全文获取类型
收费全文 | 86788篇 |
免费 | 6467篇 |
国内免费 | 2965篇 |
专业分类
电工技术 | 4377篇 |
技术理论 | 10篇 |
综合类 | 4694篇 |
化学工业 | 15579篇 |
金属工艺 | 4463篇 |
机械仪表 | 5256篇 |
建筑科学 | 7098篇 |
矿业工程 | 1998篇 |
能源动力 | 2501篇 |
轻工业 | 4925篇 |
水利工程 | 1454篇 |
石油天然气 | 4580篇 |
武器工业 | 491篇 |
无线电 | 10472篇 |
一般工业技术 | 11346篇 |
冶金工业 | 4752篇 |
原子能技术 | 832篇 |
自动化技术 | 11392篇 |
出版年
2024年 | 327篇 |
2023年 | 1326篇 |
2022年 | 2307篇 |
2021年 | 3124篇 |
2020年 | 2354篇 |
2019年 | 2038篇 |
2018年 | 2270篇 |
2017年 | 2540篇 |
2016年 | 2370篇 |
2015年 | 2964篇 |
2014年 | 4054篇 |
2013年 | 5093篇 |
2012年 | 5280篇 |
2011年 | 5547篇 |
2010年 | 4914篇 |
2009年 | 4738篇 |
2008年 | 4483篇 |
2007年 | 4421篇 |
2006年 | 4667篇 |
2005年 | 4150篇 |
2004年 | 2796篇 |
2003年 | 2513篇 |
2002年 | 2202篇 |
2001年 | 2028篇 |
2000年 | 2294篇 |
1999年 | 2574篇 |
1998年 | 2396篇 |
1997年 | 1895篇 |
1996年 | 1751篇 |
1995年 | 1460篇 |
1994年 | 1220篇 |
1993年 | 886篇 |
1992年 | 658篇 |
1991年 | 543篇 |
1990年 | 410篇 |
1989年 | 367篇 |
1988年 | 319篇 |
1987年 | 175篇 |
1986年 | 167篇 |
1985年 | 113篇 |
1984年 | 99篇 |
1983年 | 63篇 |
1982年 | 60篇 |
1981年 | 54篇 |
1980年 | 38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
63.
Hai Huang Haichao An Haibo Ma Shenyan Chen 《International journal for numerical methods in engineering》2019,117(3):291-315
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
64.
Jianmou Lu Yanli Huang Shunyan Ren 《International Journal of Control, Automation and Systems》2020,18(5):1250-1263
This paper investigates the general decay synchronization and general decay H∞ synchronization problems of multi-weighted coupled reaction-diffusion 相似文献
65.
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
66.
Guankui Long Yecheng Zhou Mingtao Zhang Randy Sabatini Abdullah Rasmita Li Huang Girish Lakhwani Weibo Gao 《Advanced materials (Deerfield Beach, Fla.)》2019,31(17)
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
67.
Qiang Wang Lei Shen Tong Xue Gao Cheng Cheng Zhi Huang Hong Jin Fan Yuan Ping Feng 《Advanced functional materials》2021,31(2):2002187
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
68.
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
69.
Petre Badica Dan Batalu Mihail Burdusel Mihai A. Grigoroscuta Gheorghe V. Aldica Monica Enculescu Raluca A. Gabor Zhiyong Wang Ruoxuan Huang Peifeng Li 《Ceramics International》2018,44(9):10181-10191
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