全文获取类型
收费全文 | 139篇 |
免费 | 1篇 |
国内免费 | 8篇 |
专业分类
化学 | 81篇 |
晶体学 | 3篇 |
力学 | 1篇 |
数学 | 36篇 |
物理学 | 27篇 |
出版年
2023年 | 4篇 |
2021年 | 3篇 |
2020年 | 1篇 |
2019年 | 1篇 |
2018年 | 4篇 |
2017年 | 2篇 |
2016年 | 3篇 |
2015年 | 7篇 |
2014年 | 7篇 |
2013年 | 8篇 |
2012年 | 11篇 |
2011年 | 11篇 |
2010年 | 7篇 |
2009年 | 8篇 |
2008年 | 8篇 |
2007年 | 10篇 |
2006年 | 7篇 |
2005年 | 9篇 |
2004年 | 5篇 |
2003年 | 6篇 |
2002年 | 2篇 |
2001年 | 3篇 |
2000年 | 7篇 |
1999年 | 1篇 |
1998年 | 4篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1991年 | 1篇 |
1988年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有148条查询结果,搜索用时 31 毫秒
61.
62.
Muglali MI Liu J Bashir A Borissov D Xu M Wang Y Wöll C Rohwerder M 《Physical chemistry chemical physics : PCCP》2012,14(14):4703-4712
Palladium nanoparticles have been deposited electrochemically onto self-assembled monolayers (SAMs) of 4-(4-(4-pyridyl)phenyl)phenylmethanethiol. A pronounced correlation between the kinetics of the complexation between pyridine nitrogens and Pd cations and the sample potential has been observed. The amount of the Pd deposit significantly increases by adjusting the sample potential during the complexation step to values below the point of zero charge. The size of the spherical shaped Pd nanoparticles varies within a certain limit according to the amount of Pd(2+) ions initially coordinated on top of the SAM. The metallic state of these particles was confirmed by X-ray photoelectron spectroscopy and infrared reflection-absorption spectroscopy. Moreover, CO adsorption on the clean Pd deposit revealed further information about the crystallographic orientation of the nanoparticles. 相似文献
63.
Two approaches to the aza-tricyclo dodecane skeleton of (-)-FR901483 are reported. Both routes utilized a Grignard addition to an N-acylpyridinium salt to establish the absolute stereochemistry at C-6 and a highly diastereoselective conjugate allylation reaction to form the quaternary center at C-1 of the natural product in an excellent yield. Although the desired polysubstituted piperidine intermediates were prepared regio- and stereoselectively, the construction of the C-8/C-9 bond connectivity could not be achieved. All attempts at a pinacol cyclization or an intramolecular 6-exo-tet epoxide opening were unsuccessful because of an unfavorable A(1,3) strain inherent in the molecule. 相似文献
64.
Reactivity of sodium arenesulfinates in the substitution reaction to γ‐functionalized allyl bromides
Galina Khamis Stoyanka Stoeva Dimitar Aleksiev 《Journal of Physical Organic Chemistry》2010,23(5):461-467
The kinetics of nucleophilic bimolecular substitution reactions of γ‐functionalized allyl bromides with non‐substituted and p‐substituted sodium arenesulfinates has been studied. Both the structure of allyl bromides and nucleophilicity of arenesulfinate ions exerted a significant effect on the values of the kinetic parameters such as the second‐order rate constants k, activation energy EA, and changes in the entropy ΔS≠, enthalpy ΔH≠, and free energy ΔG≠ of the formation of the activated complex from reactants. Based on the evaluation of kinetic parameters, the reactants could be arranged, according to their decreasing reactivity in the SN2‐reactions as follows: p‐toluenesulfinate ion > benzenesulfinate ion > p‐chlorobenzenesulfinate ion and 4‐bromo‐2‐butenenitrile > 1,3‐ dibromopropene, respectively. Comparison was also made between the kinetic data obtained and some delocalization reactivity indexes for both the substrates and nucleophiles. The enthalpy–entropy compensation effect was observed for the reactions of sodium arenesulfinates with γ‐functionalized allyl bromides. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
65.
