全文获取类型
收费全文 | 353516篇 |
免费 | 2390篇 |
国内免费 | 638篇 |
专业分类
化学 | 168970篇 |
晶体学 | 4384篇 |
力学 | 18500篇 |
综合类 | 9篇 |
数学 | 52525篇 |
物理学 | 112156篇 |
出版年
2019年 | 2291篇 |
2018年 | 11088篇 |
2017年 | 11870篇 |
2016年 | 8212篇 |
2015年 | 3412篇 |
2014年 | 4389篇 |
2013年 | 10780篇 |
2012年 | 12034篇 |
2011年 | 21171篇 |
2010年 | 13571篇 |
2009年 | 13464篇 |
2008年 | 18862篇 |
2007年 | 22220篇 |
2006年 | 9056篇 |
2005年 | 13929篇 |
2004年 | 10449篇 |
2003年 | 9879篇 |
2002年 | 7943篇 |
2001年 | 7474篇 |
2000年 | 5963篇 |
1999年 | 4397篇 |
1998年 | 3899篇 |
1997年 | 3778篇 |
1996年 | 3485篇 |
1995年 | 3338篇 |
1994年 | 3474篇 |
1993年 | 3157篇 |
1992年 | 3626篇 |
1991年 | 3637篇 |
1990年 | 3577篇 |
1989年 | 3459篇 |
1988年 | 3546篇 |
1987年 | 3475篇 |
1986年 | 3267篇 |
1985年 | 4368篇 |
1984年 | 4672篇 |
1983年 | 3888篇 |
1982年 | 4021篇 |
1981年 | 3937篇 |
1980年 | 3910篇 |
1979年 | 3906篇 |
1978年 | 4239篇 |
1977年 | 4093篇 |
1976年 | 4183篇 |
1975年 | 3844篇 |
1974年 | 3906篇 |
1973年 | 4081篇 |
1972年 | 2854篇 |
1971年 | 2370篇 |
1970年 | 2194篇 |
排序方式: 共有10000条查询结果,搜索用时 437 毫秒
991.
Eremenko L. T. Oreshko G. V. Nesterenko D. A. Lagodzinskaya G. V. Eremenko I. L. 《Russian Chemical Bulletin》2002,51(1):157-159
The reactions of ethylene glycol mononitrate and glycerol 1,3-dinitrate with methylphosphonic dichloride afforded new nitroxyalkyl methylphosphonates. 相似文献
992.
A class of exact analytical solutions of Einstein-Maxwell equations is obtained for static spheres of Maugin's anisotropic magnetofluid where the space-time geometry is assumed to admit a nonstatic conformai symmetry. These solutions are found by utilizing special physical considerations. 相似文献
993.
994.
The nanocrystal samples of titanium dioxide doped with europium ion (Eu3+/TiO2 nanocrystal) are synthesized by the sol-gel method with hydrothermal treatment. The Eu3+ contents (molar ratio) in the samples are 0, 0.5%, 1%, 2%, 3% and 4%. The X-ray diffraction, UV-Vis spectroscopy data and scanning electron microscope image show that crystallite size is reduced by the doping of Eu3+ into TiO2. Comparing the Raman spectra of TiO2 with Eu3+/TiO2 (molar ratio Eu3+/TiO2=1%, 2% and 4%) nanocrystals at different annealing temperatures indicates that the anatase-to-rutile phase transformation temperatures of Eu3+/TiO2 nanocrystals are higher than that of TiO2. This is due to the formation of Eu-O-Ti bonds on the surface of the TiO2 crystallite, as characterized by the X-ray photoelectron spectroscopy. The photoluminescence spectra of TiO2 in Eu3+/TiO2 nanocrystals are interpreted by the surface self-trapped and defect-trapped exciton relaxation. The photoluminescence of Eu3+ in Eu3+/TiO2 nanocrystals has the strongest emission intensity at 2% of Eu3+ concentration. 相似文献
995.
Y. Qu J.X. Zhang A. Uddin C.Y. Liu S. Yuan M.C.Y. Chan B. Bo G. Liu H. Jiang 《Applied Physics A: Materials Science & Processing》2006,82(2):305-308
Ridge-waveguide InGaAsN triple-quantum-well strain-compensated lasers grown by metal organic chemical vapor deposition were fabricated with pulsed anodic oxidation. The laser’s output power reached 145 mW in continuous-wave mode at room temperature for a 4-?m -stripe-width laser. Continuous-wave single longitudinal mode operation was maintained at a high injection current level with a wavelength of 1287.3 nm at room temperature. Single longitudinal mode operation at 1317.2 nm was achieved at twice the threshold current at 100 °C. The band gap of InGaAsN in the quantum wells at different temperatures was calculated and compared to the measured temperature-dependent laser wavelength. 相似文献
996.
The deformation surrounding Vickers indentations on InGaAsP/InP epilayers have been studied in detail. The surface topography was characterized by using atomic force microscopy (AFM). The material pile-up and sink-in regions around the indentation impression was observed for the quaternary InGaAsP/InP epilayers. The sectional analysis mode of the AFM shows the depth profile at the indented region. Microindentation studies were carried out for different atomic fraction of the quaternary InGaAsP/InP compound semiconductor alloys. The microhardness values of InGaAsP/InP epilayers were found to be in the range of 5.08 and 5.73 GPa. These results show that the hardness value of the quaternary alloy drastically increases as the composition of As was increased by 0.01 atomic fraction and when the phosphorous concentration decreases from 0.4 to 0.38. The reason may be that the increase in As concentration hardens the lattice when phosphorous concentration was less and hardness decreases when phosphorous was increased. 相似文献
997.
M. G. Voronkov E. A. Grebneva O. M. Trofimova A. I. Albanov N. F. Chernov N. N. Chipanina 《Russian Journal of General Chemistry》2006,76(12):1851-1853
Reaction of tetrafluorosilane with tris(2-hydroxyethyl)-and tris(2-trimethylsiloxyethyl)amine results in formation of 1-fluorosilatrane and fluorosilatrane in 75 and 53% yield, respectively. Reaction of tetrafluorosilane with bis(2-trimethylsiloxyethyl)amine and its N-methyl derivative leads to the hitherto unknown 1,1-difluoroquasisilatranes (N → Si) F2Si(OCH2CH2)2NR (R = H, Me) containing donor-acceptor bond N → Si and pentacoordinate silicon atom. The structure of the synthesized compounds was proved by 1H, 13C, 15N, 19F, 29Si NMR and IR spectroscopy. 相似文献
998.
The peak effect (PE) in the critical current density in both low and high temperature superconductors has been the subject
of a large amount of experimental and theoretical work in the last few/several years. In the case of YBCO, crucial discussions
describing a dynamic or a static picture are not settled. In that region of field and temperature the mobility of the vortex
lattice (VL) is found to be dependent on the dynamical history. Recently we reported evidence that the VL reorganizes and
accesses to robust VL configurations (VLCs) with different effective pinning potential wells arising in response to different
system histories. One of the keys to understand the nature of the PE is to investigate the VL behavior in the vicinity of
the various VLCs in the region of the PE. The stability of these VLCs was investigated and it was found that they have distinct
characteristic relaxation times, which may be related to elastic or plastic creep processes. In this paper we review some
of these results and propose a scenario to describe the PE in YBCO crystals. 相似文献
999.
1000.