全文获取类型
收费全文 | 1092篇 |
免费 | 48篇 |
国内免费 | 11篇 |
专业分类
化学 | 751篇 |
晶体学 | 11篇 |
力学 | 10篇 |
数学 | 135篇 |
物理学 | 244篇 |
出版年
2024年 | 3篇 |
2023年 | 7篇 |
2022年 | 53篇 |
2021年 | 28篇 |
2020年 | 29篇 |
2019年 | 37篇 |
2018年 | 35篇 |
2017年 | 30篇 |
2016年 | 56篇 |
2015年 | 25篇 |
2014年 | 38篇 |
2013年 | 123篇 |
2012年 | 59篇 |
2011年 | 60篇 |
2010年 | 47篇 |
2009年 | 50篇 |
2008年 | 44篇 |
2007年 | 33篇 |
2006年 | 31篇 |
2005年 | 32篇 |
2004年 | 47篇 |
2003年 | 22篇 |
2002年 | 28篇 |
2001年 | 10篇 |
2000年 | 12篇 |
1999年 | 4篇 |
1998年 | 15篇 |
1997年 | 4篇 |
1996年 | 13篇 |
1995年 | 6篇 |
1994年 | 19篇 |
1993年 | 12篇 |
1992年 | 15篇 |
1991年 | 10篇 |
1990年 | 7篇 |
1989年 | 14篇 |
1988年 | 9篇 |
1987年 | 3篇 |
1985年 | 8篇 |
1984年 | 9篇 |
1983年 | 8篇 |
1982年 | 7篇 |
1981年 | 10篇 |
1980年 | 5篇 |
1979年 | 6篇 |
1977年 | 6篇 |
1975年 | 4篇 |
1972年 | 3篇 |
1971年 | 4篇 |
1969年 | 2篇 |
排序方式: 共有1151条查询结果,搜索用时 0 毫秒
131.
Mohamed Hassan Magda A. Barsy Eman A. El Rady Abdullah Sulaiman Al-Ayed Mona Frempong Kamal U. Sadek 《Journal of heterocyclic chemistry》2024,61(4):543-549
An efficient synthesis of novel benzo[f]Chromeno[2,3-d]pyrimidine and unknown benzo[f]chromeno[2,3-d][1,2,4]triazolopyrimidine derivatives is described utilizing ethyl-2-amino-4-phenyl-4H-benzo[f]chromene-3-carboxylate as precursor via aza-Wittig reaction. The process proved to be simple, high-yielding, and efficient. 相似文献
132.
Y. M. Temerk M. M. Kamal Z. A. Ahmed M. S. Ibrahim 《Fresenius' Journal of Analytical Chemistry》1990,336(7):589-592
Summary A differential pulse polarographic method has been applied to the determination of trace concentrations of polycytidylic acid (Poly-C) in absence and presence of metal ions. The applicability of differential pulse polarography for the trace determination of the investigated biological compound was examined with regard to the dependence of differential pulse current on various parameters such as pH, pulse amplitude, scan rate and drop time. The selectivity of this technique for the determination of binary and a ternary mixtures of poly-C and some metal ions has been also reported. Limits of detection and quantitation have been calculated for the differential pulse polarographic determination of the poly-C and various metal ions. The validity of this method is supported by the constancy of the ip/C values and a statistical analysis is included on calibration curve parameters and observed concentration. 相似文献
133.
Kamal Sarabandi 《International Journal of Infrared and Millimeter Waves》1990,11(11):1303-1321
A periodic, corrugated, dielectric layer is simulated by an anisotropic dielectric layer of equal thickness. The tensor elements of the equivalent dielectric layer are given in terms of the permittivity of the dielectric material, the period of the surface corrugation, and the width of the corrugations. The validity of this technique is verified by comparing the reflection coefficient of the equivalent layer with that of the corresponding corrugated layer using the moment method. Employing a multiple layer approach, the technique is extended to handle periodic surfaces with arbitrary cross sections which can be used to design millimeter wave dielectric plate polarizers and absorbers. 相似文献
134.
The zinc mediated reductive dimerization and cyclization of α,β-unsaturated ketones gives functionalized cyclopentanols in good yield in the presence of a catalytic amount of mercury(II) chloride in N,N-dimethylformamide as solvent at room temperature. The reaction is regio- and stereo-selective producing 3,4-trans-diarylcyclopentanols selectively. 相似文献
135.
Tungstophosphoric acid catalyzed rapid and good yielding reactions of α,β-unsaturated aldehydes with arenethiols to give the corresponding 4-thioaryl-1,2,3,4-tetrahydro-1-benzothiopyrans (thiochromans) under solvent-free and room temperature conditions. 相似文献
136.
137.
In an exactly solvable model of separable potentials a two channel scattering problem is solved in l = 0 state. The location and the width of a resonance are then defined in three different ways and the resonance parameters so extracted are then compared. This problem is of interest vis-a-vis the Δ(3, 3) resonance parameters. 相似文献
138.
Kamal K. Bharadwaj Mohan K. Kadalbajoo R. Sankar 《Applied mathematics and computation》1984,15(2):137-149
The symmetric marching technique has been developed to solve the Poisson equation with Dirichlet boundary conditions. The method has been combined with a mesh refinement technique, which is used as an appropriate interpolation scheme to obtain a solution of the problem on finer grids. The effectiveness of the method has been demonstrated by solving some test examples. 相似文献
139.
Energy levels: 1s 1/2, 2p 1/2, 2p 3/2, 3d 3/2, and 3d 5/2 of the muon in the spherical nuclei:120Sn,197Au and208Pb have been calculated under the assumption of harmonic oscillator potential. The levels are corrected for vacuum polarisation. The agreement with experimental values is better than 0·5%. An accurate method of solving the Dirac equation to obtain the energy eigenvalues is outlined. The importance of choosing the ‘classical turning point’ as the radius for matching the interior and exterior solutions is discussed. 相似文献
140.
The kinetics of the solvolysis of [Co(CN)5Cl]3? ions have been investigated in mixtures formed by the addition of ethane-1,2-diol or ethanonitrile to water where the physical properties indicate little enhancement of structure in water-rich conditions. The effect on the kinetics of this solvolysis of this lack of structural change in the solvent shows in the linearity of the variation of log (rate constant) with the reciprocal of the dielectric constant for the addition of ethane-1,2-diol to water and the absence of any prominent extrema in the enthalpy or entropy of activation using either co-solvent. However, the effect of changes in solvation on the solvolysis with these two co-solvents appears to operate in a similar manner to the effects found when the hydrophobic co-solvent propan-2-ol is added to water. The application of a free energy cycle to the process of the initial state going to the transition state for this dissociative process suggests that, with both co-solvents, [Co(CN)5]2? in the transition state is more stable than [Co(CN)5Cl]3? in the initial state. © John Wiley & Sons, Inc. 相似文献