全文获取类型
收费全文 | 4335篇 |
免费 | 118篇 |
国内免费 | 26篇 |
专业分类
化学 | 3183篇 |
晶体学 | 27篇 |
力学 | 110篇 |
数学 | 570篇 |
物理学 | 589篇 |
出版年
2023年 | 26篇 |
2022年 | 22篇 |
2021年 | 96篇 |
2020年 | 70篇 |
2019年 | 63篇 |
2018年 | 51篇 |
2017年 | 53篇 |
2016年 | 93篇 |
2015年 | 99篇 |
2014年 | 126篇 |
2013年 | 232篇 |
2012年 | 283篇 |
2011年 | 301篇 |
2010年 | 196篇 |
2009年 | 194篇 |
2008年 | 255篇 |
2007年 | 276篇 |
2006年 | 257篇 |
2005年 | 248篇 |
2004年 | 234篇 |
2003年 | 181篇 |
2002年 | 173篇 |
2001年 | 77篇 |
2000年 | 76篇 |
1999年 | 57篇 |
1998年 | 47篇 |
1997年 | 44篇 |
1996年 | 47篇 |
1995年 | 46篇 |
1994年 | 36篇 |
1993年 | 33篇 |
1992年 | 23篇 |
1991年 | 30篇 |
1990年 | 39篇 |
1989年 | 33篇 |
1988年 | 36篇 |
1987年 | 33篇 |
1986年 | 30篇 |
1985年 | 31篇 |
1984年 | 33篇 |
1983年 | 26篇 |
1982年 | 23篇 |
1981年 | 18篇 |
1980年 | 19篇 |
1979年 | 16篇 |
1978年 | 20篇 |
1977年 | 11篇 |
1976年 | 11篇 |
1975年 | 9篇 |
1973年 | 10篇 |
排序方式: 共有4479条查询结果,搜索用时 515 毫秒
1.
AbstractRealistic stochastic modeling is increasingly requiring the use of bounded noises. In this work, properties and relationships of commonly employed bounded stochastic processes are investigated within a solid mathematical ground. Four families are object of investigation: the Sine-Wiener (SW), the Doering–Cai–Lin (DCL), the Tsallis–Stariolo–Borland (TSB), and the Kessler–Sørensen (KS) families. We address mathematical questions on existence and uniqueness of the processes defined through Stochastic Differential Equations, which often conceal non-obvious behavior, and we explore the behavior of the solutions near the boundaries of the state space. The expression of the time-dependent probability density of the Sine-Wiener noise is provided in closed form, and a close connection with the Doering–Cai–Lin noise is shown. Further relationships among the different families are explored, pathwise and in distribution. Finally, we illustrate an analogy between the Kessler–Sørensen family and Bessel processes, which allows to relate the respective local times at the boundaries. 相似文献
2.
3.
4.
5.
6.
Marcelino Maneiro Manuel R. Bermejo M. Isabel Fernndez Ana M. Gonzlez‐Noya Alexei M. Tyryshkin Robin G. Pritchard 《无机化学与普通化学杂志》2003,629(2):285-290
A new MnIII‐Schiff base complex, [MnL(OH2)](ClO4) ( 1 ) (H2L = N, N′‐bis‐(3‐Br‐5‐Cl‐salicylidene)‐1, 2‐diimino‐2‐methylethane), an inorganic model of the catalytic center (OEC, Oxygen Evolving Complex) in photosystem II (PSII), has been synthesized and characterized by elemental analysis, IR and EPR spectroscopy, mass spectrometry, magnetic susceptibility measurement and the study of its redox properties by cyclic and normal pulse voltammetry. This complex mimics reactivity (showing a relevant photolytic activity), and also some structural characteristics (parallel‐mode MnIII EPR signal from partially assembled OEC cluster) of the natural OEC. The complex 1 was found to rearrange in solution into a crystallographically solved square‐pyramidal complex, [MnLL′] ( 2 ) (HL′ = 6‐bromo‐4‐chloro‐2‐cyanophenol), through a process, which probably liberates radical species (detected by EPR), and provokes a C—N bond cleavage in the ligand. A photo‐radical mechanism is discussed to explain this rearrangement. 相似文献
7.
An efficient way of obtaining travelling waves in a periodic fluid system is described and tested. We search for steady states in a reference frame travelling at the wave phase velocity using a first‐order pseudospectral semi‐implicit time scheme adapted to carry out the Newton's iterations. The method is compared to a standard Newton–Raphson solver and is shown to be highly efficient in performing this task, even when high‐resolution grids are used. This method is well suited to three‐dimensional calculations in cylindrical or spherical geometries. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
8.
9.
L. Torrisi A.M. Mezzasalma J. Badziak J. Wolowski G. Franco 《Applied Surface Science》2006,252(24):8533-8538
High energy laser plasma-produced Cu ions have been implanted in silicon substrates placed at different distances and angles with respect to the normal to the surface of the ablated target. The implanted samples have been produced using the iodine high power Prague Asterix Laser System (PALS) using 438 nm wavelength irradiating in vacuum a Cu target. The high laser pulse energy (up to 230 J) and the short pulse duration (400 ps) produced a non-equilibrium plasma expanding mainly along the normal to the Cu target surface. Time-of-flight (TOF) technique was employed, through an electrostatic ion energy analyzer (IEA) placed along the target normal, in order to measure the ion energy, the ion charge state, the energy distribution and the charge state distribution. Ions had a Boltzmann energy distributions with an energy increasing with the charge state. At a laser fluence of the order of 6 × 106 J/cm2, the maximum ion energy was about 600 keV and the maximum charge state was about 27+.In order to investigate the implantation processes, Cu depth profiles have been performed with Rutherford backscattering spectrometry (RBS) of 1.5 MeV helium ions, Auger electron spectroscopy (AES) with 3 keV electron beam and 1 keV Ar sputtering ions in combination with scanning electron microscopy (SEM). Surface analysis results indicate that Cu ions are implanted within the first surface layers and that the ion penetration ranges are in agreement with the ion energy measured with IEA analysis. 相似文献
10.
Rafael R. del Río Castillo 《Communications in Mathematical Physics》1991,142(2):421-431
In this work we study the behavior of embedded eigenvalues of Sturm-Liouville problems in the half axis under local perturbations. When the derivative of the spectral function is strictly positive, we prove that the embedded eigenvalues either disappear or remain fixed. In this case we show that local perturbations cannot add eigenvalues in the continuous spectrum. If the condition on the spectral function is removed then a local perturbation can add infinitely many eigenvalues. 相似文献