全文获取类型
收费全文 | 220篇 |
免费 | 7篇 |
专业分类
化学 | 164篇 |
晶体学 | 3篇 |
力学 | 6篇 |
数学 | 15篇 |
物理学 | 39篇 |
出版年
2023年 | 1篇 |
2022年 | 3篇 |
2021年 | 4篇 |
2020年 | 9篇 |
2019年 | 6篇 |
2018年 | 6篇 |
2017年 | 3篇 |
2016年 | 6篇 |
2015年 | 4篇 |
2014年 | 5篇 |
2013年 | 12篇 |
2012年 | 16篇 |
2011年 | 9篇 |
2010年 | 5篇 |
2009年 | 10篇 |
2008年 | 12篇 |
2007年 | 17篇 |
2006年 | 16篇 |
2005年 | 8篇 |
2004年 | 8篇 |
2003年 | 10篇 |
2002年 | 5篇 |
2001年 | 3篇 |
2000年 | 5篇 |
1999年 | 3篇 |
1998年 | 3篇 |
1997年 | 7篇 |
1996年 | 4篇 |
1994年 | 4篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1989年 | 2篇 |
1986年 | 1篇 |
1984年 | 2篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1974年 | 2篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1965年 | 1篇 |
1943年 | 2篇 |
1881年 | 2篇 |
排序方式: 共有227条查询结果,搜索用时 468 毫秒
21.
The influence of poly(ethylene glycol) on the partition of a charged long chain spin probe between membranes and an external phase is studied. The partition coefficient is derived from the ESR spectra. Membranes of different properties are used (egg lecithin liposomes, erythrocytes) to differentiate between the influence of the external phase and the specific properties of the membrane.The partition coefficient is decreased in an exponential manner on increasing the PEG concentration, which indicates a lowering of the thermodynamic stability of the membranes. The determination of the change in the difference of the chemical potential is dependent on the PEG concentration.The membrane destabilization induced by PEG is caused in an indirect manner by a change of the chemical potential difference as result of the changed water structure and the osmotic pressure, surface tension and hydration of the membrane. This destabilization could be connected with the high fusogenic activity of PEG. 相似文献
22.
23.
Solvent effect on the tautomers' stabilities of protonated N,N‐dimethylnitrosamine: The role of hydrogen bonds network 下载免费PDF全文
Railton B. de Andrade Elizete Ventura Silmar A. do Monte 《International journal of quantum chemistry》2017,117(4)
DFT calculations have been applied in order to study the free energies of the structures corresponding to the three different protonation sites of N,N‐dimethylnitrosamine (DMNA). The solvent effect has been taken into account through the study of clusters consisting of protonated DMNA and up to four explicit water molecules, either in the absence or in the presence of a continuum (CPCM) solvation model. Addition of water molecules has been done by a careful screening procedure through which all important hydrogen bonds are likely to be considered. Protonation of DMNA makes all their lone pairs no longer available for hydrogen bond formation with water molecules, such that hydrogen bonds have been observed, for almost all structures, only between water molecules and between one water molecule and the protonated DMNA, in this latter case intermediated by the proton. The stabilities of the solvated structures are governed not only by the number of hydrogen bonds but also by the positions of the water molecules involved in these bonds, as well as by which of them donate or accept H atoms. Our results indicate that oxygen protonation is the most favorable one, regardless of the presence of water molecules. In vacuum protonation at the N‐amino ( 2a ) is approximately as favorable as protonation at the N nitroso ( 2c ). However, in water the former protonation is by far the less favorable one. Our best estimates for the ΔG values in bulk solvent are: ΔG( 2a ) ≈ 17.9, ΔG( 1c ) ≈ 4.3, and ΔG( 2c ) ≈ 4.9 kcal/mol. 相似文献
24.
25.
Paula Santos Nunes Marília Santos Bezerra L. P. Costa Juliana Cordeiro Cardoso R. L. C. AlbuquerqueJr. M. O. Rodrigues Gabriela Borin Barin Francilene Amaral da Silva A. A. S. Araújo 《Journal of Thermal Analysis and Calorimetry》2010,99(3):1011-1014
The purpose of this study was to evaluate the physical–chemical properties of collagen (CL) and usnic acid/collagen-based
(UAC) films, using differential thermal analysis (DTA), thermogravimetry (TG/DTG), infrared spectroscopy (FTIR), and scanning
electron microscopy (SEM). Both films were prepared by casting process using polyethylene glycol 1500 (PEG 1500) as plasticizer.
In the spectrum of UAC, similar bands of the usnic acid are observed, indicating that the polymerization (film formation)
did not affect the stability of the drug. Distinctly, DTA curve of UAC did not show an endothermic peak at 201 °C, indicative
that the drug was incorporated into the polymeric system. These results were corroborated by the scanning electron microscopy
(SEM). The TG/DTG curves of UAC presented a different thermal decomposition profile compared to the individual compounds and
CL. These findings suggest the occurrence of molecular dispersion or solubilization of the drug in the collagen film. 相似文献
26.
Manuel J. S. Monte Luís M. N. B. F. Santos José M. S. Fonseca Carlos A. D. Sousa 《Journal of Thermal Analysis and Calorimetry》2010,100(2):465-474
The vapour pressures of six para-substituted benzoic acids were measured using the Knudsen effusion method within the pressure range (0.1–1 Pa) in the following
temperature intervals: 4-hydroxybenzoic acid (365.09–387.28) K; 4-cyanobenzoic acid (355.14–373.28) K; 4-(methylamino)benzoic
acid (359.12–381.29) K; 4-(dimethylamino)benzoic acid (369.29–391.01) K; 4-(acetylamino)benzoic acid (423.10–443.12) K; 4-acetoxybenzoic
acid (351.28–373.27) K. From the temperature dependence of the vapour pressure, the standard molar enthalpy, entropy and Gibbs
energy of sublimation, at the temperature 298.15 K, were derived for each of the studied compounds using estimated values
of the heat capacity differences between the gaseous and the crystalline phases. Equations for estimating the vapour pressure
of para substituted benzoic acids at the temperature of 298.15 K are proposed. 相似文献
27.
Daniel Monte 《International Journal of Game Theory》2014,43(1):137-143
In this paper I analyze a repeated coordination game between a bounded memory player and a fully rational player. A bounded memory player is a player who is subject to imperfect recall, but, conditional on this constraint, acts optimally every point in time given her beliefs over the actual history of the game. I show that the results contrast with the ones in the finite automata literature. In particular, a result denoted the “tyranny of the weak” in Gilboa and Samet (Games Econ Behav 1: 213–221, 1989) is no longer present here. 相似文献
28.
Optimization of the pore sizes of various silica gels used as supports in the immobilization of 8-quinolinol is described. Increased capacity is observed as pore size decrease to the opt? at about 6 nm. At smaller pore sizes, steric effects appear to predominate, ? capacities decrease sharply. An explanation for these effects is proposed, it was confirmed by using molecular models. 相似文献
29.
The preparation of 5-hydroxy-4-nitroso- and 7-hydroxy-4-nitrosobenzofurazan as well as of their 6-chloro and methyl derivatives is described and the oxime structure of these compounds is established. NMR spectra of benzofurazan-4,5-dione-4-monoxime and benzofurazan-4,7-dione-4-monoxime show evidence for an interconversion, in solution, of two monoximes, the 4,5- and 4,7-derivative prevailing in organic solvents and aqueous alkaline media, respectively. Chloro and methyl derivatives of benzofurazan-4,5- and 4,7-dione-4-monoximes show a similar interconversion in organic solvents. 相似文献
30.