全文获取类型
收费全文 | 75374篇 |
免费 | 9060篇 |
国内免费 | 5162篇 |
专业分类
电工技术 | 6401篇 |
技术理论 | 5篇 |
综合类 | 6042篇 |
化学工业 | 10536篇 |
金属工艺 | 4513篇 |
机械仪表 | 5261篇 |
建筑科学 | 6365篇 |
矿业工程 | 2727篇 |
能源动力 | 2252篇 |
轻工业 | 5570篇 |
水利工程 | 1877篇 |
石油天然气 | 3639篇 |
武器工业 | 982篇 |
无线电 | 9724篇 |
一般工业技术 | 7713篇 |
冶金工业 | 2885篇 |
原子能技术 | 1079篇 |
自动化技术 | 12025篇 |
出版年
2024年 | 512篇 |
2023年 | 1482篇 |
2022年 | 3080篇 |
2021年 | 4322篇 |
2020年 | 3237篇 |
2019年 | 2410篇 |
2018年 | 2629篇 |
2017年 | 2954篇 |
2016年 | 2567篇 |
2015年 | 3966篇 |
2014年 | 4868篇 |
2013年 | 5566篇 |
2012年 | 6624篇 |
2011年 | 6796篇 |
2010年 | 6038篇 |
2009年 | 5569篇 |
2008年 | 5262篇 |
2007年 | 4663篇 |
2006年 | 3977篇 |
2005年 | 3205篇 |
2004年 | 2100篇 |
2003年 | 1398篇 |
2002年 | 1249篇 |
2001年 | 969篇 |
2000年 | 831篇 |
1999年 | 749篇 |
1998年 | 476篇 |
1997年 | 426篇 |
1996年 | 363篇 |
1995年 | 301篇 |
1994年 | 252篇 |
1993年 | 163篇 |
1992年 | 123篇 |
1991年 | 119篇 |
1990年 | 73篇 |
1989年 | 55篇 |
1988年 | 52篇 |
1987年 | 29篇 |
1986年 | 24篇 |
1985年 | 9篇 |
1984年 | 12篇 |
1983年 | 4篇 |
1982年 | 12篇 |
1981年 | 11篇 |
1980年 | 21篇 |
1979年 | 16篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1959年 | 16篇 |
1951年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
Lei He Yan Xuan Feng Zhang Xue Wang Huaqing Pan Junfeng Ren Meina Chen 《International Journal of Hydrogen Energy》2021,46(1):1096-1105
Bulk and surface properties of proton stability and transportation in Y and Nd co-doped BaCeO3 (BCYN), especially the effect of Nd segregation, were investigated by first-principles calculations. Since the structure of doped BaCeO3 at the operating temperature of proton-conducting has been unclear for a long time, we have summarized the latest experimental results and calculated the structure of the asymmetric BCYN for the first time. The results show that compared with Y, Nd doping promotes oxygen vacancy formation, however reduces proton stability. Our calculation can also provide a possible explanation for the formation of space charge layer at the grain boundary of doped BaCeO3 in experiment. Unlike the stable Y in BCYN, Nd is calculated to be easily segregated, which can facilitate both proton hydration and proton transportation near the surface. Moreover, Nd segregation at the grain boundary is predicted to be beneficial for proton transportation between grains. 相似文献
32.
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
33.
Shank S. Kulkarni Kyoo Sil Choi Wenbin Kuang Nalini Menon Bernice Mills Ayoub Soulami Kevin Simmons 《International Journal of Hydrogen Energy》2021,46(36):19001-19022
The use of hydrogen as a fuel is increasing exponentially, and the most economical way to store and transport hydrogen for fuel use is as a high-pressure gas. Polymers are widely used for hydrogen distribution and storage systems because they are chemically inert towards hydrogen. However, when exposed to high-pressure hydrogen, some hydrogen diffuses through polymers and occupies the preexisting cavities inside the material. Upon depressurization, the hydrogen trapped inside polymer cavities can cause blistering or cracking by expanding these cavities. A continuum mechanics–based deformation model was deployed to predict the stress distribution and damage propagation while the polymer undergoes depressurization after high-pressure hydrogen exposure. The effects of cavity size, cavity location, and pressure inside the cavity on damage initiation and evolution inside the polymer were studied. The stress and damage evolution in the presence of multiple cavities was also studied, because interaction among cavities alters the damage and stress field. It was found that all these factors significantly change the stress state in the polymer, resulting in different paths for damage propagation. The effect of adding carbon black filler particles and plasticizer on the damage was also studied. It was found that damage tolerance of the polymer increases drastically with the addition of carbon black fillers, but decreases with the addition of the plasticizer. 相似文献
34.
35.
36.
针对领域自适应问题中源域和目标域的联合分布差异最小化问题,提出两阶段领域自适应学习方法.在第一阶段考虑样本标签和数据结构的判别信息,通过学习一个共享投影变换,使投影后的共享空间中边缘分布的差异最小.第二阶段利用源域标记数据和目标域非标记数据学习一个带结构风险的自适应分类器,不仅能最小化源域和目标域条件分布差异,还能进一步保持源域和目标域边缘分布的流形一致性.在3个基准数据集上的实验表明,文中方法在平均分类准确率和Kappa系数两项评价指标上均表现较优. 相似文献
37.
38.
Huimin Zhao Wensi Wang Yunmei Du Yu Yang Minghui Wang Shaoxiang Li Ruixin Chen Yanru Liu Lei Wang 《International Journal of Hydrogen Energy》2021,46(18):10763-10772
In this work, we synthesized Se doped MoS2@Ni3S2 with nanosheets coated nanorods structure supported on Ni foam (MoNiSeS). Firstly, MoS2@Ni3S2 (MoNiS) nanorods was synthesized by hydrothermal method. After selenization treatment, MoSe2 successfully formed on the edge of MoS2 nanosheets and particle Ni3S2 transformed into NiSe, in which MoSe2 and NiSe acted as new phase in MoNiSeS. The obtained MoNiSeS only needs a low overpotential of 68 mV to reach the current density of 10 mA cm?2, and has a low Tafel plots of 72.77 mV dec?1 and good electrochemical durability, whose electrochemical activity is much better than that of MoNiS and NiSeS, implying the introduction of Mo and Se is beneficial to improve the electrocatalytic performance of NiS for HER. In addition, the proper amount of Mo source, which has an effect on the morphology of product, has also been investigated. For MoNiSeS, the typical nanosheets coated nanarods expose more active sites and the synergic effects is good to the improvement of the catalytic activity. Meanwhile, WNiSeS has also been prepared using the same method and the corresponding results show that the electrochemical activity of WNiSeS is much better than that of NiSeS, proving the universality of this strategy. 相似文献
39.
40.
Jiaao Yan Gao Zhiming Tan Qingchao Yang Xian Hu Wenbin 《Protection of Metals and Physical Chemistry of Surfaces》2020,56(5):965-972
Protection of Metals and Physical Chemistry of Surfaces - The Al2O3 powder was added as a filler to polyurea and the effect of doping amount on Shore hardness and wetting property were... 相似文献