Dimitar Grantcharov Ji Hye Jung Seok-Jin Kang Myungho Kim 《Communications in Mathematical Physics》2010,296(3):827-860
In this paper, we investigate the structure of highest weight modules over the quantum queer superalgebra
Uq(\mathfrak q(n)){U_q(\mathfrak {q}(n))}. The key ingredients are the triangular decomposition of
Uq(\mathfrak q(n)){U_q(\mathfrak {q}(n))} and the classification of finite dimensional irreducible modules over quantum Clifford superalgebras. The main results we
prove are the classical limit theorem and the complete reducibility theorem for
Uq(\mathfrak q(n)){U_q(\mathfrak {q}(n))}-modules in the category Oq 3 0{\mathcal {O}_{q}^{\geq 0}}. 相似文献
66.
Ralitsa P. Ivanova Darinka Y. Bojinova Ivan N. Gruncharov Dimitar L. Damgaliev 《Phosphorus, sulfur, and silicon and the related elements》2013,188(11):2541-2554
Bases of the production of phosphoric fertilizers are classical methods involving acid dissolution of rock phosphates. The development of new methods applicable both to high-quality and low-quality phosphates is important for solving technological and ecological problems and to increase the economical effectiveness of phosphorus fertilizer technologies. In this respect, the bioconversion of rock phosphates in order to obtain phosphorus fertilizers is very promising. The basic principle of the biotechnological processing of natural phosphates is the production of organic acids, mainly citric, oxalic, and gluconic acid, that attack and dissolve the phosphates, converting the phosphorus to a form utilizable for the plants. The aim of this research is to optimize the process of Tunisian phosphorite solubilization with citric, oxalic, and gluconic acids in relation to the following main factors: the acid concentration, reaction time, solid/liquid phases ratio, and natural phosphate fraction. Two objective functions have been investigated: the quantity of the available acid in the system and the extent of phosphate dissolution. The research data has been processed according to the standard statistical tests. A mathematical model describing the phosphate decomposition process by organic acids has been obtained. A multicriteria optimization has been performed to determine the optimum levels of the examined factors. It was established that the different factors have a different effect on the goal parameters. A maximum degree of 91.89% of phosphorus extraction has been reached at phosphate solubilization by citric acid. 相似文献
67.
Dimitar Stoychev 《Journal of Solid State Electrochemistry》2013,17(2):497-509
It has been ascertained that the electrochemically deposited thin films of cerium oxides, containing mainly CeO2 and also some insignificant amount of Ce2O3, are acting as an effective cathodic coating, leading to restoration of the passive state of the studied stainless steel (OC 404) samples. This effect is associated with a strong shifting of the stationary corrosion potential of the steel in positive direction, moving over from potentials characteristic of corrosion in active state to potentials falling within the zone of passivity. In this respect, another basic purpose of the investigations was the elucidation of the mechanism of action of the cerium oxide film and in particular collecting experimental evidence for the supposition about the occurrence of an efficient depolarization reaction of CeO2 reduction (resulting in a state of passivity—improved ability of self-passivation) instead of hydrogen depolarization reaction. For this purpose, we considered also the decrease in the surface concentration of ceria in the passive layer under the conditions of the actual corrosion process (self-dissolution) of the stainless steel by means of XPS, SEM, ICP-AES, and gravimetric analyses. A decrease in the surface concentration of CeO2 (Ce4+) has been observed, which is known to be chemically inert in acidic media. The obtained results prove the occurrence of an effective cathodic process of Ce4+ (CeO2) reduction into Ce3+ (soluble in acids Ce2O3 ) in the superficial oxide film. 相似文献
68.
69.
70.
The purpose of this study was to develop and evaluate a method for automatic endoscopic motion compensation (MC) specialized for laryngeal high-speed videoendoscopy (HSV) of sustained phonation. Specifically, the left-right and posterior-anterior endoscopic shifts were addressed. The method is based on the hypothesis that the difference between endoscopic and vocal fold dynamics is sufficient for accurate estimation of the endoscopic motion relative to the vocal folds. The research questions of particular interest were as follows: is MC of laryngeal HSV possible at the subpixel level, and what are the validity, reliability, and accuracy of the proposed MC method? First, the MC accuracy was assessed on simulated HSV data with exactly known motion trajectories. Then, the accuracy and reliability of MC were evaluated on real HSV data. Finally, the validity of MC was established by correlating objective to perceptual ratings. The method demonstrated subpixel accuracy and reliable performance when tested on both simulated and real data. Perceptual ratings of the endoscopic motion demonstrated high intrarater and interrater reliabilities. Perceptual and quantitative assessments of endoscopic motion were in agreement. The reported result is encouraging for resolving a persistent problem toward building better methods for visual and quantitative voice assessment. 相似文献