全文获取类型
收费全文 | 318408篇 |
免费 | 1410篇 |
国内免费 | 390篇 |
专业分类
化学 | 144364篇 |
晶体学 | 4561篇 |
力学 | 18432篇 |
综合类 | 7篇 |
数学 | 49947篇 |
物理学 | 102897篇 |
出版年
2020年 | 2509篇 |
2019年 | 3045篇 |
2018年 | 11270篇 |
2017年 | 11958篇 |
2016年 | 8888篇 |
2015年 | 3221篇 |
2014年 | 4900篇 |
2013年 | 9607篇 |
2012年 | 11242篇 |
2011年 | 19291篇 |
2010年 | 13071篇 |
2009年 | 13437篇 |
2008年 | 17273篇 |
2007年 | 20189篇 |
2006年 | 7925篇 |
2005年 | 11747篇 |
2004年 | 9025篇 |
2003年 | 8846篇 |
2002年 | 7427篇 |
2001年 | 6902篇 |
2000年 | 5316篇 |
1999年 | 3881篇 |
1998年 | 3540篇 |
1997年 | 3308篇 |
1996年 | 3169篇 |
1995年 | 2818篇 |
1994年 | 2733篇 |
1993年 | 2786篇 |
1992年 | 2872篇 |
1991年 | 3209篇 |
1990年 | 3078篇 |
1989年 | 3181篇 |
1988年 | 2987篇 |
1987年 | 2952篇 |
1986年 | 2778篇 |
1985年 | 3443篇 |
1984年 | 3544篇 |
1983年 | 3048篇 |
1982年 | 3128篇 |
1981年 | 2983篇 |
1980年 | 2741篇 |
1979年 | 3106篇 |
1978年 | 3374篇 |
1977年 | 3411篇 |
1976年 | 3437篇 |
1975年 | 3201篇 |
1974年 | 3164篇 |
1973年 | 3348篇 |
1972年 | 2643篇 |
1971年 | 2415篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
43.
44.
45.
46.
We summarize the results of our recent work on Bäcklund transformations (BTs), particularly focusing on the relation between BTs and infinitesimal symmetries. We present a BT for an associated Degasperis–Procesi (aDP) equation and its superposition principle and investigate the solutions generated by applying this BT. Following our general methodology, we use the superposition principle of the BT to generate the infinitesimal symmetries of the aDP equation. 相似文献
47.
Mesoscopic modeling at the pore scale offers great promise in exploring the underlying structure transport performance of flow through porous media. The present work studies the fluid flow subjected to capillarity-induced resonance in porous media characterized by different porous structure and wettability. The effects of porosity and wettability on the displacement behavior of the fluid flow through porous media are discussed. The results are presented in the form of temporal evolution of percentage saturation and displacement of the fluid front through porous media. The present study reveals that the vibration in the form of acoustic excitation could be significant in the mobilization of fluid through the porous media. The dependence of displacement of the fluid on physicochemical parameters like wettability of the surface, frequency along with the porosity is analyzed. It was observed that the mean displacement of the fluid is more in the case of invading fluid with wetting phase where the driving force strength is not so dominant. 相似文献
48.
49.
Dr. Antonio M. Rodríguez Dr. Pilar Prieto Prof. Antonio de la Hoz Prof. Ángel Díaz-Ortiz D. Raúl Martín Prof. José I. García 《ChemistryOpen》2015,4(3):308-317
The aim of this work was to determine the parameters that have decisive roles in microwave-assisted reactions and to develop a model, using computational chemistry, to predict a priori the type of reactions that can be improved under microwaves. For this purpose, a computational study was carried out on a variety of reactions, which have been reported to be improved under microwave irradiation. This comprises six types of reactions. The outcomes obtained in this study indicate that the most influential parameters are activation energy, enthalpy, and the polarity of all the species that participate. In addition to this, in most cases, slower reacting systems observe a much greater improvement under microwave irradiation. Furthermore, for these reactions, the presence of a polar component in the reaction (solvent, reagent, susceptor, etc.) is necessary for strong coupling with the electromagnetic radiation. We also quantified that an activation energy of 20–30 kcal mol−1 and a polarity (μ) between 7–20 D of the species involved in the process is required to obtain significant improvements under microwave irradiation. 相似文献
50.
K.V. Stepurska О.О. Soldatkin I.S. Kucherenko V.M. Arkhypova S.V. Dzyadevych A.P. Soldatkin 《Analytica chimica acta》2015
This study was aimed at the development of a conductometric biosensor based on acetylcholinesterase considering the feasibility of its application for the inhibitory analysis of various toxicants. In this paper, the optimum conditions for enzyme immobilization on the transducer surface are selected as well as the optimum concentration of substrate for inhibitory analysis. Sensitivity of the developed biosensor to different classes of toxic compounds (organophosphorus pesticides, heavy metal ions, surfactants, aflatoxin, glycoalkaloids) was tested. It is shown that the developed biosensor can be successfully used for the analysis of pesticides and mycotoxins, as well as for determination of total toxicity of the samples. A new method of biosensor analysis of toxic substances of different classes in complex multicomponent aqueous samples is proposed. 相似文献