全文获取类型
收费全文 | 220643篇 |
免费 | 2981篇 |
国内免费 | 1319篇 |
专业分类
化学 | 122729篇 |
晶体学 | 3228篇 |
力学 | 8888篇 |
综合类 | 61篇 |
数学 | 24365篇 |
物理学 | 65672篇 |
出版年
2020年 | 1754篇 |
2019年 | 1896篇 |
2018年 | 2483篇 |
2017年 | 2531篇 |
2016年 | 3646篇 |
2015年 | 2424篇 |
2014年 | 3537篇 |
2013年 | 8872篇 |
2012年 | 7688篇 |
2011年 | 9395篇 |
2010年 | 6649篇 |
2009年 | 6451篇 |
2008年 | 8792篇 |
2007年 | 8900篇 |
2006年 | 8384篇 |
2005年 | 7705篇 |
2004年 | 6870篇 |
2003年 | 6053篇 |
2002年 | 5985篇 |
2001年 | 6703篇 |
2000年 | 5067篇 |
1999年 | 3669篇 |
1998年 | 3038篇 |
1997年 | 3008篇 |
1996年 | 3011篇 |
1995年 | 2618篇 |
1994年 | 2718篇 |
1993年 | 2581篇 |
1992年 | 2829篇 |
1991年 | 2894篇 |
1990年 | 2703篇 |
1989年 | 2616篇 |
1988年 | 2557篇 |
1987年 | 2497篇 |
1986年 | 2520篇 |
1985年 | 3300篇 |
1984年 | 3359篇 |
1983年 | 2804篇 |
1982年 | 3046篇 |
1981年 | 2811篇 |
1980年 | 2607篇 |
1979年 | 2790篇 |
1978年 | 2996篇 |
1977年 | 3032篇 |
1976年 | 3059篇 |
1975年 | 2793篇 |
1974年 | 2906篇 |
1973年 | 2956篇 |
1972年 | 2318篇 |
1971年 | 1845篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
251.
The lattice IR reflection spectra of a ZnTe/Zn0.8Cd0.2Te superlattice measured at temperatures of 300 and 10 K are analyzed. The ZnTe/Zn0.8Cd0.2Te superlattice is grown by molecular-beam epitaxy on a GaAs substrate with a ZnTe buffer layer. It is found that the lattice IR reflection spectra of the studied structure exhibit only one reflection band. Dispersion analysis of the experimental spectrum has revealed the presence of one lattice TO mode close in frequency to the mode of pure ZnTe. This result is explained by a shift in the frequency of the lattice modes of the ZnTe and Zn0.8Cd0.2Te layers of the superlattice toward each other. In turn, this shift is caused by internal elastic stresses in the superlattice due to a mismatch between the lattice parameters of the materials of these layers. 相似文献
252.
V. Bradnova M. M. Chernyavsky L. Just S. P. Kharlamov A. D. Kovalenko M. Haiduc K. A. Kotel’nikov V. A. Krasnov V. G. Larionova F. G. Lepekhin A. I. Malakhov G. I. Orlova N. G. Peresadko N. G. Polukhina P. A. Rukoyatkin V. V. Rusakova N. A. Salmanova B. B. Simonov S. Vokal P. I. Zarubin 《Physics of Atomic Nuclei》2003,66(9):1646-1650
A physical program of irradiation of emulsions in beams of relativistic nuclei named the BECQUEREL Project is reviewed. It is destined to study in detail the processes of relativistic fragmentation of light radioactive and stable nuclei. The expected results would make it possible to answer some topical questions concerning the cluster structure of light nuclei. Owing to the best spatial resolution, the nuclear emulsions would enable one to obtain unique and evident results. The most important irradiations will be performed in the secondary beams of He, Be, B, C, and N radioactive nuclei formed on the basis of JINR Nuclotron beams of stable nuclei. We present results on the charged state topology of relativistic fragmentation of the 10B nucleus at low energy-momentum transfers as the first step of the research. 相似文献
253.
254.
