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   325481篇
  免费   3181篇
  国内免费   1284篇
电工技术   5985篇
综合类   266篇
化学工业   47863篇
金属工艺   18403篇
机械仪表   13114篇
建筑科学   6460篇
矿业工程   3077篇
能源动力   6783篇
轻工业   19623篇
水利工程   4479篇
石油天然气   10059篇
武器工业   61篇
无线电   32910篇
一般工业技术   73367篇
冶金工业   49116篇
原子能技术   9352篇
自动化技术   29028篇
  2021年   2724篇
  2019年   2574篇
  2018年   11437篇
  2017年   11886篇
  2016年   9169篇
  2015年   3381篇
  2014年   5037篇
  2013年   11689篇
  2012年   9555篇
  2011年   16148篇
  2010年   14200篇
  2009年   13954篇
  2008年   14118篇
  2007年   15600篇
  2006年   7360篇
  2005年   9361篇
  2004年   7770篇
  2003年   7432篇
  2002年   6337篇
  2001年   5920篇
  2000年   5713篇
  1999年   5537篇
  1998年   13399篇
  1997年   9417篇
  1996年   7202篇
  1995年   5474篇
  1994年   4803篇
  1993年   5034篇
  1992年   3820篇
  1991年   3881篇
  1990年   3767篇
  1989年   3707篇
  1988年   3627篇
  1987年   3200篇
  1986年   3253篇
  1985年   3587篇
  1984年   3313篇
  1983年   3166篇
  1982年   2845篇
  1981年   2812篇
  1980年   2862篇
  1979年   2876篇
  1978年   2859篇
  1977年   3112篇
  1976年   3673篇
  1975年   2638篇
  1974年   2499篇
  1973年   2599篇
  1972年   2315篇
  1971年   2114篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
Dynamic modeling of lung C18O diffusion is used to measure the C18O transfer factor (TLco) of 14 newborns aged 1-4 mo. The model equation is based on the alveolar fractions of C18O and on changing alveolar ventilation induced by the rebreathing conditions. The model does not involve the volume of the rebreathing bag which is usually needed when applying rebreathing technique add which is a source of error. The equation is discretized and solved for recorded data obtained with equipment adapted to use in newborns. A least-square parameter calculation technique is applied to estimate TLco. Results show a strong relationship between this index and the biometrical ones and confirm those found in the literature featuring that the measurement duration can be considerably shortened  相似文献   
942.
An optimal design for the RLSA (radial line slot array) antenna useful for DBS reception is presented. Classical geometries and structures given in the literature are first used. It is found that in some cases these are not suitable. So, optimization techniques by using the right objective functions have been applied. Two different methods were developed and three antennas were designed. Numerical results and comparisons with other similar antennas give the advantages of our design  相似文献   
943.
944.
945.
946.
Translated from Kibernetika i Sistemnyi Analiz, No. 5, pp. 137–145, September–October, 1993.  相似文献   
947.
The authors present the basic philosophy, construction, design features, and test results of a new fault locating system. This fault locating system helps to shorten the time required for restoration of service after the occurrence of a busbar fault in an air-insulated distribution substation. Recent optical and electronic technologies allow the design of a highly accurate and compact fault locating system which consists of optical current detectors using the Faraday effect and a fault locating processor using a digital data processing technique. The fault location is carried out by discriminating between the directions of zero-sequence currents. Through various tests and field operations, it has been confirmed that the system has sufficient performance for practical applications  相似文献   
948.
Two laboratory-scale plasma reactors, an alternating current (AC) energized ferroelectric (high dielectric ceramic) packed bed reactor and a nanosecond pulsed corona reactor, were constructed. This study was done to develop baseline engineering data to demonstrate the feasibility of the application of plasma reactors to the destruction of various volatile organic compounds (VOCs) at PPM levels. Complete destruction was obtained for toluene. Conversions of methylene chloride at 95% and trichlorotrifluoroethane (known as CFC-113) at 67% were achieved for the plasma reactors used. The conversion was dependent on the mean electron energy in the reactor and was also related to how strongly halogen species were bonded with carbon  相似文献   
949.
A fault section detection system that uses optical magnetic field sensors and instantly detects the section in which a ground fault occurred was developed for 66 kV underground multiterminal systems having Y-branch joint boxes. The optical magnetic field sensor, which is based on the Faraday effect in Bi-doped YIG ((BiYbGd)3Fe5O12) having a large Verdet constant, detects cable conductor currents of 0 to 2000 A with high precision with the use of a laminated magnetic ring core of silicon steel plates. Sensors and a fault section detector/indicator of a system are connected with optical fibers capable of nonrepeated transmission of over 6 km  相似文献   
950.
Translated from Khimicheskoe i Neftyanoe Mashinostroenie, No. 11, pp. 28–30, November, 1993.  相似文献   
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