全文获取类型
收费全文 | 16050篇 |
免费 | 2714篇 |
国内免费 | 1660篇 |
专业分类
化学 | 11798篇 |
晶体学 | 285篇 |
力学 | 880篇 |
综合类 | 160篇 |
数学 | 1533篇 |
物理学 | 5768篇 |
出版年
2024年 | 39篇 |
2023年 | 339篇 |
2022年 | 389篇 |
2021年 | 585篇 |
2020年 | 785篇 |
2019年 | 687篇 |
2018年 | 564篇 |
2017年 | 530篇 |
2016年 | 885篇 |
2015年 | 845篇 |
2014年 | 973篇 |
2013年 | 1313篇 |
2012年 | 1537篇 |
2011年 | 1567篇 |
2010年 | 1013篇 |
2009年 | 933篇 |
2008年 | 1026篇 |
2007年 | 961篇 |
2006年 | 798篇 |
2005年 | 750篇 |
2004年 | 526篇 |
2003年 | 389篇 |
2002年 | 416篇 |
2001年 | 337篇 |
2000年 | 266篇 |
1999年 | 230篇 |
1998年 | 203篇 |
1997年 | 152篇 |
1996年 | 146篇 |
1995年 | 154篇 |
1994年 | 145篇 |
1993年 | 115篇 |
1992年 | 105篇 |
1991年 | 87篇 |
1990年 | 89篇 |
1989年 | 51篇 |
1988年 | 62篇 |
1987年 | 45篇 |
1986年 | 47篇 |
1985年 | 46篇 |
1984年 | 37篇 |
1983年 | 28篇 |
1982年 | 32篇 |
1981年 | 30篇 |
1980年 | 19篇 |
1979年 | 22篇 |
1978年 | 20篇 |
1977年 | 16篇 |
1975年 | 12篇 |
1974年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
We propose a weighted evolving network model in which the underlying topological structure is still driven by the degree according to the preferential attachment rule while the weight assigned to the newly established edges is dependent on the degree in a nonlinear form. By varying the parameter a that controls the function determining the assignment of weight, a wide variety of power-law behaviours of the total weight distributions as well as the diversity of the weight distributions of edges are displayed. Variation of correlation and heterogeneity in the network is illustrated as well. 相似文献
62.
Using polarized neutron reflectivity (PNR) measurements together with associated simulation, magnetic structures of two Ni80Fe20 (1 1 1)/Ru (0 0 0 1) multilayer samples with Ru thickness of 9 and 21 Å were investigated under various external magnetic fields at room temperature. The results reveal the existence of layer thickness, interface roughness, magnetic moment, interlayer coupling angle and non-collinear coupling. The former three are independent of Ru thickness; while the latter two are strongly dependent of Ru thickness. 相似文献
63.
Hongrui Zhang Mingju Chao Mingyi Gao Liwen Zhang Jianquan Yao 《Optics & Laser Technology》2003,35(6):573-449
A fiber-coupled diode-single-end-pumped Nd:YVO4 laser with an Nd:YVO4 crystal of 0.3 at% doping concentration and 3×3×10 mm3 dimensions was reported. 14.850 W of continuous-wave output power in an M2 factor of 1.12 was obtained under pump power of 27.365 W, with an optical conversion efficiency of 60.49%, and a slope efficiency of 64.5%. 相似文献
64.
Shu Fen Wang Wen Guo Zou Su Wen Liu Dong Xu Duo Rong Yuan Guang Jun Zhou 《Journal of Physics and Chemistry of Solids》2004,65(7):1243-1245
The photoluminescence properties of the Bi3+ in sol-gel derived ZnTiO3 nanocrystals have been investigated. An ultra-violet emission at 360 nm and a visible emission band at 506 nm have been observed, originating from two kinds of emission centers. The former is ascribed to the 3P1-1S0 transition of Bi3+ and the latter to the recombination of the electrons with the photo-generated holes trapped in the zinc vacancies. In all cases the latter contribution is predominant. 相似文献
65.
L. K. Seah U. S. Dinish S. K. Ong Z. X. Chao V. M. Murukeshan 《Optics & Laser Technology》2004,36(5):371-376
Imaging of latent fingerprints using time-resolved (TR) method offers a broader platform to eliminate the unwanted background emission. In this paper, a novel TR imaging technique is demonstrated and implemented, which facilitates the detection of latent fingerprints with nanosecond resolution. Simulated experiments were carried out with two overlapping fingerprints treated with two fluorescent powders having different lifetimes in nanosecond range. The dependence of the fluorescence emission intensity in nanosecond resolution of TR imaging is also revealed. 相似文献
66.
多目标半定规划的互补弱鞍点和G-鞍点最优性条件 总被引:1,自引:0,他引:1
对于含矩阵函数半定约束和多个目标函数的多目标半定规划问题,给出Lagrange函数在弱有效意义下的互补弱鞍点和Geofrrion恰当有效意义下的G-鞍点的定义及其等价定义.然后,在较弱的凸性条件下,利用含矩阵和向量约束的择一性定理,建立多目标半定规划的互补弱鞍点和G-鞍点充分必要条件. 相似文献
67.
本文利用比较原理以及一种特殊变换研究了一类非线性退化方程的混合问题,得到了这类复杂问题解的渐进性质。 相似文献
68.
I. El-Kady R. Biswas Y. Ye M. F. Su I. Puscasu Martin Pralle E. A. Johnson J. Daly A. Greenwald 《Photonics and Nanostructures》2003,1(1):69-77
In this work, we present both the theoretical basis as well as supporting experimental measurements for development of a novel mid-infrared thermally stimulated narrow band emitter with a spectral bandwidth of less than 10%. To achieve this, we utilize a metallized-surface 2D photonic crystal of air voids in a silicon background with hexagonal structure symmetry. Our results are based on the generation of discrete surface plasmon (SP) modes in the thin metallized layer residing on the top surface. This yields a series of adequately spaced discrete peaks in the reflection spectrum, dominated by a single sharp feature corresponding to the lowest plasmon order, in an otherwise uniform highly reflective spectrum (>90%) over most of the IR spectrum. This, in turn, gives rise to a sharp absorption feature with a correspondingly narrow thermal emission peak in the emission spectrum. Transfer matrix calculations simulate well both the position and strengths of the absorption peaks. By altering the period of the surface photonic lattice, the SP peak and emissive band can be tuned to the desired wavelength. These devices promise a new class of tunable infrared emitters with high power in a narrow spectral bandwidth. Such narrow band sources are critical to achieving high efficiency gas sensors. 相似文献
69.
几种常见光源特性的研究 总被引:2,自引:1,他引:1
本通过大学物理实验中常用光源特性的分析,说明了实验中光源使用的合理性。 相似文献
70.