全文获取类型
收费全文 | 3831篇 |
免费 | 285篇 |
国内免费 | 371篇 |
专业分类
化学 | 1564篇 |
晶体学 | 13篇 |
力学 | 292篇 |
综合类 | 66篇 |
数学 | 1800篇 |
物理学 | 752篇 |
出版年
2024年 | 3篇 |
2023年 | 23篇 |
2022年 | 59篇 |
2021年 | 85篇 |
2020年 | 86篇 |
2019年 | 88篇 |
2018年 | 85篇 |
2017年 | 98篇 |
2016年 | 125篇 |
2015年 | 59篇 |
2014年 | 154篇 |
2013年 | 237篇 |
2012年 | 215篇 |
2011年 | 193篇 |
2010年 | 228篇 |
2009年 | 228篇 |
2008年 | 221篇 |
2007年 | 272篇 |
2006年 | 219篇 |
2005年 | 230篇 |
2004年 | 173篇 |
2003年 | 186篇 |
2002年 | 132篇 |
2001年 | 130篇 |
2000年 | 116篇 |
1999年 | 94篇 |
1998年 | 77篇 |
1997年 | 70篇 |
1996年 | 66篇 |
1995年 | 45篇 |
1994年 | 82篇 |
1993年 | 52篇 |
1992年 | 56篇 |
1991年 | 35篇 |
1990年 | 33篇 |
1989年 | 30篇 |
1988年 | 28篇 |
1987年 | 26篇 |
1986年 | 27篇 |
1985年 | 29篇 |
1984年 | 18篇 |
1983年 | 7篇 |
1982年 | 19篇 |
1981年 | 6篇 |
1980年 | 8篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 7篇 |
1969年 | 3篇 |
排序方式: 共有4487条查询结果,搜索用时 15 毫秒
71.
P. Calderoni A. Pellegrinotti E. Presutti M. E. Vares 《Journal of statistical physics》1989,55(3-4):523-577
We consider a system of spins which have values ±1 and evolve according to a jump Markov process whose generator is the sum of two generators, one describing a spin-flipGlauber process, the other aKawasaki (stirring) evolution. It was proven elsewhere that if the Kawasaki dynamics is speeded up by a factor –2, then, in the limit 0 (continuum limit), propagation of chaos holds and the local magnetization solves a reaction-diffusion equation. We choose the parameters of the Glauber interaction so that the potential of the reaction term in the reaction-diffusion equation is a double-well potential with quartic maximum at the origin. We assume further that for each the system is in a finite interval ofZ with –1 sites and periodic boundary conditions. We specify the initial measure as the product measure with 0 spin average, thus obtaining, in the continuum limit, a constant magnetic profile equal to 0, which is a stationary unstable solution to the reaction-diffusion equation. We prove that at times of the order –1/2 propagation of chaos does not hold any more and, in the limit as 0, the state becomes a nontrivial superposition of Bernoulli measures with parameters corresponding to the minima of the reaction potential. The coefficients of such a superposition depend on time (on the scale –1/2) and at large times (on this scale) the coefficient of the term corresponding to the initial magnetization vanishes (transient bimodality). This differs from what was observed by De Masi, Presutti, and Vares, who considered a reaction potential with quadratic maximum and no bimodal effect was seen, as predicted by Broggi, Lugiato, and Colombo. 相似文献
72.
采用半微量相平衡方法测定了三元体系La(NCS)3.4.5H2O-B15C5-C2H5OH在298.15K的溶解度,测定了各饱和溶液的折光率。 相似文献
73.
74.
A new algorithm/program has been elaborated for simultaneous processing of different sets of vapour–liquid equilibrium data. The program was tested with six binary hexane + isomeric pentanol systems, each of them measured at three different isobaric conditions and one isothermal system of tert-butyl-methyl-ether + 2-methyl-2-propanol measured at three different temperatures. The correlation uses the maximum likelihood method, taking into account real behaviour of vapour phase. The parameters obtained are valid within the whole temperature range of the data, and are consistent in comparison with those obtained from individual correlations of isobars or isotherms. Results are presented for the Wilson and NRTL equations. 相似文献
75.
