全文获取类型
收费全文 | 147025篇 |
免费 | 1293篇 |
国内免费 | 397篇 |
专业分类
化学 | 80198篇 |
晶体学 | 2387篇 |
力学 | 6063篇 |
综合类 | 3篇 |
数学 | 13571篇 |
物理学 | 46493篇 |
出版年
2021年 | 1031篇 |
2020年 | 1182篇 |
2019年 | 1250篇 |
2018年 | 1638篇 |
2017年 | 1689篇 |
2016年 | 2540篇 |
2015年 | 1560篇 |
2014年 | 2348篇 |
2013年 | 6035篇 |
2012年 | 4841篇 |
2011年 | 5936篇 |
2010年 | 4181篇 |
2009年 | 4209篇 |
2008年 | 5725篇 |
2007年 | 5509篇 |
2006年 | 5378篇 |
2005年 | 4942篇 |
2004年 | 4447篇 |
2003年 | 4116篇 |
2002年 | 4007篇 |
2001年 | 5543篇 |
2000年 | 3974篇 |
1999年 | 3074篇 |
1998年 | 2112篇 |
1997年 | 2207篇 |
1996年 | 2070篇 |
1995年 | 1916篇 |
1994年 | 1915篇 |
1993年 | 1727篇 |
1992年 | 2215篇 |
1991年 | 2301篇 |
1990年 | 2135篇 |
1989年 | 2099篇 |
1988年 | 2078篇 |
1987年 | 2087篇 |
1986年 | 1912篇 |
1985年 | 2371篇 |
1984年 | 2391篇 |
1983年 | 1912篇 |
1982年 | 1914篇 |
1981年 | 1752篇 |
1980年 | 1740篇 |
1979年 | 2029篇 |
1978年 | 2101篇 |
1977年 | 2051篇 |
1976年 | 1975篇 |
1975年 | 1860篇 |
1974年 | 1842篇 |
1973年 | 1874篇 |
1972年 | 1235篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
131.
Mutual precipitates of poly (N, N-dimethyl acrylamide) and poly (4-hydroxystyrene) were collected from dioxane, methanol, or acetone. The glass transition (Tg) temperatures of the precipitates are higher than the weight-average values. Clear films cast from dimethylformamide solutions have lower Tg values. Complexation also occurred between poly (ethyl oxazoline) and poly (4-hydroxystyrene) in dioxane and between poly (vinyl pyrrolidone) and poly (4-hydroxystyrene) in methanol. Again, the glass transition temperatures of the precipitates are higher than the values for the blend films. The ΔCp values associated with the glass transitions of the complexes are smaller than those of the blends having the same compositions. Negative excess heat capacities of mixing have been observed for several precipitates. 相似文献
132.
Muonium in liquid SiCl has been observed for the first time at low temperature (−65°C) The observed polarization of muonium
is as much as 25% of the total spin polarization and shows a fast relaxation rate. 相似文献
133.
L. S. de C. Oliveira M. T. X. Silva A. Vasquez J. A. H. da Jornada 《Hyperfine Interactions》1991,66(1-4):267-270
An exploratory Mössbauer spectroscopy study of the Fe-C system in the C rich region, prepared by high pressure-high temperature treatment near the graphite-diamond stability line, was made. The results obtained for the different processing conditions give no evidence of Fe intercalation in graphite. The presence of some water in the cell produced hydrated Fe complexes, which can explain the deleterious effect of water or hydrogen in the high pressure diamond synthesis. 相似文献
134.
Unsteady flow dynamics in doubly constricted 3D vessels have been investigated under pulsatile flow conditions for a full cycle of period T. The coupled non‐linear partial differential equations governing the mass and momentum of a viscous incompressible fluid has been numerically analyzed by a time accurate Finite Volume Scheme in an implicit Euler time marching setting. Roe's flux difference splitting of non‐linear terms and the pseudo‐compressibility technique employed in the current numerical scheme makes it robust both in space and time. Computational experiments are carried out to assess the influence of Reynolds' number and the spacing between two mild constrictions on the pressure drop across the constrictions. The study reveals that the pressure drop across a series of mild constrictions can get physiologically critical and is also found to be sensitive both to the spacing between the constrictions and the oscillatory nature of the inflow profile. The flow separation zone on the downstream constriction is seen to detach from the diverging wall of the constriction leading to vortex shedding with 3D features earlier than that on the wall in the spacing between the two constrictions. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
135.
V. A. Donchenko M. V. Kabanov V. T. Kalaida B. I. Kulakov E. V. Ovcharenko I. G. Sokovets 《Russian Physics Journal》1998,41(5):476-484
The problems of determining and investigating the informative parameters of atmospheric electricity are discussed. It is shown
that short-period variations in atmospheric electricity are ecologically significant. An automated system for monitoring atmospheric
electricity and a method of processing the results of measurements are described.
V. D. Kuznetsov Siberian Physicotechnical Institute, Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh
Zavedenii, Fizika, No. 5, pp. 88–98, May, 1998. 相似文献
136.
It is predicted that resonance coupling between two discrete electron energy levels corresponding to different size-quantization
quantum numbers and different Landau quantum numbers can occur in a quantum well in a quantizing magnetic field. The resonance
coupling is due to the interaction of an electron with LO phonons and results in the formation of polaron states of a new type. It is shown that for a certain value of the magnetic
field, which depends on the splitting of the electron size-quantization levels, the absorption peak and the two-phonon resonance
Raman scattering peak split into two components, the separation between which is determined by the electron-phonon coupling
constant. The resonance coupling between size-quantization levels with the same Landau quantum numbers is also studied. The
splitting of the peaks in this case is virtually independent of the magnetic field and can be observed in much weaker fields.
The experimental observation of the effect will make it possible to determine the relative position of the electronic levels
and the electron-phonon coupling constant.
Pis’ma Zh. éksp. Teor. Fiz. 65, No. 7, 511–515 (10 April 1997) 相似文献
137.
We have performed structural and optical characterizations of the propolis (an organic entity of biological nature) films grown on various non-organic substrates. The films were grown from a propolis melt or a propolis alcohol solution. The crystal structure has been observed in the films precipitated from the solution onto substrates such as an amorphous glass and sapphire or semiconductor indium monoselenide. For any growth method, the propolis film is a semiconductor with the bandgap of 3.07 eV at 300 K that is confirmed by a maximum in photoluminescence spectra at 2.86 eV. We argue that propolis films might be used in various optoelectronic device applications. 相似文献
138.
Journal of Applied Spectroscopy - 相似文献
139.
140.