全文获取类型
收费全文 | 133633篇 |
免费 | 18079篇 |
国内免费 | 13934篇 |
专业分类
电工技术 | 11682篇 |
技术理论 | 8篇 |
综合类 | 17395篇 |
化学工业 | 11185篇 |
金属工艺 | 4309篇 |
机械仪表 | 9605篇 |
建筑科学 | 12903篇 |
矿业工程 | 4524篇 |
能源动力 | 6104篇 |
轻工业 | 4401篇 |
水利工程 | 8543篇 |
石油天然气 | 7221篇 |
武器工业 | 1994篇 |
无线电 | 10930篇 |
一般工业技术 | 11818篇 |
冶金工业 | 4700篇 |
原子能技术 | 1310篇 |
自动化技术 | 37014篇 |
出版年
2024年 | 742篇 |
2023年 | 2106篇 |
2022年 | 4075篇 |
2021年 | 4673篇 |
2020年 | 5016篇 |
2019年 | 4365篇 |
2018年 | 4183篇 |
2017年 | 5169篇 |
2016年 | 5935篇 |
2015年 | 6172篇 |
2014年 | 8201篇 |
2013年 | 8741篇 |
2012年 | 9738篇 |
2011年 | 10509篇 |
2010年 | 8298篇 |
2009年 | 8626篇 |
2008年 | 8652篇 |
2007年 | 9781篇 |
2006年 | 8458篇 |
2005年 | 7412篇 |
2004年 | 5985篇 |
2003年 | 5242篇 |
2002年 | 4124篇 |
2001年 | 3408篇 |
2000年 | 2953篇 |
1999年 | 2262篇 |
1998年 | 1913篇 |
1997年 | 1569篇 |
1996年 | 1469篇 |
1995年 | 1287篇 |
1994年 | 1049篇 |
1993年 | 746篇 |
1992年 | 615篇 |
1991年 | 486篇 |
1990年 | 385篇 |
1989年 | 324篇 |
1988年 | 199篇 |
1987年 | 130篇 |
1986年 | 100篇 |
1985年 | 98篇 |
1984年 | 103篇 |
1983年 | 48篇 |
1982年 | 66篇 |
1981年 | 35篇 |
1980年 | 48篇 |
1979年 | 47篇 |
1978年 | 16篇 |
1974年 | 9篇 |
1959年 | 18篇 |
1951年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
21.
A comparative study of numerical solutions to non-linear discrete crack modelling of concrete beams involving sharp snap-back 总被引:1,自引:0,他引:1
Numerical problems are often encountered in modelling crack propagation in concrete beams using non-linear finite element (FE) analysis, especially when sharp snap-back behaviour in load-displacement relations occurs. This paper firstly identifies 16 arc-length control based numerical strategies based on extensive literature review. They are then used to carefully model the structural behaviour of a four-point single notched shear beam using discrete crack modelling approach in which cracks are represented by interface elements with bilinear softening constitutive laws. Based on extensive FE analyses, detailed comparisons of the merits and demerits of these numerical algorithms are then made. The results indicate that the effectiveness and efficiency of different algorithms may vary considerably from one to another, with the local arc-length based procedures in conjunction with tangential stiffness strategy and reversible unloading model being the most robust. 相似文献
22.
Dongchang Sun Liyong Tong 《International journal for numerical methods in engineering》2004,60(11):1911-1932
A novel finite element model is presented for static and dynamic analysis of composite plates integrated with a laminated piezoelectric layer, a host laminated composite plate and an adhesive layer between them. A new adhesive element is developed which includes both peel and shear effects in the adhesive layer based on first‐order shear deformation plate theory. The thin adhesive layer between the piezoelectric layer and the host plate is modelled by assuming that it carries constant shear and peel strains throughout its thickness. In addition, a weighted static shape control scheme for finding the optimal voltage distribution for static shape control is given. By selecting different weighting matrices, a variety of items such as displacements, slopes, curvatures, strains and even generalized forces, can be included in finding the optimal actuating voltage for static shape control. The present model is validated by comparing with those results available in the literature. The numerical results show that the weighted linear least method can give a satisfactory voltage distribution to best match the desired shape. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
23.
24.
This study demonstrates that state observers can be developed and applied to infer the composition profiles of reactive distillation columns from noise-contaminated temperature measurements. The design and implementation of a Kalman filter (KF) and a Luenberger observer (LO) are carried out, and their performances are quantitatively assessed. The reliability, accuracy, and robustness of the two designs method are examined and compared quantitatively. The design and implementation of a Luenberger observer are simpler and easier to carry out than those of a Kalman filter. On the other hand, a Kalman filter is found to be more robust to a noisy measurements, erroneous initial estimates, and model uncertainties. A Luenberger observer could be used for composition estimation of reactive distillation when an ideal model of the system can reasonably approximate the real system; otherwise, a Kalman filter is recommended to be applied in more practical situations. 相似文献
25.
26.
The main difficulty with EM algorithm for mixture model concerns the number of components, say g. This is the question of model selection, and the EM algorithm itself could not estimate g. On the contrary, the algorithm requires g to be specified before the remaining parameters can be estimated. To solve this problem, a new algorithm, which is called stepwise split-and-merge EM (SSMEM) algorithm, is proposed. The SSMEM algorithm alternately splits and merges components, estimating g and other parameters of components simultaneously. Also, two novel criteria are introduced to efficiently select the components for split or merge. Experimental results on simulated and real data demonstrate the effectivity of the proposed algorithm. 相似文献
27.
28.
29.
R. LUNDÉN 《Fatigue & Fracture of Engineering Materials & Structures》2007,30(10):905-914
Propagation of small subsurface cracks subjected to shear under repeated rolling contact load is studied. An analytical crack model (Dugdale) with plastic strips at the two crack tips is employed. Compressive stresses promoting crack closure and friction between crack faces are considered. The triaxial stress state is used in the yield criterion. A damage criterion is suggested based on experimental LCF data. In a numerical study, critical crack lengths are found below which propagation of an existing crack should be effectively suppressed. 相似文献
30.
腐败是与政府行政权力相伴生的痼疾,既是一个历史现象又是一个国际现象。贪污腐败和寻租腐败是委托一代理模型中最典型的腐败方式,文章在此基础上对贪污腐败和寻租腐败进行成本一收益分析和市场均衡分析,并探讨治理行政权力腐败的有效途径。 相似文献