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   86281篇
  免费   6257篇
  国内免费   2946篇
电工技术   4361篇
技术理论   9篇
综合类   4667篇
化学工业   15237篇
金属工艺   4486篇
机械仪表   5287篇
建筑科学   7005篇
矿业工程   1971篇
能源动力   2486篇
轻工业   4935篇
水利工程   1468篇
石油天然气   4510篇
武器工业   513篇
无线电   10480篇
一般工业技术   11298篇
冶金工业   4631篇
原子能技术   843篇
自动化技术   11297篇
  2024年   242篇
  2023年   1257篇
  2022年   1930篇
  2021年   3045篇
  2020年   2312篇
  2019年   1998篇
  2018年   2233篇
  2017年   2494篇
  2016年   2329篇
  2015年   2956篇
  2014年   4032篇
  2013年   5083篇
  2012年   5282篇
  2011年   5557篇
  2010年   4935篇
  2009年   4752篇
  2008年   4514篇
  2007年   4442篇
  2006年   4690篇
  2005年   4162篇
  2004年   2807篇
  2003年   2523篇
  2002年   2208篇
  2001年   2034篇
  2000年   2304篇
  1999年   2587篇
  1998年   2401篇
  1997年   1884篇
  1996年   1753篇
  1995年   1460篇
  1994年   1215篇
  1993年   884篇
  1992年   655篇
  1991年   545篇
  1990年   404篇
  1989年   367篇
  1988年   312篇
  1987年   170篇
  1986年   154篇
  1985年   104篇
  1984年   91篇
  1983年   60篇
  1982年   57篇
  1981年   51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 15 毫秒
71.
This paper investigates the general decay synchronization and general decay H∞ synchronization problems of multi-weighted coupled reaction-diffusion  相似文献   
72.
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   
73.
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   
74.
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   
75.
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   
76.
Pristine and (SiC+Te)-added MgB2 powders, green and spark plasma sintered (SPS) compacts were investigated from the viewpoint of quasi-static and dynamic (Split-Hopkinson Pressure Bar, SHPB) compressive mechanical properties The amount of the additive (SiC+Te) was selected to be the optimum one for maximization of the superconducting functional parameters. Pristine and added MgB2 show very similar compressive parameters (tan δ, fracture strength, Vickers hardness, others) and fragment size in the SHPB test. However, for the bulk SPSed samples the ratio of intergranular to transgranular fracturing changes, the first one being stronger in the added sample. This is reflected in the quasi-static KIC that is higher for the added sample. Despite this result, sintered samples are brittle and have roughly similar fragmentation behavior as for brittle engineering ceramics. In the fragmentation process, the composite nature of our samples should be considered with a special focus on MgB2 blocks (colonies) that show the major contribution to fracturing. The Glenn-Chudnovsky model of fracturing under dynamic load provides the closest values to our experimental fragment size data.  相似文献   
77.
78.
79.
Metallurgical and Materials Transactions B - Basic oxygen furnace (BOF) steel slag is a main byproduct that is produced during the converter steelmaking process. The volume instability and fast...  相似文献   
80.
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