全文获取类型
收费全文 | 813篇 |
免费 | 36篇 |
专业分类
化学 | 655篇 |
晶体学 | 5篇 |
力学 | 17篇 |
数学 | 79篇 |
物理学 | 93篇 |
出版年
2024年 | 1篇 |
2023年 | 8篇 |
2022年 | 31篇 |
2021年 | 52篇 |
2020年 | 30篇 |
2019年 | 60篇 |
2018年 | 37篇 |
2017年 | 33篇 |
2016年 | 37篇 |
2015年 | 38篇 |
2014年 | 28篇 |
2013年 | 57篇 |
2012年 | 64篇 |
2011年 | 58篇 |
2010年 | 49篇 |
2009年 | 32篇 |
2008年 | 52篇 |
2007年 | 32篇 |
2006年 | 38篇 |
2005年 | 30篇 |
2004年 | 12篇 |
2003年 | 20篇 |
2002年 | 12篇 |
2001年 | 9篇 |
2000年 | 6篇 |
1999年 | 5篇 |
1998年 | 5篇 |
1997年 | 4篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有849条查询结果,搜索用时 62 毫秒
51.
Valentina S. Borovkova Yuriy N. Malyar Irina G. Sudakova Anna I. Chudina Andrey M. Skripnikov Olga Yu. Fetisova Alexander S. Kazachenko Angelina V. Miroshnikova Dmitriy V. Zimonin Vladislav A. Ionin Anastasia A. Seliverstova Ekaterina D. Samoylova Noureddine Issaoui 《Molecules (Basel, Switzerland)》2022,27(1)
Spruce (Picea abies) wood hemicelluloses have been obtained by the noncatalytic and catalytic oxidative delignification in the acetic acid-water-hydrogen peroxide medium in a processing time of 3–4 h and temperatures of 90–100 °C. In the catalytic process, the H2SO4, MnSO4, TiO2, and (NH4)6Mo7O24 catalysts have been used. A polysaccharide yield of up to 11.7 wt% has been found. The hemicellulose composition and structure have been studied by a complex of physicochemical methods, including gas and gel permeation chromatography, Fourier-transform infrared spectroscopy, and thermogravimetric analysis. The galactose:mannose:glucose:arabinose:xylose monomeric units in a ratio of 5:3:2:1:1 have been identified in the hemicelluloses by gas chromatography. Using gel permeation chromatography, the weight average molar mass Mw of hemicelluloses has been found to attain 47,654 g/mol in noncatalytic delignification and up to 42,793 g/mol in catalytic delignification. Based on the same technique, a method for determining the α and k parameters of the Mark–Kuhn–Houwink equation for hemicelluloses has been developed; it has been established that these parameters change between 0.33–1.01 and 1.57–472.17, respectively, depending on the catalyst concentration and process temperature and time. Moreover, the FTIR spectra of the hemicellulose samples contain all the bands characteristic of heteropolysaccharides, specifically, 1069 cm−1 (C–O–C and C–O–H), 1738 cm−1 (ester C=O), 1375 cm−1 (–C–CH3), 1243 cm−1 (–C–O–), etc. It has been determined by the thermogravimetric analysis that the hemicelluloses isolated from spruce wood are resistant to heating to temperatures of up to ~100 °C and, upon further heating, start destructing at an increasing rate. The antioxidant activity of the hemicelluloses has been examined using the compounds simulating the 2,2-diphenyl-2-picrylhydrazyl free radicals. 相似文献
52.
53.
54.
Elena?F.?ShekaEmail author Ekaterina?A.?Nikitina Valentin?A.?Zayets Ilya?Ya.?Ginzburg Joop?Schoonman 《Journal of nanoparticle research》2005,7(2-3):171-186
The current paper presents results of a quantum-chemical study of the surface structure of nanoparticles of both rutile and anatase crystallographic modifications. Different stages of the surface relaxation are discussed. Water adsorption is considered. The calculations were performed in the spd-basis by using semi-empirical quantum-chemical codes, both sequential and parallel. The results are mainly addressed to the study of the interface formed by titania nanoparticles and a set of carboxylated species, namely, benzoic, bi-isonicotinic acids as well as tris-(2,2′-dcbipyridine) Fe(II) complex placed on the surface of either rutile or anatase polymorphs.This revised version was published online in August 2005 with a corrected issue number. 相似文献
55.
