全文获取类型
收费全文 | 2011篇 |
免费 | 96篇 |
国内免费 | 25篇 |
专业分类
化学 | 1375篇 |
晶体学 | 32篇 |
力学 | 40篇 |
综合类 | 1篇 |
数学 | 256篇 |
物理学 | 428篇 |
出版年
2023年 | 25篇 |
2022年 | 46篇 |
2021年 | 65篇 |
2020年 | 61篇 |
2019年 | 51篇 |
2018年 | 47篇 |
2017年 | 46篇 |
2016年 | 77篇 |
2015年 | 44篇 |
2014年 | 84篇 |
2013年 | 113篇 |
2012年 | 150篇 |
2011年 | 148篇 |
2010年 | 94篇 |
2009年 | 69篇 |
2008年 | 107篇 |
2007年 | 116篇 |
2006年 | 98篇 |
2005年 | 88篇 |
2004年 | 63篇 |
2003年 | 68篇 |
2002年 | 70篇 |
2001年 | 26篇 |
2000年 | 42篇 |
1999年 | 33篇 |
1998年 | 15篇 |
1997年 | 30篇 |
1996年 | 23篇 |
1995年 | 22篇 |
1994年 | 14篇 |
1993年 | 15篇 |
1992年 | 20篇 |
1991年 | 12篇 |
1990年 | 9篇 |
1989年 | 10篇 |
1988年 | 8篇 |
1987年 | 7篇 |
1986年 | 9篇 |
1985年 | 13篇 |
1984年 | 14篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1979年 | 5篇 |
1978年 | 8篇 |
1976年 | 5篇 |
1975年 | 8篇 |
1973年 | 4篇 |
1971年 | 3篇 |
1966年 | 3篇 |
排序方式: 共有2132条查询结果,搜索用时 109 毫秒
1.
Complementary regioselective esterification of non-reducing oligosaccharides catalyzed by different hydrolases 总被引:1,自引:0,他引:1
The enzymatic transesterification of several tri- and tetrasaccharides with vinyl laurate is described. The lipases from Candida antarctica B (Novozym 435) and Thermomyces lanuginosus (Lipozyme TL IM) and the alkaline protease from Bacillus licheniformis (subtilisin Carlsberg) have been used with each carbohydrate to obtain different regioisomers. By using the sugars in their amorphous form, complete solubility is achieved in the reaction media (tert-butanol/pyridine mixtures for the lipases and pyridine for the protease) and high isolated yields of the corresponding monoesters are obtained. Good to excellent regioselectivity is observed for all the enzymes, showing a final complementary picture respect to the primary hydroxyls of the oligosaccharides studied. 相似文献
2.
Ludmila C. Fidale Sarah Köhler Martin H.G. Prechtl Thomas Heinze Omar A. El Seoud 《Cellulose (London, England)》2006,13(5):581-592
The concentrations of water, W, and electrolytes present in solutions of LiCl in N,N-dimethylacetamide, LiCl/DMAc, and of tetrabutylammonium fluoride. x-hydrate in DMSO, TBAF.xW/DMSO can be accurately and expediently determined by three independent methods, UV–vis, FTIR and EMF measurement. The first relies on the use of solvatochromic probes whose spectra are sensitive to solution composition. It is applicable to W/LiCl/DMAc solutions but not to TBAF.xW/DMSO, because the charge-transfer complex bands of the probes are suppressed by strong interactions with the latter electrolyte. Integration of νOH band of water may be employed in order to determine [W], hence [electrolyte] by weight difference. EMF measurement uses ion-selective electrodes in order to determine [electrolyte], hence [W] by weight difference. Results of the latter method were in excellent agreement with those of FTIR. The reason for the failure of Karl Fischer titration is addressed, and the relevance of the results obtained to functionalization of cellulose under homogenous solution conditions is briefly commented on. 相似文献
3.
Foda Omar Leclerc Bernard Okado Masato Thibon Jean-Yves Welsh Trevor A. 《Letters in Mathematical Physics》1998,43(1):31-42
A special family of partitions occurs in two apparently unrelated contexts: the evaluation of one-dimensional configuration sums of certain RSOS models, and the modular representation theory of symmetric groups or their Hecke algebras Hm. We provide an explanation of this coincidence by showing how the irreducible Hm-modules which remain irreducible under restriction to Hm_1 (Jantzen–Seitz modules) can be determined from the decomposition of a tensor product of representations sln. 相似文献
4.
5.
We present a general risk model where the aggregate claims, as well as the premium function, evolve by jumps. This is achieved by incorporating a Lévy process into the model. This seeks to account for the discrete nature of claims and asset prices. We give several explicit examples of Lévy processes that can be used to drive a risk model. This allows us to incorporate aggregate claims and premium fluctuations in the same process. We discuss important features of such processes and their relevance to risk modeling. We also extend classical results on ruin probabilities to this model. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
6.
M A Aguilar-Mendez E San Martin-Martinez J E Morales A Cruz-Orea M R Jaime-Fonseca 《Analytical sciences》2007,23(4):457-461
Water vapor diffusion coefficient (WVDC) and thermal diffusivity (alpha) were determined in gelatin-starch films through photothermal techniques. The effect of different variables in the elaboration of these films, such as starch and glycerol concentrations and pH, were evaluated through the response surface methodology. The results indicated that an increase in the glycerol concentration and pH favored the WVDC of the films. On the other hand, alpha was influenced principally by the starch content and pH of the film-forming solution. The minimum alpha value was 4.5 x 10(-4) cm2/s, which is compared with alpha values reported for commercial synthetic polymers. 相似文献
7.
Antonio Jimé nez-Melado Claudio H. Morales 《Proceedings of the American Mathematical Society》2006,134(2):501-507
We show a fixed point theorem for condensing mappings under a new condition of the Leray-Schauder type. We call it the Interior Condition. We also discuss examples that demonstrate the independence of these two conditions.
8.
SbPO4, a phosphate with a layered structure, was tested as an electrode material for lithium cells spanning the 3.0-0.0 V range. Two main electrochemical processes were detected as extensive plateaus at ca. 1.6 and 0.7 V in galvanostatic measurements. The first process was found to be irreversible, thus excluding a potential intercalation-like mechanism for the reaction and being better interpreted as a decomposition reaction leading to the formation of elemental Sb. This precludes the use of this compound as a cathodic material for lithium cells. By contrast, the process at 0.7 V is reversible and can be ascribed to the formation of lithium-antimony alloys. The best electrochemical response was obtained by cycling the cell at a C/20 discharge rate over the voltage range 1.25-0.25 V. Under these conditions, the cell delivers an average capacity of 165 Ah/kg—a value greater than those reported for other phosphates—upon successive cycling. 相似文献
9.
I. R. Martin V. D. Rodriguez M. Morales U. R. Rodriguez-Mendoza V. Lavin 《Journal of Applied Spectroscopy》1995,62(5):865-871
This work has been partially supported by Gobierno Autonomo de Canarias under contact number 226–265/93. 相似文献
10.
An analytical method for the simultaneous speciation of butylin and phenyltin compounds has been applied to a study of the water quality in six locations (rivers and sea) in South West Spain. It was not intended to provide a comprehensive survey of the area but to establish what the maximum levels might be for a subsequent and more detailed study. Phenyltin species were not found in any sample, however tributyltin was present (100-400 ng l-1) in the Cadiz Bay samples, which suggests that the biological water quality may sometimes be depressed. Wherever tributyltin was present, dibutyltin and monobutyltin occurred, possibly, as a result of a degradation process. 相似文献