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   271791篇
  免费   8283篇
  国内免费   3337篇
电工技术   7337篇
技术理论   6篇
综合类   4575篇
化学工业   41556篇
金属工艺   11917篇
机械仪表   10849篇
建筑科学   9992篇
矿业工程   3707篇
能源动力   7325篇
轻工业   21849篇
水利工程   3294篇
石油天然气   9312篇
武器工业   468篇
无线电   30585篇
一般工业技术   49206篇
冶金工业   41077篇
原子能技术   5826篇
自动化技术   24530篇
  2022年   3035篇
  2021年   4482篇
  2020年   3355篇
  2019年   3517篇
  2018年   4859篇
  2017年   5131篇
  2016年   4837篇
  2015年   4479篇
  2014年   6495篇
  2013年   13111篇
  2012年   9357篇
  2011年   11823篇
  2010年   9734篇
  2009年   10256篇
  2008年   10233篇
  2007年   10181篇
  2006年   9325篇
  2005年   8620篇
  2004年   7247篇
  2003年   6946篇
  2002年   6374篇
  2001年   6276篇
  2000年   6355篇
  1999年   6747篇
  1998年   13092篇
  1997年   9525篇
  1996年   7790篇
  1995年   5839篇
  1994年   5220篇
  1993年   4782篇
  1992年   3766篇
  1991年   3500篇
  1990年   3193篇
  1989年   3202篇
  1988年   3047篇
  1987年   2536篇
  1986年   2428篇
  1985年   2808篇
  1984年   2567篇
  1983年   2385篇
  1982年   2132篇
  1981年   2233篇
  1980年   2054篇
  1979年   2137篇
  1978年   2123篇
  1977年   2373篇
  1976年   3196篇
  1975年   1838篇
  1974年   1763篇
  1973年   1773篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
A circuit design is proposed and the possibilities for incorporation of an input double-notch low-frequency ripple filter are considered. Recommendations regarding the use of mathematical models for the calculation of transient processes in a DC electric-traction network are given. An analysis of the simulation of processes in a low-frequency filter shows that the emission of interference by the electric rolling stock should be estimated using the wavelet analysis since this approach best suits the studies of nonstationary signals.  相似文献   
992.
This work discusses the potential of three multistage zeolite drying systems (counter-, co-, and cross-current) with a varying number of stages. The evaluation showed that for 2-4 stages with heat recovery the efficiency of the systems ranges between 80 and 90%. Additionally, by introducing a compressor, the latent heat in the exhaust air from the regenerator is recovered and used to heat the inlet air for an additional drying stage. As a result, for the counter-current drying system and compressor pressure 1.5-2 bar, a maximum energy efficiency of 120% is achieved, which results in halving the energy consumption compared to conventional drying systems.  相似文献   
993.
994.
995.
996.
Two experiments examined how cross-list directional associations influenced list-method directed forgetting and the degree of interference observed on each list. Each List 1 item had a (a) bidirectionally related item on List 2 (chip ←→ potato), (b) forward association with an item on List 2 (chip → wood), (c) backward association from an item on List 2 (chip ← chisel), or (d) no relationship with List 2 items. The results revealed that associative relationships that eliminated retroactive interference in the baseline condition also eliminated the directed forgetting costs. In contrast, associative relationships did not affect List 2 recall in the forget group, which remained unchanged across experimental conditions. However, certain conditions reduced proactive interference in the remember group, thereby eliminating the benefits of directed forgetting. The directed forgetting costs and benefits were observed independently of each other. The authors propose that these effects emerged from a combination of item and context strengthening induced by different associative directions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
997.
The applicability of fluidised-bed reactor (FBR) based sulphate reducing bioprocess was investigated for the treatment of iron containing (40-90 mg/L) acidic wastewater at 65 degrees C. The FBR was inoculated with sulphate-reducing bacteria (SRB) originally enriched from a hot mining environment. Ethanol or acetate was supplemented as carbon and electron source for the SRB. A rapid startup with 99.9, 46 and 29% ethanol, sulphate and acetate removals, in respective order, was observed even after 6 days. Iron was almost completely removed with a rate of 90 mg/L.d. The feed pH was decreased gradually from its initial value of 6 to around 3.7 during 100 days of operation. The wastewater pH of 4.3-4.4 was neutralised by the alkalinity produced in acetate oxidation and the average effluent pH was 7.8 +/- 0.8. Although ethanol removal was complete, acetate accumulated. Later the FBR was fed with acetate only. Although acetate was present in the reactor for 295 days, its oxidation rates did not improve, which may be due to low growth rate and poor attachment ability of acetate oxidising SRB. Hence, the oxidation of acetate is the rate limiting step in the sulphidogenic ethanol oxidation by the thermophilic SRB.  相似文献   
998.
根据中原油田地层高温、高盐、易塌、易漏失及水平井的特点,优选了适用于水平井的强抑制强封堵聚合物钻井液体系,并进行了现场应用.室内实验结果表明,优选的强抑制强封堵聚合物钻井液具有良好的井眼净化、摩阻控制、井壁稳定及油层保护等性能.现场应用时能满足钻井、录井、测井的需要,钻井施工顺利,取得了良好的经济和社会效益.  相似文献   
999.
1000.
The Open Channel     
Estell  B. 《Computer》1987,20(11):90-91
  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