全文获取类型
收费全文 | 362篇 |
免费 | 9篇 |
国内免费 | 2篇 |
专业分类
化学 | 193篇 |
晶体学 | 6篇 |
力学 | 12篇 |
数学 | 54篇 |
物理学 | 108篇 |
出版年
2023年 | 4篇 |
2022年 | 6篇 |
2021年 | 7篇 |
2019年 | 4篇 |
2018年 | 9篇 |
2017年 | 8篇 |
2016年 | 25篇 |
2015年 | 7篇 |
2014年 | 5篇 |
2013年 | 12篇 |
2012年 | 23篇 |
2011年 | 24篇 |
2010年 | 6篇 |
2009年 | 9篇 |
2008年 | 14篇 |
2007年 | 11篇 |
2006年 | 11篇 |
2005年 | 13篇 |
2004年 | 6篇 |
2003年 | 4篇 |
2002年 | 6篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1999年 | 6篇 |
1998年 | 5篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1994年 | 3篇 |
1993年 | 9篇 |
1992年 | 8篇 |
1991年 | 4篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1986年 | 3篇 |
1985年 | 6篇 |
1982年 | 4篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 6篇 |
1975年 | 6篇 |
1974年 | 4篇 |
1973年 | 3篇 |
1972年 | 6篇 |
1971年 | 5篇 |
1969年 | 3篇 |
1967年 | 3篇 |
1939年 | 4篇 |
排序方式: 共有373条查询结果,搜索用时 15 毫秒
31.
32.
An analysis of the semiclassical regime of the quantum-classical transition is given for open, bounded, one-dimensional chaotic dynamical systems. Environmental fluctuations-characteristic of all realistic dynamical systems-suppress the development of a fine structure in classical phase space and damp nonlocal contributions to the semiclassical Wigner function, which would otherwise invalidate the approximation. This dual regularization of the singular nature of the semiclassical limit is demonstrated by a numerical investigation of the chaotic Duffing oscillator. 相似文献
33.
A tight-binding representation of the kicked Harper model is used to obtain an integrable semiclassical Hamiltonian consisting of "quantized" bands of orbits. New bands appear when renormalized Harper parameters exceed integer multiples of pi/2. Orbits with frequencies commensurate with the kicking frequency are shown to correlate with classical accelerator modes in the original kicked problem. Signatures of this superdiffusive and, in our view, resonant transport are seen in both classical and quantum behavior. An important feature of our analysis is the emergence of a natural scaling relating classical and quantum couplings which is necessary for establishing correspondence. 相似文献
34.
Three disparate food systems (gummy candy, Mozzarella cheese, and cooked ham) were characterized for their viscoelastic behavior
under isothermal conditions over an extended frequency range of 10−3 to 104 Hz using broadband viscoelastic spectroscopy (BVS). The materials were tested for any stress-induced fluid flow. However,
no evidence of fluid flow was found under the tested frequency range. Validity of time–temperature superposition for the selected
materials was also tested and compared with data from BVS. 相似文献
35.
Density functional theory (DFT) studies were performed to investigate the effect of substituents on the properties of benzdiyne derivatives. Twelve substituted benzdiynes-C(6)X(2), where X = F, Cl, Br, Me, CF(3), CN, OH, NO(2), NH(2), OMe, NMe(2), and Ph-were considered along with the unsubstituted 1,4-benzdiyne. The structures, vibrational frequencies, and IR intensities of these benzdiynes were studied with a popular three-parameter hybrid density functional (B3LYP) combined with the split-valence 6-31G(d) basis set and Dunning's correlation-consistent polarized triple-zeta (cc-pVTZ) basis set. The relative stabilities of the substituted benzdiynes were studied with the help of reaction energies of isodesmic reactions, which showed that the electron-withdrawing groups destabilized the benzdiynes more than they did the corresponding benzenes, whereas the electron-donating groups stabilized the benzdiynes more than they did their benzene counterparts. Correlation analyses revealed that field/inductive effects played a more important role than did resonance effects. The changes in atomic charges and spin populations due to the substituents were also studied. The asymmetric nu(Ctbd1;C) stretching modes obtained were close to the 1500-cm(-)(1) mark. Reinvestigation of the experimental results supported these results; a weak IR band at 1486 cm(-)(1) was assigned to this asymmetric stretching mode in C(6)(CF(3))(2) F. Some other benzdiynes also had large IR intensity values for their asymmetric nu(Ctbd1;C) vibrational modes due to the coupling with other vibrational modes. Heats of formation for the substituted benzdiynes were obtained from the reaction energies calculated at the B3LYP/cc-pVTZ level of theory. 相似文献
36.
37.
Diluted Sn doped TiO2 nanocrystals (Sn/Ti ratio: x ≤ 1.37 %) were synthesized by a simple hydrothermal method using pure reagents without any surfactant and dispersant material. The XRD of these samples showed an anatase phase, anatase and rutile mixed phases, and a rutile phase of TiO2 and SnO2 with the increase of Sn dopant concentrations. 119Sn Mössbauer spectra gave the broad peaks, which were decomposed into doublets and sextets because almost all these samples showed magnetic hysteresis even at room temperature. The titanium oxides doped with x ≤ 0.12 % showed the relatively large magnetic hysteresis and high photocatalytic activity. Mössbauer spectra of samples doped with x > 0.3 % were analyzed by one doublet and two sextets although the samples showed weak ferromagnetism. Three kinds of Sn species may be distinguished as Sn 4+ substituted TiO2 and two different magnetic arrangements of Sn doped TiO2: one with more oxygen defects and other at the interface of TiO2 and precipitated SnO2 containing Ti atoms. The correlation between various amounts of Sn sites and photocatalytic activity and/ or magnetic property was discussed. 相似文献
38.
This paper deals with the propagation of solitons in real fibres, governed by the system of inhomogeneous nonlinear Schrödinger (INLS) equations. The Painlevé singularity structure analysis is utilized to check for the integrability of the system and from the analysis, the system is found to admit soliton-type lossless wave propagation. The system is transformed to its homogeneous counterpart using a suitable variable transformation and the soliton solutions are obtained through Bäcklund transformation after constructing the explicit Lax pair for the system. The one-soliton solutions are plotted for different choices of inhomogeneity parameters and the evolutionary characteristics of the solutions are analyzed. 相似文献
39.
40.