全文获取类型
收费全文 | 49372篇 |
免费 | 3917篇 |
国内免费 | 2030篇 |
专业分类
电工技术 | 2595篇 |
技术理论 | 8篇 |
综合类 | 3027篇 |
化学工业 | 8638篇 |
金属工艺 | 2706篇 |
机械仪表 | 3229篇 |
建筑科学 | 3701篇 |
矿业工程 | 1708篇 |
能源动力 | 1428篇 |
轻工业 | 2759篇 |
水利工程 | 781篇 |
石油天然气 | 3857篇 |
武器工业 | 443篇 |
无线电 | 5324篇 |
一般工业技术 | 5911篇 |
冶金工业 | 2647篇 |
原子能技术 | 490篇 |
自动化技术 | 6067篇 |
出版年
2024年 | 242篇 |
2023年 | 910篇 |
2022年 | 1483篇 |
2021年 | 2016篇 |
2020年 | 1563篇 |
2019年 | 1326篇 |
2018年 | 1488篇 |
2017年 | 1644篇 |
2016年 | 1459篇 |
2015年 | 1932篇 |
2014年 | 2365篇 |
2013年 | 2896篇 |
2012年 | 2934篇 |
2011年 | 3309篇 |
2010年 | 2766篇 |
2009年 | 2680篇 |
2008年 | 2762篇 |
2007年 | 2520篇 |
2006年 | 2599篇 |
2005年 | 2288篇 |
2004年 | 1437篇 |
2003年 | 1351篇 |
2002年 | 1224篇 |
2001年 | 1100篇 |
2000年 | 1211篇 |
1999年 | 1433篇 |
1998年 | 1175篇 |
1997年 | 966篇 |
1996年 | 873篇 |
1995年 | 779篇 |
1994年 | 644篇 |
1993年 | 479篇 |
1992年 | 361篇 |
1991年 | 264篇 |
1990年 | 222篇 |
1989年 | 159篇 |
1988年 | 138篇 |
1987年 | 88篇 |
1986年 | 66篇 |
1985年 | 37篇 |
1984年 | 29篇 |
1983年 | 31篇 |
1982年 | 24篇 |
1981年 | 15篇 |
1980年 | 11篇 |
1979年 | 4篇 |
1977年 | 4篇 |
1976年 | 2篇 |
1969年 | 2篇 |
1968年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
A globally convergent algorithm for transportation continuous network design problem 总被引:2,自引:0,他引:2
The continuous network design problem (CNDP) is characterized by a bilevel programming model, in which the upper level problem
is generally to minimize the total system cost under limited expenditure, while at the lower level the network users make
choices with regard to route conditions following the user equilibrium principle. In this paper, the bilevel programming model
for CNDP is transformed into a single level convex programming problem by virtue of an optimal-value function tool and the
relationship between System Optimum (SO) and User Equilibrium (UE). By exploring the inherent nature of the CNDP, the optimal-value
function for the lower level user equilibrium problem is proved to be continuously differentiable and its derivative in link
capacity enhancement can be obtained efficiently by implementing user equilibrium assignment subroutine. However, the reaction
(or response) function between the upper and lower level problem is implicit and its gradient is difficult to obtain. Although,
here we approximately express the gradient with the difference concept at each iteration, based on the method of successive
averages (MSA), we propose a globally convergent algorithm to solve the single level convex programming problem. Comparing
with widely used heuristic algorithms, such as sensitivity analysis based (SAB) method, the proposed algorithm needs not strong
hypothesis conditions and complex computation for the inverse matrix. Finally, a numerical example is presented to compare
the proposed method with some existing algorithms. 相似文献
73.
Piezoelectric Nanogenerators for Self-Powered Nanodevices 总被引:1,自引:0,他引:1
A novel approach converts nanoscale mechanical energy into electric energy for self-powering nanodevices.In our own work, we've used piezoelectric zinc-oxide nanowire (ZnO NW) arrays to demonstrate a novel approach for converting nanoscale mechanical energy into electric energy. Here, we review the fundamental principle behind the nanogenerator, present an approach for improving its performance, and discuss some of the challenges we face in pushing this technology to reach its potential. 相似文献
74.
GPS定位精度的提高及其应用 总被引:7,自引:6,他引:1
本文简明介绍了美国全球定位系统(GPS)的工作原理和误差来源,通过了解误差来源阐述了较准准确的定位技术DGPS的原理和应用。 相似文献
75.
76.
The thermokinetics of liquid-liquid reaction of dysprosium nitrate with histidine were studied using a microcalorimeter. On the basis of experimental and calculated results, threethermodynamic parameters (the activation enthalpy, the activation entropy and the activation free enegy),the rate constant, three kinetic parameters (the activation energy, the pre-exponential constant and the reaction order) wereobtained. On the basis of thermodynamics and kinetics, the for marion reaction of the complex was discussed. 相似文献
77.
无氢类金刚石碳膜的研究进展 总被引:1,自引:0,他引:1
介绍了无氢类金刚石碳膜的制备方法 ,它们的机械、光学、电学性能 ,将无氢与含氢的类金刚石碳膜进行了简单比较 ,总结及探讨了它们的应用 相似文献
78.
79.
LOW-CYCLE FATIGUE UNDER NON-PROPORTIONAL LOADING 总被引:4,自引:0,他引:4
X. Chen Q. Gao X.-F. Sun 《Fatigue & Fracture of Engineering Materials & Structures》1996,19(7):839-854
A series of strain-controlled, low-cycle fatigue experiments have been conducted on 42CrMo steel under various loading paths including circular, square, cruciform, and rectangular paths. Present experiments have shown that there is additional hardening under non-proportional cyclic loading. Non-proportional cyclic additional hardening also results in a shorter life for multiaxial low cycle fatigue. A non-proportionality measure of strain path based on both a physical basis and macromechanical phenomena is proposed. The loading path effect on additional hardening is also described well. Low-cycle fatigue damage accumulation and the evolution process under non-proportional loading is analysed via the Continuum Damage Mechanics Model of Chaboche. A non-proportinality measure is introduced in the damage evolution equation and a modified Coffin-Manson type formula is derived. A novel fatigue life prediction approach based on the critical-plane concept of Brown and Miller is proposed. 相似文献
80.
本文提出线性系统的结构控制问题,并针对定常线性二次型系统加以研究,得到有关最优控制结构和。最优控制结构的设计方法。 相似文献