全文获取类型
收费全文 | 10065篇 |
免费 | 682篇 |
国内免费 | 854篇 |
专业分类
化学 | 2760篇 |
晶体学 | 51篇 |
力学 | 903篇 |
综合类 | 83篇 |
数学 | 3080篇 |
物理学 | 4724篇 |
出版年
2024年 | 9篇 |
2023年 | 115篇 |
2022年 | 104篇 |
2021年 | 134篇 |
2020年 | 216篇 |
2019年 | 173篇 |
2018年 | 192篇 |
2017年 | 292篇 |
2016年 | 341篇 |
2015年 | 287篇 |
2014年 | 518篇 |
2013年 | 897篇 |
2012年 | 530篇 |
2011年 | 734篇 |
2010年 | 537篇 |
2009年 | 651篇 |
2008年 | 662篇 |
2007年 | 684篇 |
2006年 | 587篇 |
2005年 | 469篇 |
2004年 | 429篇 |
2003年 | 402篇 |
2002年 | 364篇 |
2001年 | 331篇 |
2000年 | 313篇 |
1999年 | 257篇 |
1998年 | 234篇 |
1997年 | 173篇 |
1996年 | 158篇 |
1995年 | 161篇 |
1994年 | 90篇 |
1993年 | 89篇 |
1992年 | 92篇 |
1991年 | 63篇 |
1990年 | 42篇 |
1989年 | 39篇 |
1988年 | 36篇 |
1987年 | 32篇 |
1986年 | 22篇 |
1985年 | 29篇 |
1984年 | 21篇 |
1983年 | 11篇 |
1982年 | 11篇 |
1981年 | 8篇 |
1980年 | 13篇 |
1979年 | 14篇 |
1978年 | 6篇 |
1976年 | 7篇 |
1973年 | 7篇 |
1971年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
51.
Boniface Nkemzi 《Mathematical Methods in the Applied Sciences》2006,29(9):1053-1080
This paper is concerned with the structure of the singular and regular parts of the solution of time‐harmonic Maxwell's equations in polygonal plane domains and their effective numerical treatment. The asymptotic behaviour of the solution near corner points of the domain is studied by means of discrete Fourier transformation and it is proved that the solution of the boundary value problem does not belong locally to H2 when the boundary of the domain has non‐acute angles. A splitting of the solution into a regular part belonging to the space H2, and an explicitly described singular part is presented. For the numerical treatment of the boundary value problem, we propose a finite element discretization which combines local mesh grading and the singular field methods and derive a priori error estimates that show optimal convergence as known for the classical finite element method for problems with regular solutions. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
52.
We study the four-directional traffic flow on a two-dimensional lattice. In the case of discrete densities, we assume equal number of vehicles in each lane. Except for the minimum density, the gridlock emerges swiftly. Two kinds of gridlock have been observed. The global gridlock dominates the system when the density is twice the minimum value. At higher densities, the system is pervaded by local gridlocks. We also analyze the time evolution of average speed. In the case of continuous densities, the vehicle numbers vary from lane to lane. The global gridlock is then destroyed by the fluctuations; while the local gridlock can still be observed. 相似文献
53.
In-plane single domain and vortex magnetization configurations of the magnetic dot in the hybrid superconductor–ferromagnet system are considered. Single domain configuration energy shift due to the presence of superconductor is calculated. The change of the phase curve of the ferromagnetic dot magnetization due to the repulsion of the magnetic field by the superconductor is obtained. Up to the two-fold decrease of the ferromagnetic dot critical radius due to the presence of the superconductor is predicted. 相似文献
54.
Tristrom Cooke 《Journal of multivariate analysis》2004,89(2):191-383
The quadratic discriminant function is often used to separate two classes of points in a multidimensional space. When the two classes are normally distributed, this results in the optimum separation. In some cases however, the assumption of normality is a poor one and the classification error is increased. The current paper derives an upper bound for the classification error due to a quadratic decision surface. The bound is strict when the class means and covariances and the quadratic discriminant surface satisfy certain specified symmetry conditions. 相似文献
55.
V.B. Nalbandyan 《Journal of Physics and Chemistry of Solids》2004,65(6):1201
The irreproducibility of electrical properties of Na0.88Li0.12NbO3 solid solution on thermal cycling reported by M.A.L. Nobre and S. Lanfredi is explained by gradual decomposition of the supersaturated solid solution below ca. 800 °C. 相似文献
56.
A. Savin 《Journal of Physics and Chemistry of Solids》2004,65(12):2025-2029
The phase transition under pressure in iodine is analyzed using the electron localization function (ELF), explaining that the increase of the c/a ratio under compression is due to the presence of the lone pairs.A probabilistic interpretation is given for ELF. 相似文献
57.
The crystal structure of [N(CH3)4]3[As2Cl9] is determined at 293 K. It crystallizes in trigonal space group P31c: a = 9.2199(8), c = 21.065(3)Å, Z = 2, R1 = 0.0505, wR2 = 0.1283. The crystal is built of the discrete bioctahedral [As2Cl9]3— anions and the deformed tetramethylammonium cations. A structural phase transition in [N(CH3)4]3[As2Cl9] is detected by the DSC and dilatometric techniques at 146/151 K (on cooling/heating). Dielectric relaxation studies in the frequency range 75 kHz — 5 MHz indicate reorientations of the tetramethylammonium cations within the high temperature phase. Optical observations show the existence of the ferroelastic domain structure below 146 K. The possible mechanism of phase transition is discussed on the basis of the presented results. 相似文献
58.
Some previous works show that symmetric fixed- and variable-stepsize linear multistep methods for second-order systems which do not have any parasitic root in their first characteristic polynomial give rise to a slow error growth with time when integrating reversible systems. In this paper, we give a technique to construct variable-stepsize symmetric methods from their fixed-stepsize counterparts, in such a way that the former have the same order as the latter. The order and symmetry of the integrators obtained is proved independently of the order of the underlying fixed-stepsize integrators. As this technique looks for efficiency, we concentrate on explicit linear multistep methods, which just make one function evaluation per step, and we offer some numerical comparisons with other one-step adaptive methods which also show a good long-term behaviour.
59.
用迈克耳逊干涉仪测量气体折射率的误差的研究 总被引:1,自引:0,他引:1
研究在用迈克尔逊干涉仪测量气体折射率时存在的系统和方法误差,提出了误差修正方法。 相似文献
60.
As predicted by Haldane, spin, S=1 one-dimensional (1D) Heisenberg antiferromagnet (HAF) has an energy gap between the singlet ground state and first excited triplet. On application of magnetic field, the triplet state Zeeman splits and the energy of one of the triplet state becomes zero at a critical field, Hc. Above Hc the system recovers magnetism. Then, we expect that a quasi-1D HAF will show a magnetic long-range ordering (LRO) at low temperatures due to the inter-chain coupling. This field-induced LRO has not been observed before due to complication of the crystal structure in the materials studied so far and/or technical difficulty.From a heat capacity measurement on a single crystal of an S=1 quasi-Q1D HAF, Ni(C5H14N2)2N3(PF6), we found an anomaly at a temperature in finite fields indicating a field-induced phase transition. A magnetic LRO is confirmed by a neutron diffraction measurement on the same sample. The temperature versus magnetic field phase diagram of this compound is constructed and discussed. 相似文献