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   30077篇
  免费   2376篇
  国内免费   1219篇
电工技术   1637篇
综合类   2302篇
化学工业   5265篇
金属工艺   1412篇
机械仪表   1734篇
建筑科学   2084篇
矿业工程   718篇
能源动力   767篇
轻工业   2672篇
水利工程   656篇
石油天然气   1756篇
武器工业   213篇
无线电   3285篇
一般工业技术   3511篇
冶金工业   1325篇
原子能技术   348篇
自动化技术   3987篇
  2024年   65篇
  2023年   420篇
  2022年   717篇
  2021年   1104篇
  2020年   864篇
  2019年   707篇
  2018年   776篇
  2017年   921篇
  2016年   798篇
  2015年   1154篇
  2014年   1485篇
  2013年   1837篇
  2012年   2074篇
  2011年   2256篇
  2010年   2078篇
  2009年   1969篇
  2008年   1971篇
  2007年   1848篇
  2006年   1815篇
  2005年   1553篇
  2004年   1086篇
  2003年   820篇
  2002年   755篇
  2001年   605篇
  2000年   624篇
  1999年   608篇
  1998年   502篇
  1997年   431篇
  1996年   413篇
  1995年   326篇
  1994年   257篇
  1993年   200篇
  1992年   152篇
  1991年   113篇
  1990年   67篇
  1989年   69篇
  1988年   64篇
  1987年   27篇
  1986年   27篇
  1985年   21篇
  1984年   14篇
  1983年   14篇
  1982年   8篇
  1980年   10篇
  1979年   6篇
  1978年   5篇
  1976年   8篇
  1969年   4篇
  1968年   5篇
  1951年   5篇
排序方式: 共有10000条查询结果,搜索用时 406 毫秒
61.
居勤章  魏国君  夏欣鹏 《炼铁》2003,22(3):13-16
对宝钢2号高炉4号热风炉凉炉的原因、凉炉的前期族备工作、凉炉的设备和方法以及凉炉的实际效果进行了总结。通过这次凉炉实践,取得了一些有价值的经验,这些经验对今后宝钢砖硅热风炉的凉炉具有重要的参考意义。  相似文献   
62.
63.
催化裂化汽油选择性加氢脱硫催化剂RSDS-1的开发   总被引:24,自引:4,他引:20  
介绍了用于催化裂化汽油选择性加氢脱硫催化剂RSDS-1的研究开发,考察了载体、活性组元、金属原子比以及助剂对催化剂选择性的影响。研究结果表明,催化裂化汽油中烯烃的加氢饱和受扩散限制;Co—Mo组合对烯烃饱和的能力相对较弱;较高的Co/Mo原子比有利于提高催化剂选择性;助剂的加入对催化剂选择性有明显的影响;RSDS—1催化剂用于催化裂化汽油选择性脱硫,对不同原料油适应性好,脱硫率可达80%,RON损失小于2个单位,且可长周期稳定运转。  相似文献   
64.
Toughness variation of non-notched poly(acrylonitrile-butadiene-styrene) (ABS) subjected to uniaxial fatigue loading was investigated. The experiments were conducted by applying fatigue loading to strip specimens first, from which dog-bone specimens were machined. The dog-bone specimens were tested to measure the strain for the on-set of fracture, named cracking strain here, thus to monitor the toughness change due to the fatigue loading.The test results showed that the fatigue loading caused the toughness drop in ABS, even before any visible crack was developed. Damage development and fracture behavior were then analyzed using scanning electron microscopy (SEM). The SEM analysis revealed that damage zones, not cracks, were initiated during the fatigue loading, and were the main cause of the toughness drop. Mechanisms for the damage initiation include matrix crazing and debonding of small rubber particles; however, large rubber particles remained intact. Based on the results, a deformation model is proposed for the damage zone initiation, which provides an explanation for the toughness change under the fatigue loading.  相似文献   
65.
Order reduction is a computationally efficient method to estimate some lowest eigenvalues and the corresponding eigenvectors of large structural systems by reducing the order of the original model to a smaller one. But its accuracy is limited to a small range of frequencies that depends on the selection of the retained degrees of freedom. This paper proposes a new iterative order reduction (IOR) technique to obtain accurately the eigensolutions of large structural systems. The technique retains all the inertia terms associated with the removed degrees of freedom. This hence leads to the reduced mass matrix being in an iterated form and the reduced stiffness matrix constant. From these mass and stiffness matrices, the eigensolutions of the reduced system can be obtained iteratively. On convergence the reduced system reproduces the eigensolutions of the original structure. A proof of the convergence property is also presented. Applications of the method to a practical GARTEUR structure as well as a plate have demonstrated that the proposed method is comparable to the commonly used Subspace Iteration method in terms of numerical accuracy. Moreover, it has been found that the proposed method is computationally more efficient than the Subspace Iteration method. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   
66.
随着电容测量技术的迅速发展,电容传感器在非电量测量和自动检测中得到广泛应用,但它在使用过程中也存在一些问题,针对在使用电容传感器过程中存在的几个问题,从电容传感器的原理和工作过程两个方面进行了讨论,并提出行之有效的处理方法。  相似文献   
67.
Transition-metal compound TiC60 thin films were grown by co-deposition from two separated sources of fullerene C60 powder and titanium. Study of structural properties of the films, by Raman spectroscopy, atomic force microscopy, and scanning tunneling spectroscopy reveals that the films have a deformed C60 structure with certain amount of sp3 bonds and a rough surface with a large number of nanoclusters. zV tunnelling spectroscopic measurements suggest that several charge transport mechanisms are involved in as the tip penetrates into the thin film. Conventional field electron emission (FEE) measurements show a high emission current density of 10 mA/cm2 and a low turn-on field less than 8 V/μm, with the field enhancement factors being 659 and 1947 for low-field region and high-field region, respectively. By exploiting STM tunneling spectroscopy, local FEE on nanometer scale has also been characterized in comparison with the conventional FEE. The respective field enhancement factors are estimated to be 99–355 for a gap varying from 36 to 6 nm. The enhanced FEE of TiC60 thin films can be ascribed to structural variation of C60 in the films and the electrical conducting paths formed by titanium nanocrystallites embedded in C60 matrix.  相似文献   
68.
介绍并分析了春光油田现代油藏经营管理模式的构建与运作及实施效果.  相似文献   
69.
70.
本文分析了"十五"期间农村水电发展情况,对"十一五"农村水电发展政策环境及增长情况进行了预测。  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