全文获取类型
收费全文 | 52850篇 |
免费 | 8830篇 |
国内免费 | 5653篇 |
专业分类
化学 | 37306篇 |
晶体学 | 641篇 |
力学 | 3077篇 |
综合类 | 328篇 |
数学 | 5958篇 |
物理学 | 20023篇 |
出版年
2024年 | 182篇 |
2023年 | 1122篇 |
2022年 | 2077篇 |
2021年 | 2117篇 |
2020年 | 2270篇 |
2019年 | 2143篇 |
2018年 | 1829篇 |
2017年 | 1776篇 |
2016年 | 2606篇 |
2015年 | 2639篇 |
2014年 | 3100篇 |
2013年 | 3953篇 |
2012年 | 4850篇 |
2011年 | 4786篇 |
2010年 | 3322篇 |
2009年 | 3112篇 |
2008年 | 3338篇 |
2007年 | 2957篇 |
2006年 | 2653篇 |
2005年 | 2277篇 |
2004年 | 1743篇 |
2003年 | 1389篇 |
2002年 | 1277篇 |
2001年 | 1020篇 |
2000年 | 895篇 |
1999年 | 1045篇 |
1998年 | 857篇 |
1997年 | 806篇 |
1996年 | 794篇 |
1995年 | 726篇 |
1994年 | 613篇 |
1993年 | 519篇 |
1992年 | 430篇 |
1991年 | 392篇 |
1990年 | 331篇 |
1989年 | 242篇 |
1988年 | 178篇 |
1987年 | 163篇 |
1986年 | 159篇 |
1985年 | 139篇 |
1984年 | 89篇 |
1983年 | 93篇 |
1982年 | 55篇 |
1981年 | 39篇 |
1980年 | 29篇 |
1979年 | 18篇 |
1977年 | 18篇 |
1976年 | 20篇 |
1975年 | 21篇 |
1972年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
The breakthrough and stoichiometric SO2 adsorption efficiencies of a biomass supported Na2CO3 system (80 wt %Na2CO3/straw) have reached 48.9% and 80.6% respectively at a desulfurization temperature of 80℃. 相似文献
62.
63.
Haifeng Yang Guangming XieTianguang Chu Long Wang 《Nonlinear Analysis: Theory, Methods & Applications》2006
In the paper, commuting and stable feedback design for switched linear systems is investigated. This problem is formulated as to build up suitable state feedback controller for each subsystem such that the closed-loop systems are not only asymptotically stable but also commuting each other. A new concept, common admissible eigenvector set (CAES), is introduced to establish necessary/sufficient conditions for commuting and stable feedback controllers. For second-order systems, a necessary and sufficient condition is established. Moreover, a parametrization of the CAES is also obtained. The motivation comes from stabilization of switched linear systems which consist of a family of LTI systems and a switching law specifying the switching between them, where if all the subsystems are stable and commuting each other, then the total system is stable under arbitrary switching. 相似文献
64.
Liyue Liu Yingge Yang Yafei Zhang 《Physica E: Low-dimensional Systems and Nanostructures》2004,24(3-4):343-348
The electrical conductivity was investigated for multi-walled carbon nanotubes (MWNTs) dissolved in chloroform and toluene, respectively. The electrical conductivity remarkably increased with increase in the content of MWNTs, which is in accordance with Archie's equation . Furthermore, a hypothesis of the electronic transport process was proposed to explain the difference between the solution and the solid compound. In addition, the temperature dependence of the electrical conductivity shows that log σ vs. 1/T exist in a good linear relationship. The activation energy of the electrical conductivity decreased with increase in concentration and an inflexion was observed at 60 °C in MWNT/toluene solution. 相似文献
65.
The Iyengar Type Inequalities with Exact Estimations and the Chebyshev Central Algorithms of Integrals 总被引:3,自引:0,他引:3
Xing Hua WANG Shi Jun YANG 《数学学报(英文版)》2005,21(6):1361-1376
In this paper, both low order and high order extensions of the Iyengar type inequality are obtained. Such extensions are the best possible in the same sense as that of the Iyengar inequality. hzrthermore, the Chebyshev central algorithms of integrals for some function classes and some related problems are also considered and investigated. 相似文献
66.
67.
证明了当超越亚纯函数的级小于1时,其Norel例外值最多只有一个.由于存在任何级的整函数,因此一个例外值总可达到,故所得结果不能再改进。 相似文献
68.
Fei Chang Dongheng Zhang Haijian Yang Haibin Song 《Journal of organometallic chemistry》2004,689(5):936-946
The synthesized 1-aryliminomethylenylnaphthalen-2-ol derivatives reacted with nickel chloride to form bis(1-aryliminomethylenylnaphthalen-2-oxy)nickel complexes. All resultant compounds were structurally characterized by elemental analyses, IR and H NMR, and the structures of the formed complexes were elucidated by X-ray crystal structure analysis. The complexes show high catalytic activities for the vinyl polymerization of norbornene in the presence of methylaluminoxane. The catalytic activity variations have been followed by gas chromatography through monitoring the conversion of norbornene. 相似文献
69.
学生学习知识,一般来说,是从生动的具体的直观开始的,生动的直观能使学生获得关于事物生动而具体的感性认识。但是,感性认识并没有揭露事物的本质,人们对事物本质的认识要通过一系列的抽象来完成。 相似文献
70.
Rhythmic growth of ring‐banded spherulites in blends of liquid crystalline methoxy‐poly(aryl ether ketone) (M‐PAEK) and poly(aryl ether ether ketone) (PEEK) has been investigated by means of differential scanning calorimetry (DSC), polarized light microscopy (PLM), and scanning electron microscopy (SEM) techniques. The measurements reveal that the formation of the rhythmically grown ring‐banded spherulites in the M‐PAEK/PEEK blends is strongly dependent on the blend composition. In the M‐PAEK‐rich blends, upon cooling, an unusual ring‐banded spherulite is formed, which is ascribed to structural discontinuity caused by a rhythmic radial growth. For the 50:50 M‐PAEK/PEEK blend, ring‐banded spherulites and individual PEEK spherulites coexist in the system. In the blends with PEEK as the predominant component, M‐PAEK is rejected into the boundary of PEEK spherulites. The cooling rate and crystallization temperature have great effect on the phase behavior, especially the ring‐banded spherulite formation in the blends. In addition, the effects of M‐PAEK phase transition rate and phase separation rate on banded spherulite formation is discussed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3011–3024, 2007 相似文献