J. A. Poulis C. H. Massen E. Robens G. Reichenauer 《Journal of Thermal Analysis and Calorimetry》2004,76(2):583-592
On the basis of a molecular model for adsorption kinetics Jäntti introduced a method to calculate equilibriums shortly after a change of the pressure of the sorptive gas. In the present paper we show that this method is useful in many more situations than those intended originally. 相似文献
76.
前言卟啉在生物化学、分析化学、药物化学等领域有着广泛研究和重要应用[1~3]。近年来虽然对卟啉类化合物的研究报道很多[4~6],但对卟啉在酸性介质中的研究很少。较早期的研究工作认为卟啉类化合物在酸性介质中仅以其二酸形式存在[7]。本文实验结果显示me... 相似文献
77.
The phase analysis of cryolite (Na3AlF6) and sodium metasilicate (Na2SiO3) was performed by thermal analysis. The eutectic system with a region of two immiscible substances at a concentration of Na2SiO3 between 42.8 and 46.3 mol‐% was identified and the eutectic temperature determined to (886±2) °C. Based on the results of mass‐loss measurements, it was assumed that the introduced Na2SiO3 reacts with Na3AlF6 due to the formation of some nonvolatile stable compounds. The stable reaction products were identified by X‐ray diffraction analysis and IR spectroscopy of the spontaneously cooled samples, which established the formation of NaF and stable amorphous aluminosilicate compounds. 相似文献
78.
The thermodynamic model of inorganic arsenic was validated by comparing the predicted As(III) concentration with the experimentally determined one in several river waters samples of the Basque Country (Spain) collected in two sampling campaigns: spring and autumn 2000. This model takes into account the acid-base equilibria of As(III) and As(V) together with the redox equilibria between the H3AsO3 and H3AsO4 species. A correct prediction of As(III) concentration requires the knowledge of the total concentration of arsenic, pH, redox potential (referred to hydrogen electrode), and ionic strength values of the solution. The estimation of the activity coefficients of the arsenic species was performed by means of the Modified Bromley’s Methodology (MBM).In order to perform the experimental As(III) determination, an analytical method was implemented by using an ion exchange separation of As(III)/As(V) on a continuous FIA-IE-HG-AAS system. The total arsenic concentration was determined together with total concentration of the main alkaline or alkaline-earth metals and anions in the natural waters. Temperature compensated measurements of the pH and redox potentials were made in-situ at the sampling sites.For both seasonal campaigns, the agreement between predicted and experimental As(III) is really high for those samples belonging to non polluted river waters. 相似文献
79.
Titration calorimetry was used to construct the solid-liquid equilibrium line in ternary systems containing the solute and an aqueous mixed solvent by measuring the heat of dissolution of the solid solute during successive additions of the liquid solvent. The plot of cumulated heats versus the mole ratio, nsolvent/nsolute, yields two (almost) linear increases of different slopes. These two lines represent successively the enthalpy of dissolution then the enthalpy of dilution of the medium; their intersection gives the solubility and the enthalpy of dissolution of the solute. Phase diagrams have been established over the whole concentration range for o-anisaldehyde, 1,3,5-trimethoxybenzene and vanillin, in water + methanol, +ethanol, or +n-propanol at 303, 313 and 318 K. 相似文献
80.
Thermodynamic and Equilibrium Composition Analysis of Using Iron Oxide as an Oxygen Carrier in Nonflame Combustion Technology 总被引:1,自引:0,他引:1
Jiayu Xin Hua Wang* Fang He Zhimin Zhang Faculty of Materials Metallurgical Engineering Kunming University of Science Technology Kunming China 《天然气化学杂志》2005,14(4)
1. Introduction The utilization of fossil fuels causes serious neg- ative impacts on the environment and human life. There are many pollutants such as SOx, NOx and CO2 emission produced from the combustion of coal, oil and natural gas. It has been known for more than 100 years that CO2 is a greenhouse gas and that the release of CO2 from fossil fuel combustion may affect the climate of the earth. In the last years the concern over the aspects of an increased release of greenhouse gases has… 相似文献