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   85356篇
  免费   6144篇
  国内免费   2886篇
电工技术   4290篇
技术理论   9篇
综合类   4627篇
化学工业   14966篇
金属工艺   4418篇
机械仪表   5222篇
建筑科学   6962篇
矿业工程   1958篇
能源动力   2477篇
轻工业   4876篇
水利工程   1434篇
石油天然气   4448篇
武器工业   488篇
无线电   10372篇
一般工业技术   11192篇
冶金工业   4595篇
原子能技术   819篇
自动化技术   11233篇
  2024年   214篇
  2023年   1248篇
  2022年   1751篇
  2021年   2960篇
  2020年   2290篇
  2019年   1981篇
  2018年   2216篇
  2017年   2469篇
  2016年   2316篇
  2015年   2918篇
  2014年   3993篇
  2013年   5050篇
  2012年   5244篇
  2011年   5517篇
  2010年   4898篇
  2009年   4713篇
  2008年   4465篇
  2007年   4402篇
  2006年   4648篇
  2005年   4132篇
  2004年   2783篇
  2003年   2497篇
  2002年   2192篇
  2001年   2018篇
  2000年   2282篇
  1999年   2556篇
  1998年   2381篇
  1997年   1875篇
  1996年   1706篇
  1995年   1437篇
  1994年   1207篇
  1993年   874篇
  1992年   650篇
  1991年   538篇
  1990年   401篇
  1989年   363篇
  1988年   311篇
  1987年   167篇
  1986年   154篇
  1985年   103篇
  1984年   91篇
  1983年   59篇
  1982年   57篇
  1981年   50篇
  1980年   37篇
  1979年   32篇
  1978年   13篇
  1977年   33篇
  1976年   16篇
  1975年   15篇
排序方式: 共有10000条查询结果,搜索用时 765 毫秒
81.
栖霞—大柳行地区位于胶东中部栖霞—蓬莱金矿成矿带内,是胶东重要的金成矿区,成矿条件优越。为了对圈定靶区进行优选分类,通过对该区地质背景、找矿靶区评价、找矿靶区优选方面展开综合研究,并结合勘查工作程度和矿业权设置情况,划分出3类预测区,选定了5个靶区为今后优先部署勘查工作的方向。  相似文献   
82.
83.
84.
85.
This work presents an engineering method for optimizing structures made of bars, beams, plates, or a combination of those components. Corresponding problems involve both continuous (size) and discrete (topology) variables. Using a branched multipoint approximate function, which involves such mixed variables, a series of sequential approximate problems are constructed to make the primal problem explicit. To solve the approximate problems, genetic algorithm (GA) is utilized to optimize discrete variables, and when calculating individual fitness values in GA, a second-level approximate problem only involving retained continuous variables is built to optimize continuous variables. The solution to the second-level approximate problem can be easily obtained with dual methods. Structural analyses are only needed before improving the branched approximate functions in the iteration cycles. The method aims at optimal design of discrete structures consisting of bars, beams, plates, or other components. Numerical examples are given to illustrate its effectiveness, including frame topology optimization, layout optimization of stiffeners modeled with beams or shells, concurrent layout optimization of beam and shell components, and an application in a microsatellite structure. Optimization results show that the number of structural analyses is dramatically decreased when compared with pure GA while even comparable to pure sizing optimization.  相似文献   
86.
This paper investigates the general decay synchronization and general decay H∞ synchronization problems of multi-weighted coupled reaction-diffusion  相似文献   
87.
The in-situ fabrication of an electron-blocking layer between the Ba-containing anode and the ceria-based electrolyte is an effective approach in suppressing the internal electronic leakage in ceria-based solid oxide fuel cell (SOFC). To improve the thickness of the electron-blocking layer and to research the effect of the layer thickness on the improvement of SOFC, a Ba-containing compound (0.6NiO-0.4BaZr0.1Ce0.7Y0.2O3-δ) modified by Y stabilized zirconia (YSZ) was employed as a composite anode in this research. SEM analyses demonstrated that the thickness of the interlayer can be simply controlled by regulating the proportion of YSZ at anode. The in-situ formed interlayer in the cell with the anode modified by 20?mol% YSZ possesses a thickness of 0.9?µm which is more suitable for the cell achieving an enhanced performance.  相似文献   
88.
Hybrid organic–inorganic perovskites (HOIPs), in particular 3D HOIPs, have demonstrated remarkable properties, including ultralong charge‐carrier diffusion lengths, high dielectric constants, low trap densities, tunable absorption and emission wavelengths, strong spin–orbit coupling, and large Rashba splitting. These superior properties have generated intensive research interest in HOIPs for high‐performance optoelectronics and spintronics. Here, 3D hybrid organic–inorganic perovskites that implant chirality through introducing the chiral methylammonium cation are demonstrated. Based on structural optimization, phonon spectra, formation energy, and ab initio molecular dynamics simulations, it is found that the chirality of the chiral cations can be successfully transferred to the framework of 3D HOIPs, and the resulting 3D chiral HOIPs are both kinetically and thermodynamically stable. Combining chirality with the impressive optical, electrical, and spintronic properties of 3D perovskites, 3D chiral perovskites is of great interest in the fields of piezoelectricity, pyroelectricity, ferroelectricity, topological quantum engineering, circularly polarized optoelectronics, and spintronics.  相似文献   
89.
The {100} facet of single-crystalline TiO2(B) is an ideal platform for inserting Li ions, but it is hard to be obtained due to its high surface energy. Here, the single-crystalline TiO2(B) nanobelts from H2Ti3O7 with nearly 70% {100} facets exposed are synthesized, which significantly enhances Li-storage capacity. The first-principle calculations demonstrate an ab in-plane 2D diffusion through the exposed {100} facets. As a consequence, the nanobelts can significantly accommodate Li ions in LiTiO2 formula with specific capacity up to 335 mAh g−1, which is in good agreement with the electrochemical characterizations. Coating with conductive and protective poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate), the cut-off discharge voltage is as low as 0.5 V, leading to a capacity of 160.7 mAh g−1 after 1500 cycles with a retention rate of 66% at 1C. This work provides a practical strategy to increase the Li-ion capacity and cycle stability by tailoring the crystal orientation and nanostructures.  相似文献   
90.
Neural Computing and Applications - More and more enterprises hope to achieve cooperation and win–win. However, many companies often have problems such as insufficient partner credit, which...  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