全文获取类型
收费全文 | 323篇 |
免费 | 3篇 |
专业分类
化学 | 172篇 |
晶体学 | 11篇 |
力学 | 9篇 |
数学 | 29篇 |
物理学 | 105篇 |
出版年
2023年 | 7篇 |
2022年 | 5篇 |
2021年 | 5篇 |
2020年 | 9篇 |
2019年 | 2篇 |
2018年 | 7篇 |
2017年 | 2篇 |
2016年 | 7篇 |
2015年 | 3篇 |
2014年 | 7篇 |
2013年 | 18篇 |
2012年 | 27篇 |
2011年 | 18篇 |
2010年 | 9篇 |
2009年 | 7篇 |
2008年 | 15篇 |
2007年 | 15篇 |
2006年 | 20篇 |
2005年 | 9篇 |
2004年 | 10篇 |
2003年 | 6篇 |
2002年 | 6篇 |
2001年 | 6篇 |
2000年 | 9篇 |
1999年 | 7篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1995年 | 2篇 |
1994年 | 6篇 |
1993年 | 6篇 |
1992年 | 3篇 |
1991年 | 8篇 |
1990年 | 5篇 |
1987年 | 7篇 |
1986年 | 2篇 |
1984年 | 2篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 11篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1975年 | 2篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1961年 | 1篇 |
1939年 | 2篇 |
1934年 | 1篇 |
排序方式: 共有326条查询结果,搜索用时 15 毫秒
71.
The Born→Green→Yvon equation for molecular fluid has been deduced considering the orientational distribution functions. The
isotropic and anisotropic parts of the distribution function have been separated. The expressions deduced can be used in the
case of mixtures and for the non-central type of intermolecular potential energy. 相似文献
72.
Bidyut Guha Thakurta 《Proceedings Mathematical Sciences》1986,95(1):53-59
In this paper, Weisner’s group-theoretic method of obtaining generating functions is utilized in the study of Jacobi polynomialsP> n (a,ß)(x) by giving suitable interpretations to the index (n) and the parameter (β) to find out the elements for constructing a six-dimensional Lie algebra. 相似文献
73.
Stimulated Brillouin Scattering has been investigated in a two-electron-temperature plasma and it is found that the growth rate can be controlled by injecting hot electrons in the plasma. For typical values of the magnetosphere plasmas the values of growth rates for different concentrations of hot to cold alectrons are calculated. 相似文献
74.
Mineralogical studies on five plastic fire clays of India have been carried out by DTA, TG and electron microscopy. Studies were done on both as received and <1 fraction of clays. Results indicated that all the clays were predominantly kaolinite in nature and showed the main endothermic peak between 540° and 590°C and the exothermic peak between 920° and 985°C. A large exothermic peak at 810°C and a weight loss of 5.35% between 700° and 900°C in case of Barachatarma clay indicated the presence of graphitic carbon in the same. Both Neyveli and Badampahar clays contained illite and goethite. Electron micrographs of Mohuamilan and Neyveli clays showed hexagonal flakes of well-ordered kaolinite. Some tubular particles were seen in Chittorpur, Neyveli and Badampahar clays in addition to the kaolinite particles.The authors are thankful to Dr. B. K. Sarkar, director of the Institute for his kind permission to publish this paper. 相似文献
75.
Precise measurements of the electrical conductances of solutions of potassium thiocyanate (KCNS), ammonium thiocyanate (NH4CNS), sodium nitrate (NaNO3) and ammonium nitrate (NH4NO3) in 2-ethoxyethanol (EE) at temperatures 35, 40, 45 and 50,∘C are reported. The conductance data have been analyzed by the 1978 Fuoss conductance equation. A thermodynamic analysis of the ionic association processes has also been made and the Coulombic forces are found to play a major role in the association processes. The ionic contributions to the limiting equivalent conductances have been determined using the reference electrolyte method. Strong association was found for all these electrolytes in this solvent medium. The cations are found to be substantially solvated in 2-ethoxyethanol, whereas the anions appear to have only weak interaction with the solvent molecules. 相似文献
76.
The reaction of CO with bilirubin which is not detectable in homogeneous aqueous medium proceeds almost with diffusion controlled rate in CTAB micellar system. This could be explained on the basis of catalysis caused by the possible electrostatic surface potential of cationic CTAB Micelles. The rate constant for the oxidation of bilirubin by haloperoxyl radicals have been shown to increase with increasing solvent polarity. Although the polarity effect was small, it followed a trend in the expected direction. Micellar effect was not observed in the oxidation reactions when alcohol was present in high concentration. But a small increase in the rate constant was observed when alcohol concentration was lower. © 1994 John Wiley & Sons, Inc. 相似文献
77.
