全文获取类型
收费全文 | 103690篇 |
免费 | 18749篇 |
国内免费 | 24043篇 |
专业分类
化学 | 75318篇 |
晶体学 | 2721篇 |
力学 | 7093篇 |
综合类 | 2158篇 |
数学 | 14048篇 |
物理学 | 45144篇 |
出版年
2024年 | 319篇 |
2023年 | 1672篇 |
2022年 | 3944篇 |
2021年 | 4066篇 |
2020年 | 4142篇 |
2019年 | 3944篇 |
2018年 | 3528篇 |
2017年 | 4268篇 |
2016年 | 4453篇 |
2015年 | 5248篇 |
2014年 | 6329篇 |
2013年 | 8037篇 |
2012年 | 8907篇 |
2011年 | 9228篇 |
2010年 | 7803篇 |
2009年 | 7752篇 |
2008年 | 8499篇 |
2007年 | 7672篇 |
2006年 | 7131篇 |
2005年 | 6165篇 |
2004年 | 4775篇 |
2003年 | 3504篇 |
2002年 | 3422篇 |
2001年 | 3236篇 |
2000年 | 3231篇 |
1999年 | 2361篇 |
1998年 | 1598篇 |
1997年 | 1345篇 |
1996年 | 1322篇 |
1995年 | 1225篇 |
1994年 | 1096篇 |
1993年 | 984篇 |
1992年 | 840篇 |
1991年 | 685篇 |
1990年 | 636篇 |
1989年 | 546篇 |
1988年 | 387篇 |
1987年 | 361篇 |
1986年 | 312篇 |
1985年 | 263篇 |
1984年 | 226篇 |
1983年 | 187篇 |
1982年 | 146篇 |
1981年 | 134篇 |
1980年 | 96篇 |
1979年 | 97篇 |
1978年 | 34篇 |
1977年 | 39篇 |
1976年 | 36篇 |
1975年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Chong-Guang Cao Zhong-Peng Yang Xian Zhang 《Journal of Applied Mathematics and Computing》2002,10(1-2):101-109
We extend two inequalities involving Hadamard products of positive definite Hermitian matrices to positive semi-definite Hermitian matrices. Simultaneously, we also show the sufficient conditions for equalities to hold. Moreover, some other matrix inequalities are also obtained. Our results and methods are different from those which are obtained by S. Liu in [J. Math. Anal. Appl. 243:458–463(2000)] and B.-Y. Wang et al. in [Lin. Alg. Appl. 302–303: 163–172(1999)]. 相似文献
62.
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
63.
64.
65.
通过分析计算,设计了一种大口径宽视场折射式红外相机光学系统。该系统设计用于超长线阵扫描红外相机的地面演示成像,它能同时对短波2μm—3μm、中波3μm—4.5μm双波段成像,且同时具有24°的大视场和150mm的宽口径,成像质量接近衍射极限。该系统在航天遥感领域应用广泛。 相似文献
66.
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
67.
68.
69.
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
70.