全文获取类型
收费全文 | 12004篇 |
免费 | 2882篇 |
国内免费 | 1350篇 |
专业分类
化学 | 7437篇 |
晶体学 | 71篇 |
力学 | 1268篇 |
综合类 | 108篇 |
数学 | 1275篇 |
物理学 | 6077篇 |
出版年
2024年 | 19篇 |
2023年 | 136篇 |
2022年 | 217篇 |
2021年 | 277篇 |
2020年 | 417篇 |
2019年 | 404篇 |
2018年 | 470篇 |
2017年 | 447篇 |
2016年 | 527篇 |
2015年 | 605篇 |
2014年 | 879篇 |
2013年 | 1072篇 |
2012年 | 857篇 |
2011年 | 941篇 |
2010年 | 760篇 |
2009年 | 862篇 |
2008年 | 891篇 |
2007年 | 777篇 |
2006年 | 740篇 |
2005年 | 710篇 |
2004年 | 633篇 |
2003年 | 631篇 |
2002年 | 434篇 |
2001年 | 333篇 |
2000年 | 335篇 |
1999年 | 260篇 |
1998年 | 247篇 |
1997年 | 231篇 |
1996年 | 175篇 |
1995年 | 184篇 |
1994年 | 128篇 |
1993年 | 119篇 |
1992年 | 85篇 |
1991年 | 42篇 |
1990年 | 61篇 |
1989年 | 43篇 |
1988年 | 34篇 |
1987年 | 42篇 |
1986年 | 27篇 |
1985年 | 30篇 |
1984年 | 35篇 |
1982年 | 23篇 |
1981年 | 12篇 |
1980年 | 8篇 |
1979年 | 13篇 |
1978年 | 8篇 |
1977年 | 12篇 |
1974年 | 6篇 |
1971年 | 7篇 |
1957年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 42 毫秒
81.
Hong-wei Zhang Shao-ying Zhang Bao-gen Shen Helmut Kronmüller 《Journal of magnetism and magnetic materials》2003,260(3):352-360
The magnetization behavior in nanocrystalline permanent magnets has been investigated using mean field Stoner–Wohlfarth model. The model is comparatively simple but allows the numerical treatment of extended nanostructures. The predominant intergrain exchange coupling is expressed by a mean field constant Nm in spite of no explicit relationship between Nm and the microstructure. By this model, the experimental phenomena, such as the remanence enhancement, the shape of demagnetization curve, the irreversible magnetization, the exchange bias field and their respective temperature dependence, can be well explained. The Nm dependence of magnetic properties has been extensively discussed in the present paper. 相似文献
82.
Kyu Hwang Yeon Suk Seong Kim Chung In Um Thomas F. George 《International Journal of Theoretical Physics》2003,42(9):2043-2059
Quantum Hamiltonian systems corresponding to classical systems related by a general canonical transformation are considered. The differential equation to find the unitary operator, which corresponds to the canonical transformation and connects quantum states of the original and transformed systems, is obtained. The propagator associated with their wave functions is found by the unitary operator. Quantum systems related by a linear canonical point transformation are analyzed. The results are tested by finding the wave functions of the under-, critical-, and over-damped harmonic oscillator from the wave functions of the harmonic oscillator, free-particle system, and negative harmonic potential system, using the unitary operator to connect them, respectively. 相似文献
83.
本文讨论了复调和函数在无穷远点的性质,揭示出有界区域上复调和函数的两类表示式之间的关系. 相似文献
84.
85.
86.
The vibronic spectra of charge transfer excitons (CTE) in a molecular one-component or alternatingly ordered two-component chain are treated in the framework of a dynamic approach (neglecting thermal excitations of the intramolecular vibrations). The model introduces two mechanisms of coupling between CTEs and vibrational quanta: (1) shift of the equilibrium positions of the nuclei in the ionized donor or acceptor; (2) change of the vibrational frequency in the ionized molecule. This model allows to generalize the simple CTE Hamiltonian and the vibronic Hamiltonian of Frenkel excitons. The linear optical susceptibility is calculated in the vibronic region (one CTE and one vibrational quantum). The double splitting of vibronics of CTEs was analyzed: (1) the splitting connected with the location of the intramolecular vibration on the donors or on the acceptors; (2) the splitting connected with the symmetry of the vibronic spectra (in the degenerate case). The general structure of the vibronic spectra of CTEs is established. It contains structureless absorption lines, which correspond to two-particle bands (the phonon is excited on a neutral molecule neighboring the donor or the acceptor) and Lorentz-type lines of one-particle states, which correspond to the bound propagation of the CTE and the phonon. 相似文献
87.
Photoinduced optical and second-order non-linear optical effects in the interfaces separating In2O3–SiON (O/N ratio equals 1) films doped with A1, Sn and glass substrates were investigated using the photoinduced optical second harmonic generation. The photoinduced effective second-order optical susceptibility deff (at λ=1.76 μm) shows a good correlation with the linear optical susceptibility, particularly with the shift of the absorption edge. The maximal response of the photoinduced optical response signal was observed for the pump–probe delaying time of 34 ps. The performed experimental measurements indicate that the observed effects are mainly caused by the interface potential gradients on the border glass–In2O3–SiON film and by additional polarization due to insertion of the Al and Sn atoms. The observed phenomenon may be proposed as a sensitive tool for investigation of thin semiconducting interfacial layers and simultaneously such films may be used as materials for non-linear optical devices. 相似文献
88.
It is shown that data on the dissociation rate of deuterium obtained in an experiment at the Sudbury Neutrino Observatory provides evidence that the Continuous Spontaneous Localization wavefunction collapse model should have mass–proportional coupling to be viable. 相似文献
89.
The influence of the parameter of amplitude-phase coupling for nonlinear amplification on the phase-frequency characteristics of an injection laser in the regime of pumping current modulation has been investigated theoretically. The parameter is defined as the coefficient of proportionality between changes in the real and imaginary parts of the refractive index during variation of the density of photons in the cavity. The substantial dependence of the coefficient of phase modulation on the parameter of the amplitude-phase coupling for nonlinear amplification at small modulation frequencies is shown. A technique to determine the indicated parameter based on the frequency dependence of the ratio between the coefficients of phase and amplitude modulation is suggested. 相似文献
90.
Joji Ohshita Ryosuke Taketsugu Yuki Nakahara Atsutaka Kunai 《Journal of organometallic chemistry》2004,689(20):3258-3264
Selective dehydrogenative coupling of di- and trihydrosilanes with alcohols catalyzed by PdCl2 or NiCl2 afforded alkoxyhydro- and dialkoxyhydrosilanes in good yield. Further treatment of the resulting alkoxyhydrosilanes with carbon tetrachloride or allyl bromide in the presence of the same catalyst led to the formation of alkoxychloro- and alkoxybromosilanes, respectively. Similar reactions of dialkoxyhydrosilanes with carbon tetrachloride afforded dialkoxychlorosilanes in good yield, although contamination of small amounts of trialkoxysilanes and alkoxydichlorosilanes was detected in the products. Selective substitution of the alkoxyhalosilanes with nucleophiles is also reported. 相似文献