Two stable thiazolylazo anion radical complexes of ruthenium(II), [Ru(L1•−)(Cl)(CO)(PPh3)2] (1) and [Ru(L2•−)(Cl)(CO)(PPh3)2] (2) (where L1 = 2′-Thiazolylazo-2-imidazole and L2 = 4-(2′-Thiazolylazo)-1-n-hexadecyloxy-naphthalene), have been synthesized
and characterized by spectroscopic and electrochemical techniques. The radical nature of the complexes has been confirmed
from their room temperature magnetic moments and X-band ESR spectra. The radical complexes display a moderately intense (ε ~ 104 M−1 cm−1) and relatively broad band in 430–460 nm region. In the microcrystalline state, complexes (1) and (2) display strong ESR
signals at g = 1.951 and g = 1.988, respectively. In CH2Cl2 solution, complexes (1) and (2) show a quasireversible one-electron response near −0.64 and −0.59 V, respectively, versus
Ag/AgCl due to the radical redox couple [RuII(L)(Cl)(CO)(PPh3)2]/[RuII (L•−)(Cl)(CO)(PPh3)2]. 相似文献
78.
Guha D Mandal A Koll A Filarowski A Mukherjee S 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2000,56(14):2669-2677
Ground and excited state inter- and intramolecular proton transfer reactions of a new o-hydroxy Schiff base, 7-ethylsalicylidenebenzylamine (ESBA) have been investigated by means of absorption, emission and nanosecond spectroscopy in different protic solvents at room temperature and 77 K. The excited state intramolecular proton transfer (ESIPT) is evidenced by a large Stokes shifted emission (approximately 11000 cm(-1)) at a selected excited energy in alcoholic solvents. Spectral characteristics obtained reveal that ESBA exists in more than one structural form in most of the protic solvents, both in the ground and excited states. From the nanosecond measurements and quantum yield of fluorescence we have estimated the decay rate constants, which are mainly represented by nonradiative decay rates. At 77 K the fluorescence spectra are found to be contaminated with phosphorescence spectra in glycerol and ethylene glycol. It is shown that the fluorescence intensity and nature of the species present are dependent upon the excitation energy. 相似文献
79.
80.
Kuang GC Guha PM Brotherton WS Simmons JT Stankee LA Nguyen BT Clark RJ Zhu L 《Journal of the American Chemical Society》2011,133(35):13984-14001
A mechanistic model is formulated to account for the high reactivity of chelating azides (organic azides capable of chelation-assisted metal coordination at the alkylated azido nitrogen position) and copper(II) acetate (Cu(OAc)(2)) in copper(II)-mediated azide-alkyne cycloaddition (AAC) reactions. Fluorescence and (1)H NMR assays are developed for monitoring the reaction progress in two different solvents, methanol and acetonitrile. Solvent kinetic isotopic effect and premixing experiments give credence to the proposed different induction reactions for converting copper(II) to catalytic copper(I) species in methanol (methanol oxidation) and acetonitrile (alkyne oxidative homocoupling), respectively. The kinetic orders of individual components in a chelation-assisted, copper(II)-accelerated AAC reaction are determined in both methanol and acetonitrile. Key conclusions resulting from the kinetic studies include (1) the interaction between copper ion (either in +1 or +2 oxidation state) and a chelating azide occurs in a fast, pre-equilibrium step prior to the formation of the in-cycle copper(I)-acetylide, (2) alkyne deprotonation is involved in several kinetically significant steps, and (3) consistent with prior experimental and computational results by other groups, two copper centers are involved in the catalysis. The X-ray crystal structures of chelating azides with Cu(OAc)(2) suggest a mechanistic synergy between alkyne oxidative homocoupling and copper(II)-accelerated AAC reactions, in which both a bimetallic catalytic pathway and a base are involved. The different roles of the two copper centers (a Lewis acid to enhance the electrophilicity of the azido group and a two-electron reducing agent in oxidative metallacycle formation, respectively) in the proposed catalytic cycle suggest that a mixed valency (+2 and +1) dinuclear copper species be a highly efficient catalyst. This proposition is supported by the higher activity of the partially reduced Cu(OAc)(2) in mediating a 2-picolylazide-involved AAC reaction than the fully reduced Cu(OAc)(2). Finally, the discontinuous kinetic behavior that has been observed by us and others in copper(I/II)-mediated AAC reactions is explained by the likely catalyst disintegration during the course of a relatively slow reaction. Complementing the prior mechanistic conclusions drawn by other investigators, which primarily focus on the copper(I)/alkyne interactions, we emphasize the kinetic significance of copper(I/II)/azide interaction. This work not only provides a mechanism accounting for the fast Cu(OAc)(2)-mediated AAC reactions involving chelating azides, which has apparent practical implications, but suggests the significance of mixed-valency dinuclear copper species in catalytic reactions where two copper centers carry different functions. 相似文献