全文获取类型
收费全文 | 37134篇 |
免费 | 2912篇 |
国内免费 | 1478篇 |
专业分类
电工技术 | 1921篇 |
综合类 | 2108篇 |
化学工业 | 6449篇 |
金属工艺 | 1834篇 |
机械仪表 | 2219篇 |
建筑科学 | 3337篇 |
矿业工程 | 737篇 |
能源动力 | 1172篇 |
轻工业 | 2323篇 |
水利工程 | 595篇 |
石油天然气 | 2133篇 |
武器工业 | 256篇 |
无线电 | 4475篇 |
一般工业技术 | 4839篇 |
冶金工业 | 1933篇 |
原子能技术 | 476篇 |
自动化技术 | 4717篇 |
出版年
2024年 | 106篇 |
2023年 | 520篇 |
2022年 | 878篇 |
2021年 | 1360篇 |
2020年 | 1048篇 |
2019年 | 889篇 |
2018年 | 979篇 |
2017年 | 1106篇 |
2016年 | 1034篇 |
2015年 | 1363篇 |
2014年 | 1711篇 |
2013年 | 2140篇 |
2012年 | 2303篇 |
2011年 | 2462篇 |
2010年 | 2056篇 |
2009年 | 2037篇 |
2008年 | 1940篇 |
2007年 | 1917篇 |
2006年 | 1940篇 |
2005年 | 1750篇 |
2004年 | 1215篇 |
2003年 | 1067篇 |
2002年 | 1040篇 |
2001年 | 874篇 |
2000年 | 953篇 |
1999年 | 1039篇 |
1998年 | 997篇 |
1997年 | 813篇 |
1996年 | 802篇 |
1995年 | 662篇 |
1994年 | 513篇 |
1993年 | 464篇 |
1992年 | 321篇 |
1991年 | 236篇 |
1990年 | 232篇 |
1989年 | 168篇 |
1988年 | 132篇 |
1987年 | 93篇 |
1986年 | 73篇 |
1985年 | 52篇 |
1984年 | 45篇 |
1983年 | 31篇 |
1982年 | 34篇 |
1981年 | 19篇 |
1980年 | 22篇 |
1979年 | 10篇 |
1977年 | 10篇 |
1976年 | 12篇 |
1973年 | 8篇 |
1970年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
33.
This paper considers a novel distributed iterative learning consensus control algorithm based on neural networks for the control of heterogeneous nonlinear multiagent systems. The system's unknown nonlinear function is approximated by suitable neural networks; the approximation error is countered by a robust term in the control. Two types of control algorithms, both of which utilize distributed learning laws, are provided to achieve consensus. In the provided control algorithms, the desired reference is considered to be an unknown factor and then estimated using the associated learning laws. The consensus convergence is proven by the composite energy function method. A numerical simulation is ultimately presented to demonstrate the efficacy of the proposed control schemes. 相似文献
34.
35.
对原始态、步冷态、脱脆态和脱脆步冷态2.25Cr-1Mo-0.25V钢母材及焊缝冲击试验结果进行分析,得到了母材和焊缝在不同状态下的韧脆转变温度vTr54.2和FATT以及脆化度ΔvTr54.2和ΔFATT。试验结果表明,步冷试验之后,母材发生较低程度脆化或脱脆现象,但是脆化度或脱脆度较低,表明母材具有良好的抗回火脆化性能;经脱脆试验后,母材和焊缝都发生较高程度的脱脆,表明材料的脆化主要是由于回火脆化引起的,脱脆试验使得材料的韧脆转变温度降低;脱脆步冷试验后,焊缝发生较高程度的脆化,焊缝对脱脆步冷试验的敏感性较高,脱脆步冷试验有效促进了焊缝的脆化。在相同脆化条件下,母材的脆化敏感性低于焊缝,焊缝更易发生脆化。 相似文献
36.
37.
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
38.
The strategies for nanosol from metal alkoxide have enabled production of ultratransparent and mechanically robust polymer nanocomposites at extremely high loading. Herein, a simple approach to fabricate high‐performance polyurethane‐based nanocomposites via unmodified boehmite nanoparticles is reported. Evaluating their physical properties, the uniform dispersion of boehmite in the matrix caused nanocomposites retains ultrahigh transparency. Hydrogen bonding and intermolecular entanglement between boehmite and polyurethane brings about the mechanical properties of the nanocomposites material enhanced, i.e., strength, stiffness, and toughness. Optimized strength, stiffness, and toughness of Boehmite/Cationic waterborne polyurethane at 40 wt% (BNC40) are up to 58.1 MPa, 1096.7 MPa, 249.5 MJ m?3, respectively. Furthermore, the feasibility and mechanism of polymer strengthening and toughening by inorganic rigid nanoparticles is explored from the aspects of crystallinity and micromorphology. 相似文献
39.
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
40.
Haibo Zhang Guohua Geng Kang Li Cheng Liu Yuqing Hou 《Journal of Modern Optics》2018,65(20):2278-2289
Cone-beam X-ray luminescence computed tomography (CB-XLCT) is an attractive hybrid imaging modality, and it has the potential of monitoring the metabolic processes of nanophosphors-based drugs in vivo. However, the XLCT imaging suffers from a severe ill-posed problem. In this work, a sparse nonconvex Lp (0?p?1) regularization was utilized for the efficient reconstruction for early detection of small tumour in CB-XLCT imaging. Specifically, we transformed the non-convex optimization problem into an iteratively reweighted scheme based on the L1 regularization. Further, an iteratively reweighted split augmented lagrangian shrinkage algorithm (IRW_SALSA-Lp) was proposed to efficiently solve the non-convex Lp (0?p?1) model. We studied eight different non-convex p-values (1/16, 1/8, 1/4, 3/8, 1/2, 5/8, 3/4, 7/8) in both 3D digital mouse experiments and in vivo experiments. The results demonstrate that the proposed non-convex methods outperform L2 and L1 regularization in accurately recovering sparse targets in CB-XLCT. And among all the non-convex p-values, our Lp(1/4?p?1/2) methods give the best performance. 相似文献