首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   248963篇
  免费   1663篇
  国内免费   265篇
电工技术   4039篇
综合类   91篇
化学工业   40320篇
金属工艺   15143篇
机械仪表   10061篇
建筑科学   4175篇
矿业工程   3759篇
能源动力   3872篇
轻工业   9696篇
水利工程   4087篇
石油天然气   13006篇
武器工业   28篇
无线电   20186篇
一般工业技术   62749篇
冶金工业   32130篇
原子能技术   11134篇
自动化技术   16415篇
  2021年   2754篇
  2019年   2730篇
  2018年   5428篇
  2017年   5709篇
  2016年   6044篇
  2015年   3051篇
  2014年   5322篇
  2013年   10079篇
  2012年   7303篇
  2011年   8925篇
  2010年   7293篇
  2009年   8103篇
  2008年   8172篇
  2007年   7856篇
  2006年   6356篇
  2005年   5562篇
  2004年   5478篇
  2003年   5299篇
  2002年   5133篇
  2001年   4947篇
  2000年   4937篇
  1999年   4252篇
  1998年   7172篇
  1997年   5831篇
  1996年   4420篇
  1995年   3653篇
  1994年   3422篇
  1993年   3623篇
  1992年   3214篇
  1991年   3359篇
  1990年   3481篇
  1989年   3369篇
  1988年   3267篇
  1987年   3260篇
  1986年   3156篇
  1985年   3314篇
  1984年   3252篇
  1983年   3146篇
  1982年   2993篇
  1981年   3045篇
  1980年   3071篇
  1979年   3257篇
  1978年   3490篇
  1977年   3460篇
  1976年   3911篇
  1975年   3209篇
  1974年   3293篇
  1973年   3341篇
  1972年   2987篇
  1971年   2754篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
The functional of receptor sensitivity of a territory to the disposition of emission sources can adequately be calculated with the use of the mathematical apparatus of adjoint equations. The solutions of these equations allow one to determine the action of pollutants in the form of aerosols or harmful gaseous impurities on the environment and human health. Examples of calculation of the sensitivity functional on the basis of solution of adjoint equations have been presented. Mathematical models for the typical equations on optimum placement of industrial plants have been formulated. An interpretation of the results obtained has been given.  相似文献   
942.
Translated from Fiziko-Khimicheskaya Mekhanika Materialov, No. 5, pp. 19–26, September–October, 1990.  相似文献   
943.
944.
We report the results of examination of incorporation of chlorine and fluorine into silica as revealed from secondary ion mass spectroscopy (SIMS) and Raman spectroscopy measurements. The samples were preform-like rods made by the MCVD process. SIMS spectra were used for quantitative analysis of Cl concentration in glass. The concentrations of F were obtained from the Raman spectra. Both spectroscopic methods indicated the presence of Si---Cl groups in SiO2 synthesized from chlorine-rich vapour gaseous blend. The difference in structural roles of Cl and F in chemically deposited silica manifests itself in the efficiency of their bonding to Si and in interaction with intrinsic structural defects.  相似文献   
945.
The results of Monte-Carlo calculations of simple spherically symmetric systems, simulating an aperiodic booster, are presented. The purpose of the calculations is to give a clear demonsration of the specific features of the kinetics of cascade reactor systems and the possibilities which the application of the cascade principle in an aperiodic booster adds to increasing safety and improving the time parameters of the pulses. Another goal is to determine the materials for the moderator which are best from the standpoint of optimizing the parameters of the booster. It is shown that for the same total number of fissions the neutron pulses in a cascade booster are generated under conditions of much greater subcriticality and are much shorter in duration than for a single-section booster. The best pulse parameters are obtained in cascade boosters with tungsten, lead, and molybdenum neutron moderators.  相似文献   
946.
The qualitative and quantitative radiochemical composition of liquid wastes is substantiated. This makes possible further safe operation of deep waste disposal sites at the Mining-Chemical Plant and the Siberian Chemical Plant. The toxicity and temperature in a formation with the wastes removed are used as the assessment criteria, satisfaction of which guarantees that the wastes will remain localized within the assigned boundaries of the waste-disposal formation site. It is concluded that the standard limit should be imposed on the specific activity of the long-lived group of radionuclides – 90Sr and 137Cs – rather than on the total specific activity of the wastes placed in deep disposal sites. For maximum specific activity of 90Sr and 137Cs of 37 GBq/dm3 and total specific activity not exceeding 185 GBq/dm3 for buried wastes with radionuclide composition characteristic of modern radiochemical production operations, it is impossible for potentially dangerous radiation and thermochemical processes to occur in the waste-disposal formation site. The recommended limit permits reducing substantially the volume of buried wastes and therefore the region over which the wastes propagate in the deep disposal site.  相似文献   
947.
948.
949.
The article investigates the dependences of porosity and of the permeability tensor of an elastic fissured medium on the characteristics of its state of stress and the pressure of the permeating liquid.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 49, No. 5, pp. 818–826, November, 1985.  相似文献   
950.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号