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   170023篇
  免费   1259篇
  国内免费   195篇
电工技术   2565篇
综合类   125篇
化学工业   27118篇
金属工艺   9510篇
机械仪表   5752篇
建筑科学   3035篇
矿业工程   1904篇
能源动力   2735篇
轻工业   8934篇
水利工程   2738篇
石油天然气   8705篇
武器工业   12篇
无线电   14605篇
一般工业技术   38590篇
冶金工业   27864篇
原子能技术   6971篇
自动化技术   10314篇
  2021年   1638篇
  2018年   3031篇
  2017年   3132篇
  2016年   3408篇
  2015年   1714篇
  2014年   3037篇
  2013年   6442篇
  2012年   4396篇
  2011年   5501篇
  2010年   4509篇
  2009年   4991篇
  2008年   5025篇
  2007年   4928篇
  2006年   4199篇
  2005年   3869篇
  2004年   3672篇
  2003年   3561篇
  2002年   3480篇
  2001年   3474篇
  2000年   3371篇
  1999年   3220篇
  1998年   7028篇
  1997年   5167篇
  1996年   3835篇
  1995年   2919篇
  1994年   2602篇
  1993年   2733篇
  1992年   2259篇
  1991年   2306篇
  1990年   2410篇
  1989年   2321篇
  1988年   2320篇
  1987年   2194篇
  1986年   2252篇
  1985年   2301篇
  1984年   2212篇
  1983年   2143篇
  1982年   1988篇
  1981年   2200篇
  1980年   2057篇
  1979年   2278篇
  1978年   2433篇
  1977年   2433篇
  1976年   3101篇
  1975年   2245篇
  1974年   2307篇
  1973年   2342篇
  1972年   2156篇
  1971年   1911篇
  1970年   1701篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
An Imhoff tank was reconstructed into a 250 m3 UASB reactor in order to treat a malting plant wastewater. The UASB was inoculated with sludge from an anaerobic lagoon used for slaughterhouse wastewater treatment. After two months of operation the reactor achieved full load with an HRT of 17 h, a COD removal higher than 80% and a biogas production of 300 m3/day (77% average methane content), with an organic loading rate of 3.6 kgCOD/m3.d (0.24 kgCOD/kgVSS.d). A yield coefficient of 0.09 gVSS/gCODrem was found from a mass balance. The fat present in the inoculated sludge (48 mg/gSSV) did not affect the start up performance. Sludge from the inoculum with high content of fat (270 mg/gSSV), was separated by flotation in the first week of operation. The COD removal efficiency was scarcely influenced by the reactor operation temperature (17-25 degrees C).  相似文献   
12.
Towards intelligent dressing   总被引:1,自引:0,他引:1  
The aim of this article is to state the principles of an intelligent monitoring and control system for the grinding machine, comprising the dressing process as well as grinding stability.  相似文献   
13.
V. I. Pipa 《Semiconductors》2006,40(6):665-667
Radiative lifetimes of nondegenerate electrons and holes distributed uniformly in a semiconductor layer either deposited on a substrate or bounded by two dielectric media are calculated. The obtained expression takes into account the radiation reabsorbtion and interference effects and determines the dependences of the radiative lifetimes on the refractive indices of the external media and on the layer thickness.  相似文献   
14.
Proton-exchanged planar waveguides have been fabricated on Z-cut and X-cut lithium niobate crystals by using a new proton source formed by a mixture of benzoic and adipic acids. Waveguide index profiles and optical characteristics have been obtained at different values of the adipic-benzoic acid concentration ratio. The samples have been structurally characterized by Raman and infrared (IR) absorption spectroscopy and double-crystal X-ray diffraction. Good quality samples have been fabricated by using 30 mol% ratio dilution, showing very low scattering levels (<0.1 dB/cm), relatively high electrooptic coefficient (r33=0.88 pm/V), and low relative percentage of interstitial protons (26%). The main factor limiting the waveguide optical properties is the substitutional-interstitial proton ratio, which can be easily controlled to produce good quality waveguides. A demonstration of the repeatability of the exchange process in the acid mixture is also provided  相似文献   
15.
16.
17.
18.
Communication network design is becoming increasingly complex, involving making networks more usable, affordable, and reliable. To help with this, we have proposed an expert network designer (END) for configuring, modeling, simulating, and evaluating large structured computer networks, employing artificial intelligence, knowledge representation, and network simulation tools. We present a neural network/knowledge acquisition machine-learning approach to improve the END's efficiency in solving the network design problem and to extend its scope to acquire new networking technologies, learn new network design techniques, and update the specifications of existing technologies  相似文献   
19.
Conclusions 1. Use of dewatering systems based on voidless drainage is most effective when dewatering slightly permeable soils in regions with a deep seasonal frost. 2. Two-story drainage with the upper and lower stories spaced 30 m apart accelerates the discharge of gravitational water from the arable layer. Results of observations on two-story drainage in experimental-production sections indicated that it discharges 2 – 3.8 times more water than systematic tubular drainage with an interdrain spacing of 10 m and a 0.2-m thick three-dimensional filter of a sandy-gravelly mixture. 3. It is recommended to use crushed stone and porous-clay gravel with a fineness of 10 – 20 mm as a filler. In that case, protection of the drain filler is, as a rule, required only from the intrusion of soil from above during construction in cohesive soils with a plasticity indexW p≥7. 4. seepage rate in a voidless drain should be lower than the scouring velocity for the soil in which the voidless drainage is placed. In the opposite case, it is necessary to lower the grade of the drains or select a filler gradation such that the seepage rate in the drain be lower than the scouring velocity. Translated from Gidrotekhnicheskoe Stroitel’stvo, No. 8, pp. 41–43, August, 1998.  相似文献   
20.
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