全文获取类型
收费全文 | 71144篇 |
免费 | 14685篇 |
国内免费 | 5906篇 |
专业分类
化学 | 65268篇 |
晶体学 | 797篇 |
力学 | 2647篇 |
综合类 | 389篇 |
数学 | 6314篇 |
物理学 | 16320篇 |
出版年
2024年 | 59篇 |
2023年 | 694篇 |
2022年 | 977篇 |
2021年 | 1298篇 |
2020年 | 2458篇 |
2019年 | 3663篇 |
2018年 | 2031篇 |
2017年 | 1686篇 |
2016年 | 4791篇 |
2015年 | 4912篇 |
2014年 | 5130篇 |
2013年 | 6354篇 |
2012年 | 5995篇 |
2011年 | 5527篇 |
2010年 | 5001篇 |
2009年 | 4877篇 |
2008年 | 4791篇 |
2007年 | 4096篇 |
2006年 | 3535篇 |
2005年 | 3407篇 |
2004年 | 2892篇 |
2003年 | 2522篇 |
2002年 | 3266篇 |
2001年 | 2352篇 |
2000年 | 2144篇 |
1999年 | 1191篇 |
1998年 | 685篇 |
1997年 | 620篇 |
1996年 | 600篇 |
1995年 | 512篇 |
1994年 | 531篇 |
1993年 | 447篇 |
1992年 | 359篇 |
1991年 | 337篇 |
1990年 | 303篇 |
1989年 | 211篇 |
1988年 | 197篇 |
1987年 | 168篇 |
1986年 | 142篇 |
1985年 | 150篇 |
1984年 | 119篇 |
1983年 | 101篇 |
1982年 | 76篇 |
1981年 | 70篇 |
1980年 | 63篇 |
1979年 | 43篇 |
1977年 | 39篇 |
1976年 | 38篇 |
1974年 | 51篇 |
1973年 | 45篇 |
排序方式: 共有10000条查询结果,搜索用时 578 毫秒
101.
Propagation of the Hermite–Gaussian beams through misaligned optical system with a circular aperture
By means of expanding a hard-edged aperture into a finite sum of complex Gaussian functions, the approximate analytical formula of one kind of higher-order Gaussian beams called the Hermite–Gaussian beams (HGBs) passing through circular apertured and misaligned optical system is obtained in this paper. The result provides more convenience for studying its propagation than the usual way by using diffraction integral directly. Some numerical simulations are also given for illustrating the propagation properties of the HGBs through the circular apertured optical systems. 相似文献
102.
103.
104.
Time-domain numerical computation of noise reduction by diffraction and finite impedance of barriers
Chang Woo Lim 《Journal of sound and vibration》2003,268(2):385-401
A new time-domain numerical method is presented for the estimation of noise reduction by the diffraction and finite impedance of barriers. High order finite difference schemes conventionally used for computational aeroacoustics, and time-domain impedance boundary conditions are utilized for the development of the time-domain method. Compared with other methods, this method can be applied more easily to the problems related to nonlinear noise propagation such as impulsive noise and broadband noise. Linearized Euler equations in Cartesian co-ordinates are considered and solved numerically. Straight and T-shaped barriers with and without surface admittance are calculated. In order to assess the accuracy of this time-domain method, comparison with the results of SYSNOISE software (Ver. 5.3) are made. There are very good agreements between the results of the present time-domain numerical method and the boundary element method of the SYSNOISE software. 相似文献
105.
106.
The crystal structure, magnetic and magnetotransport properties of the variation of B′-site transition metal in Sr2FeMO6 (M=Mo, W) with double perovskites structure have been investigated systematically. Measurements of magnetization vs. temperature at H=5 T show that Sr2FeMoO6 is a ferromagnet and Sr2FeWO6 is an antiferromagnet with TN∼35 K. Additionally, the large magnetoresistance ratio (MR) of ∼22% (H=3 T) at room temperature (RT) was observed in the Sr2FeWO6 compound. However, the Sr2FeMoO6 compound did not show any significant MR even at high fields and RT (MR∼1%; H=3 T and 300 K). The implications of these findings are supported by band structure calculations to explain the interaction between the 4d(Mo) and 5d(W) orbitals of transition metal ions and oxygen ions. 相似文献
107.
根据Co P非晶态合金结构的短程有序和结构中可能存在P -P相互作用的实验事实 ,选择了单磷原子簇模型ConP(n =1~ 5 )和双磷原子簇模型ConP2 (n =1~ 4 ) ,用密度泛函理论方法对其进行计算 .结果表明 ,在单磷Co2 P( 2 ) 、Co3 P( 1) 及Co4P( 2 ) 模型体系中 ,Co原子供给P原子电子 ,与电负性规则一致 ,同时Co和P之间具较强化学作用 ,可以形成稳定的原子簇 ;而在双磷和单磷原子簇Co5P( 1) 模型体系中 ,形成的原子簇不稳定 ,采用单磷Co2 P( 2 ) 、Co3 P( 1) 及Co4P( 2 ) 模型能较好地反映Co P非晶态合金的结构特点 . 相似文献
108.
109.
110.
A graph G is N2‐locally connected if for every vertex ν in G, the edges not incident with ν but having at least one end adjacent to ν in G induce a connected graph. In 1990, Ryjá?ek conjectured that every 3‐connected N2‐locally connected claw‐free graph is Hamiltonian. This conjecture is proved in this note. © 2004 Wiley Periodicals, Inc. J Graph Theory 48: 142–146, 2005 相似文献