全文获取类型
收费全文 | 381417篇 |
免费 | 88558篇 |
国内免费 | 60070篇 |
专业分类
电工技术 | 44984篇 |
技术理论 | 4篇 |
综合类 | 40863篇 |
化学工业 | 48829篇 |
金属工艺 | 37707篇 |
机械仪表 | 21335篇 |
建筑科学 | 27713篇 |
矿业工程 | 19025篇 |
能源动力 | 13499篇 |
轻工业 | 41091篇 |
水利工程 | 14286篇 |
石油天然气 | 18499篇 |
武器工业 | 5978篇 |
无线电 | 51208篇 |
一般工业技术 | 47601篇 |
冶金工业 | 13606篇 |
原子能技术 | 4965篇 |
自动化技术 | 78852篇 |
出版年
2024年 | 3329篇 |
2023年 | 7326篇 |
2022年 | 12163篇 |
2021年 | 15157篇 |
2020年 | 15126篇 |
2019年 | 21600篇 |
2018年 | 23190篇 |
2017年 | 25201篇 |
2016年 | 24562篇 |
2015年 | 26688篇 |
2014年 | 27944篇 |
2013年 | 29759篇 |
2012年 | 32046篇 |
2011年 | 29598篇 |
2010年 | 27661篇 |
2009年 | 24426篇 |
2008年 | 22861篇 |
2007年 | 22023篇 |
2006年 | 19148篇 |
2005年 | 16249篇 |
2004年 | 16041篇 |
2003年 | 12128篇 |
2002年 | 11870篇 |
2001年 | 10476篇 |
2000年 | 8909篇 |
1999年 | 6612篇 |
1998年 | 5080篇 |
1997年 | 4466篇 |
1996年 | 4194篇 |
1995年 | 4154篇 |
1994年 | 3421篇 |
1993年 | 3113篇 |
1992年 | 2920篇 |
1991年 | 2140篇 |
1990年 | 1687篇 |
1989年 | 1540篇 |
1988年 | 1198篇 |
1987年 | 415篇 |
1986年 | 349篇 |
1985年 | 257篇 |
1984年 | 175篇 |
1983年 | 132篇 |
1982年 | 179篇 |
1981年 | 179篇 |
1980年 | 141篇 |
1976年 | 232篇 |
1975年 | 209篇 |
1972年 | 236篇 |
1971年 | 128篇 |
1960年 | 205篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
Xi Chen Zhengkun Yu Chen Yang Yao Chen Chao Jin Yuejiao Ding Wenbin Li Zhongmin Wan 《International Journal of Hydrogen Energy》2021,46(19):11127-11139
Flow field structure can largely determine the output performance of Polymer electrolyte membrane fuel cell. Excellent channel configuration accelerates electrochemical reactions in the catalytic layer, effectively avoiding flooding on the cathode side. In present study, a three-dimensional, multi-phase model of PEMFC with a 3D wave flow channel is established. CFD method is applied to optimize the geometry constructions of three-dimensional wave flow channels. The results reveal that 3D wave flow channel is overall better than straight channel in promoting reactant gases transport, removing liquid water accumulated in microporous layer and avoiding thermal stress concentration in the membrane. Moreover, results show the optimal flow channel minimum depth and wave length of the 3D wave flow channel are 0.45 mm and 2 mm, respectively. Due to the periodic geometric characteristics of the wave channel, the convective mass transfer is introduced, improving gas flow rate in through-plane direction. Furthermore, when the cell output voltage is 0.4 V, the current density in the novel channel is 23.8% higher than that of conventional channel. 相似文献
73.
针对目前运动想象脑电(EEG)信号识别率较低的问题,考虑到脑电信号蕴含着丰富的时频信息,提出一种基于时频域的卷积神经网络(CNN)运动想象脑电信号识别方法。首先,利用短时傅里叶变换(STFT)对脑电信号的相关频带进行预处理,并将多个电极的时频图组合构造出一种二维时频图;然后,针对二维时频图的时频特性,通过一维卷积的方法设计了一种新颖的CNN结构;最后,通过支持向量机(SVM)对CNN提取的特征进行分类。基于BCI数据集的实验结果表明,所提方法的平均识别率为86.5%,优于其他传统运动想象脑电信号识别方法;同时将该方法应用在智能轮椅上,验证了其有效性。 相似文献
74.
75.
76.
77.
Muhammad Sheeraz Mamoon Ur Rashid Asad Ali Fazli Akram Ho Jeong Lee Jin San Choi Jong-Seong Bae Yong Soo Kim Young-Han Shin Chang Won Ahn Tae Heon Kim 《Journal of the European Ceramic Society》2021,41(10):5155-5162
We demonstrate the structural evolution of polymorphic phases in Al2O3-inserted SrMnO3 ceramics synthesized by solid state reaction. While the 4H-hexagonal phase is predominant in pure SrMnO3 ceramics, a small amount of 6H-hexagonal polymorph is identified in addition to the primary 4H-hexagonal SrMnO3 and the secondary hexagonal SrAl2O4 phases in the as-sintered ceramics, evidenced by x-ray diffraction and subsequent Rietveld refinement analyses. The existence of the 6H-hexagonal SrMnO3 phase is corroborated using Raman spectroscopy. The chemical compositions and electronic structures of the Al2O3-inserted SrMnO3 compounds are also examined using energy dispersive spectroscopy and x-ray photoelectron spectroscopy, respectively. The first-principles calculations reveal that there is no clear difference between the total energies of 4H- and 6H-hexagonal polymorphs regardless of the presence/absence of Sr and oxygen vacancies. Possible origins are discussed with the estimation of actual strain based on the refined lattice parameter of 6H SrMnO3. 相似文献
78.
79.
80.
Thermosetting materials are widely used as encapsulation in the electrical packaging to protect the core electronic components from external force, moisture, dust, and other factors. However, the spreading and curing behaviors of such kind of fluid on a heated surface have been rarely explored. In this study, we experimentally and numerically investigated the spreading and curing behaviors of the silicone(OE6550 A/B, which is widely used in the light-emitting diode packaging) droplet with diameter of ~2.2 mm on a heated surface with temperature ranging from 25 ℃ to 250 ℃. For the experiments, we established a setup with high-speed camera and heating unit to capture the fast spreading process of the silicone droplet on the heated surface. For the numerical simulation, we built a viscosity model of the silicone by using the Kiuna's model and combined the viscosity model with the Volume of Fluid(VOF) model by the User Defined Function(UDF) method. The results show that the surface temperature significantly affected the spreading behaviors of the silicone droplet since it determines the temperature and viscosity distribution inside the droplet. For surface temperature varied from 25 ℃ to 250 ℃, the final contact radius changed from ~2.95 mm to ~1.78 mm and the total spreading time changed from ~511 s to ~0.15 s. By further analyzing the viscosity evolution of the droplet, we found that the decreasing of the total spreading time was caused by the decrease of the viscosity under high surface temperature at initial spreading stage, while the reduction of the final contact radius was caused by the curing of the precursor film. This study supplies a strategy to tuning the spreading and curing behavior of silicone by imposing high surface temperature, which is of great importance to the electronic packaging. 相似文献