全文获取类型
收费全文 | 290篇 |
免费 | 107篇 |
国内免费 | 77篇 |
专业分类
化学 | 129篇 |
晶体学 | 12篇 |
力学 | 38篇 |
综合类 | 26篇 |
数学 | 70篇 |
物理学 | 199篇 |
出版年
2024年 | 1篇 |
2023年 | 18篇 |
2022年 | 15篇 |
2021年 | 7篇 |
2020年 | 7篇 |
2019年 | 10篇 |
2018年 | 12篇 |
2017年 | 16篇 |
2016年 | 10篇 |
2015年 | 10篇 |
2014年 | 26篇 |
2013年 | 24篇 |
2012年 | 27篇 |
2011年 | 15篇 |
2010年 | 26篇 |
2009年 | 25篇 |
2008年 | 25篇 |
2007年 | 18篇 |
2006年 | 23篇 |
2005年 | 9篇 |
2004年 | 17篇 |
2003年 | 15篇 |
2002年 | 9篇 |
2001年 | 4篇 |
2000年 | 9篇 |
1999年 | 7篇 |
1998年 | 8篇 |
1997年 | 6篇 |
1996年 | 1篇 |
1995年 | 5篇 |
1994年 | 8篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1986年 | 8篇 |
1985年 | 10篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1962年 | 1篇 |
排序方式: 共有474条查询结果,搜索用时 27 毫秒
51.
The periodically forced spatially extended Brusselator is investigated in the oscillating regime. The temporal response and pattern formation within the 2:1 frequency-locking band where the system oscillates at one half of the forcing frequency are examined. An hexagonal standing-wave pattern and other resonant patterns are observed. The detailed phase diagram of resonance structure in the forcing frequency and forcing amplitude parameter space is calculated. The transitions between the resonant standing-wave patterns are of hysteresis when control parameters are varied, and the presence of multiplicity is demonstrated. Analysis in the framework of amplitude equation reveals that the spatial patterns of the standing waves come out as a result of Turing bifurcation in the amplitude equation. 相似文献
52.
讨论在实际中常常会碰到的删失数据情形下的极值指数估计问题.限于极值数据本来就不多,将删失限定为适度删失.构造了适度右删失时Pareto型分布的一个子族—Hall族的极值指数的估计量.借助于估计量的信息,巧妙地构造了加权二乘估计的权数.从理论上说明了加权二乘估计的可行性,并利用MC方法,对Burr(1,1,1)、Burr(1,0.5,2)、Fréchet(1)、Fréchet(2)、学生-t1、学生-t4等几种常见的极值分布进行模拟,说明了加权二乘估计方法对门限值的选取并不敏感,具有很好的稳健性.同时,将利用Burr(1,1,1)、Burr(1,0.5,2)、Fréchet(1)分布模拟所得结果与Beirlant等人(2001)利用指数回归模型所得结果进行比较,说明了新方法比指数回归模型更为理想. 相似文献
53.
54.
55.
56.
测量了含有9个CC共轭双键的链状多烯类生物分子β胡萝卜素在9种溶剂中的紫外—可见吸收和拉曼光谱.结果表明,β胡萝卜素C—C,CC键拉曼散射截面随溶剂体密度增加而线性增加,其机理是β胡萝卜素分子在体密度大的溶剂中受浮动干扰小,分子结构有序性高,π电子离域扩展,产生强的相干弱阻尼CC键振动,而产生大的拉曼散射截面.密度对分子拉曼散射截面影响研究还没见过报道,本文为多烯类链状分子的光散射理论研究提供了实验线索,也对多烯类链状分子性能研究及光电器件研制有参考价值.
关键词:
拉曼散射截面
多烯分子
吸收光谱
分子结构有序 相似文献
57.
Investigation of hydrogen bonding in neat dimethyl sulfoxide and binary mixture (dimethyl sulfoxide + water) by concentration-dependent Raman study and ab initio calculation 下载免费PDF全文
In this study,our vibrational spectroscopic analysis is made on hydrogen-bonding between dimethyl sulfoxide and water comprises both experimental Raman spectra and ab initio calculations on structures of various dimethyl sulfoxide/water clusters with increasing water content.The Raman peak position of the v(S=O) stretching mode of dimethyl sulfoxide serves as a probe for monitoring the degree of hydrogen-bonding between dimethyl sulfoxide and water.In addition,the two vibrational modes,namely,the CH 3 symmetric stretching mode and the CH 3 asymmetric stretching mode have been analysed under different concentrations.We relate the computational results to the experimental vibrational wavenumber trends that are observed in our concentration-dependent Raman study.The combination of experimental Raman data with ab initio calculation leads to a better knowledge of the nature of the hydrogen bonding and the structures of the hydrogen-bonded complexes studied. 相似文献
58.
<正>Phase mismatching for third-harmonic generation(THG) in barium metaborate(BBO) crystal is investigated in detail.Upon using BBO crystal in the TypeⅠ(oo→e) scheme,in the two independent planes (principal section of the crystal and the plane normal to principal section),when the input second-harmonic beam deviates from the expected direction,phase mismatching occurs and the angle deviation produces different effects on the conversion efficiency.We numerically simulate these two cases of phase mismatching and identify the relation between the conversion efficiency and the deviation angle in the air.The computational results indicate that the phase matching tolerance in the principal section is 0.2°(in the air),while the phase matching tolerance in the plane normal to principal section is 4.5°(in the air).After conducting a lab experiment,the results agree perfectly with the computational results,indicating that the deviation angle in the principal section has a greater effect on the conversion efficiency. 相似文献
59.
We study and experimentally demonstrate a sensitive single-shot correlation system in which only a diffraction grating is used to produce a transverse time delay (TTD) in the reference pulse.The mechanism of the TTD introduced by the grating and the formation of the relative time delay (RTD) in the noncollinear correlation system are analyzed in detail.By using our system,we successfully measured the temporal duration of picosecond laser pulses,and a time resolution of ~0.047 ps is obtained at 1047 nm.The impact of the grating dispersion and the second harmonic beam walk-off effect on the measurement are considered. 相似文献
60.