Photothermal image flow cytometry in vivo 总被引:1,自引:0,他引:1
The capability of photothermal (PT) microscopy to image moving, unlabeled cells in real time in vivo is demonstrated in a study of circulating red and white blood cells in blood and lymph microvessels of rat mesentery. Potential applications of this optical tool, called PT flow cytometry, are discussed. 相似文献
56.
Režnar Tomáš Martinovič Jan Slaninová Kateřina Grakova Ekaterina Vondrák Vít 《Central European Journal of Operations Research》2017,25(3):545-560
Central European Journal of Operations Research - The probabilistic time-dependent vehicle routing problem is presented in this paper. It is a novel variant of the vehicle routing problem. The... 相似文献
57.
Maria Yurova 《General Relativity and Gravitation》2000,32(11):2219-2227
The inverse scattering problem method application to the construction of exact solutions, for the Maxwell dilaton gravity system is considered. By use of Belinsky and Zakharov L-A pair the solution of the theory is constructed. The rotating Kerr-like configuration with NUT-parameter is obtained. 相似文献
58.
Anastasia Glinskikh Olga Snytnikova Ekaterina Zelentsova Maria Borisova Yuri Tsentalovich Andrey Akulov 《Molecules (Basel, Switzerland)》2021,26(11)
(1) Recently, metabolic profiling of the tissue in the native state or extracts of its metabolites has become increasingly important in the field of metabolomics. An important factor, in this case, is the presence of blood in a tissue sample, which can potentially lead to a change in the concentration of tissue metabolites and, as a result, distortion of experimental data and their interpretation. (2) In this paper, the metabolomic profiling based on NMR spectroscopy was performed to determine the effect of blood contained in the studied samples of brain tissue on their metabolomic profile. We used 13 male laboratory CD-1® IGS mice for this study. The animals were divided into two groups. The first group of animals (n = 7) was subjected to the perfusion procedure, and the second group of animals (n = 6) was not perfused. The brain tissues of the animals were homogenized, and the metabolite fraction was extracted with a water/methanol/chloroform solution. Samples were studied by high-frequency 1H-NMR spectroscopy with subsequent statistical data analysis. The group comparison was performed with the use of the Student’s test. We identified 36 metabolites in the brain tissue with the use of NMR spectroscopy. (3) For the major set of studied metabolites, no significant differences were found in the brain tissue metabolite concentrations in the native state and after the blood removal procedure. (4) Thus, it was shown that the presence of blood does not have a significant effect on the metabolomic profile of the brain in animals without pathologies. 相似文献
59.
Ekaterina A. Shilova Valery P. Perevalov Corinne Moustrou 《Tetrahedron letters》2008,49(21):3453-3457
The novel photochromic [2]rotaxane based on chromene molecule introduced into a crown-containing macrocyclic receptor was synthesized. The photochemical properties of rotaxane could be modified by the complexation of the crown ether moiety. 相似文献
60.
Ekaterina Alekseeva Yuri Kochetov Alexander Plyasunov 《European Journal of Operational Research》2008
We study the complexity of finding local minima for the p-median problem. The relationship between Swap local optima, 0–1 local saddle points, and classical Karush–Kuhn–Tucker conditions is presented. It is shown that the local search problems with some neighborhoods are tight PLS-complete. Moreover, the standard local descent algorithm takes exponential number of iterations in the worst case regardless of the tie-breaking and pivoting rules used. To illustrate this property, we present a family of instances where some local minima may be hard to find. Computational results with different pivoting rules for random and Euclidean test instances are discussed. These empirical results show that the standard local descent algorithm is polynomial in average for some pivoting rules. 相似文献