全文获取类型
收费全文 | 623篇 |
免费 | 19篇 |
国内免费 | 2篇 |
专业分类
化学 | 423篇 |
晶体学 | 3篇 |
力学 | 16篇 |
数学 | 87篇 |
物理学 | 115篇 |
出版年
2023年 | 7篇 |
2022年 | 23篇 |
2021年 | 26篇 |
2020年 | 36篇 |
2019年 | 33篇 |
2018年 | 23篇 |
2017年 | 12篇 |
2016年 | 14篇 |
2015年 | 14篇 |
2014年 | 22篇 |
2013年 | 40篇 |
2012年 | 42篇 |
2011年 | 56篇 |
2010年 | 31篇 |
2009年 | 12篇 |
2008年 | 24篇 |
2007年 | 25篇 |
2006年 | 33篇 |
2005年 | 46篇 |
2004年 | 20篇 |
2003年 | 15篇 |
2002年 | 18篇 |
2001年 | 6篇 |
2000年 | 3篇 |
1999年 | 6篇 |
1998年 | 8篇 |
1997年 | 9篇 |
1996年 | 2篇 |
1995年 | 6篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1982年 | 2篇 |
1977年 | 2篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1969年 | 2篇 |
1955年 | 1篇 |
1935年 | 1篇 |
排序方式: 共有644条查询结果,搜索用时 31 毫秒
121.
We obtained new exact inequalities that estimate the L ?? -norm of the Riesz derivative D ?? f of a function f defined on $ {\mathbb{R}^m} $ in terms of the uniform norm of the function itself and the L s -norm of the function acted by the Laplace operator. On a class of functions f such that ||??f||s ?? 1, we solved the problem of approximation of an unbounded operator D ?? by bounded ones and the problem of optimal recovery of the operator D ?? on elements of this class given with known error. 相似文献
122.
Victor S. Aksenov Dmitrii I. Baklanov Sergey V. Golovastov Victor V. Golub Vladimir P. Efremov Andrey S. Saveliev Vladislav V. Volodin 《Flow, Turbulence and Combustion》2010,84(4):607-616
The present paper describes the influence of magnetic field on the spark discharge utilized for initialization of detonation. The method of schlieren time-based scanning shows the increase of shock wave velocity in the case when magnetic field was applied to the area of electrical discharge in the air. The critical energy values are obtained for a direct initialization of detonation in hydrogen–air and hexane–air mixtures. Magnetic field has a significant influence on the deflagration–combustion transition in both mixtures at the critical energy values. Pressure and velocity of the shock front were measured by ICP pressure transducers, flame front was recorded by photo-diodes. Two cases were studied experimentally: external magnetic field is produced by inductance coils connected to capacitor; own magnetic field is induced directly by discharge current in the cables positioned in special way. 相似文献
123.
The results of measuring the pressure fluctuations on the wall of the nozzle of a hypersonic wind tunnel beneath a developed turbulent boundary layer are presented for the Mach number M∞ = 7.5. On the basis of a statistical analysis, it is shown that the action of the turbulent flow is dynamically similar to the propagation of a random sequence of wave packets with continuously distributed temporal and spatial scales. Low-frequency disturbances are associated with large-scale structures of long duration that propagate at a mean-statistical velocity similar in value to the outer flow velocity. The continuous generation of weakly-correlated small-scale disturbances ensuring the maintenance and development of turbulence occurs chiefly in the inner region of the boundary layer. Spectral estimates of the power generated by the turbulent flow in the wall region of the boundary layer are presented. 相似文献
124.
Ekaterina A. Martynova Vladislav A. Voloshkin Sbastien G. Guillet Francis Bru Marek Beli Kristof Van Hecke Catherine S. J. Cazin Steven P. Nolan 《Chemical science》2022,13(23):6852
We present the use of gold sensitizers [Au(SIPr)(Cbz)] (PhotAu 1) and [Au(IPr)(Cbz)] (PhotAu 2) as attractive alternatives to state-of-the-art iridium-based systems. These novel photocatalysts are deployed in [2 + 2] cycloadditions of diallyl ethers and N-tosylamides. The reactions proceed in short reaction times and in environmentally friendly solvents. [Au(SIPr)Cbz] and [Au(IPr)(Cbz)] have higher triplet energy (ET) values (66.6 and 66.3 kcal mol−1, respectively) compared to commonly used iridium photosensitizers. These ET values permit the use of these gold complexes as sensitizers enabling energy transfer catalysis involving unprotected indole derivatives, a substrate class previously inaccessible with state-of-the-art Ir photocatalysts. The photosynthesis of unprotected tetracyclic spiroindolines via intramolecular [2 + 2] cycloaddition using our simple mononuclear gold sensitizer is readily achieved. Mechanistic studies support the involvement of triplet–triplet energy transfer (TTEnT) for both [2 + 2] photocycloadditions.We present the use of gold sensitizers [Au(SIPr)(Cbz)] (PhotAu 1) and [Au(IPr)(Cbz)] (PhotAu 2) as attractive alternatives to state-of-the-art iridium-based systems. 相似文献
125.
Barkov Alexey Yu. Kochnev Ivan A. Simonov Nikita S. Kutyashev Igor B. Zimnitskiy Nikolay S. Korotaev Vladislav Yu. Sosnovskikh Vyacheslav Ya. 《Chemistry of Heterocyclic Compounds》2021,57(12):1204-1211
Chemistry of Heterocyclic Compounds - A diastereoselective method was developed for the synthesis of 4-trifluoromethyl- and 4-phenyl-substituted... 相似文献
126.
127.
Vladislav Chernysh 《Proceedings of the American Mathematical Society》2006,134(9):2771-2777
In this paper we show that for Riemannian manifolds with boundary the natural restriction map is a quasifibration between spaces of metrics of positive scalar curvature. We apply this result to study homotopy properties of spaces of such metrics on manifolds with boundary.
128.
129.
NAD+ is degraded by horse liver alcohol dehydrogenase in a reaction with p-methylbenzyl hydroperoxide, which acts as a pseudo-substrate. An unstable intermediate product (called compound I) is formed, and this is converted into the final product NADX. The reaction can be monitored by capillary electrophoresis. NADX migrates as two well resolved peaks (NADX1 and NADX2), which belong probably to the tautomers of the same substance. The intermediate product, compound I, has the same effective mobility as the conformer NADX2 and it was impossible to separate compound I from NADX2. The spectra taken during the separation show clearly that the “9-min” peak contains different compounds during the course of the reaction and the NADX2 is not identical with compound I. 相似文献
130.
A comparison between two models of proton transfer in the symmetric H-bond interacting in a thermal reservoir is made. It is shown that in a more general model (including both previous ones as special cases) a new qualitative feature in proton damping appears. 相似文献