全文获取类型
收费全文 | 129169篇 |
免费 | 9740篇 |
国内免费 | 8431篇 |
专业分类
化学 | 44810篇 |
晶体学 | 1972篇 |
力学 | 5425篇 |
综合类 | 1252篇 |
数学 | 42306篇 |
物理学 | 51575篇 |
出版年
2023年 | 640篇 |
2022年 | 2149篇 |
2021年 | 1978篇 |
2020年 | 1700篇 |
2019年 | 2071篇 |
2018年 | 1851篇 |
2017年 | 1655篇 |
2016年 | 1734篇 |
2015年 | 1674篇 |
2014年 | 2920篇 |
2013年 | 5233篇 |
2012年 | 3077篇 |
2011年 | 4118篇 |
2010年 | 4506篇 |
2009年 | 9583篇 |
2008年 | 10733篇 |
2007年 | 9187篇 |
2006年 | 8083篇 |
2005年 | 5841篇 |
2004年 | 5463篇 |
2003年 | 5556篇 |
2002年 | 8515篇 |
2001年 | 5066篇 |
2000年 | 4639篇 |
1999年 | 4314篇 |
1998年 | 3716篇 |
1997年 | 2876篇 |
1996年 | 2558篇 |
1995年 | 2852篇 |
1994年 | 2756篇 |
1993年 | 2260篇 |
1992年 | 1748篇 |
1991年 | 1275篇 |
1990年 | 1074篇 |
1989年 | 942篇 |
1988年 | 947篇 |
1987年 | 679篇 |
1986年 | 488篇 |
1985年 | 1329篇 |
1984年 | 913篇 |
1983年 | 678篇 |
1982年 | 971篇 |
1981年 | 1135篇 |
1980年 | 1025篇 |
1979年 | 907篇 |
1978年 | 829篇 |
1977年 | 691篇 |
1976年 | 674篇 |
1974年 | 423篇 |
1973年 | 568篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
1.
2.
This paper infers from a generalized Picone identity the uniqueness of the stable positive solution for a class of semilinear equations of superlinear indefinite type, as well as the uniqueness and global attractivity of the coexistence state in two generalized diffusive prototypes of the symbiotic and competing species models of Lotka–Volterra. The optimality of these uniqueness theorems reveals the tremendous strength of the Picone identity. 相似文献
3.
《Indagationes Mathematicae》2021,32(1):55-85
We show that the differential structure of the orbit space of a proper action of a Lie group on a smooth manifold is weakly reflexive. This implies that the orbit space is a differentiable space in the sense of Smith, which ensures that the orbit space has an exterior algebra of differential forms, that satisfies Smith’s version of de Rham’s theorem. Because the orbit space is a locally closed subcartesian space, it has vector fields and their flows. 相似文献
4.
A finite support product of clones of Jensen's minimal singleton forcing is used to define a model in which any non-empty analytically definable set of reals contains an analytically definable real (the full basis theorem), but there is no analytically definable wellordering of the reals. 相似文献
5.
6.
Dr. Joaquim Torra Dr. Felipe Viela Dr. Diego Megías Dr. Begoña Sot Prof. Cristina Flors 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(19):e202200026
CRANAD-2 is a fluorogenic curcumin derivative used for near-infrared detection and imaging in vivo of amyloid aggregates, which are involved in neurodegenerative diseases. We explore the performance of CRANAD-2 in two super-resolution imaging techniques, namely stimulated emission depletion (STED) and single-molecule localization microscopy (SMLM), with markedly different fluorophore requirements. By conveniently adapting the concentration of CRANAD-2, which transiently binds to amyloid fibrils, we show that it performs well in both techniques, achieving a resolution in the range of 45–55 nm. Correlation of SMLM with atomic force microscopy (AFM) validates the resolution of fine features in the reconstructed super-resolved image. The good performance and versatility of CRANAD-2 provides a powerful tool for near-infrared nanoscopic imaging of amyloids in vitro and in vivo. 相似文献
7.
In this article, we construct and analyze a residual-based a posteriori error estimator for a quadratic finite volume method (FVM) for solving nonlinear elliptic partial differential equations with homogeneous Dirichlet boundary conditions. We shall prove that the a posteriori error estimator yields the global upper and local lower bounds for the norm error of the FVM. So that the a posteriori error estimator is equivalent to the true error in a certain sense. Numerical experiments are performed to illustrate the theoretical results. 相似文献
8.
9.
10.
In this work, a vanillin complex is immobilized onto MCM-41 and characterized by FT-IR, X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, thermogravimetric analysis, and BET techniques. This supported Schiff base complex was found to be an efficient and recoverable catalyst for the chemoselective oxidation of sulfides into sulfoxides and thiols into their corresponding disulfides (using hydrogen peroxide as a green oxidant) and also a suitable catalyst for the preparation of 2,3-dihydroquinazolin-4(1H)-one derivatives in water at 90°C. Using this protocol, we show that a variety of disulfides, sulfoxides, and 2,3-dihydroquinazolin-4(1H)-one derivatives can be synthesized in green conditions. The catalyst can be recovered and recycled for further reactions without appreciable loss of catalytic performance. 相似文献