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   27829篇
  免费   1914篇
  国内免费   861篇
电工技术   1325篇
技术理论   1篇
综合类   1379篇
化学工业   4507篇
金属工艺   1319篇
机械仪表   1319篇
建筑科学   1861篇
矿业工程   578篇
能源动力   884篇
轻工业   1639篇
水利工程   340篇
石油天然气   1342篇
武器工业   118篇
无线电   3108篇
一般工业技术   3244篇
冶金工业   4046篇
原子能技术   314篇
自动化技术   3280篇
  2024年   84篇
  2023年   407篇
  2022年   700篇
  2021年   1031篇
  2020年   719篇
  2019年   676篇
  2018年   694篇
  2017年   808篇
  2016年   758篇
  2015年   924篇
  2014年   1239篇
  2013年   1583篇
  2012年   1574篇
  2011年   1723篇
  2010年   1397篇
  2009年   1442篇
  2008年   1342篇
  2007年   1239篇
  2006年   1350篇
  2005年   1163篇
  2004年   842篇
  2003年   762篇
  2002年   760篇
  2001年   541篇
  2000年   522篇
  1999年   676篇
  1998年   1445篇
  1997年   961篇
  1996年   702篇
  1995年   511篇
  1994年   430篇
  1993年   354篇
  1992年   184篇
  1991年   136篇
  1990年   111篇
  1989年   105篇
  1988年   117篇
  1987年   69篇
  1986年   65篇
  1985年   47篇
  1984年   33篇
  1983年   24篇
  1982年   39篇
  1981年   28篇
  1980年   32篇
  1979年   15篇
  1978年   7篇
  1977年   59篇
  1976年   146篇
  1975年   6篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
In this work the synergistic effects of microwave (MW) irradiation induced oxidation processes and CoFe2O4 were studied for the degradation of brilliant green (BG) from aqueous solutions. Under the optimum condition, the ratio of solid to liquid was 1:167 (0.3 g CoFe2O4 mixed with 50 mL of 20 mg L−1 BG solution), MW power 600 W, and the time of the irradiation 2 min. And the decolorization rate could reach up to 100%. Further investigation showed that BG was degraded by MW-induced oxidation combined with CoFe2O4 surface adsorption. The CoFe2O4 could increase the efficiencies of MW degradation and be used repeatedly. The experimental results indicated that the method of MW degradation BG in the presence of CoFe2O4 could reduce reaction time and increase product yield.  相似文献   
32.
Abstract The whole DNA of soybean was implanted into four varieties of wheat of Zhongyu5, Huaiyin 9628, Wenyou 1, Jimai 5 respectively via ion-beam mediation. There were 5 plantsobtained whose protein content was higher than 18.5%, the highest one was 21.44%. There were 3plants obtained whose protein content was lower than 11.5%, the lowest one was 10.96%. We cansee that the whole DNA of soybean transformed into wheat via ion beam implantation can inducethe increase in wheat protein content dramatically. The result also shows that the transformationefficiency of different gene types of wheat receptor varies greatly that the implanting time has acertain effect on the efficiency of transformation.  相似文献   
33.
Polycrystalline A1N thin films were deposited by RF reactive magnetron sputtering on Pt(111)/Ti electrode films. The substrates were tilted by an angle ranging from 40 degrees to 70 degrees with respect to the target normal. A low deposition temperature and a high sputter gas pressure were found ideal for tilted growth. The resulting grain tilt angle amounts to about half the substrate tilt angle. For coupling evaluation, 5 GHz solidly mounted resonator structures have been realized. The tilted grain A1N films exhibited a permittivity in the 9.5-10.5 range and loss tangent of 0.3%. Two shear modes as well as the longitudinal mode could be clearly identified. The coupling coefficient k2(eff) of the fundamental thickness shear mode (TS0) was found to be about 0.5%, which is compatible with a c-axis tilt of about 6 degrees.  相似文献   
34.
35.
Since the late 1980s, the eight-component model of the comprehensive school health program (CSHP), has been adopted widely in the United States and internationally. While it is acknowledged that the eight program elements should be delivered in a coordinated, interactive manner, numerous issues regarding how this integration best can be achieved, including who at the school level should have this responsibility and how the eight components relate conceptually and logistically, have not been addressed adequately. In essence, a CSHP transforms several solo performers into an orchestra. This article proposes the school health coordinator as an essential element in the eight-component model of the CSHP--the maestro, without whom there can be no symphony. The coordinator's principal responsibilities include administration, integration of personnel and programs, evaluation, and direct intervention. Three program elements--staff wellness, healthy environment, and community/family involvement--are subsumed within the coordinator's role, effectively reducing the number of program elements from eight to five. Potential benefits in addition to issues regarding feasibility of the SHC, are discussed and studies examining the effectiveness of the SHC model are recommended.  相似文献   
36.
Matrix rank is determined by the nonsingularity of its submatrices. For matrices in which entries are quadratic functions of some uncertain parameters, this paper derives sufficient conditions on parameters to that ensure the matrices preserve to some degrees the ranks they have when the parameters are all zero. The rank preservation problem is converted to the nonsingularity analysis problem of the minors of the matrix in discussion, and suitable tools such as the μ-analysis method are used to solve the problem. Applications in robust control theory, including tests for robust controllability/observability, minimum phaseness, coprimeness, and Schur stability, are given, together with illustrative examples,  相似文献   
37.
38.
39.
40.
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