全文获取类型
收费全文 | 54270篇 |
免费 | 9680篇 |
国内免费 | 7307篇 |
专业分类
化学 | 27574篇 |
晶体学 | 587篇 |
力学 | 2358篇 |
综合类 | 395篇 |
数学 | 4083篇 |
物理学 | 15240篇 |
无线电 | 21020篇 |
出版年
2024年 | 237篇 |
2023年 | 1226篇 |
2022年 | 1778篇 |
2021年 | 2140篇 |
2020年 | 2065篇 |
2019年 | 2033篇 |
2018年 | 1805篇 |
2017年 | 1977篇 |
2016年 | 2388篇 |
2015年 | 2881篇 |
2014年 | 3480篇 |
2013年 | 4245篇 |
2012年 | 4878篇 |
2011年 | 4840篇 |
2010年 | 3968篇 |
2009年 | 4014篇 |
2008年 | 4244篇 |
2007年 | 3670篇 |
2006年 | 3409篇 |
2005年 | 2693篇 |
2004年 | 2040篇 |
2003年 | 1751篇 |
2002年 | 1705篇 |
2001年 | 1423篇 |
2000年 | 1191篇 |
1999年 | 920篇 |
1998年 | 673篇 |
1997年 | 582篇 |
1996年 | 534篇 |
1995年 | 431篇 |
1994年 | 413篇 |
1993年 | 302篇 |
1992年 | 256篇 |
1991年 | 190篇 |
1990年 | 178篇 |
1989年 | 108篇 |
1988年 | 96篇 |
1987年 | 70篇 |
1986年 | 79篇 |
1985年 | 54篇 |
1984年 | 31篇 |
1983年 | 32篇 |
1982年 | 19篇 |
1981年 | 18篇 |
1980年 | 12篇 |
1979年 | 20篇 |
1977年 | 13篇 |
1975年 | 9篇 |
1974年 | 10篇 |
1925年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
12.
13.
刘伟 《信息技术与信息化》2015,(2):80-81
本文据国内矫直机的使用情况,提出完善弯辊功能,解决辊缝标定清零及运行中的问题,提升轧钢厂运行效率与产品质量。 相似文献
14.
15.
In the present research, hierarchical structure observation and mechanical property characterization for a type of biomaterial are carried out. The investigated biomaterial is Hyriopsis cumingii, a typical limnetic shell, which consists of two different structural layers, a prismatic "pillar"structure and a nacreous "brick and mortar" structure. The prismatic layer looks like a "pillar forest" with variationsection pillars sized on the order of several tens of microns.The nacreous material looks like a "brick wall" with bricks sized on the order of several microns. Both pillars and bricks are composed of nanoparticles. The mechanical properties of the hierarchical biomaterial are measured by using the nanoindentation test. Hardness and modulus are measured for both the nacre layer and the prismatic layer, respectively.The nanoindentation size effects for the hierarchical structural materials are investigated experimentally. The results show that the prismatic nanostructured material has a higher stiffness and hardness than the nacre nanostructured material.In addition, the nanoindentation size effects for the hierarchical structural materials are described theoretically, by using the trans-scale mechanics theory considering both strain gradient effect and the surface/interface effect. The modeling results are consistent with experimental ones. 相似文献
16.
Journal of Thermal Analysis and Calorimetry - A complete analysis of the thermal process about melamine was presented, in which different methods were applied to determine the characteristic of the... 相似文献
17.
Wang Hay Kan Chenxi Wei Dongchang Chen Tao Bo Bao‐Tian Wang Yan Zhang Yangchao Tian Jun‐Sik Lee Yijin Liu Guoying Chen 《Advanced functional materials》2019,29(17)
Lithium‐rich disordered rock‐salt oxides have attracted great interest owing to their promising performance as Li‐ion battery cathodes. While experimental and theoretical efforts are critical in advancing this class of materials, a fundamental understanding of key property changes upon Li extraction is largely missing. In the present study, single‐crystal synthesis of a new disordered rock‐salt cathode material, Li1.3Ta0.3Mn0.4O2 (LTMO), and its use as a model compound to investigate Li concentration–driven evolution of local cationic ordering, charge compensation, and chemical distribution are reported. Through the combined use of 2D and 3D X‐ray nanotomography, it is shown that Li removal accompanied by oxygen oxidation is correlated with the development of morphological defects such as particle cracking. Chemical heterogeneity, quantified by subparticle level distribution of Mn valence state, is minimal during Mn redox, which drastically increases upon the formation of cracks during oxygen redox. Density functional theory and bond valence sum mismatch calculations reveal the presence of local short‐range ordering in the pristine oxide, which gradually disappears along with the extraction of Li. The study suggests that with cycling the transformation into true cation–disordered state can be expected, which likely impacts the voltage profile and obtainable energy density of the oxide cathodes. 相似文献
18.
19.
Nonlinear Dynamics - Global dynamics of a flexible asymmetrical rotor resting on vibrating supports is investigated. Hamilton’s principle is used to derive the partial differential governing... 相似文献
20.
Yaping Chen Dr. Kun Rui Prof. Jixin Zhu Prof. Shi Xue Dou Dr. Wenping Sun 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(3):703-713
Developing clean and sustainable energies as alternatives to fossil fuels is in strong demand within modern society. The oxygen evolution reaction (OER) is the efficiency-limiting process in plenty of key renewable energy systems, such as electrochemical water splitting and rechargeable metal–air batteries. In this regard, ongoing efforts have been devoted to seeking high-performance electrocatalysts for enhanced energy conversion efficiency. Apart from traditional precious-metal-based catalysts, nickel-based compounds are the most promising earth-abundant OER catalysts, attracting ever-increasing interest due to high activity and stability. In this review, the recent progress on nickel-based oxide and (oxy)hydroxide composites for water oxidation catalysis in terms of materials design/synthesis and electrochemical performance is summarized. Some underlying mechanisms to profoundly understand the catalytic active sites are also highlighted. In addition, the future research trends and perspectives on the development of Ni-based OER electrocatalysts are discussed. 相似文献