全文获取类型
收费全文 | 2186篇 |
免费 | 180篇 |
国内免费 | 192篇 |
专业分类
化学 | 1114篇 |
晶体学 | 21篇 |
力学 | 118篇 |
综合类 | 20篇 |
数学 | 567篇 |
物理学 | 718篇 |
出版年
2024年 | 2篇 |
2023年 | 21篇 |
2022年 | 28篇 |
2021年 | 43篇 |
2020年 | 31篇 |
2019年 | 33篇 |
2018年 | 37篇 |
2017年 | 52篇 |
2016年 | 57篇 |
2015年 | 59篇 |
2014年 | 67篇 |
2013年 | 142篇 |
2012年 | 91篇 |
2011年 | 109篇 |
2010年 | 93篇 |
2009年 | 112篇 |
2008年 | 121篇 |
2007年 | 150篇 |
2006年 | 131篇 |
2005年 | 126篇 |
2004年 | 87篇 |
2003年 | 87篇 |
2002年 | 115篇 |
2001年 | 70篇 |
2000年 | 67篇 |
1999年 | 66篇 |
1998年 | 91篇 |
1997年 | 58篇 |
1996年 | 31篇 |
1995年 | 25篇 |
1994年 | 38篇 |
1993年 | 38篇 |
1992年 | 39篇 |
1991年 | 16篇 |
1990年 | 15篇 |
1989年 | 13篇 |
1988年 | 19篇 |
1987年 | 16篇 |
1986年 | 10篇 |
1985年 | 20篇 |
1984年 | 22篇 |
1983年 | 7篇 |
1982年 | 19篇 |
1981年 | 13篇 |
1980年 | 7篇 |
1979年 | 37篇 |
1978年 | 14篇 |
1977年 | 5篇 |
1976年 | 2篇 |
1974年 | 3篇 |
排序方式: 共有2558条查询结果,搜索用时 296 毫秒
11.
12.
Cao H. P. Chen G. Grechkoseeva M. A. Mazurov V. D. Shi W. J. Vasil'ev A. V. 《Siberian Mathematical Journal》2004,45(6):1031-1035
The spectrum of a finite group is the set of its element orders. A finite group G is said to be recognizable by spectrum, if every finite group with the same spectrum as G is isomorphic to G. The purpose of the paper is to prove that for every natural m the finite simple Chevalley group F
4(2
m
) is recognizable by spectrum. 相似文献
13.
14.
Nikolaos S. PAPAGEORGIOU Nikolaos YANNAKAKIS 《数学学报(英文版)》2005,21(5):977-996
This is the first part of a work on second order nonlinear, nonmonotone evolution inclusions defined in the framework of an evolution triple of spaces and with a multivalued nonlinearity depending on both x(t) and x(t). In this first part we prove existence and relaxation theorems. We consider the case of an usc, convex valued nonlinearity and we show that for this problem the solution set is nonempty and compact in C^1 (T, H). Also we examine the Isc, nonconvex case and again we prove the existence of solutions. In addition we establish the existence of extremal solutions and by strengthening our hypotheses, we show that the extremal solutions are dense in C^1 (T, H) to the solutions of the original convex problem (strong relaxation). An example of a nonlinear hyperbolic optimal control problem is also discussed. 相似文献
15.
16.
Ekatherina A. Karatsuba 《Numerical Algorithms》2007,45(1-4):127-137
A new approach to the study of the Jaynes–Cummings sum, which determines the atomic inversion in quantum model of a single
two-level atom interacting with a single mode of the quantized radiation field, based on the number theory theorems on approximation
of trigonometric sums is presented.
相似文献
17.
The change of the superstructure of different polyethylenes during uniaxial deformation is investigated. The method used is small-angle scattering with synchrotron radiation. For branched polyethylene (Lupolen 1840D) the whole deformation range is analyzed. Beginning with superstructure of the lamellar cluster type, the superstructure partly disappears on a time scale of a few minutes and the fibrillar structure is built up. The degree of destruction and rebuilding depends on the drawing temperature. For very high molecular weight polyethylene (GUR) a reversible change of the superstructure at higher deformation ratios and at different temperatures is observed. The superstructure of (ethylene—hexene) copolymers (TIPELIN) at high draw ratios depends on the drawing temperature and is almost independent of the side group content. Interfibrillar microcracks parallel to the draw direction are produced in samples with a low side group content for draw ratios λ ≥ 1.5. 相似文献
18.
The electron-stimulated desorption (ESD) of D− and H− ions from condensed D2O and H2O films is investigated. Three low-energy peaks are observed in the ESD anion yield, which are identified as arising from excitation of 2B1, 2A1 and 2B2 dissociative electron attachment (DEA) resonances. Additional structure is observed between 18 and 32 eV, which may be due to ion pair formation or to DEA resonances involving the 2a1 orbital. The ion yield resulting from excitation of the 2B1 resonance increases as the film is heated. We attribute the increase in the ion yield to thermally induced hydrogen bond breaking near the surface, which enhances the lifetimes of the excited states that lead to desorption. 相似文献
19.
Poly (n-butylisocyanate)-benzene solutions prepared by solubilization at 45°C, followed by aging at room temperature were found to be metastable for months, although, eventually, they separated into a birefringent polymer-rich phase and an isotropic solution. These metastable solutions, as well as isothermally phase-separated biphasic samples, flowed and exhibited dynamic moduli indicative of low polymer connectivity. By contrast samples prepared by a freeze-thaw cycle were uniformly and highly birefringent and showed network (gel) behavior at room temperature. The mechanism of gel formation is most likely the exclusion of the polymer from the benzene crystal during crystallization, forcing the polymer to align and exist at grain boundaries. Films formed from solutions have different moduli than those formed from gels, and are consistent with the proposed mechanism. 相似文献
20.
B. Velázquez-Martí C. Gracia-López 《International Journal of Infrared and Millimeter Waves》2004,25(7):1109-1122
The thermal treatment by millimeter waves for the soil disinfection can be one possible alternative to chemical treatments. This physical method is based on incrementing the soil temperature and its pathogens irradiating with high frequency electromagnetic waves. So the previous knowledge of the temperature distribution in the irradiated soil is essential for achieving an effective bad microorganism and weed seeds elimination. This report analyse the heating kinetic and spatial distribution of the maximum temperatures reached by the soil. It is presented a mathematic model about how are distributed the reached temperatures in the depth of the irradiated soil. This model concludes that when an orchard soil is irradiated superficially by microwaves, the microwaves have a big attenuation due to the soil dielectric properties and the water located in the pores of the most superficial layer. This fact causes a shield effect blocking the waves penetration in few centimetres. The heating by radiation is reduced to the superficial layer. The heating propagation in the depth is occurred by conduction following the Fourier equations. 相似文献