全文获取类型
收费全文 | 3422篇 |
免费 | 428篇 |
国内免费 | 504篇 |
专业分类
化学 | 1711篇 |
晶体学 | 36篇 |
力学 | 443篇 |
综合类 | 63篇 |
数学 | 1541篇 |
物理学 | 560篇 |
出版年
2024年 | 7篇 |
2023年 | 29篇 |
2022年 | 44篇 |
2021年 | 68篇 |
2020年 | 91篇 |
2019年 | 85篇 |
2018年 | 86篇 |
2017年 | 130篇 |
2016年 | 112篇 |
2015年 | 118篇 |
2014年 | 193篇 |
2013年 | 296篇 |
2012年 | 196篇 |
2011年 | 207篇 |
2010年 | 156篇 |
2009年 | 191篇 |
2008年 | 180篇 |
2007年 | 206篇 |
2006年 | 172篇 |
2005年 | 180篇 |
2004年 | 189篇 |
2003年 | 168篇 |
2002年 | 151篇 |
2001年 | 109篇 |
2000年 | 122篇 |
1999年 | 131篇 |
1998年 | 104篇 |
1997年 | 110篇 |
1996年 | 66篇 |
1995年 | 64篇 |
1994年 | 61篇 |
1993年 | 40篇 |
1992年 | 40篇 |
1991年 | 37篇 |
1990年 | 30篇 |
1989年 | 16篇 |
1988年 | 21篇 |
1987年 | 20篇 |
1986年 | 23篇 |
1985年 | 15篇 |
1984年 | 13篇 |
1982年 | 11篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1979年 | 12篇 |
1978年 | 10篇 |
1977年 | 9篇 |
1976年 | 5篇 |
1975年 | 3篇 |
1972年 | 4篇 |
排序方式: 共有4354条查询结果,搜索用时 828 毫秒
931.
Abuduheiremu Awati Halidan Maimaiti Bo Xu Shixin Wang 《Surface and interface analysis : SIA》2020,52(3):98-109
Fluorescent carbon nanoparticles (FCNPs) have broad application prospects in the fields of bioimaging, ion detection, and photocatalysis. In this paper, coal-based FCNPs were prepared by using mixed acid oxidation, hydrogen peroxide etching, and organic solvent extraction methods (marked as FCNPs-AO, FCNPs-HE, and FCNPs-OS, respectively), and the structures and properties of the as-prepared products were compared. It was found that the coal-based FCNPs obtained by three kinds of methods are all aromatic structural nanomaterials linked with oxygen-containing groups. Among them, FCNPs-AO is a kind of hollow annular spherical particles and FCNPs-HE and FCNPs-OS are solid spherical particles. These FCNPs not only have similar fluorescence properties as traditional quantum dots, but also can be photoexcited to generate photogenerated electrons and holes, and it can also suppress the recombination of photogenerated electrons and holes by using its own surface defects. In particular, the electron transport capability of the FCNPs-AO is stronger than that of FCNPs-HE and FCNPs-OS because of its lower charge transfer impedance, so it can be excited to generate more photogenerated electrons and has the best photogenerated carrier separation efficiency. 相似文献
932.
933.
934.
O. J. Staffans 《Journal of Optimization Theory and Applications》1991,70(1):173-189
Up to this time, the only known method to solve the discrete-time mixed sensitivity minimization problem inl
1 has been to use a certain infinite-dimensional linear programming approach, presented by Dahleh and Pearson in 1988 and later modified by Mendlovitz. That approach does not give in general true optimal solutions; only suboptimal ones are obtained. Here, for the first time, the truel
1-optimal solutions are found for some mixed sensitivity minimization problems. In particular, Dahleh and Pearson construct an 11h order suboptimal compensator for a certain second-order plan with first-order weight functions; it is shown that the unique optimal compensator for that problem is rational and of order two. The author discovered this fact when trying out a new scheme of solving the infinite-dimensional linear programming system. This scheme is of independent interest, because when it is combined with the Dahleh-Pearson-Mendlovitz scheme, it gives both an upper bound and a lower bound on the optimal performance; hence, it provides the missing error bound that enables one to truncate the solution. Of course, truncation is appropriate only if the order of the optimal compensator is too high. This may indeed be the case, as is shown with an example where the order of the optimal compensator can be arbitrarily high. 相似文献
935.
In this paper, based on the Naghdi shell model, we analyze the uniform convergence of mixed finite element methods for cylindrical
shell problems using macroelement techniques. We show that Taylor–Hood elements p
2-P
1 and P
1
iso P
2 are locking free elements for the model problems. Optimal error estimates are presented with these elements.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
936.
摘要:本文利用半序方法。研究了一类非线性算子方程的最小最大耦合拟解的存在性。得到几个新的存在性定理,并且改进和推广了中相关结果. 相似文献
937.
L. Boulaajine M. Farhloul L. Paquet 《Numerical Methods for Partial Differential Equations》2005,21(5):938-960
In this article, we propose a residual based reliable and efficient error estimator for the new dual mixed finite element method of the elasticity problem in a polygonal domain, introduced by M. Farhloul and M. Fortin. With the help of a specific generalized Helmholtz decomposition of the error on the strain tensor and the classical decomposition of the error on the gradient of the displacements, we show that our global error estimator is reliable. Efficiency of our estimator follows by using classical inverse estimates. The lower and upper error bounds obtained are uniform with respect to the Lamé coefficient λ, in particular avoiding locking phenomena. © 2005 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2005. 相似文献
938.
Songxiao Li 《Czechoslovak Mathematical Journal》2007,57(3):1013-1023
This article provided some sufficient or necessary conditions for a class of integral operators to be bounded on mixed norm
spaces in the unit ball.
The author is supported in part by the NNSF China (No. 10671115), grants from Specialized Research Fund for the doctoral program
of Higher Education (No. 20060560002) and NSF of Guangdong Province (No. 06105468). 相似文献
939.
Embedding theorems in the Sobolev-Morrey type spaces S
p,a,ℵτ
W
W(G) with dominant mixed derivatives
A. M. Nadzhafov 《Siberian Mathematical Journal》2006,47(3):505-516
We construct Sobolev-Morrey type spaces with dominant mixed derivatives and, using the obtained integral representation, prove some embedding theorems in these spaces. 相似文献
940.
本文先扼要介绍一类三阶双曲抛物混合型偏微分方程的边值问题,然后讨论了与之有关的一类变系数三阶双曲型方程以特征线为支柱的边值问题,得到了有唯一解时此变系数应满足的充分必要条件。 相似文献