<正> 七十年代曾是美国农业的全盛时期。由于农业机械化水平的提高和技术革新在整个农业领域里的发展,大大提高了农业劳动生产率,扩大了生产规模,使美国一举成为世界性的粮仓,并以每年平均递增17.6％的速度扩大粮食对全世界的出日。然而到了八十年代,由于连年丰收,粮食大量过剩,使得农产品
在是的一个煤矿的一张充分使机械化的工作的脸建原型，我们调查了由在它由空气的一个窗帘的隔离的过程期间的模拟，流动地和灰尘分发，使用 CFD 软件，流畅。结果证明有效地在 sheare
Stability level of tunnels that exist in an underground mine has a great influence on the safety,production and economic performance of mines.Ensuring of stabil
The FLAC3D software was used to simulate and analyze numerically the displacement, stress and plastic zone distribu-tion characteristics of a large span interse
The time evolution of coal structure during low temperature oxidation was investigated by oxidizing coal samples in air at 120 ℃ for periods of up to 14 days.T
Fault fracture zones and water-bearing bodies in front of the driving head are the main disasters in mine laneways,thus it is important to perform their advance
In order to study the time-frequency characteristics of blasting vibration signals, measured in milliseconds, we carried out site blasting vibration tests at an
Mining-induced fracture zone will be produced in the overlying strata after the coal was mined.In this article,the mining-induced deformation of overlying strat
<正> 在积极对内搞活经济,坚定不移对外执行开放政策这一新的形势下,商检工作如何更好地为外贸工作服务?在今年春季广州交易会期间,记者访问了张尔端同志,现将她介绍的情况记述如下。
<正> 外贸企业的经济效益,同其他企业一样,概括地说就是以尽量少的劳动消耗换得尽量多的经济效益。说得具体一些,就是既要重视贸易额的增长和外汇收入的增加,又要重视成本核算,努力为国家增加积累。因此,要使对外贸易稳定发展,不仅要促使贸易额不断增长,还要不断提高经济效益,把外贸工作转移到提高经济效益的轨道上来。十一届三中全会以来,北京市在对外开放、对内搞活经济等一系列方针、政策的指引下,进出口贸易发展较快,同世界上130多个国家和地区建立了贸易往来关系。1982年出口额比1978年增长了1.18倍