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   7940篇
  免费   662篇
  国内免费   403篇
电工技术   404篇
综合类   479篇
化学工业   1239篇
金属工艺   542篇
机械仪表   407篇
建筑科学   608篇
矿业工程   370篇
能源动力   180篇
轻工业   463篇
水利工程   155篇
石油天然气   672篇
武器工业   57篇
无线电   967篇
一般工业技术   969篇
冶金工业   403篇
原子能技术   54篇
自动化技术   1036篇
  2024年   51篇
  2023年   151篇
  2022年   288篇
  2021年   364篇
  2020年   313篇
  2019年   275篇
  2018年   268篇
  2017年   296篇
  2016年   257篇
  2015年   358篇
  2014年   404篇
  2013年   524篇
  2012年   510篇
  2011年   541篇
  2010年   468篇
  2009年   452篇
  2008年   392篇
  2007年   427篇
  2006年   418篇
  2005年   355篇
  2004年   220篇
  2003年   187篇
  2002年   154篇
  2001年   144篇
  2000年   160篇
  1999年   204篇
  1998年   163篇
  1997年   120篇
  1996年   114篇
  1995年   105篇
  1994年   92篇
  1993年   56篇
  1992年   47篇
  1991年   36篇
  1990年   22篇
  1989年   21篇
  1988年   15篇
  1987年   6篇
  1986年   7篇
  1985年   7篇
  1984年   2篇
  1983年   2篇
  1982年   4篇
  1980年   3篇
  1977年   1篇
  1976年   1篇
排序方式: 共有9005条查询结果,搜索用时 15 毫秒
1.
Reliable joints of Ti3SiC2 ceramic and TC11 alloy were diffusion bonded with a 50 μm thick Cu interlayer. The typical interfacial structure of the diffusion boned joint, which was dependent on the interdiffusion and chemical reactions between Al, Si and Ti atoms from the base materials and Cu interlayer, was TC11/α-Ti + β-Ti + Ti2Cu + TiCu/Ti5Si4 + TiSiCu/Cu(s, s)/Ti3SiC2. The influence of bonding temperature and time on the interfacial structure and mechanical properties of Ti3SiC2/Cu/TC11 joint was analyzed. With the increase of bonding temperature and time, the joint shear strength was gradually increased due to enhanced atomic diffusion. However, the thickness of Ti5Si4 and TiSiCu layers with high microhardness increased for a long holding time, resulting in the reduction of bonding strength. The maximum shear strength of 251 ± 6 MPa was obtained for the joint diffusion bonded at 850 °C for 60 min, and fracture primarily occurred at the diffusion layer adjacent to the Ti3SiC2 substrate. This work provided an economical and convenient solution for broadening the engineering application of Ti3SiC2 ceramic.  相似文献   
2.
3.
4.
In this paper, we first re-examine the previous protocol of controlled quantum secure direct communication of Zhang et al.’s scheme, which was found insecure under two kinds of attacks, fake entangled particles attack and disentanglement attack. Then, by changing the party of the preparation of cluster states and using unitary operations, we present an improved protocol which can avoid these two kinds of attacks. Moreover, the protocol is proposed using the three-qubit partially entangled set of states. It is more efficient by only using three particles rather than four or even more to transmit one bit secret information. Given our using state is much easier to prepare for multiqubit states and our protocol needs less measurement resource, it makes this protocol more convenient from an applied point of view.  相似文献   
5.
6.
7.
Artificial nitrogen fixation is emerging as a promising approach for synthesis of ammonia at mild conditions. Inspired by biological nitrogen fixation based on bacteria containing iron, zinc doped Fe2O3 nanoparticles are proposed as an efficient and earth abundant electrocatalyst for converting N2 to NH3. In neutral media, it achieves a maximum Faradaic efficiency (FE) of 10.4% and a large NH3 yield rate of 15.1 μg h?1 mg?1cat. at ?0.5 V vs. reversible hydrogen electrode. This catalyst also exhibits excellent selectivity and stability. Theoretical calculations suggest the reaction follows the associative enzymatic mechanism and it has a barrier of as low as 0.68 eV.  相似文献   
8.
通过工程实例及理论分析 ,对横向风振“锁住区”问题进行了探讨 ,对《建筑结构荷载规范》(GB5 0 0 0 9— 2 0 0 1 )中有关这一方面内容存在的一些问题进行了分析 ,希望对工程设计人员能有所帮助  相似文献   
9.
对尼龙1010/NBR/增塑剂体系进行了系统研究,发现在挤出机中环氧扩链剂可以对尼龙进行扩链反应,且环氧树脂对尼龙1010的扩链反应活性较高,扩链效果比较明显;N-丁基苯磺酰胺是尼龙的良好增塑剂,经增塑、增韧后可以使经扩链后的尼龙1010柔韧性有明显提高.采用SEM和TEM对所制备的材料进行了形貌分析,发现用NBR增韧尼龙,对于不同的基体材料,橡胶粒子的形貌有很大不同,粒子由增韧纯尼龙的椭球形变为在增塑尼龙基体中不规则的形状.  相似文献   
10.
The generalized compact (GC) schemes and some of their important properties are presented. And a new way for constructing high order accuracy and high-resolution GC schemes is presented. The schemes constructed by using this way could satisfy some principles and demands prescribed in advance to ensure some desired properties to the schemes, such as the principle about suppression of the oscillations, the principle of stability, the order of accuracy and number of scheme points, etc. As two examples, a three-point third-order compact scheme and a three-point fifth-order GC scheme satisfying the principle about suppression of the oscillations and the principle of stability are described in this paper. Numerical results show that these schemes are shock-capturing. The time-dependent boundary conditions proposed by Thompson are well employed when the algorithm is applied to the Euler equations of gas dynamics. Fourier analysis shows that the resolution characteristics are spectral-like.  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