全文获取类型
收费全文 | 144783篇 |
免费 | 19698篇 |
国内免费 | 14818篇 |
专业分类
电工技术 | 13199篇 |
技术理论 | 8篇 |
综合类 | 18590篇 |
化学工业 | 12729篇 |
金属工艺 | 4968篇 |
机械仪表 | 10544篇 |
建筑科学 | 13837篇 |
矿业工程 | 4955篇 |
能源动力 | 6570篇 |
轻工业 | 4887篇 |
水利工程 | 8785篇 |
石油天然气 | 7564篇 |
武器工业 | 2147篇 |
无线电 | 12466篇 |
一般工业技术 | 13031篇 |
冶金工业 | 5038篇 |
原子能技术 | 1442篇 |
自动化技术 | 38539篇 |
出版年
2024年 | 822篇 |
2023年 | 2325篇 |
2022年 | 4433篇 |
2021年 | 5081篇 |
2020年 | 5461篇 |
2019年 | 4761篇 |
2018年 | 4514篇 |
2017年 | 5650篇 |
2016年 | 6447篇 |
2015年 | 6728篇 |
2014年 | 9032篇 |
2013年 | 9501篇 |
2012年 | 10635篇 |
2011年 | 11428篇 |
2010年 | 8990篇 |
2009年 | 9284篇 |
2008年 | 9296篇 |
2007年 | 10491篇 |
2006年 | 9069篇 |
2005年 | 7913篇 |
2004年 | 6411篇 |
2003年 | 5591篇 |
2002年 | 4484篇 |
2001年 | 3708篇 |
2000年 | 3217篇 |
1999年 | 2462篇 |
1998年 | 2072篇 |
1997年 | 1663篇 |
1996年 | 1585篇 |
1995年 | 1367篇 |
1994年 | 1124篇 |
1993年 | 791篇 |
1992年 | 655篇 |
1991年 | 508篇 |
1990年 | 407篇 |
1989年 | 352篇 |
1988年 | 211篇 |
1987年 | 144篇 |
1986年 | 111篇 |
1985年 | 104篇 |
1984年 | 106篇 |
1983年 | 51篇 |
1982年 | 70篇 |
1981年 | 36篇 |
1980年 | 51篇 |
1979年 | 50篇 |
1978年 | 16篇 |
1974年 | 10篇 |
1959年 | 19篇 |
1951年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
数据包络分析模型及其应用研究 总被引:1,自引:1,他引:0
郑明贵 《南方冶金学院学报》2004,25(4):62-66
通过对传统的C^2R模型进行研究并加以改进,建立了C2RHZ模型,利用有色金属矿采选业1993-2001年科技创新的相关数据进行了计算分析。说明了C^2RHZ模型的应用价值. 相似文献
43.
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
44.
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
45.
Bedich ika Helena Bendov Ivan Macha
《Chemical Engineering and Processing: Process Intensification》2005,44(12):1312-1319
A procedure has been proposed for the estimation of the terminal falling velocity of non-spherical particles moving in a Carreau model fluid in the transition flow region. The procedure is based on a modification of the relationship formerly developed for the fall of spherical particles including the particle dynamic shape factor. The suitability of the proposed procedure has been confirmed by good agreement between experimental and calculated terminal falling velocity data. In the experiments, the terminal falling velocity of short cylinders and rectangular prisms in polymer solutions of different measure of shear thinning and elasticity has been measured. 相似文献
46.
以水资源可持续发展为出发点,探讨了一种可以同时兼顾经济发展、水资源利用和社会效益的多目标水资源宏观经济模型的建立方法,通过引入带权2-模评价函数,将多目标优化问题转变成单目标优化问题。以2002年为现状水平年,对安徽省2010年的产业结构及产业规模进行优化分析。结果表明,多目标模型求得的总用水量较单目标模型明显降低,而两模型优化的产业规模与结构差别不大,体现了高用水效率行业优先发展的要求。 相似文献
47.
48.
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
49.
50.
Lie‐Fern Hsu 《Quality and Reliability Engineering International》2007,23(2):269-272
He and Grigoryan (Quality and Reliability Engineering International 2002; 18 :343–355) formulated the design of a double‐sampling (DS) s control chart as an optimization problem and solved it with a genetic algorithm. They concluded that the DS s control charts can be a more economically preferable alternative in detecting small shifts than traditional s control charts. We explain that, since they only considered the average sample size when the process is in control, their conclusion is questionable. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献