全文获取类型
收费全文 | 13095篇 |
免费 | 2405篇 |
国内免费 | 1545篇 |
专业分类
化学 | 699篇 |
晶体学 | 115篇 |
力学 | 1307篇 |
综合类 | 235篇 |
数学 | 8268篇 |
物理学 | 6421篇 |
出版年
2024年 | 23篇 |
2023年 | 115篇 |
2022年 | 170篇 |
2021年 | 193篇 |
2020年 | 307篇 |
2019年 | 337篇 |
2018年 | 334篇 |
2017年 | 384篇 |
2016年 | 437篇 |
2015年 | 328篇 |
2014年 | 768篇 |
2013年 | 955篇 |
2012年 | 651篇 |
2011年 | 948篇 |
2010年 | 834篇 |
2009年 | 1077篇 |
2008年 | 1061篇 |
2007年 | 1055篇 |
2006年 | 955篇 |
2005年 | 816篇 |
2004年 | 725篇 |
2003年 | 684篇 |
2002年 | 625篇 |
2001年 | 495篇 |
2000年 | 488篇 |
1999年 | 425篇 |
1998年 | 368篇 |
1997年 | 335篇 |
1996年 | 222篇 |
1995年 | 158篇 |
1994年 | 128篇 |
1993年 | 103篇 |
1992年 | 86篇 |
1991年 | 67篇 |
1990年 | 54篇 |
1989年 | 47篇 |
1988年 | 41篇 |
1987年 | 24篇 |
1986年 | 15篇 |
1985年 | 25篇 |
1984年 | 35篇 |
1983年 | 19篇 |
1982年 | 28篇 |
1981年 | 22篇 |
1980年 | 26篇 |
1979年 | 16篇 |
1978年 | 9篇 |
1977年 | 6篇 |
1976年 | 6篇 |
1936年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
We consider some types of packet discretization for continuous spectra in quantum scattering problems. As we previously showed, this discretization leads to a convenient finite-dimensional (i.e., matrix) approximation for integral operators in the scattering theory and allows reducing the solution of singular integral equations connected with the scattering theory to some suitable purely algebraic equations on an analytic basis. All singularities are explicitly singled out. Our primary emphasis is on realizing the method practically. 相似文献
122.
A detailed study of the generalized M2 factor of hard-edged diffracted beams based on the truncated second-order moments method, asymptotic analysis and self-convergent beam width approach is performed. The dependence of the generalized M2 factor on the parameters characterizing the spatial profile, and beam truncation, etc. is analyzed. 相似文献
123.
A mathematical model of laser beam treatment of double layer alloys (Ni/Fe, Al/Fe and Cr/Fe systems) describing the effect of laser beam on different physical and geometrical parameters of coated layer system has been adapted. The numerical solutions of the non-homogeneous heat-transport differential equation could estimate the temperature of the treated region.The suggested model allows investigation of the temperature distribution as a function of treated surface and laser parameters. The physical parameters of the treated materials were taken as functions of temperature due to the change in the temperature of the treated double layer materials. 相似文献
124.
Based on the generalized Huygens–Fresnel diffraction integral and the expansion of the hard aperture function into a finite sum of complex Gaussian functions, the approximate analytical expression of elegant Laguerre–Gaussian beams passing through a paraxial ABCD optical system with an annular aperture is derived. Meanwhile, the corresponding closed-forms for the unapertured, circular apertured or circular black screen cases are also given. The obtained results provide more convenience for studying their propagation and transformation than the usual way by using diffraction integral formula directly. Some numerical examples are given to illustrate the propagation properties of elegant Laguerre–Gaussian beams. 相似文献
125.
Under the nonresonant case where the carrier frequency of a Gaussian beam deviates from the resonant frequency of a Fabry–Perot etalon, the transmission of a Gaussian beam after incidenting nonnormally on a Fabry–Perot etalon has been investigated. The results show that under the nonresonant case, variations of the peak intensity, the position of the peak intensity and the spot size of the transmitted beam with the input angle behave differently and even with a reversed tendency compared with those obtained under the resonant case. 相似文献
126.
Letters in Mathematical Physics - 相似文献
127.
128.
129.
Kyu Hwang Yeon Suk Seong Kim Chung In Um Thomas F. George 《International Journal of Theoretical Physics》2003,42(9):2043-2059
Quantum Hamiltonian systems corresponding to classical systems related by a general canonical transformation are considered. The differential equation to find the unitary operator, which corresponds to the canonical transformation and connects quantum states of the original and transformed systems, is obtained. The propagator associated with their wave functions is found by the unitary operator. Quantum systems related by a linear canonical point transformation are analyzed. The results are tested by finding the wave functions of the under-, critical-, and over-damped harmonic oscillator from the wave functions of the harmonic oscillator, free-particle system, and negative harmonic potential system, using the unitary operator to connect them, respectively. 相似文献
130.