全文获取类型
收费全文 | 34123篇 |
免费 | 4125篇 |
国内免费 | 2864篇 |
专业分类
电工技术 | 684篇 |
综合类 | 3395篇 |
化学工业 | 4696篇 |
金属工艺 | 4483篇 |
机械仪表 | 2180篇 |
建筑科学 | 5278篇 |
矿业工程 | 2002篇 |
能源动力 | 1503篇 |
轻工业 | 798篇 |
水利工程 | 1959篇 |
石油天然气 | 1352篇 |
武器工业 | 246篇 |
无线电 | 2292篇 |
一般工业技术 | 5506篇 |
冶金工业 | 1794篇 |
原子能技术 | 166篇 |
自动化技术 | 2778篇 |
出版年
2024年 | 145篇 |
2023年 | 704篇 |
2022年 | 978篇 |
2021年 | 1396篇 |
2020年 | 1397篇 |
2019年 | 1155篇 |
2018年 | 1135篇 |
2017年 | 1380篇 |
2016年 | 1515篇 |
2015年 | 1466篇 |
2014年 | 2027篇 |
2013年 | 2195篇 |
2012年 | 2412篇 |
2011年 | 2649篇 |
2010年 | 1900篇 |
2009年 | 2076篇 |
2008年 | 1790篇 |
2007年 | 2228篇 |
2006年 | 2069篇 |
2005年 | 1685篇 |
2004年 | 1376篇 |
2003年 | 1311篇 |
2002年 | 1029篇 |
2001年 | 890篇 |
2000年 | 872篇 |
1999年 | 669篇 |
1998年 | 505篇 |
1997年 | 412篇 |
1996年 | 311篇 |
1995年 | 295篇 |
1994年 | 240篇 |
1993年 | 157篇 |
1992年 | 159篇 |
1991年 | 106篇 |
1990年 | 113篇 |
1989年 | 100篇 |
1988年 | 76篇 |
1987年 | 31篇 |
1986年 | 28篇 |
1985年 | 24篇 |
1984年 | 23篇 |
1983年 | 14篇 |
1982年 | 15篇 |
1981年 | 5篇 |
1980年 | 8篇 |
1979年 | 13篇 |
1978年 | 2篇 |
1975年 | 2篇 |
1959年 | 6篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
Few literature studies have investigated the relationships between different uses and gratifications (U&Gs) of mobile instant messaging (MIM) apps, continuation, and purchase intentions. To address this gap, the researchers aimed to examine the influence of the content, social, process, and technology U&Gs of MIM on continuation intentions toward MIMs, and purchase intentions toward virtual goods available on MIMs. A comprehensive research model was developed based on the U&G theory, which was tested using cross-sectional data from 309 Japanese MIM users. The study considered six different U&Gs of MIM as independent variables and purchase intentions towards stickers and continuation intentions towards MIM as dependent variables. The study results suggest that exposure U&G has a significant positive association with MIM sticker purchase intentions. The entertainment and affection U&G are positively associated with continuation intentions towards MIM use. The study contributes to the literature by investigating U&Gs that motivate MIM users to have both positive purchase intentions toward virtual goods, such as stickers, and continuation intentions toward MIMs. The study has significant theoretical and practical implications for both researchers and practitioners who are interested in virtual goods, the virtual economy, MIM apps, social media, new media, and the service economy. 相似文献
32.
AbstractGeneralized thermoelastic interactions due to three-phase-lag time-nonlocal heat transfer in a Kelvin-Voigt type infinitely extended visco-thermoelastic continuum with cylindrical cavity has been investigated. The two-temperature generalized thermoelasticity theory has also been taken into account. The problem has been solved in the domain of Laplace on the assumption that the surface of the cavity is free from traction and is subjected to a smooth and time-dependent-heating effect. Laplace inversion of the transformed solutions has been carried out numerically. The obtained numerical data for different considerations are plotted in graphs to study the effects of time-nonlocal parameter, two-temperature parameter and visco-thermoelastic relaxation parameter on different thermoelastic quantities of physical interest. 相似文献
33.
