全文获取类型
收费全文 | 1267篇 |
免费 | 39篇 |
国内免费 | 2篇 |
专业分类
化学 | 794篇 |
晶体学 | 8篇 |
力学 | 37篇 |
数学 | 170篇 |
物理学 | 299篇 |
出版年
2024年 | 3篇 |
2023年 | 10篇 |
2022年 | 37篇 |
2021年 | 36篇 |
2020年 | 32篇 |
2019年 | 31篇 |
2018年 | 30篇 |
2017年 | 22篇 |
2016年 | 59篇 |
2015年 | 32篇 |
2014年 | 56篇 |
2013年 | 85篇 |
2012年 | 78篇 |
2011年 | 94篇 |
2010年 | 70篇 |
2009年 | 97篇 |
2008年 | 82篇 |
2007年 | 76篇 |
2006年 | 48篇 |
2005年 | 35篇 |
2004年 | 35篇 |
2003年 | 27篇 |
2002年 | 19篇 |
2001年 | 30篇 |
2000年 | 28篇 |
1999年 | 13篇 |
1998年 | 13篇 |
1997年 | 12篇 |
1996年 | 25篇 |
1995年 | 14篇 |
1994年 | 11篇 |
1993年 | 6篇 |
1992年 | 7篇 |
1991年 | 11篇 |
1990年 | 2篇 |
1989年 | 7篇 |
1988年 | 3篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1973年 | 1篇 |
1956年 | 1篇 |
1955年 | 1篇 |
1937年 | 1篇 |
1933年 | 1篇 |
排序方式: 共有1308条查询结果,搜索用时 25 毫秒
61.
62.
François Clautiaux Cláudio Alves José Valério de Carvalho 《Annals of Operations Research》2010,179(1):317-342
Dual-feasible functions are valuable tools that can be used to compute both lower bounds for different combinatorial problems
and valid inequalities for integer programs. Several families of functions have been used in the literature. Some of them
were defined explicitly, and others not. One of the main objectives of this paper is to survey these functions, and to state
results concerning their quality. We clearly identify dominant subsets of functions, i.e. those which may lead to better bounds or stronger cuts. We also describe different frameworks that can be used to create
dual-feasible functions. With these frameworks, one can get a dominant function based on other ones. Two new families of dual-feasible
functions obtained by applying these methods are proposed in this paper. 相似文献
63.
64.
65.
66.
Cleoci Beninca Tiago André Denck Colman Luiz Gustavo Lacerda Marco Aurélio da Silva Carvalho Filho Ivo Mottin Demiate Gilbert Bannach Egon Schnitzler 《Journal of Thermal Analysis and Calorimetry》2013,111(3):2217-2222
The use of chemically modified starches is widely accepted in various industries, with several applications. In this research, natural cassava starch granules were treated with standard sodium hypochlorite solution at 0.8, 2.0, and 5.0 g Cl/100 g starch. The native and modified starch samples were investigated by means of the following techniques: simultaneous thermogravimetry–differential thermal analysis, which allowed us to verify the thermal decomposition associated with endothermic or exothermic phenomena; and differential scanning calorimetry that was used to determine gelatinization enthalpy as well as the rapid viscoamylographic analysis that provided the pasting temperature and viscosity. By means of non-contact-atomic force microscopy method and X-ray powder patterns diffractometry, it was possible to observe the surface morphology, topography of starch granules, and alterations in the granules’ crystallinity. 相似文献
67.
Michelle Gonçalves Mothé Cheila Gonçalves Mothé Carlos Henrique Monteiro de Carvalho Marcia Cristina Khalil de Oliveira 《Journal of Thermal Analysis and Calorimetry》2013,113(2):525-531
Present study investigates thermal behavior of two heavy crude oils with different °API values by simultaneous thermogravimetry–differential scanning calorimetry–fourier transform infrared spectroscopy (TG–DSC–FTIR), and an evaluation of the chemical element levels present in the oils’ ashes was done by energy dispersive X-ray fluorescence spectrometry. TG and DSC curves were obtained for two samples in nitrogen atmosphere. Among all inorganic components evaluated, the highest concentration in the two oils was SO3. Thus this study may contribute to a better understanding of the thermal behavior of heavy crude oils and their composition. 相似文献
68.
