全文获取类型
收费全文 | 3266篇 |
免费 | 1405篇 |
国内免费 | 241篇 |
专业分类
化学 | 57篇 |
晶体学 | 30篇 |
力学 | 288篇 |
综合类 | 68篇 |
数学 | 664篇 |
物理学 | 3805篇 |
出版年
2024年 | 26篇 |
2023年 | 112篇 |
2022年 | 116篇 |
2021年 | 121篇 |
2020年 | 68篇 |
2019年 | 127篇 |
2018年 | 56篇 |
2017年 | 118篇 |
2016年 | 101篇 |
2015年 | 134篇 |
2014年 | 343篇 |
2013年 | 166篇 |
2012年 | 205篇 |
2011年 | 250篇 |
2010年 | 204篇 |
2009年 | 278篇 |
2008年 | 365篇 |
2007年 | 281篇 |
2006年 | 208篇 |
2005年 | 212篇 |
2004年 | 218篇 |
2003年 | 198篇 |
2002年 | 137篇 |
2001年 | 135篇 |
2000年 | 111篇 |
1999年 | 96篇 |
1998年 | 74篇 |
1997年 | 78篇 |
1996年 | 62篇 |
1995年 | 54篇 |
1994年 | 43篇 |
1993年 | 30篇 |
1992年 | 50篇 |
1991年 | 35篇 |
1990年 | 41篇 |
1989年 | 31篇 |
1988年 | 11篇 |
1987年 | 9篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 2篇 |
排序方式: 共有4912条查询结果,搜索用时 109 毫秒
11.
在北京同步辐射装置(BSRF)1W1B光束线和XAFS实验站上国内首次建立了硬X射线波段的磁圆二色实验(XMCD)方法. 以单晶金刚石作为相位延迟片, 在透射劳埃(Laue)模式下, 利用衍射双折射效应, 将入射的单色线偏振光转变为相应的左旋和右旋圆偏振光, 测量磁化样品对左旋和右旋圆偏振光吸收的差异, 获得了XMCD信号. 本实验使用透射方法测量了Pt-Fe合金Pt L2,3边的XMCD, 获得了XMCD信号. XMCD实验方法的建立, 为研究磁性材料尤其是磁性薄膜材料的电子结构和磁结构提供了实验基础. 相似文献
12.
We establish the formalism of nuclear spin-isospin excitations,especially the Gamow-Teller resonance in a fully consstent relativistic random-phase approximation.A relativistic form of the Landau-Migdal parameter g‘ is adopted as a residual spin-isospin correlation force.In the non-relativistic limit it reproduces the excitation energy of the giant Gamow-Teller resonance state obtained in the non-relativistic model.The Gamow-Teller resonance for finite nuclei is investigated in a relativistic approach for the first time.It is found that the Ikeda sum rule of 90Zr is quenched about 8% in the Hartree as well as the correlated strengths due to the poles of the negative Dirac states at energies above 1 GeV. 相似文献
13.
14.
Optimization of High-Order Harmonic by Genetic Algorithm for the Chirp and Phase of Few-Cycle Pulses 下载免费PDF全文
The brightness of a particular harmonic order is optimized for the chirp and initial phase of the laser pulse by genetic algorithm. The influences of the chirp and initial phase of the excitation pulse on the harmonic spectra are discussed in terms of the semi-classical model including the propagation effects. The results indicate that the harmonic intensity and cutoff have strong dependence on the chirp of the laser pulse, but slightly on its initial phase. The high-order harmonics can be enhanced by the optimal laser pulse and its cutoff can be tuned by optimization of the chirp and initial phase of the laser pulse. 相似文献
15.
16.
17.
18.
Based on phase space delay-coordinate reconstruction of a chaotic dynamics system, we propose a local prediction of chaotic time series using a support vector machine (SVM) to overcome the shortcomings of traditional local prediction methods. The simulation results show that the performance of this proposed predictor for making onestep and multi-step prediction is superior to that of the traditional local linear prediction method and global SVM method. In addition, it is significant that its prediction performance is insensitive to the selection of embedding dimension and the number of nearest neighbours, so the satisfying results can be achieved even if we do not know the optimal embedding dimension and how to select the number of nearest neighbours. 相似文献
19.
High-Average-Power Nanosecond Quasi-Phase-Matched Single-Pass Optical Parametric Generator in Periodically Poled Lithium Niobate 总被引:2,自引:0,他引:2 下载免费PDF全文
A pulsed nanosecond optical parametric generator (OPG) in periodically poled lithium niobate (PPLN) crysal is presented. The pump laser is an acousto-optically Q-switched Nd:YVO4 laser with the maximum average power of 6.58 W. When the repetition rate is 50kHz and the pulse width of the pump source is 80ns, the maximum average total output power of the single-pass PPLN OPG is about 1.9 W, which includes 1.322 W of 1.536μm signal radiation. The length of the PPLN crystal is only 38.7mm (at room temperature) with a grating period of 28.93μm (at room temperature). The 1.502-1.536μm signal radiation and 3.652-3.465μm idler radiation are obtained by adjusting the PPLN crystal temperature from 155℃ to 250℃. 相似文献
20.
用相位调制方法测量光盘盘基应力双折射的精度分析 总被引:4,自引:2,他引:2
偏振相位调制方法是测量微小双折射的一种高精度检测方法。本文系统全面地分析了以PMCSA结构形式测量光盘盘基应力双折射的相位调制方法中,由各种误差源造成的对测试结果的影响。 相似文献