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   4779篇
  免费   115篇
  国内免费   1篇
电工技术   25篇
综合类   3篇
化学工业   427篇
金属工艺   69篇
机械仪表   54篇
建筑科学   28篇
矿业工程   4篇
能源动力   61篇
轻工业   328篇
水利工程   9篇
石油天然气   18篇
无线电   102篇
一般工业技术   250篇
冶金工业   3354篇
原子能技术   11篇
自动化技术   152篇
  2024年   7篇
  2023年   16篇
  2022年   69篇
  2021年   87篇
  2020年   48篇
  2019年   65篇
  2018年   65篇
  2017年   78篇
  2016年   61篇
  2015年   35篇
  2014年   69篇
  2013年   126篇
  2012年   98篇
  2011年   105篇
  2010年   89篇
  2009年   78篇
  2008年   80篇
  2007年   52篇
  2006年   52篇
  2005年   52篇
  2004年   33篇
  2003年   40篇
  2002年   20篇
  2001年   15篇
  2000年   20篇
  1999年   129篇
  1998年   1079篇
  1997年   682篇
  1996年   402篇
  1995年   235篇
  1994年   173篇
  1993年   219篇
  1992年   26篇
  1991年   39篇
  1990年   31篇
  1989年   33篇
  1988年   32篇
  1987年   28篇
  1986年   19篇
  1985年   22篇
  1984年   3篇
  1983年   5篇
  1982年   15篇
  1981年   15篇
  1980年   20篇
  1979年   5篇
  1978年   11篇
  1977年   70篇
  1976年   130篇
  1955年   6篇
排序方式: 共有4895条查询结果,搜索用时 93 毫秒
1.
Analog Integrated Circuits and Signal Processing - This paper presents the complete design of a phase locked loop-based clock synthesizer for reconfigurable analog-to-digital converters. The...  相似文献   
2.
3.
4.
5.

This paper presents a PVS development of relevant results of the theory of rings. The PVS theory includes complete proofs of the three classical isomorphism theorems for rings, and characterizations of principal, prime and maximal ideals. Algebraic concepts and properties are specified and formalized as generally as possible allowing in this manner their application to other algebraic structures. The development provides the required elements to formalize important algebraic theorems. In particular, the paper presents the formalization of the general algebraic-theoretical version of the Chinese remainder theorem (CRT) for the theory of rings, as given in abstract algebra textbooks, proved as a consequence of the first isomorphism theorem. Also, the PVS theory includes a formalization of the number-theoretical version of CRT for the structure of integers, which is the version of CRT found in formalizations. CRT for integers is obtained as a consequence of the general version of CRT for the theory of rings.

  相似文献   
6.
Epoxy novolac/anhydride cure kinetics has been studied by differential scanning calorimetry under isothermal conditions. The system used in this study was an epoxy novolac resin (DEN431), with nadic methyl anhydride as hardener and benzyldimethylamine as accelerator. Kinetic parameters including the reaction order, activation energy and kinetic rate constants, were investigated. The cure reaction was described with the catalyst concentration, and a normalized kinetic model developed for it. It is shown that the cure reaction is dependent on the cure temperature and catalyst concentration, and that it proceeds through an autocatalytic kinetic mechanism. The curing kinetic constants and the cure activation energies were obtained using the Arrhenius kinetic model. A suggested kinetic model with a diffusion term was successfully used to describe and predict the cure kinetics of epoxy novolac resin compositions as a function of the catalyst content and temperature. Copyright © 2003 Society of Chemical Industry  相似文献   
7.
Quantum yields of photolysis of the cobalt-carbon bond for three cobalamin compounds were measured with a continuous-wave laser at 442 nm under both aerobic and anaerobic conditions. Aerobically, the initial homolysis product, Co(II) cobalamin, is trapped by oxygen to form aquocobalamin. Use of an excess of the radical trapping reagent 2,2,6,6-tetramethyl-1-piperidinyloxyl, under anaerobic conditions, scavenges the carbon radical and allows detection of the cobalt(II) photoproduct. Quantum yields measured under anaerobic conditions for 5'-deoxyadenosylcobalamin (phi (Co-C alpha),442 = 0.20 +/- 0.03) and methylcobalamin (phi (Co-C alpha),442 = 0.35 +/- 0.03) are in agreement with the values obtained under aerobic conditions (phi (Co-C alpha),442 = 0.19 +/- 0.04 and phi (Co-C alpha),442 = 0.36 +/- 0.04, respectively). Additionally, the quantum yield values for 5'-deoxyadenosylcobalamin and its base-off derivative (phi (Co-C alpha),442 = 0.045 +/- 0.015) match those obtained on a nanosecond time scale [Chen, E., & Chance, M. R. (1990) J. Biol. Chem. 256, 12987-12994]. A comparison of quantum yields obtained anaerobically for 5'-deoxyadenosylcobalamin and methylcobalamin in H2O versus ethylene glycol shows a 4-fold decrease for the former cobalamin and no change for the latter. These quantum yields are evaluated in terms of time-independent radical separation distances.  相似文献   
8.
A 47-year-old woman with seronegative polyarthritis, diarrhea, and photosensitivity dermatitis was found to have Crohn's disease and pellagra. The presence of high values of 5-hydroxyindolacetic acid in the urine began the exhaustive investigations and finally enterotomy. No mass lesion was found. Argyrophilic cells were not increased in areas of inflamed intestinal mucosa or the normal mucosa. The disagreement between biochemical and histologic findings was attributed to sampling error. Antiinflammatory treatment for Crohn's disease was given and the gastrointestinal and articular symptoms improved, excretion of 5-hydroxyindolacetic acid returned to normal and there was no relapse of pellagra. Pellagra as a complication of Crohn's disease has been described in 4 cases; malnutrition and intestinal malabsorption were the proposed mechanisms for the niacin deficiency and pellagra of those patients. In the current case, the pathogenesis of pellagra may be accounted to wastage of tryptophan by an increased pool of intestinal argyrophilic cells, suggested by increased urinary excretion of 5-hydroxyindolacetic acid.  相似文献   
9.
Atrial geometry is preserved in the bicaval technique of cardiac transplantation. Using Doppler echocardiography, we investigated the impact of this technique on preservation of atrial function and found that echocardiographic indexes of atrial function are improved in bicaval cardiac transplants versus the standard orthotopic transplants.  相似文献   
10.
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