全文获取类型
收费全文 | 54115篇 |
免费 | 6993篇 |
国内免费 | 3968篇 |
专业分类
电工技术 | 5381篇 |
技术理论 | 3篇 |
综合类 | 5236篇 |
化学工业 | 9781篇 |
金属工艺 | 2248篇 |
机械仪表 | 4620篇 |
建筑科学 | 2783篇 |
矿业工程 | 1661篇 |
能源动力 | 5250篇 |
轻工业 | 1200篇 |
水利工程 | 5404篇 |
石油天然气 | 4050篇 |
武器工业 | 661篇 |
无线电 | 1921篇 |
一般工业技术 | 4652篇 |
冶金工业 | 3009篇 |
原子能技术 | 1413篇 |
自动化技术 | 5803篇 |
出版年
2024年 | 277篇 |
2023年 | 830篇 |
2022年 | 1527篇 |
2021年 | 1799篇 |
2020年 | 1908篇 |
2019年 | 1634篇 |
2018年 | 1554篇 |
2017年 | 1968篇 |
2016年 | 2189篇 |
2015年 | 2263篇 |
2014年 | 3128篇 |
2013年 | 3670篇 |
2012年 | 3675篇 |
2011年 | 4225篇 |
2010年 | 2944篇 |
2009年 | 3197篇 |
2008年 | 2941篇 |
2007年 | 3508篇 |
2006年 | 3291篇 |
2005年 | 2957篇 |
2004年 | 2438篇 |
2003年 | 2192篇 |
2002年 | 1787篇 |
2001年 | 1481篇 |
2000年 | 1298篇 |
1999年 | 1083篇 |
1998年 | 900篇 |
1997年 | 744篇 |
1996年 | 697篇 |
1995年 | 625篇 |
1994年 | 533篇 |
1993年 | 399篇 |
1992年 | 337篇 |
1991年 | 214篇 |
1990年 | 219篇 |
1989年 | 160篇 |
1988年 | 116篇 |
1987年 | 86篇 |
1986年 | 59篇 |
1985年 | 29篇 |
1984年 | 48篇 |
1983年 | 33篇 |
1982年 | 20篇 |
1981年 | 9篇 |
1980年 | 9篇 |
1979年 | 15篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1959年 | 21篇 |
1951年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
32.
In order to improve the process effectiveness and joint quality, ultrasonic vibrations were integrated with friction stir lap welding. Effect of ultrasonic exertion on the process and joint quality of AA 6061-T6 were investigated. Upon ultrasonic exertion, joints owned larger effective lap width, shorter hooks and improved strength. Weld fracture mode changed from a ductile–brittle mixed mode to a more ductile mode while the fracture path shifted from lap interface to beyond the stir zone. Material flow and interface defects were characterised using lap welded dissimilar aluminium alloy joints. Ultrasonic vibration improved the material flow and reduced the interfacial defects. Variations in failure load of joints were found in accordance with the variations in material flow and interfacial defects. 相似文献
33.
34.
A novel dual-rotation bobbin tool friction stir welding (DBT-FSW) was developed, in which the upper shoulder (US) and lower shoulder (LS) have different rotational speeds. This process was tried to weld 3.2 mm thick aluminum-lithium alloy sheets. The metallographic analysis and torque measurement were carried out to characterize the weld formability. Experimental results show that compared to conventional bobbin tool friction stir welding, the DBT-FSW has an excellent process stability, and can produce the defect-free joints in a wider range of welding parameters. These can be attributed to the significant improvement of material flow caused by the formation of a staggered layer structure and the unbalanced force between the US and LS during the DBT-FSW process. 相似文献
35.
《岩石力学与岩土工程学报(英文版)》2020,12(3):630-641
Structure is an evident determinant for macroscopic behaviors of soils. However, this is not taken into account in most constitutive models, as structure is a rather complex issue in models. For this, it is important to develop and implement simple models that can reflect this important aspect of soil behavior. This paper tried to model structured soils based on well-established concepts, such as critical state and sub-loading. Critical state is the core of the classic Cam Clay model. The sub-loading concept implies adoption of an inner (sub-loading) yield surface, according to specific hardening rules for some internal strain-like state variables. Nakai and co-workers proposed such internal variables for controlling density (ρ) and structure (ω), using a modified stress space, called tij. Herein, similar variables are used in the context of the better-known invariants (p and q) of the Cam Clay model. This change requires explicit adoption of a non-associated flow rule for the sub-loading surface. This is accomplished by modifying the dilatancy ratio of the Cam Clay model, as a function of the new internal variables. These modifications are described and implemented under three-dimensional (3D) conditions. The model is then applied to simulating laboratory tests under different stress paths and the results are compared to experiments reported for different types of structured soils. The good agreements show the capacity and potential of the proposed model. 相似文献
36.
径向基函数网络(RBFN)已广泛应用于参考腾发量预测等领域,但常用的K均值聚类和自组织特征映射等方法在求取径向基函数网络隐层节点中心时存在较大不足。针对这一问题,本文引入投影寻踪方法,在投影降维的基础上实现对大量高维数据的聚类,建立了基于投影寻踪的径向基函数网络模型,并将该模型应用于山西潇河灌区参考腾发量的预测,研究了不同气象因子输入对参考腾发量预测精度的影响。结果表明,基于投影寻踪的径向基函数网络具有较强的适用性,只需使用最高温度、最低温度、日照时数和旬序数作为输入因子,就能以较高的精度预测参考腾发量。 相似文献
37.
38.
通过物理模型试验,研究了有植被的河道水流紊动特性.试验结果表明,在复式断面河道滩地种植柔性植被后,滩地糙率增大,水流紊动更为剧烈,河道水流紊动强度峰值由原先的滩槽交界区转移到滩地区.滩地的水流紊动强度沿程递减;滩槽交界区的水流紊动强度沿程不断增大;主槽的水流紊动强度主要与床面糙率有关,滩地植被影响了滩地水流的归槽时间,使主槽水流流速沿程增大. 相似文献
39.
Effect of Strain Rate on Discontinuous Flow and Mechanical Characteristics of High-Nitrogenous Steel
Experimental study on the effect of strain rate on discontinuous flow and mechanical characteristics of the high-nitrogenous steel Kh23AG19F has been performed. Within the range of strain rates from 4.62 · 10-5 to 1.85 · 10 -4 s-1, discontinuous flow, reflected by serration on the tensile diagram, is chiefly determined by intergranular deformation mechanisms. Under strain rates over 1.85 · 10-2 s-1, combined deformation modes prevail, which cause a change in the character of discontinuous flow and transform a serrated tensile diagram into a wavy graph, with the yield stress of steel increased significantly. 相似文献
40.