全文获取类型
收费全文 | 676篇 |
免费 | 13篇 |
国内免费 | 3篇 |
专业分类
化学 | 423篇 |
晶体学 | 4篇 |
力学 | 24篇 |
数学 | 92篇 |
物理学 | 149篇 |
出版年
2022年 | 19篇 |
2021年 | 11篇 |
2019年 | 9篇 |
2018年 | 21篇 |
2017年 | 23篇 |
2016年 | 16篇 |
2015年 | 12篇 |
2014年 | 22篇 |
2013年 | 45篇 |
2012年 | 34篇 |
2011年 | 33篇 |
2010年 | 20篇 |
2009年 | 26篇 |
2008年 | 27篇 |
2007年 | 24篇 |
2006年 | 17篇 |
2005年 | 13篇 |
2004年 | 13篇 |
2003年 | 10篇 |
2002年 | 13篇 |
2001年 | 5篇 |
2000年 | 7篇 |
1999年 | 6篇 |
1997年 | 4篇 |
1995年 | 5篇 |
1994年 | 5篇 |
1993年 | 7篇 |
1990年 | 7篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1987年 | 8篇 |
1986年 | 4篇 |
1985年 | 9篇 |
1984年 | 12篇 |
1982年 | 4篇 |
1981年 | 9篇 |
1980年 | 11篇 |
1979年 | 12篇 |
1978年 | 12篇 |
1977年 | 16篇 |
1976年 | 6篇 |
1974年 | 10篇 |
1973年 | 9篇 |
1972年 | 8篇 |
1971年 | 8篇 |
1970年 | 4篇 |
1967年 | 4篇 |
1957年 | 7篇 |
1954年 | 5篇 |
1936年 | 4篇 |
排序方式: 共有692条查询结果,搜索用时 296 毫秒
81.
Alain Leborgne Shadi Lal Malhotra Louis-Philippe Blanchard 《Journal of polymer science. Part A, Polymer chemistry》1976,14(12):2853-2866
The polymerization of 1,2-butylene oxide initiated with triphenylmethyl hexafluoroarsinate in the ?20 to +25°C temperature range with 1,2-dichloroethane as solvent is characterized by a rapid nonstationary initial stage. This is followed by a second slower stage, during which the disappearance of monomer is first-order with respect to its concentration. The conversion of monomer at the end of the first stage is related to the initial catalyst concentration but not to the initial monomer concentration. Invoking the hypothesis of an instantaneous initiation reaction, the experimental results lead to the conclusion of the existence of a unimolecular termination step. Propagation-to-termination rate constant ratios yield a propagation–termination activation energy difference of 5.9 kcal/mole. The termination step proposed is thought to involve the formation of stable macrocyclic oxonium ions. These, in turn, can reactivate the polymerization by an intramolecular reaction leading to the formation of new active centers. An energy of activation of 8.7 kcal/mole was calculated for this reactivation. GPC analyses of the reaction products recovered at the end of the first stage revealed the presence of large proportions of oligomers. Based on kinetic data, the formation of oligomers is explained by a backbiting process similar to the reactivation reaction suggested for the initiation of the second stage. 相似文献
82.
An exact solution of Einstein-Maxwell-Yukawa field equations has been obtained in a space-time with a static metric. A critical analysis reveals that the results previously obtained by Patel [9], Singh [10], and Taub [11] are particular cases of our solution. The singular behavior of the solutions has also been discussed in this paper. Further, extending the technique developed by Janis et al. [12], for static fields, to the case of nonstatic fields, an exact time-dependent axially symmetric solution of EMY fields has been obtained. Our solution in the nonstatic case is nonsingular in the sense of Bonnor [15] and presents a generalization of the results obtained by Misra [7] to the case when a zero-mass scalar field coexists with a source free electromagnetic field. 相似文献
83.
84.
85.
Poor beam collimation leads to overcompensation of suppression of coherent bremsstrahlung in the axial channelling case. This fact has been used to study the effect of beam divergence on the radiation emitted by relativistic (axially) channelled positrons. It has been found that due to beam divergence in the experiment of Alguard and co-workers in which radiation of 56 MeV positrons channelling along 〈110〉 rows of a silicon crystal is observed, coherent bremsstrahlung becomes an important contributing factor to the high frequency part of the observed spectrum. 相似文献
86.
87.
88.
The level scheme of75Se has been studied through the75As (p, n) reaction at proton energies from 1.5 to 5.0 MeV.γ-ray and internal conversion electron measurements were made using NaI (T1) and Ge(Li) detectors and a six-gap electron spectrometer. A proportional counter and a thin window NaI(T1) detector were used to detectγ-rays with energies less than 30 keV. The level scheme has been established by observing the thresholds of variousγ-rays and byγ-γ and e?-γ coincidence measurements. New levels at 133.0, 293.2, 790.0, 953.0, 1020.8, 1184.3, 1198.5 and 1258.2 keV not observed in earlier (p, n) studies have been established. Conversion coefficients of most of the low-lying transitions have been determined. Angular distributions of some of theγ-rays were also measured and compared with the statistical model calculations. DefiniteJ π assignments have been made to most of the low-lying levels. Life-times of the 112.1, 133.0, 286.7 and 293.2 keV levels have been measured to be 0.69±0.12, 5.3±0.6, 1.35±0.15 and 31±2 nsec respectively. The reduced transition probabilities for various low-lying transitions have been determined and compared with recent calculations. The 1/2? and 9/2+ levels hitherto unknown in this nucleus has been identified. The structure of the low-lying levels is discussed in terms of the existing models. 相似文献
89.
90.
The present paper aims at deriving a systematic expression of the second order reduced density matrixΩ 2 in the case of a condensed system of identical spinless bosons. The derivation lends itself to generalization leading to higher order reduced density matricesΩ n ,n>2, that are consistent with the hierarchical set of equations of motion for the differentΩ n . 相似文献