全文获取类型
收费全文 | 1307篇 |
免费 | 132篇 |
国内免费 | 108篇 |
专业分类
化学 | 688篇 |
晶体学 | 11篇 |
力学 | 173篇 |
综合类 | 17篇 |
数学 | 215篇 |
物理学 | 443篇 |
出版年
2023年 | 13篇 |
2022年 | 27篇 |
2021年 | 27篇 |
2020年 | 23篇 |
2019年 | 38篇 |
2018年 | 34篇 |
2017年 | 40篇 |
2016年 | 55篇 |
2015年 | 42篇 |
2014年 | 51篇 |
2013年 | 125篇 |
2012年 | 91篇 |
2011年 | 70篇 |
2010年 | 46篇 |
2009年 | 77篇 |
2008年 | 69篇 |
2007年 | 86篇 |
2006年 | 67篇 |
2005年 | 61篇 |
2004年 | 69篇 |
2003年 | 68篇 |
2002年 | 41篇 |
2001年 | 23篇 |
2000年 | 38篇 |
1999年 | 38篇 |
1998年 | 28篇 |
1997年 | 23篇 |
1996年 | 18篇 |
1995年 | 27篇 |
1994年 | 24篇 |
1993年 | 17篇 |
1992年 | 20篇 |
1991年 | 10篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 8篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1981年 | 5篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1972年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有1547条查询结果,搜索用时 15 毫秒
121.
The classical risk process that is perturbed by diffusion is studied .The explicit expressions for the runi probability and the surplus distribution of the risk process at the time of runi are obtained when the claim amount distribution is a finite mixture of exponential distributions of a Gamma (2,α) distribution. 相似文献
122.
《Physics and Chemistry of Liquids》2012,50(6):777-800
The excess molar volume, viscosity deviation and excess Gibbs free energy of activation of viscous flow have been investigated from the density and shear viscosity measurements of water–dioxane mixtures over the entire range of mole fractions from 293.15 to 309.15?K. The results were fitted by the Redlich–Kister equation. Partial molar volume and Gibbs energy at infinite dilution were deduced from four methods, activation parameters and partial molar Gibbs energy of activation of viscous flow against compositions were investigated. The water–dioxane interactions have principally an H-bound character and there are two principal types’ structures limited by 0.08?mole fraction in dioxane. The reduced Redlich–Kister excess properties provide an indication of the intermolecular interactions and for dioxane–water cluster formation as suggested in the literature. 相似文献
123.
《Physics and Chemistry of Liquids》2012,50(6):712-734
Excess molar volumes and viscosity deviations in N,N-dimethylacetamide?+?dimethylformamide binary mixtures at 298.15, 308.15 and 318.15?K were calculated from experimental density and viscosity data presented in the previous work. Here these experimental values were used to test the applicability of the correlative reduced Redlich–Kister equation and the recently proposed Herráez equation. Their correlation ability at different temperatures, and the use of different number of parameters, is discussed for the case of limited experimental data. These relative functions are important to reduce the effect of temperature and, consequently, to reveal the effects of different types of interactions. Limiting excess partial molar volumes at infinite dilution were deduced from different methods, parameters of molar Gibbs energy of activation of viscous flow against compositions were investigated. The results of these observations have been interpreted in terms of structural effects of the solvents. 1H-NMR studies of these mixtures are also reported. 相似文献
124.
Hong‐Lin Zhang Zhe Kong Yong‐Mei Yan Li Yu Fei Geng 《Journal of Dispersion Science and Technology》2013,34(6):958-964
The critical micelle concentration (CMC) of two kinds of anionic surfactant (including sodium laurate (SLA) and sodium dodecyl sulfate (SDS)) in mixed alcohol and N, N‐dimethyl formamide solvent (DMF) were investigated through measuring power‐time curves by titration microcalorimetry. From data of the lowest point and the area of the power‐time curves, their CMC and ΔH m 0 can be obtained. According to standard thermodynamic equations, ΔG m 0 and ΔS m 0 also can be calculated. For different surfactant, the influences of the carbon number and the concentration of alcohol on the CMC and standard thermodynamic functions are different in DMF polar medium. These thermodynamic functions for micelle formation can be further interpreted. 相似文献
125.
