什么是经济周期
经济活动比率(按就业、价格和生产的水平计量)周期性的波动。经济学家长期以来一直为繁荣时期之後为什麽总是出现经济危机(股市崩盘、银行倒闭、失业等)而争论不休。有人提出每八~十年为一个周期,康得拉季耶夫则主张更长的周期。除了偶然的冲击(战争、技术变化等等)之外,投资和消费是影响经济活动水平的主要因素。增加投资,譬如建造工厂,除原有开支本身之外还要创造其他的收入,因为建厂的工人们还得用掉他们的工资。相反地,如果消费需求增加了,为了满足需求最终还得建造新的工厂。最终经济总会到达它容量的极致,这时候很少自由资本,没有新的需求,因此程序又颠倒过来,结果产生紧缩。农业市场的自然波动、时尚风潮等心理因素以及货币供给(money supply)的变化,是投资或消费方面造成这些变化的起因。自第二次世界大战以来,政府以货币政策做为调节经济周期的手段:在经济呆滞时期起刺激作用以避免停滞性通货膨胀或经济萧条,在经济扩张时期起抑制作用。
business cycle
Periodic fluctuation in the rate of economic activity, as measured by levels of employment, prices, and production. Economists have long debated why periods of prosperity are eventually followed by economic crises (stock-market crashes, bankruptcies, unemployment, etc.). Some have identified recurring eight-to-ten-year cycles in market economies; longer cycles have also been proposed, notably by Nikolay Kondratev. Apart from random shocks to the economy, such as wars and technological changes, the main influences on the level of economic activity are investment and consumption. An increase in investment, as when a factory is built, leads to consumption because the workers employed to build the factory have wages to spend. Conversely, increases in consumer demand cause new factories to be built to satisfy the demand. Eventually the economy reaches its full capacity, and, with little free capital and no new demand, the process reverses itself and contraction ensues. Natural fluctuations in agricultural markets, psychological factors such as a bandwagon mentality, and changes in the money supply have all been proposed as explanations for initial changes in investment and consumption. Since World War II, government monetary policy has aimed at moderating the business cycle, preventing the extremes of inflation and depression by stimulating the economy in slack times and restraining it during expansions.
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什么是洗涤作用
在机械的搅动下从浸在洗涤剂水溶液的固体表面清除污垢的过程。污垢可分液体油污(如动、植物油和矿物油)和固体质点(如灰、铁锈和炭黑)两类。这两类污垢除去的机理是不同的。液体油污的去除(滚走机理)从固体表面清除液体油污,其实质是洗涤剂液体对固体表面的润湿(图1)。...
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什么是三边测量
在地面上布设一系列连续的三角形,采取测边方式来测定各三角形顶点水平位置的方法。是建立大地控制网和工程测量控制网的方法之一。由于在地面上直接丈量距离一般困难很多,三边测量要求丈量所有的边,困难尤甚。直到1948年和1956年先后出现光电测距仪和微波测距仪后...
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什么是ÏËάËØÃÑ
ÊÇÏËάËظ߷Ö×ÓÖÐôÇ»ùµÄÇâ±»Ìþ»ùÈ¡´úµÄÉú³ÉÎï¡£ÏËάËØÊÇÒ»ÖּȲ»ÈܽâÒ²²»ÈÛÈڵĶàôÇ»ù¸ß·Ö×Ó»¯ºÏÎï¡£ÏËάËؾÃÑ»¯ºóÔòÄÜÈÜÓÚË®¡¢...
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什么是空间天文技术
在地面上观测天体,必须通过大气窗口,因而只能在几个电磁波段内进行,就是在这些波段观测,也要受到大气和尘埃的干扰。空间天文观测的特点,在于越过地球大气这个障碍,对天体作全电磁波段的探测。人造卫星、火箭和气球技术为空间天文学的发展提供了必要的手段。为了控制...