34.
This paper discusses the effects of the grinding-induced cyclic heating on the properties of the hardened layer in a plunge cylindrical grinding process on the high strength steel EN26. It was found that a multi-pass grinding brings about a uniform and continuous hardened layer along the circumference of the cylindrical workpiece. An increase of the number of grinding passes, leads to a thicker layer of hardening, a larger compressive residual stress and a deeper plastic deformation zone. Within the plastic deformation zone, the martensitic grains are refined by the thermo-mechanical loading, giving rise to a hardness of 12.5% higher than that from a conventional martensitic transformation. The coupled effects of heat accumulation and wheel wear in the multi-pass grinding are the main causes for the thickening of the hardened layer. A too small infeed per workpiece revolution would result in insufficient grinding heat, and in turn, bring about an undesirable tempered hardened layer and a reduction of its hardness. 相似文献
35.
36.
Porous polyimide (PI) films with low dielectric constants and excellent thermal properties have been a pressing demand for the next generation of high-performance, miniature, and ultrathin microelectronic devices. A series of novel porous PI films containing fluorenyl-adamantane groups were prepared successfully via thermolysis of poly(ethylene glycol) (PEG) added in the PI matrix. The cross-sectional morphologies of porous PI films showed closed pores with diameters ranging from 135 to 158 nm, which were uniform and regular in shape without interconnectivity. These porous PI films exhibited excellent thermal properties with a glass-transition temperature at 376 °C whereas the 5% weight loss temperature in air excess of 405 °C due to enhanced rigidity afforded by fluorenyl-adamantane groups. Accompanied by thermolysis content of PEG increasing from 0 to 20 wt %, the density of porous PI films decreased, and the corresponding porosity grew significantly from 0 to 11.48%. Depending on porosity, the dielectric constant and dielectric loss of porous PI films significantly declined from 2.89 to 2.37 and from 0.050 to 0.021, respectively. These excellent properties benefit the as-prepared porous PI films for application as interlayer dielectrics, integrated circuit chips, or multichip modules in microelectronic fields. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47313. 相似文献
37.
The flame front deformation instability of low-velocity filtration combustion within an inert packed bed is studied based on the initial preheating non-uniformity. Based on the experimental phenomena, an initial thermal perturbation model is numerically proposed so as to predict the deformation behaviors of the flame front instabilities. The numerical prediction indicates that the assumption of an initial thermal perturbation is a feasible explanation as the cause of the flame front inclination instability. As the initial thermal perturbation increases, the phenomena of the flame front break and shrinking instabilities could easily occur at high filtration velocity or low equivalence ratio. Moreover, the evolutions of the flame front break rate and the shrinking rate are quantitatively analyzed. 相似文献
38.
最大塑性功原理在烧结体上限分析中的应用 总被引:1,自引:0,他引:1
最大塑性功原理又称第二塑性变分原理,在致密体塑性变形分析叶l是运用能量法进行变形力能计算的基础。本文从分析Drucker公设的亢要条件出发,证明了烧结体塑性变形最大塑性功原理的存在,片在该原理的荩础卜,推导出塑性变形的上限功率表达式,并以平面挤压条件下的上限法应用作为实例加以说明。 相似文献
39.
轻质滤料滤池的试验与研究 总被引:1,自引:0,他引:1
轻质滤料滤池是以比水密度略小的滤料为滤床的滤池,通过以净水厂的原水和污水处理厂的二级处理出水为过滤试验对象,所取得的结果表明:下向流轻质滤料滤池对浊度和悬浮固体(SS)的去除率分别可以达到80%和45%,而滤床的水头损失不超过15cm。因此轻质滤料滤池可以以预过滤的形式配置在过滤处理的净水和污水的处理工艺中。 相似文献
40.