaux in France in 1861, and by 1865 their company was manufacturing 400 vélocipèdes a year. A lighter version produced in England in 1870 (nicknamed the “penny-farthing”) featured a large front wheel and small back wheel. By the 1890s the standard bicycle design was established, and with the smooth ride enabled by the new pneumatic tires its popularity exploded. 20th-century improvements included lighter frames and improved gears and brakes. Widely used throughout the world, it is a basic means of transportation in many countries. See also bicycle industry.
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什麼是戈巴契夫
Gorbachev,Mikhail(Sergeyevich)蘇聯官員及最後一任總統(1990~1991)。1955年獲國立莫斯科大學法學學位,1980年成為中央委員會政治局正式委員,1985年被推選為蘇聯共產黨總書記。戈巴契夫開始對蘇聯的經濟和政治制度實施改革,但他的開放政策(glasnost)和重建政策(perestro...
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什麼是殘毒積累
有毒污染物在人和生物體內殘留和蓄積的現象。在人和生物體內殘留和蓄積的有毒污染物主要是金屬、農藥等。在中國部分地區所作的調查表明,在農作物、禽肉、蛋、茶葉、水產品中都有農藥殘毒(見農藥殘留)。如有機氯農藥DDT和六六六,在某些地區的農副產品中檢出率可達...
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什麼是聲望遠鏡
一種指向性很強的聲接收系統。將聲望遠鏡對準某方向來的聲波,這方向的聲波在望遠鏡上的響應最大,而其他方向來的聲波則相對較小。藉助於聲望遠鏡,可以求得聲源的空間分佈,能對一定範圍內的環境進行聲學分析,求出各個噪聲源的位置和強度,為防治噪聲污染提供科學依據。...
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什麼是店肆
泛指各種商店,又有店鋪、鋪席、店、鋪、肆等名稱。沿革中國古代城市中的商店有兩大類:按行業分的專業商店和供應居民日常生活食用品的主副食、雜貨店。唐代以前的裏坊制城市中,前者集中於市,有專門官員管理;後者則在坊內沿街設置。宋代以後的街巷制城市中,專業商店演...