全文获取类型
收费全文 | 63678篇 |
免费 | 5059篇 |
国内免费 | 10123篇 |
专业分类
化学 | 47433篇 |
晶体学 | 984篇 |
力学 | 1695篇 |
综合类 | 884篇 |
数学 | 11439篇 |
物理学 | 16425篇 |
出版年
2024年 | 89篇 |
2023年 | 665篇 |
2022年 | 1013篇 |
2021年 | 2318篇 |
2020年 | 1721篇 |
2019年 | 1777篇 |
2018年 | 1494篇 |
2017年 | 1773篇 |
2016年 | 2095篇 |
2015年 | 1858篇 |
2014年 | 2630篇 |
2013年 | 4442篇 |
2012年 | 4058篇 |
2011年 | 3672篇 |
2010年 | 3192篇 |
2009年 | 3986篇 |
2008年 | 4147篇 |
2007年 | 4366篇 |
2006年 | 3470篇 |
2005年 | 2787篇 |
2004年 | 2549篇 |
2003年 | 2259篇 |
2002年 | 4640篇 |
2001年 | 2108篇 |
2000年 | 1658篇 |
1999年 | 1417篇 |
1998年 | 1311篇 |
1997年 | 966篇 |
1996年 | 929篇 |
1995年 | 894篇 |
1994年 | 863篇 |
1993年 | 769篇 |
1992年 | 805篇 |
1991年 | 556篇 |
1990年 | 464篇 |
1989年 | 356篇 |
1988年 | 339篇 |
1987年 | 282篇 |
1986年 | 276篇 |
1985年 | 379篇 |
1984年 | 268篇 |
1983年 | 171篇 |
1982年 | 326篇 |
1981年 | 483篇 |
1980年 | 439篇 |
1979年 | 480篇 |
1978年 | 376篇 |
1977年 | 286篇 |
1976年 | 246篇 |
1973年 | 156篇 |
排序方式: 共有10000条查询结果,搜索用时 97 毫秒
151.
Continuous dependence on a modelling parameter is established for solutions of a problem for a complex Ginzburg–Landau equation. A homogenizing boundary condition is also used to discuss the continuous dependence results. We derive a priori estimates that indicate that solutions depend continuously on a parameter in the governing differential equation. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
152.
Aldehydes undergo smooth conjugate addition to α,β-unsaturated ketones in the presence of 5-(2-hydroxyethyl)-1,3-thiazolium halides and DBU adsorbed onto the surface of basic alumina under microwave irradiation and solvent-free conditions to afford 1,4-diketones in enhanced yields and reduced reaction times compared to conventional methods. 相似文献
153.
两相同部件温贮备可修的人机系统解的性质分析 总被引:5,自引:1,他引:4
郭卫华 《数学的实践与认识》2003,33(7):88-95
本文首先用强连续算子半群理论证明了两相同部件温贮备可修的人机系统动态非负解的存在唯一性 ,然后证明了 0是系统主算子的本征值 ,并得到 0本征值对应的本征向量是正的 ,从而系统存在稳态正解 . 相似文献
154.
J. T. Hoeft M. Polcik D. I. Sayago M. Kittel R. Terborg R. L. Toomes J. Robinson D. P. Woodruff M. Pascal G. Nisbet C. L. A. Lamont 《Surface science》2003,540(2-3):441-456
The local adsorption geometry of CO adsorbed in different states on Ni(1 0 0) and on Ni(1 0 0) precovered with atomic hydrogen has been determined by C 1s (and O 1s) scanned-energy mode photoelectron diffraction, using the photoelectron binding energy changes to characterise the different states. The results confirm previous spectroscopic assignments of local atop and bridge sites both with and without coadsorbed hydrogen. The measured Ni–C bondlengths for the Ni(1 0 0)/CO states show an increase of 0.16 ± 0.04 Å in going from atop to bridge sites, while comparison with similar results for Ni(1 1 1)/CO for threefold coordinated adsorption sites show a further lengthening of the bond by 0.05 ± 0.04 Å. These changes in the Ni–CO chemisorption bondlength with bond order (for approximately constant adsorption energy) are consistent with the standard Pauling rules. However, comparison of CO adsorbed in the atop geometry with and without coadsorbed hydrogen shows that the coadsorption increases the Ni–C bondlength by only 0.06 ± 0.04 Å, despite the decrease in adsorption energy of a factor of 2 or more. This result is also reproduced by density functional theory slab calculations. The results of both the experiments and the density functional theory calculations show that CO adsorption onto the Ni(1 0 0)/H surface is accompanied by significant structural modification; the low desorption energy may then be attributed to the energy cost of this restructuring rather than weak local bonding. 相似文献
155.
Zhao Fang BAI Jin Chuan HOU 《数学学报(英文版)》2005,21(5):1167-1182
Let X be a (real or complex) Banach space with dimension greater than 2 and let B0(X) be the subspace of B(X) spanned by all nilpotent operators on X. We get a complete classification of surjective additive maps Ф on B0(X) which preserve nilpotent operators in both directions. In particular, if X is infinite-dimensional, we prove that Ф has the form either Ф(T) = cATA^-1 or Ф(T) = cAT'A^-1, where A is an invertible bounded linear or conjugate linear operator, c is a scalar, T' denotes the adjoint of T. As an application of these results, we show that every additive surjective map on B(X) preserving spectral radius has a similar form to the above with |c| = 1. 相似文献
156.
François Ledrappier Mark Pollicott 《Bulletin of the Brazilian Mathematical Society》2005,36(2):143-176
In this paper we study the ergodic properties of the linear action of lattices Γ of SL(2,ℚp) on ℚp × ℚp and distribution results for orbits of Γ. Following Serre, one can define a “geodesic flow” for an associated tree (actually
associated to GL(2,ℚp)). The approach we use is based on an extension of this approach to “frame flows” which are a natural compact group extension
of the geodesic flow. 相似文献
157.
The main purpose of this paper is to use a mean value theorem of Dirichlet L-functions to study the asymptotic property of a hybrid mean value of a generalized Cochrane sum, and give an interesting mean value formula.2000 Mathematics Subject Classification: Primary—11F20; Secondary—11F99 相似文献
158.
The content of residual monomers is one of the most important characteristics of polymer dispersions. As a result of the similar physicochemical parameters of ethyl acrylate and methyl methacrylate, it is very difficult to determine the residual monomers in acrylate dispersions obtained by emulsion polymerization of both monomers. Gas chromatography with capillary columns, however, permits separation of these monomers and their quantitative determination in acrylate dispersions. 相似文献
159.
非负矩阵与有向图的谱半径 总被引:2,自引:0,他引:2
本文给出非负矩阵的谱半径的上界、下界,由此给出有向图的谱半径的界. 相似文献
160.
It is shown that the potential perturbation that shifts a chosen standing wave in space is a block of potential barrier and well for every wave bump between neighbouring knots. The algorithms shifting the range of the primary localization of a chosen bound state in a potential well of finite width are as well applicable to the scattering functions if states of the continuous spectrum are considered as bound states normalized to unity but distributed on an infinite interval with vanishing density. The potential perturbations of the same type on the half-axis concentrate the scattering wave at the origin, thus creating a bound state embedded into the continuous spectrum (zero width resonance). 相似文献