全文获取类型
收费全文 | 67261篇 |
免费 | 6292篇 |
国内免费 | 4376篇 |
专业分类
电工技术 | 6579篇 |
技术理论 | 4篇 |
综合类 | 6021篇 |
化学工业 | 5147篇 |
金属工艺 | 5195篇 |
机械仪表 | 10093篇 |
建筑科学 | 3490篇 |
矿业工程 | 2581篇 |
能源动力 | 1780篇 |
轻工业 | 3608篇 |
水利工程 | 817篇 |
石油天然气 | 1269篇 |
武器工业 | 591篇 |
无线电 | 5137篇 |
一般工业技术 | 7019篇 |
冶金工业 | 2891篇 |
原子能技术 | 478篇 |
自动化技术 | 15229篇 |
出版年
2024年 | 295篇 |
2023年 | 1072篇 |
2022年 | 1809篇 |
2021年 | 2089篇 |
2020年 | 2161篇 |
2019年 | 1862篇 |
2018年 | 1631篇 |
2017年 | 1992篇 |
2016年 | 2272篇 |
2015年 | 2647篇 |
2014年 | 3999篇 |
2013年 | 3741篇 |
2012年 | 4613篇 |
2011年 | 5239篇 |
2010年 | 3798篇 |
2009年 | 3859篇 |
2008年 | 3721篇 |
2007年 | 4539篇 |
2006年 | 4290篇 |
2005年 | 3667篇 |
2004年 | 3057篇 |
2003年 | 2645篇 |
2002年 | 2289篇 |
2001年 | 1876篇 |
2000年 | 1590篇 |
1999年 | 1329篇 |
1998年 | 998篇 |
1997年 | 887篇 |
1996年 | 730篇 |
1995年 | 643篇 |
1994年 | 556篇 |
1993年 | 423篇 |
1992年 | 338篇 |
1991年 | 240篇 |
1990年 | 222篇 |
1989年 | 176篇 |
1988年 | 152篇 |
1987年 | 69篇 |
1986年 | 71篇 |
1985年 | 37篇 |
1984年 | 47篇 |
1983年 | 41篇 |
1982年 | 37篇 |
1981年 | 25篇 |
1980年 | 18篇 |
1979年 | 24篇 |
1978年 | 17篇 |
1977年 | 9篇 |
1974年 | 8篇 |
1959年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Prediction of brittle-to-ductile transitions in polystyrene 总被引:1,自引:0,他引:1
In this study it is attempted to predict brittle-to-ductile transitions (BDTs) in polystyrene blends, induced either by an increase in temperature or by a decrease in inter-particle distance. A representative, two-dimensional volume element (RVE) of a polystyrene matrix with 20% circular voids, is deformed in tension. During deformation a hydrostatic-stress based craze-nucleation criterion [1] is evaluated. The simulations demonstrate that crazes initiate at low temperatures while a transition from crazing to shear yielding (BDT) is found around 75 °C. The numerical results correlate well with tensile tests on similar heterogeneous polystyrene. The presence of an absolute length, as experimentally found, is more difficult to explain. Near a free surface a Tg-depression is measured for polystyrene and also the resistance to indentation in polystyrene is lower than expected from bulk properties. Both observations are rationalised by an enhanced segmental mobility of chains near a free surface. As a consequence of these findings, an absolute length-scale could be incorporated in the numerical simulations. For simplicity, the length-scale is modelled by taking a temperature gradient over a thin layer near the internal free surfaces of the RVE. Deformation of the RVE with different absolute length-scales shows that indeed also the experimentally found brittle-to-ductile transition can be predicted if the ligament thickness between the inclusions (‘voids’) in polystyrene is below a critical value of ca. 15 nm. 相似文献
72.
Field Static Load Test on Kao-Ping-Hsi Cable-Stayed Bridge 总被引:1,自引:0,他引:1
Field load testing is an effective method for understanding the behavior and fundamental characteristics of a cable-stayed bridge. This paper presents the results of field static load tests on the Kao-Ping-Hsi cable-stayed bridge, the longest cable-stayed bridge in Taiwan, before it was open to traffic. A total of 40 loading cases, including the unit and distributed bending and torsion loading effects, were conducted to investigate the bridge behavior. The atmospheric temperature effect on the variations of the main girder deflections was also monitored. The results of static load testing include the main girder deflections, the flexural strains of the prestressed concrete girder, and the variations of the cable forces. A three-dimensional finite-element model was developed. The results show that the bridge under the planned load test conditions has linear superposition characteristics and the analytical model shows a very good agreement with the bridge responses. Further discussion of deflection and cable forces of the design specifications for a cable-stayed bridge is also presented. 相似文献
73.
Thermal barrier coatings (TBC) are widely used to prevent transient high temperature attack and allow components high durability. Due to strong inhomogeneous material properties the TBC failure often initiates near the interface between the brittle oxide layer and the ductile substrate. A reliable prediction of the TBC failure requires detailed information about the crack tip field and the consequent fracture criteria. In the present paper both cohesive model and gradient plasticity are used to simulate the failure process and to study interdependence of the interface stress distribution with the specific fracture energies. Computations confirm that combination of the two models is able to simulate different failure mechanisms in the TBC system. The computational model has the potential to give a realistic prediction of the crack propagation process. 相似文献
74.
基于支持向量机的多类分类研究 总被引:1,自引:0,他引:1
现今流行的分类方法的重要基础是传统的统计学,前提是要有足够的样本,当样本数目有限时容易出现过学习的问题,导致分类效果不理想。引入支持向量机方法,它基于统计学习理论,采用了结构风险最小化原则代替经验风险最小化原则,较好的解决了小样本学习的问题;又由于采用了核函数思想,把非线性空间的问题转换到线性空间,降低了算法的复杂度。对其相关内容包括优化算法及多类分类问题的解决进行了研究,最后用一个实例说明了该方法的可行性和有效性。 相似文献
75.
76.
77.
Based on the concept of complete stress–strain diagrams, we propose a new model describing the law of stress distribution in the prefracture zone in plastic materials in view of the type of the stressed state. 相似文献
78.
美国固体照明技术进展概况 总被引:2,自引:0,他引:2
介绍了美国能源部于2002年开始实施的固体照明(SSL)技术的"下一代照明计划".同时对美国SSL技术的研发、生产和使用现状以及召开学术会议的情况做了叙述. 相似文献
79.
80.