Mutual Diffusion Driven NMR: a new approach for the analysis of mixtures by spatially resolved NMR spectroscopy
下载免费PDF全文
![点击此处可从《Magnetic resonance in chemistry : MRC》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Christian F. Pantoja Jose A. Bolaños Andrés Bernal Julien Wist 《Magnetic resonance in chemistry : MRC》2017,55(6):519-524
We introduce a new approach for resolving the NMR spectra of mixtures that relies on the mutual diffusion of dissolved species when a concentration gradient is established within the NMR tube. This is achieved by cooling down a biphasic mixture of triethylamine and deuterated water below its mixing temperature, where a single phase is expected. Until equilibrium is reached, a gradient of concentration, from ‘pure’ triethylamine to ‘pure’ water, establishes within the tube. The amount of time required to reach this equilibrium is controlled by the mutual diffusion coefficient of both species. Moreover, a gradient of concentration exists for each additional compound dissolved in this system, related to the partition coefficient for that compound in the original biphasic state. Using slice selective experiments, it was possible to measure these concentration gradients and use them to separate signals from all the present species. We show the results acquired for a mixture composed of n‐octanol, methanol, acetonitrile and benzene and compare them with those obtained by pulse field gradient NMR. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
126.
混合von Mises 模型的参数估计 总被引:1,自引:0,他引:1
有限混合von Mises模型在天文学、生物学、地理和医药等许多领域都有重要的应用.可是,不论样本量有多大,此模型的似然函数都是无界的.因此,参数的最大似然估计(MLE)是不相合的.我们发现,与混合正态模型一样,上述困难可以通过引入关于分布浓度参数的一个惩罚函数或对参数空间添加适当的约束来克服.在此文中,我们从理论上证明了这两种方法是可行的,相应的参数估计是强相合的,且是渐近有效的.我们还通过计算机模拟来探讨这些新方法在有限样本情况下的统计性质,并与现有的矩估计作了比较.结果发现,惩罚极大似然估计在均方误差方面表现最佳.最后我们还分析了一组实际数据,以进一步介绍新的估计方法. 相似文献
127.
根据时间序列数据所表现的性质。提出一种新的时序混合模型。并采用一种基于优化的距离来确定成分的个数。并给出了相关的推导. 相似文献
128.
Xiaoming Wu Yulin Hua Zhaoqi Wang Jiajin Zheng Shougen Yin Jiachun Deng Kongwu Wu Songliu Feijian Zhu Xia Niu 《Optik》2006,117(8):373-376
A bright white organic light-emitting diode (OLED) has been successfully fabricated in which a greenish-white emitting host Bis-(2-(2-hydroxyphenyl) benzothiazole)zinc (Zn(BTZ)2) is doped with an orange-red fluorescent dye 5,6,11,12-tetraphenylnaphthacene (rubrene). The pure white light emission with CIE coordinates of (0.341, 0.334) is achieved at the driving voltage of 20 V, and the corresponding luminance and external quantum efficiency are 4000 Cd/m2 and 0.63%. On the other hand, the pure red, green, and blue (RGB) emissions are obtained from the white OLED combined well with RGB custom-built optical color filters (CFs) with peaks at 616, 556, and 456 nm, respectively. Moreover, based upon the color mixture principles, we build a model of multi-color display mixed by the pure RGB emissions under the controllable bias. 相似文献
129.
130.
金融资产收益分布的混合高斯分析 总被引:3,自引:0,他引:3
本文研究了金融资产收益的混合高斯分布模型 ,给出了混合高斯分布的 Kolmogorov-Smirnov检验的方法 ,分析了金融资产收益的非高斯性及市场价格运动的有效性 .此外 ,用成分数目 K*、拟合误差 DK*n和主成分系数 p*k 描述金融资产收益的性质 ,对外汇银行同业拆借市场和中国股票市场实证分析 相似文献