全文获取类型
收费全文 | 22147篇 |
免费 | 3995篇 |
国内免费 | 2767篇 |
专业分类
化学 | 16619篇 |
晶体学 | 355篇 |
力学 | 1236篇 |
综合类 | 208篇 |
数学 | 2075篇 |
物理学 | 8416篇 |
出版年
2024年 | 51篇 |
2023年 | 438篇 |
2022年 | 699篇 |
2021年 | 829篇 |
2020年 | 1058篇 |
2019年 | 1000篇 |
2018年 | 851篇 |
2017年 | 768篇 |
2016年 | 1197篇 |
2015年 | 1172篇 |
2014年 | 1363篇 |
2013年 | 1843篇 |
2012年 | 2061篇 |
2011年 | 2068篇 |
2010年 | 1425篇 |
2009年 | 1354篇 |
2008年 | 1481篇 |
2007年 | 1333篇 |
2006年 | 1154篇 |
2005年 | 1045篇 |
2004年 | 825篇 |
2003年 | 701篇 |
2002年 | 746篇 |
2001年 | 537篇 |
2000年 | 372篇 |
1999年 | 371篇 |
1998年 | 306篇 |
1997年 | 261篇 |
1996年 | 238篇 |
1995年 | 182篇 |
1994年 | 165篇 |
1993年 | 134篇 |
1992年 | 134篇 |
1991年 | 121篇 |
1990年 | 95篇 |
1989年 | 73篇 |
1988年 | 56篇 |
1987年 | 42篇 |
1986年 | 47篇 |
1985年 | 49篇 |
1984年 | 34篇 |
1983年 | 35篇 |
1982年 | 26篇 |
1981年 | 33篇 |
1980年 | 21篇 |
1979年 | 16篇 |
1978年 | 12篇 |
1975年 | 11篇 |
1974年 | 15篇 |
1973年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 546 毫秒
71.
This article studies the inshore-offshore fishery model with impulsive diffusion. The existence and global asymptotic stability of both the trivial periodic solution and the positive periodic solution are obtained. The complexity of this system is also analyzed. Moreover, the optimal harvesting policy are given for the inshore subpopulation, which includes the maximum sustainable yield and the corresponding harvesting effort. 相似文献
72.
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
73.
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
74.
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
75.
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
76.
77.
78.
Because of package, a single FBG has dual Bragg wavelength. One is sensitive to stress and the other is sensitive to temperature. By using the special mechanism, the wavelengths can be tuned by stress and temperature respectively. 相似文献
79.
80.
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