全文获取类型
收费全文 | 23599篇 |
免费 | 3370篇 |
国内免费 | 2528篇 |
专业分类
化学 | 16481篇 |
晶体学 | 290篇 |
力学 | 1435篇 |
综合类 | 202篇 |
数学 | 2394篇 |
物理学 | 8695篇 |
出版年
2024年 | 71篇 |
2023年 | 437篇 |
2022年 | 753篇 |
2021年 | 851篇 |
2020年 | 877篇 |
2019年 | 850篇 |
2018年 | 729篇 |
2017年 | 764篇 |
2016年 | 1035篇 |
2015年 | 1059篇 |
2014年 | 1195篇 |
2013年 | 1642篇 |
2012年 | 1903篇 |
2011年 | 2029篇 |
2010年 | 1334篇 |
2009年 | 1293篇 |
2008年 | 1495篇 |
2007年 | 1395篇 |
2006年 | 1269篇 |
2005年 | 1000篇 |
2004年 | 800篇 |
2003年 | 677篇 |
2002年 | 645篇 |
2001年 | 476篇 |
2000年 | 468篇 |
1999年 | 516篇 |
1998年 | 445篇 |
1997年 | 447篇 |
1996年 | 498篇 |
1995年 | 386篇 |
1994年 | 387篇 |
1993年 | 284篇 |
1992年 | 257篇 |
1991年 | 235篇 |
1990年 | 170篇 |
1989年 | 137篇 |
1988年 | 121篇 |
1987年 | 98篇 |
1986年 | 98篇 |
1985年 | 87篇 |
1984年 | 60篇 |
1983年 | 49篇 |
1982年 | 38篇 |
1981年 | 28篇 |
1980年 | 31篇 |
1979年 | 18篇 |
1978年 | 10篇 |
1977年 | 8篇 |
1975年 | 7篇 |
1973年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
Perturbation to Mei symmetry and Mei adiabatic invariants for mechanical systems in phase space 下载免费PDF全文
For a perturbed mechanical system in phase space, considering d/dt in the structure equation and process of proof including infinitesimal parameter ε obviously, this paper studies the perturbation to Mei symmetry and adiabatic invariants. Firstly, the exact invariant induced directly from the Mei symmetry of the system without perturbation is given. Secondly, based on the concept of high-order adiabatic invariant, the determining equations of the perturbation to Mei symmetry are established, the condition of existence of the Mei adiabatic invariant led by the perturbation to Mei symmetry is obtained, and its form is presented. Lastly, an example is given to illustrate the application of the results. 相似文献
993.
994.
建立了一套利用高功率YAG激光器辐照固体锡靶产生高转换效率极紫外光 (extreme ultraviolet) 源的实验装置.利用建立的实验装置开展了极紫外光源的强度和转换效率与抽运激光强度关系的实验研究,发现极紫外光源的转换效率随抽运激光强度的变化具有饱和效应.实验发现:当抽运激光能量达到250mJ时,极紫外光源的转换效率最高,波长为13.5nm处0.27nm带宽范围内的极紫外光源的能量转换效率为1.6%,此时对应的激光强度为1.8×1011W/cm2.
关键词:
极紫外光
转换效率 相似文献
995.
This paper theoretically studies the double-pumped fibre-optical parametric amplifiers (FOPAs) in photonic crystal fibres. Two distinct working regimes of FOPAs are researched, which depend on the dispersion at the central wavelength of the two pumps. Extremely broad tuning range can be obtained when the central pump wavelength is in the normal dispersion regime and is insensitive to the wavelength separation between the two pumps, while the tuning range is narrow in the anomalous dispersion regime and can be significantly enhanced by increasing the wavelength separation. Impacts of higher-order dispersions and temporal walk-off on the gain spectra are also discussed. 相似文献
996.
997.
Synchronization transition in gap-junction-coupled leech neurons 总被引:1,自引:0,他引:1
Qingyun Wang Zhisheng Duan Zhaosheng Feng Guanrong Chen Qishao Lu 《Physica A》2008,387(16-17):4404-4410
Real neurons can exhibit various types of firings including tonic spiking, bursting as well as silent state, which are frequently observed in neuronal electrophysiological experiments. More interestingly, it is found that neurons can demonstrate the co-existing mode of stable tonic spiking and bursting, which depends on initial conditions. In this paper, synchronization in gap-junction-coupled neurons with co-existing attractors of spiking and bursting firings is investigated as the coupling strength gets increased. Synchronization transitions can be identified by means of the bifurcation diagram and the correlation coefficient. It is illustrated that the coupled neurons can exhibit different types of synchronization transitions between spiking and bursting when the coupling strength increases. In the course of synchronization transitions, an intermittent synchronization can be observed. These results may be instructive to understand synchronization transitions in neuronal systems. 相似文献
998.
Transient saturation absorption spectroscopy excited near the band gap at high excitation carrier density in GaAs 下载免费PDF全文
Transient saturation absorption spectroscopy in GaAs thin films was investigated using femtosecond pump and supercontinuum probe technique at excitation densities higher than 1×10^{19}cm^{-3}. The Coulomb enhancement factor of the electron-hole plasma results in a spectrum hole at the pump wavelength. Two distinct transmission peaks at two sides of the pump wavelength are observed, arising from the bleaching of transitions from the heavy- and light-hole bands to the conduction band. The dynamic process of the transient saturation absorption is fitted using a bi-exponential function. The fast decay process is dominated by the carrier-phonon scattering and the slow process may be attributed to the electron-hole recombination. 相似文献
999.
Simple Entanglement Measure for Multipartite Pure States 总被引:3,自引:0,他引:3
Feng Pan Feng Pan Feng Pan Dan Liu Guoying Lu J. P. Draayer 《International Journal of Theoretical Physics》2004,43(5):1241-1247
A simple entanglement measure for multipartite pure states is formulated based on the partial entropy of a series of reduced density matrices. Use of the proposed new measure to distinguish disentangled, partially entangled, and maximally entangled multipartite pure states is illustrated. 相似文献
1000.
Chessboard-like substrates are introduced in this paper, in order to study the diffusion-limited aggregation (DLA)and the motion of poly-atoms on heterogeneous surfaces. The effect of morphology of such substrates upon the cluster aggregation is investigated using the Monte Carlo simulation. It is found that the growth process and the cluster morphology are governed by the energetic topography of the substrates. Our simulation also indicate that the island density and the fractal dimension of the clusters depend strongly on the substrate topography and the activation energy. 相似文献