Benjamin E. Blass Anil Srivastava Amy L. Faulkner James M. Ridgeway 《Tetrahedron letters》2004,45(6):1275-1277
The solid-phase synthesis of a series of imidazo[1,2-b]pyrazol-2-ones, an interesting 5,5-fused ring system, based on diverse set of hydrazine acids and malanonitriles is described. The method involves formation of 5-aminopyrazoles on solid support and subsequent cyclizative cleavage off the resin. Compounds were obtained in acceptable to excellent yields and are suitable for biological evaluation without further purification. 相似文献
255.
A group representation of radiation propagation in an anisotropic medium is developed. The system of wave equations for electromagnetic potentials, obtained from the Maxwell equations with account for the constitutive equations, has been factorized. It is shown that the linear differential operator of the factorized system is orthogonal in transparent crystals and unitary in gyrotropic ones and is represented through the momentum operator. On the basis of the commutation relations for the components of this operator, the eigenvalue problem has been solved and the expression for the change in the radiant energy in the crystal in the form of spherical waves has been obtained. The dependences of the ray and phase velocities and the polarization vectors of waves on the birefringence anisotropy and gyrotropy as well as on the angular momentum, displacement current, and bound charge determining them have been analyzed. It has been established that in the general case of gyrotropic crystals where the nonreciprocity phenomenon takes place and in magnetoelectrics Maxwell equations are represented in a form similar to the Dirac equations and the electromagnetic radiation is correctly described by means of bispinors and is quantized as fermions. 相似文献
256.
The composite comprised of zinc oxide quantum dots and poly(amic acid) (PAAc) was prepared and studied by X-rays diffraction, X-ray photoelectron spectroscopy, light scattering, UV absorbance and UV fluorescence. The UV absorbance of the ZnO/PAAc composite was found to be much larger than that of its components taken separately. The fluorescence of the ZnO/PAAc composite was found to be shifted to longer wavelengthes in comparison with pure ZnO. The presence of the dopant dodecylbenzenesulfonic acid was found to affect the observed fluorescence. 相似文献
257.
E. Rodriguez E. Jimenez G.J. Jacob A.A.R. Neves C.L. Cesar L.C. Barbosa 《Physica E: Low-dimensional Systems and Nanostructures》2005,26(1-4):361
Multilayer PbTe quantum dots (QDs) and SiO2 were grown by pulsed laser deposition (PLD) and Plasma enhanced chemical vapor deposition (PECVD) techniques. The crystalline structure, QD size and size dispersion were observed by high-resolution transmission electron microscopy (HRTEM) measurements. This technique allows one to grow PbTe QDs as small as 1.8 nm diameter and 0.6 nm size dispersion. The whole structure can be used in a Fabry–Perot cavity for an optical device operating at the mid-infrared region. 相似文献
258.
A switching of the S-type in the 20–200 μm thick polycrystalline n-CdTe:In layers with resistance of 103–106 Ω·cm is studied. The electric instability in the layers is found to be due to the electron-thermal breakdown mechanism. The
dependence of the switching threshold parameters on the intensity of exposure can be used for fabrication of infrared-radiation
controlled electric switches on the basis of n-CdTe:In layers.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 28–30, June, 2005. 相似文献
259.
260.
David S. McGuinness Edward L. Marshall Vernon C. Gibson Jonathan W. Steed 《Journal of polymer science. Part A, Polymer chemistry》2003,41(23):3798-3803
Hetero‐bimetallic Fe(II) alkoxide/aryloxides were evaluated as initiators for the ring‐opening polymerization of rac‐lactide. [(THF)NaFe(OtBu)3]2 ( 1 ) and [(THF)4Na2Fe(2,6‐diisopropylphenolate)4] ( 2 ) (THF = tetrahydrofuran) both polymerized lactide efficiently at room temperature, with complex 1 affording better control over the molecular weight parameters of the resultant polymer. At conversions below 70%, a linear increase in molecular weight with conversion was observed, indicative of a well‐controlled polymerization process. Complex 2 is the first example of a dianionic Fe(II) alkoxide and has been structurally characterized to reveal a distorted square planar FeO4 array in which both Na counterions bridge two aryloxide ligands and are further complexed by two THF ligands. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3798–3803, 2003 相似文献