全文获取类型
收费全文 | 2960篇 |
免费 | 516篇 |
国内免费 | 336篇 |
专业分类
化学 | 1191篇 |
晶体学 | 11篇 |
力学 | 137篇 |
综合类 | 36篇 |
数学 | 312篇 |
物理学 | 2125篇 |
出版年
2023年 | 17篇 |
2022年 | 43篇 |
2021年 | 53篇 |
2020年 | 67篇 |
2019年 | 86篇 |
2018年 | 72篇 |
2017年 | 86篇 |
2016年 | 83篇 |
2015年 | 88篇 |
2014年 | 183篇 |
2013年 | 200篇 |
2012年 | 177篇 |
2011年 | 179篇 |
2010年 | 186篇 |
2009年 | 211篇 |
2008年 | 218篇 |
2007年 | 238篇 |
2006年 | 229篇 |
2005年 | 169篇 |
2004年 | 165篇 |
2003年 | 143篇 |
2002年 | 123篇 |
2001年 | 90篇 |
2000年 | 102篇 |
1999年 | 67篇 |
1998年 | 81篇 |
1997年 | 60篇 |
1996年 | 62篇 |
1995年 | 45篇 |
1994年 | 34篇 |
1993年 | 28篇 |
1992年 | 38篇 |
1991年 | 36篇 |
1990年 | 20篇 |
1989年 | 29篇 |
1988年 | 22篇 |
1987年 | 13篇 |
1986年 | 10篇 |
1985年 | 15篇 |
1984年 | 15篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1973年 | 2篇 |
1959年 | 1篇 |
排序方式: 共有3812条查询结果,搜索用时 15 毫秒
1.
We propose to reduce the (spectral) condition number of a given linear system by adding a suitable diagonal matrix to the system matrix, in particular by shifting its spectrum. Iterative procedures are then adopted to recover the solution of the original system. The case of real symmetric positive definite matrices is considered in particular, and several numerical examples are given. This approach has some close relations with Riley's method and with Tikhonov regularization. Moreover, we identify approximately the aforementioned procedure with a true action of preconditioning. 相似文献
2.
《中国物理 B》2021,30(10):107302-107302
We study the Goos–H?nchen-like shift of single silicene barrier under the external perpendicular electric field, offresonant circularly polarized light and the exchange field modulation using the stationary-phase method. The results show that the Goos–H?nchen-like shift of silicene resulting from the external perpendicular electric field does not have the characteristics of spin or valley polarization, while that from off-resonant circularly polarized light or the exchange field is spin-polarized. More importantly, the combined effect of the external perpendicular electric field and the exchange field or off-resonant circularly polarized light can cause the Goos–H?nchen-like shift of the system to be spin and valley polarized.It is particularly worth noting that when the three modulations are considered at the same time, as the exchange field changes, the system will have a positive or negative Goos–H?nchen-like shift. 相似文献
3.
Tunable enhanced spatial shifts of reflective beam on the surface of a twisted bilayer of hBN 下载免费PDF全文
We investigated Goos-Hänchen (GH) and Imbert-Fedorov (IF) shifts of a reflective beam on a twisted bilayer of hexagonal boron nitride (hBN), where a left circularly polarized beam was incident on the surface. Our results demonstrate that the twist angle between the two optical axes plays an important role in obtaining large shifts with a high reflectivity. The GH shift with 10λ0 is achieved, while the reflectivity is near 100% by tuning the twist angle. The maximum of the IF shift is found in the certain condition satisfied by the reflective coefficients, and the shift strongly depends on the twist angle between the optical axes of the two slabs. The spatial shifts obtained directly from the GH and IF shift definitions were provided, which indicate that the theoretical results from the stationary phase method are believable. These results may open up a new way for developing the nano-optical devices. 相似文献
4.
