全文获取类型
收费全文 | 330917篇 |
免费 | 3002篇 |
国内免费 | 749篇 |
专业分类
化学 | 176143篇 |
晶体学 | 5154篇 |
力学 | 14747篇 |
综合类 | 9篇 |
数学 | 37051篇 |
物理学 | 101564篇 |
出版年
2020年 | 2864篇 |
2019年 | 3186篇 |
2018年 | 4358篇 |
2017年 | 4404篇 |
2016年 | 6245篇 |
2015年 | 3529篇 |
2014年 | 5720篇 |
2013年 | 13491篇 |
2012年 | 10529篇 |
2011年 | 12713篇 |
2010年 | 9267篇 |
2009年 | 9032篇 |
2008年 | 11854篇 |
2007年 | 11924篇 |
2006年 | 11229篇 |
2005年 | 10143篇 |
2004年 | 9334篇 |
2003年 | 8498篇 |
2002年 | 8501篇 |
2001年 | 9092篇 |
2000年 | 6956篇 |
1999年 | 5388篇 |
1998年 | 4796篇 |
1997年 | 4731篇 |
1996年 | 4400篇 |
1995年 | 4028篇 |
1994年 | 4140篇 |
1993年 | 3899篇 |
1992年 | 4377篇 |
1991年 | 4388篇 |
1990年 | 4278篇 |
1989年 | 4159篇 |
1988年 | 4173篇 |
1987年 | 4040篇 |
1986年 | 3844篇 |
1985年 | 5048篇 |
1984年 | 5364篇 |
1983年 | 4529篇 |
1982年 | 4673篇 |
1981年 | 4539篇 |
1980年 | 4471篇 |
1979年 | 4482篇 |
1978年 | 4901篇 |
1977年 | 4799篇 |
1976年 | 4818篇 |
1975年 | 4468篇 |
1974年 | 4516篇 |
1973年 | 4631篇 |
1972年 | 3300篇 |
1971年 | 2776篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
We consider the problem of determining the dielectric permittivity for a nonconducting and nonmagnetic medium. As information we take the traces of the tangential components of the electromagnetic field on the lateral surface of a cylindrical domain. These traces correspond to a solution to some direct problem for the Maxwell system. The impulse source of the current flux lies outside the domain in which the coefficient is sought. The main result of the article is a stability estimate for a solution to the inverse problem in question. 相似文献
992.
We again consider the problem of the light-cone expansion for products of currents and explain the motivations making a rethinking of old results relevant today. 相似文献
993.
This note introduces a refinement to a previously proposed tabu search algorithm for vehicle routing problems with time windows. This refinement yields new best known solutions on a set of benchmark instances of the multi-depot, the periodic and the site-dependent vehicle routing problems with time windows. 相似文献
994.
G.N Hile Alexander Stanoyevitch 《Journal of Mathematical Analysis and Applications》2004,295(2):595-610
We generalize the heat polynomials for the heat equation to more general partial differential equations, of higher order with respect to both the time variable and the space variables. Whereas the heat equation requires only one family of polynomials, for an equation of the ?th order with respect to time we introduce ? families of polynomials. These families correspond to the ? initial conditions specified by the Cauchy problem. 相似文献
995.
Leonard M Khalilov Ludmila V Parfenova Askhat G Ibragimov Usein M Dzhemilev 《Journal of organometallic chemistry》2004,689(2):444-453
This paper is dedicated to a study of properties of the following novel optically active organoaluminium compounds (OACs): (1S,2S)-l,7,7-trimethyl-2-[(dialkylalumina)oxy]-bicyclo[2.2.1]heptanes and (1S)-N-(dialkylalumina)-6,7-dimethoxy-1-methyl-1,2,3,4- tetrahydroisoquinolines. The synthesis of the chiral OACs was carried out in the reaction of either natural camphor or salsolidine with both AlEt3 and i-Bu2AlH. The main goal of the research was to investigate the stereodifferentiating activity of the chiral OACs in the olefin carbo- and cycloalumination reactions, catalyzed by Cp2ZrCl2. 相似文献
996.
I. Antoniou M. Gadella J. Mateo G.P. Pronko 《International Journal of Theoretical Physics》2003,42(10):2389-2402
Through two examples: the Friedrichs model and a particular case of central potential scattering, we illustrate the way of constructing Gamow vectors. 相似文献
997.
Salimgareeva V. N. Polevoi R. M. Kolesov S. V. Ostakhov S. S. Ponomareva V. A. Leplyanin G. V. 《Russian Journal of Applied Chemistry》2003,76(5):804-808
The luminescence and scintillation properties of poly(methyl methacrylate) containing 1,1,3-trimethyl-3-phenylindan were studied. 相似文献
998.
电镀污水净化新工艺--电浮选方法简介 总被引:2,自引:1,他引:1
综述了电浮选方法处理电镀污水的基本原理和提高电浮选净水技术的途径。重点介绍了俄罗斯门捷列夫化工大学的电浮选两种新工艺方法。 相似文献
999.
Uptake of trace elements into fish otoliths is governed by several factors such as life histories and environment in addition to stock and species differences. In an attempt to elucidate the elemental signatures of rare earth elements (REEs) in otoliths, a solid phase extraction (SPE) protocol was used in combination with electrothermal vaporization (ETV) as a sample introduction procedure for the determinations by inductively coupled plasma quadrupole mass spectrometry (ICP-MS). Effects of various parameters, such as carrier gas flow rate, atomization temperature and chemical modification, were examined for optimization of the conditions by ETV-ICP-MS. Atomization was achieved at 2800 °C. Lower temperatures (i.e. 2600 °C) resulted in severe memory problems due to incomplete atomization. Palladium was used as a chemical modifier. It was found that an increase in Pd concentration up to 0.5 μg in the injection volume (70 μl) led up to four-fold enhancement in the integrated signals. This phenomenon is attributed to the carrier effect of Pd rather than the stabilization since no significant losses were observed for high temperature drying around 700 °C even in the absence of Pd. Preconcentration was performed on-line at pH 5 by using a mini-column of Toyopearl AF-Chelate 650M chelating resin, which also eliminated the calcium matrix of otolith solutions. After preconcentration of 6.4 ml of solution, the concentrate was collected in 0.65 ml of 0.5% (v/v) HNO3 in autosampler cups, and then analyzed by ETV-ICP-MS. The method was validated with the analysis of a fish otolith certified reference material (CRM) of emperor snapper, and then applied to samples. Results obtained from otoliths of fish captured in the same habitat indicated that otolith rare earth element concentrations are more dependent on environmental conditions of the habitat than on species differences. 相似文献
1000.
María G. Armentano Ricardo G. Durn 《Numerical Methods for Partial Differential Equations》2003,19(5):653-664
In this article we analyze the effect of mass‐lumping in the linear triangular finite element approximation of second‐order elliptic eigenvalue problems. We prove that the eigenvalue obtained by using mass‐lumping is always below the one obtained with exact integration. For singular eigenfunctions, as those arising in non convex polygons, we prove that the eigenvalue obtained with mass‐lumping is above the exact eigenvalue when the mesh size is small enough. So, we conclude that the use of mass‐lumping is convenient in the singular case. When the eigenfunction is smooth several numerical experiments suggest that the eigenvalue computed with mass‐lumping is below the exact one if the mesh is not too coarse. © 2003 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 19: 653–664, 2003 相似文献