Anderson A. B. C. Júnior Gustavo S. G. De Carvalho Lippy F. Marques Charlane C. Corrêa Adilson D. Da Silva Flvia C. Machado 《Acta Crystallographica. Section C, Structural Chemistry》2013,69(8):934-936
The title compound, C14H11NO4, exists in the solid phase in the zwitterionic form, 2‐{[(4‐carboxy‐3‐hydroxyphenyl)iminiumyl]methyl}phenolate, with the H atom from the phenol group on the 2‐hydroxybenzylidene ring transferred to the imine N atom, resulting in a strong intramolecular N—H...O hydrogen bond between the iminium H atom and the phenolate O atom, forming a six‐membered hydrogen‐bonded ring. In addition, there is an intramolecular O—H...O hydrogen bond between the carboxylic acid group and the adjacent hydroxy group of the other ring, and an intermolecular C—H...O contact involving the phenol group and the C—H group adjacent to the imine bond, connecting the molecules into a two‐dimensional network in the (10) plane. π–π stacking interactions result in a three‐dimensional network. This study is important because it provides crystallographic evidence, supported by IR data, for the iminium zwitterionic form of Schiff bases.<!?tpb=12pt> 相似文献
69.
Nádia R. Aguiam Vânia I. CastroAna I.F. Ribeiro Rui D.V. FernandesCarina M. Carvalho Susana P.G. CostaSílvia M.M.A. Pereira-Lima 《Tetrahedron》2013
The multicomponent Ugi reaction is a straightforward method that can be used for the synthesis of highly hindered C-tetrasubstituted amino acids by reacting an amine, a ketone or aldehyde, a carboxylic acid and an isocyanide. In the present work, the synthesis of several α,α-dialkylglycines (α,α-diethylglycine, Deg; α,α-dipropylglycine, Dpg; 1-amino-1-cyclohexanecarboxylic acid, Ac6c) was achieved by solid phase Ugi reaction using resins functionalized with the isocyanide group. Since no resins with these features were available commercially, the functionalization of an aminomethylated resin started by the use of glycine (Gly), β-alanine (β-Ala) and γ-aminobutyric acid (GABA) as spacers. After spacer N-formylation, followed by dehydration, isocyanide functionalised resins were obtained. The resins were then used in solid phase Ugi reaction, using phenylacetic acid as the acid component, 4-methoxybenzylamine as the amine component and different ketones, to afford the desired N-acylated α,α-dialkylglycines in good overall yields (60–80%), after acidolytic cleavage from the resin, thus proving the feasibility of this approach. 相似文献
70.
Carlos Victor Montefusco-Pereira Maria José de Carvalho Ana Paula de Araújo Boleti Lorisa Simas Teixeira Humberto Reis Matos Emerson Silva Lima 《Applied biochemistry and biotechnology》2013,170(6):1367-1378
Diabetes mellitus is a metabolic disease characterized by abnormally high plasma glucose levels, leading to major complications, such as insulin resistance, obesity, hyperlipidemia, and hypertension, also with alterations in the immune and neuronal systems. Brazilian plants have been studied as important sources for new molecules with medicinal properties. The genus Passiflora known as “Maracujá” has been used as a traditional folk medicine for a long time, so an investigation was performed regarding an endemic kind of passion fruit (Passiflora nitida Kunth) from Amazonas, Brazil. Here, we aimed to determine its potential biological activity against metabolic syndrome, oxidative stress, pain, and inflammation. The hydroethanol leaf extract revealed an in vitro α-glucosidase inhibitory activity of 50 % inhibitory concentration (IC50)?=?6.78?±?0.31 μg/mL and an α-amylase inhibition of IC50?=?93.36?±?4.37. In vivo, experiments of different saccharide tolerance resulted in significant glycemia control and, with alloxan-diabetic mice, resulted in a decrease of total cholesterol, a hypoglycemic effect, and an antioxidant activity by thiobarbituric acid-reactive substances measurement. Also, it decreased the carrageenan-induced edema volume and the rate of writhing as a nociceptive response. These results indicate positive effects of P. nitida extract and its potential to inhibit metabolic syndrome. 相似文献