亲核性1,2-重排反应是有机化学的重要反应之一,重排中离去基团的离去和迁移基团的迁移步骤既可以是分步的,也可以是协同的,但是迁移基团的构型始终保持不变。本文用超共轭效应和反应过程中有机立体电子效应解释了此现象,掌握一般规律,希望能够从教学上便于教师讲授和学生学习理解。 相似文献
5.
Nonlinear feedback shift registers (NFSRs) are widely used in stream cipher design as building blocks. The cascade connection of NFSRs, known as an important architecture, has been adopted in Grain family of stream ciphers. In this paper, a new sufficient condition under which an NFSR cannot be decomposed into the cascade connection of two smaller NFSRs is presented, which is easy to be verified from the algebraic normal form (ANF) of the characteristic function. In fact, our results are also applicable to nonsingular Boolean functions, which actually improve a previous research of Rhodes [6] where the characteristic functions of NFSRs cannot be contained. 相似文献
6.
《中国物理 B》2021,30(5):53702-053702
Micromotion induced by the radio-frequency field contributes greatly to the systematic frequency shifts of optical frequency standards. Although different strategies for mitigating this effect have been proposed, trapping ions optically has the potential to provide a generic solution to the elimination of micromotion. This could be achieved by trapping a single ion in the dipole trap composed of a highpower laser field. Here, we present the setup of the dipole trap composed of a 532 nm laser at a power of 10 W aiming to optically trap a single ~(40)Ca~+ and we observe an AC-Stark shift of the fluorescence spectrum line of ~22 MHz caused by the 532 nm dipole beam. The beam waist of the dipole laser is several microns, which would provide a dipole potential strong enough for all-optical trapping of a single ~(40)Ca~+ ion. 相似文献
7.
Tunable spectral shift of high-order harmonic generation in atoms using a sinusoidally phase-modulated pulse 下载免费PDF全文
High-order harmonic generation (HHG) from an atom illuminated by a sinusoidally phase-modulated pulse is investigated by solving the time-dependent Schrödinger equation. The spectral shift that occurs in atomic HHG can be achieved easily using our laser pulse. It is shown that the photon energy of the generated harmonics is controllable within the range of 1 eV. The shift of the frequency peak position is rooted in the asymmetry of the rising and falling parts of the laser pulse. We also show that by varying the phase parameters in the frequency domain of the laser one can adjust and control the shift in atomic harmonic spectra. 相似文献
8.
Dengfeng LI 《Frontiers of Mathematics in China》2022,17(4):501
This paper introduces an open conjecture in time-frequency analysis on the linear independence of a finite set of time-frequency shifts of a given L2 function. Firstly, background and motivation for the conjecture are provided. Secondly, the main progress of this linear independence in the past twenty five years is reviewed. Finally, the partial results of the high dimensional case and other cases for the conjecture are briefly presented. 相似文献
9.
国内呼叫企业在保证每个坐席人员周内当值相同班次情况下,通过灵活安排周内当班日期与班次来制定排班方案。针对该实际排班场景,构建问题整数规划模型。通过对问题数据特征及优化性质分析,以及对班次人力有效满足区段电话服务需求的量化指标表征,分别提出两个构造性启发式算法。使用企业实例数据对模型算法进行计算实验。实验结果显示,整数规划模型适合于求解小规模排班问题最优解,而启发式算法能够以小计算成本获得大规模排班问题优化解。最后讨论保证员工上班规律性的同班次用工制度对企业人力成本控制的影响。 相似文献
10.
本文讨论了相对论教学中几个方面的问题,包括常见例子的问题,洛伦兹变换的方便形式,同时相对性例子在另一参考系的讨论,长度测量在另一参考系看到的现象,时间延缓及运动参考系各点时间不同和光的多普勒效应的简单推导.通过不同过程在不同参考系中的讨论,掌握在运动系讨论问题的方法,以及同一过程在不同惯性系内的不同表现,而所有现象的测量结论在洛伦兹变换下保持不变. 相似文献