全文获取类型
收费全文 | 608068篇 |
免费 | 4361篇 |
国内免费 | 1567篇 |
专业分类
化学 | 277989篇 |
晶体学 | 8953篇 |
力学 | 35200篇 |
综合类 | 10篇 |
数学 | 103677篇 |
物理学 | 188167篇 |
出版年
2021年 | 5080篇 |
2020年 | 5403篇 |
2019年 | 6316篇 |
2018年 | 18739篇 |
2017年 | 18759篇 |
2016年 | 17952篇 |
2015年 | 7229篇 |
2014年 | 11693篇 |
2013年 | 24275篇 |
2012年 | 22483篇 |
2011年 | 32139篇 |
2010年 | 22730篇 |
2009年 | 23448篇 |
2008年 | 27066篇 |
2007年 | 28759篇 |
2006年 | 19101篇 |
2005年 | 17629篇 |
2004年 | 16986篇 |
2003年 | 15876篇 |
2002年 | 15108篇 |
2001年 | 15830篇 |
2000年 | 12165篇 |
1999年 | 9263篇 |
1998年 | 8181篇 |
1997年 | 7837篇 |
1996年 | 7336篇 |
1995年 | 6430篇 |
1994年 | 6368篇 |
1993年 | 6267篇 |
1992年 | 6566篇 |
1991年 | 7107篇 |
1990年 | 6811篇 |
1989年 | 6753篇 |
1988年 | 6376篇 |
1987年 | 6556篇 |
1986年 | 6130篇 |
1985年 | 7436篇 |
1984年 | 7712篇 |
1983年 | 6507篇 |
1982年 | 6678篇 |
1981年 | 6250篇 |
1980年 | 6044篇 |
1979年 | 6667篇 |
1978年 | 6695篇 |
1977年 | 6825篇 |
1976年 | 6835篇 |
1975年 | 6400篇 |
1974年 | 6208篇 |
1973年 | 6405篇 |
1972年 | 5006篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The process of focusing of an inhomogeneously polarized beam passed through a system consisting of a uniaxial crystal and a polarization filter is considered. It is shown that the action of this system is equivalent to the action of a phase transparency with a complex relief of the refractive index. In particular, if the angle between the axes of the quarter-wave plate and the polarizer is equal to 45°, this transparency has a helicoidal relief. Simultaneously, two singular beams with different curvatures of their wavefronts arise in the transparency. The action of the lens consists in formation of a combined singular beam having three focal waists. The boundary wave arising upon focusing is able not only to form a new spectrum of toroidal vortices, but also to straighten the focusing region, forming a fairly extended range with a weak divergence. 相似文献
992.
The spectra of absorption (77–398 K) and luminescence (5 K) of poly(di-n-hexylsilane) films are studied in relation to the heating of the films above the phase transition temperature. Two new absorption bands in the region of the band of the gauche conformation are found. The position and intensity of these bands depend on the annealing temperature, annealing regime, and sample thickness. These bands are assumed to be associated with the appearance of a liquid crystalline phase in the polymer, which is determined by intermolecular interactions between neighboring polymer chains. The appearance of the liquid crystalline phase in the heat-treated polymer films is confirmed by the increase in their birefringence in comparison with the birefringence of the initial films and by the observation of a stable orientation of an E 7 nematic liquid crystal applied to the surface of an annealed sample. In addition, the absorption spectra of the films cooled after the annealing exhibit many new bands in comparison with the spectra of the initial samples. These bands are associated with the appearance in the polymer of defect states and longer segments as a result of orientation of polymer chains. The appearance of longer segments is consistent with the observation of a long-wavelength band in the luminescence spectra of the annealed samples. 相似文献
993.
994.
Quantum operations with a charge solid-state qubit whose logical states are formed by two spatially separated localized states of an electron in the double-dot structure are studied theoretically. We show that it is possible to perform various one-qubit rotations making use of the microwave pulses tuned to the resonances between the localized states and the excited state delocalized over the nanostructure. An explicit analytic expression for the time-dependent electron state vector is derived, and the appropriate pulse parameters are determined. 相似文献
995.
S. N. Artemenko 《JETP Letters》2004,79(6):277-281
It is shown theoretically that the Luttinger liquid can exist in quasi-one-dimensional conductors in the presence of impurities in a form of a collection of bounded Luttinger liquids. The conclusion is based on the observation by Kane and Fisher that a local impurity potential in Luttinger liquid acts, at low energies, as an infinite barrier. This leads to a discrete spectrum of collective charge and spin density fluctuations, so that interchain hopping can be considered as a small parameter at temperatures below the minimum excitation energy of the collective modes. The results are compared with recent experimental observation of a Luttinger-liquid-like behavior in thin NbSe3 and TaS3 wires. 相似文献
996.
It is shown that the introduction of heavy inert gas impurities into the condensed phase of a lighter inert gas can significantly change the kinetic properties of the latter at high pressures. The electronic structure of the ordered Ar15Xe solid solution is calculated. Doping of the condensed phase of a light inert gas with atoms of a heavier inert gas may become a new convenient tool in high-pressure experiments. 相似文献
997.
The possibility of applying the physical principles underlying the operation of a solid-state terahertz oscillator to plasma gas-discharge media is analyzed. A new method of electromagnetic wave generation in the terahertz frequency range is proposed. It is based on the excitation of plasma-oscillation current by a static electric field in a laser spark produced by an axicon lens, followed by the radiation of an electromagnetic pulse through the Cherenkov mechanism. 相似文献
998.
A. V. Dvurechenskii Zh. V. Smagina V. A. Zinov’ev V. A. Armbrister V. A. Volodin M. D. Efremov 《JETP Letters》2004,79(7):333-336
Multilayer silicon structures with built-in layers of Ge nanoclusters were studied experimentally by Raman light scattering. The built-in layers were formed by the pulsed action of a low-energy beam of intrinsic ions during molecular-beam epitaxy. It is found that the ion-stimulated nucleation and the subsequent growth make it possible to obtain Ge nanoclusters almost free of Si. 相似文献
999.
S. B. Bushuk Yu. A. Kal'vinkovskaya A. N. Rubinov 《Journal of Applied Spectroscopy》2004,71(2):291-294
Capture of an ensemble of polymeric microspheres in a water suspension under the action of optical gradient forces in the field of interfering laser beams has been investigated for the case of two-, three-, and four-beam interference. The self-diffraction and diffraction of radiation on induced ordered spatial distribution of particles have been obtained. 相似文献
1000.
The signals of a single-pulse echo (SE) generated on nonresonant excitation of an inhomogeneously broadened two-level system by a radio-frequency pulse (RFP), against the background of which a magnetic video pulse (MVP) of certain length has been switched on, have been described analytically. It is established that under the conditions of such excitation several SE signals are formed whose generation moments are determined by the duration and amplitudes of the RFP and MVP. The amplitudes of some of these signals depend on the Rabi frequency according to a quadratic law, and the amplitudes of others depend on this frequency according to a biquadratic law. It has been established that the mechanism underlying the appearance of these signals is associated with zero beats arising as a result of superposition of the magnetization fluctuations at variable frequencies and at a frequency of detuning from resonance. It is shown that in the limiting case, where the RFP duration considerably exceeds the duration of the MVP or is comparable with it, the number of SE signals decreases to two. Theoretical results on the formation of SE and the dependence of the amplitude of these signals on the MVP amplitude agree with the experimental data on NMR pulsed signals in ferromagnetic materials. 相似文献