全文获取类型
收费全文 | 154607篇 |
免费 | 27171篇 |
国内免费 | 30930篇 |
专业分类
化学 | 108706篇 |
晶体学 | 3594篇 |
力学 | 10202篇 |
综合类 | 2744篇 |
数学 | 21512篇 |
物理学 | 65950篇 |
出版年
2024年 | 512篇 |
2023年 | 2614篇 |
2022年 | 5578篇 |
2021年 | 5790篇 |
2020年 | 6013篇 |
2019年 | 5705篇 |
2018年 | 5385篇 |
2017年 | 5831篇 |
2016年 | 6736篇 |
2015年 | 7538篇 |
2014年 | 9264篇 |
2013年 | 11901篇 |
2012年 | 13416篇 |
2011年 | 13982篇 |
2010年 | 11210篇 |
2009年 | 11129篇 |
2008年 | 11991篇 |
2007年 | 10743篇 |
2006年 | 10295篇 |
2005年 | 8582篇 |
2004年 | 6659篇 |
2003年 | 5112篇 |
2002年 | 4758篇 |
2001年 | 4446篇 |
2000年 | 4305篇 |
1999年 | 3426篇 |
1998年 | 2442篇 |
1997年 | 2111篇 |
1996年 | 2077篇 |
1995年 | 1855篇 |
1994年 | 1750篇 |
1993年 | 1479篇 |
1992年 | 1373篇 |
1991年 | 1082篇 |
1990年 | 941篇 |
1989年 | 815篇 |
1988年 | 667篇 |
1987年 | 568篇 |
1986年 | 546篇 |
1985年 | 409篇 |
1984年 | 338篇 |
1983年 | 286篇 |
1982年 | 228篇 |
1981年 | 164篇 |
1980年 | 136篇 |
1979年 | 115篇 |
1978年 | 45篇 |
1977年 | 36篇 |
1976年 | 30篇 |
1965年 | 35篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
ZHONG Hui WAN Mingxi JIANG Yifeng WANG Supin 《声学学报:英文版》2006,25(2):104-115
The present study was to investigate the differential imaging method for detecting HIFU (High Intensity Focused Ultrasound)-induced lesions and the estimation of variation of attenuation for lesion evaluation with log spectral difference algorithm. Experiment results of bovine muscle and liver in vitro were acquired. Several algorithms for lesion detection - Absolute Difference (AD), Sum Absolute Differences (SAD) and Sum Squared Differences (SSD) - were analyzed with several window sizes and threshold values. Then three attenuation parameters were compared to evaluate the degree of tissue damage. It was found that variation of the mean attenuation △α was an effective parameter to evaluate lesions. 相似文献
23.
We reveal that for a realistic system, interference effects are obtained such as the suppression of central line and inner sidebands and the narrowing of the outer fluorescence sidebands. For this purpose, we consider a spontaneous decay from an excited state to a metastable state when the excited and metastable states are resonantly coupled to an auxiliary metastable state by a laser field and a microwave field, respectively. The fluorescence spectrum evolves from a five-peaked structure into a doublet of ultrasharp lines as the ratio of the laser field Rabi frequency to the microwave Rabi frequency is decreased. The physical origin is presented in terms of dressed states. 相似文献
24.
25.
本文主要研究的是相函数为齐次椭圆多项式的自由高阶Schrodinger方程.通过相函数等值面的几何性质,得到了解算子的Strichartz加权估计和极大算子加权估计. 相似文献
26.
27.
Soliton interaction under the influence of higher-order effects 总被引:6,自引:0,他引:6
In this paper, we present exact N-soliton solution by employing simple, straightforward Darboux transformation based on the Lax pair for Hirota equation, a higher-order nonlinear Schrödinger (HNLS) equation. As examples, one- and two-soliton solutions in explicit forms are given and their properties are also analyzed. A bound solution without interaction will be theoretically predicted if one can adjust frequency shift for each soliton appropriately. Further, we obtain the approximate eigenvalues by employing two-soliton solution and discuss analytically the interaction between neighboring solitons under the influence of the higher-order effects. It is shown that the combined effects of the higher-order effects can restrain the interaction between neighboring solitons to some extent. The results are proved by directly solving HNLS equation numerically. 相似文献
28.
A convective flow CO laser composed of polytetrafluoroethylene discharge tubes, nickel–chromium steel components, a cupric heat exchanger and other components is described. Operating in liquid nitrogen condition, output power of 60 W has been obtained from a non-selective cavity. 相似文献
29.
30.
By further generalizing the skew-symmetric triangular splitting iteration method studied by Krukier, Chikina and Belokon (Applied Numerical Mathematics, 41 (2002), pp. 89–105), in this paper, we present a new iteration scheme, called the modified skew-Hermitian triangular splitting iteration method, for solving the strongly non-Hermitian systems of linear equations with positive definite coefficient matrices. We discuss the convergence property and the optimal parameters of this new method in depth. Moreover, when it is applied to precondition the Krylov subspace methods like GMRES, the preconditioning property of the modified skew-Hermitian triangular splitting iteration is analyzed in detail. Numerical results show that, as both solver and preconditioner, the modified skew-Hermitian triangular splitting iteration method is very effective for solving large sparse positive definite systems of linear equations of strong skew-Hermitian parts. 相似文献