全文获取类型
收费全文 | 64900篇 |
免费 | 5418篇 |
国内免费 | 2861篇 |
学科分类
工业技术 | 73179篇 |
出版年
2024年 | 177篇 |
2023年 | 1064篇 |
2022年 | 1610篇 |
2021年 | 2526篇 |
2020年 | 1950篇 |
2019年 | 1670篇 |
2018年 | 1908篇 |
2017年 | 2114篇 |
2016年 | 1895篇 |
2015年 | 2397篇 |
2014年 | 3246篇 |
2013年 | 3709篇 |
2012年 | 4140篇 |
2011年 | 4478篇 |
2010年 | 3925篇 |
2009年 | 3724篇 |
2008年 | 3667篇 |
2007年 | 3563篇 |
2006年 | 3626篇 |
2005年 | 3121篇 |
2004年 | 2141篇 |
2003年 | 1914篇 |
2002年 | 1671篇 |
2001年 | 1621篇 |
2000年 | 1680篇 |
1999年 | 1816篇 |
1998年 | 1406篇 |
1997年 | 1181篇 |
1996年 | 1067篇 |
1995年 | 952篇 |
1994年 | 779篇 |
1993年 | 556篇 |
1992年 | 438篇 |
1991年 | 342篇 |
1990年 | 314篇 |
1989年 | 228篇 |
1988年 | 172篇 |
1987年 | 102篇 |
1986年 | 99篇 |
1985年 | 54篇 |
1984年 | 39篇 |
1983年 | 21篇 |
1982年 | 32篇 |
1981年 | 22篇 |
1980年 | 13篇 |
1979年 | 3篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1959年 | 1篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 22 毫秒
11.
12.
Grain refinement is critical for fabricating high-quality Al-Si casting components in the application of automobile and aerospace industries,while the well-known Si-poisoning effect makes it difficult.Nbbased refiners offer an effective method to refine Al-Si casting alloys,but their anti Si-poisoning capability is far from being understood.In this work,the grain refining mechanism and the anti Si-poisoning effect in the Al-10 Si/Al-5 Nb-B system were systematically investigated by combining transmission electron microscope,first-principles calculations,and thermodynamic calculations.It is revealed that NbB2provides the main nucleation site in the Al-10 Si ingot inoculated by 0.1 wt.%Nb Al-5 Nb-B refiner.The exposed Nb atoms on the(0001)NbB2and(1-100)NbB2surface can be substituted by Al to form(Al,Nb)B2intermedia layers.In addition,a layer of NbAl3-like compound(NbAl3')can cover the surface of NbB2with the orientation relation of(1-100)[11-20]NbB2//(110)[110]NbAl3'.Both of the(Al,Nb)B2and NbAl3'intermedia layers contribute to enhancing the nucleation potency of NbB2particles.These discoveries provide fundamental insight to the grain refining mechanism of the Nb-B based refiners for Al-Si casting alloys and are expected to guide the future development of stronger refiners for Al-Si casting alloys. 相似文献
13.
Bin Feng Xin Jiang Guisheng Zou Wengan Wang Tianming Sun Heng Yang Guanlei Zhao Mingye Dong Yu Xiao Hongwei Zhu Lei Liu 《Advanced functional materials》2021,31(29):2102359
The realization of liquid metal-based wearable systems will be a milestone toward high-performance, integrated electronic skin. However, despite the revolutionary progress achieved in many other components of electronic skin, liquid metal-based flexible sensors still suffer from poor sensitivity due to the insufficient resistance change of liquid metal to deformation. Herein, a nacre-inspired architecture composed of a biphasic pattern (liquid metal with Cr/Cu underlayer) as “bricks” and strain-sensitive Ag film as “mortar” is developed, which breaks the long-standing sensitivity bottleneck of liquid metal-based electronic skin. With 2 orders of magnitude of sensitivity amplification while maintaining wide (>85%) working range, for the first time, liquid metal-based strain sensors rival the state-of-art counterparts. This liquid metal composite features spatially regulated cracking behavior. On the one hand, hard Cr cells locally modulate the strain distribution, which avoids premature cut-through cracks and prolongs the defect propagation in the adjacent Ag film. On the other hand, the separated liquid metal cells prevent unfavorable continuous liquid-metal paths and create crack-free regions during strain. Demonstrated in diverse scenarios, the proposed design concept may spark more applications of ultrasensitive liquid metal-based electronic skins, and reveals a pathway for sensor development via crack engineering. 相似文献
14.
15.
16.
17.
18.
19.
20.
Dongdong Ji Zheng Liu Bailing Jiang Xiaofei Luo 《International Journal of Hydrogen Energy》2021,46(27):13960-13970
The evaluation of cell's weatherability is of practical interest. To further improve the soluble lead flow battery's weatherability, physiochemical properties of electrolytes containing fluoborate, perchlorate, methanesulfonate and trifluoromethanesulfonate are investigated from ?60 to 50 °C. Activities of CF3SO3H and HClO4 are poor in trifluoromethanesulfonate and perchlorate solutions due to common anion effect. The solubility of lead salt can be improved by increasing temperature, but worsened by increasing acid's content. With the temperature increasing, the conductivity is enhanced, and the viscosity is lowered for four solutions. The same results have been found by increasing acid's content except for CF3SO3H. The high energy efficiency can be achieved for cells over ?40–0 °C using fluoborate and perchlorate solutions, 73.2% at ?40 °C and 78.1% at ?30 °C respectively. Over the temperature range of 20–50 °C, the cells with methanesulfonate and trifluoromethanesulfonate solutions have good performance, 77.4% and 73.7% at 50 °C respectively. 相似文献