全文获取类型
收费全文 | 124687篇 |
免费 | 9374篇 |
国内免费 | 7752篇 |
专业分类
化学 | 44919篇 |
晶体学 | 1983篇 |
力学 | 6860篇 |
综合类 | 1085篇 |
数学 | 36077篇 |
物理学 | 50889篇 |
出版年
2023年 | 551篇 |
2022年 | 1998篇 |
2021年 | 1869篇 |
2020年 | 1566篇 |
2019年 | 1914篇 |
2018年 | 1713篇 |
2017年 | 1500篇 |
2016年 | 1607篇 |
2015年 | 1608篇 |
2014年 | 2746篇 |
2013年 | 4971篇 |
2012年 | 3020篇 |
2011年 | 3925篇 |
2010年 | 4281篇 |
2009年 | 9333篇 |
2008年 | 10387篇 |
2007年 | 8930篇 |
2006年 | 7781篇 |
2005年 | 5566篇 |
2004年 | 5303篇 |
2003年 | 5316篇 |
2002年 | 8317篇 |
2001年 | 4924篇 |
2000年 | 4501篇 |
1999年 | 4199篇 |
1998年 | 3606篇 |
1997年 | 2728篇 |
1996年 | 2467篇 |
1995年 | 2776篇 |
1994年 | 2717篇 |
1993年 | 2188篇 |
1992年 | 1725篇 |
1991年 | 1250篇 |
1990年 | 1060篇 |
1989年 | 920篇 |
1988年 | 864篇 |
1987年 | 636篇 |
1986年 | 434篇 |
1985年 | 1283篇 |
1984年 | 901篇 |
1983年 | 671篇 |
1982年 | 959篇 |
1981年 | 1109篇 |
1980年 | 996篇 |
1979年 | 888篇 |
1978年 | 792篇 |
1977年 | 669篇 |
1976年 | 647篇 |
1974年 | 419篇 |
1973年 | 565篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
Camillo Costantini 《Topology and its Applications》2006,153(7):1056-1078
For X a metrizable space and (Y,ρ) a metric space, with Y pathwise connected, we compute the density of (C(X,(Y,ρ)),σ)—the space of all continuous functions from X to (Y,ρ), endowed with the supremum metric σ. Also, for (X,d) a metric space and (Y,‖⋅‖) a normed space, we compute the density of (UC((X,d),(Y,ρ)),σ) (the space of all uniformly continuous functions from (X,d) to (Y,ρ), where ρ is the metric induced on Y by ‖⋅‖). We also prove that the latter result extends only partially to the case where (Y,ρ) is an arbitrary pathwise connected metric space.To carry such an investigation out, the notions of generalized compact and generalized totally bounded metric space, introduced by the author and A. Barbati in a former paper, turn out to play a crucial rôle. Moreover, we show that the first-mentioned concept provides a precise characterization of those metrizable spaces which attain their extent. 相似文献
102.
Michael Carr 《Topology and its Applications》2006,153(12):2155-2168
Given a graph Γ, we construct a simple, convex polytope, dubbed graph-associahedra, whose face poset is based on the connected subgraphs of Γ. This provides a natural generalization of the Stasheff associahedron and the Bott-Taubes cyclohedron. Moreover, we show that for any simplicial Coxeter system, the minimal blow-ups of its associated Coxeter complex has a tiling by graph-associahedra. The geometric and combinatorial properties of the complex as well as of the polyhedra are given. These spaces are natural generalizations of the Deligne-Knudsen-Mumford compactification of the real moduli space of curves. 相似文献
103.
Yevhen Zelenyuk 《Topology and its Applications》2006,153(14):2382-2385
We introduce the notion of a partially selective ultrafilter and prove that (a) if G is an extremally disconnected topological group and p is a converging nonprincipal ultrafilter on G containing a countable discrete subset, then p is partially selective, and (b) the existence of a nonprincipal partially selective ultrafilter on a countable set implies the existence of a P-point in ω∗. Thus it is consistent with ZFC that there is no extremally disconnected topological group containing a countable discrete nonclosed subset. 相似文献
104.
Addition of aqueous hydrogen peroxide significantly accelerates the substitution reactions of hydroxide salts with haloarenes bearing electron withdrawing substituents. A similar effect is observed in the reactions of hydroxide salts with halogenated heteroarenes. Reactions are carried out in water or water-THF at ambient temperature or at 50-60 °C. 相似文献
105.
N. Kiriushcheva 《Annals of Physics》2006,321(4):958-986
It is shown that the Lagrangian reduction, in which solutions of equations of motion that do not involve time derivatives are used to eliminate variables, leads to results quite different from the standard Dirac treatment of the first-order form of the Einstein-Hilbert action when the equations of motion correspond to the first class constraints. A form of the first-order formulation of the Einstein-Hilbert action which is more suitable for the Dirac approach to constrained systems is presented. The Dirac and reduced approaches are compared and contrasted. This general discussion is illustrated by a simple model in which all constraints and the gauge transformations which correspond to first class constraints are completely worked out using both methods to demonstrate explicitly their differences. These results show an inconsistency in the previous treatment of the first-order Einstein-Hilbert action which is likely responsible for problems with its canonical quantization. 相似文献
106.
General coordinate invariance and conformal invariance in nonrelativistic physics: Unitary Fermi gas
D.T. Son 《Annals of Physics》2006,321(1):197-224
We show that the Lagrangian for interacting nonrelativistic particles can be coupled to an external gauge field and metric tensor in a way that exhibits a nonrelativistic version of general coordinate invariance. We explore the consequences of this invariance on the example of the degenerate Fermi gas at infinite scattering length, where conformal invariance also plays an important role. We find the most general effective Lagrangian consistent with both general coordinate and conformal invariance to leading and next-to-leading orders in the momentum expansion. At the leading order the Lagrangian contains one phenomenological constant and reproduces the results of the Thomas-Fermi theory and superfluid hydrodynamics. At the next-to-leading order there are two additional constants. We express various physical quantities through these constants. 相似文献
107.
108.
M.F. Al-Kuhaili 《Journal of luminescence》2006,117(2):209-216
Thin films of sodium salicylate were deposited by spin coating from a solution prepared by dissolving sodium salicylate in methanol. The films were characterized by X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, UV-visible spectroscopy and spectrofluorometry. The films were crystalline with a strong blue fluorescence peak at an emission wavelength of 419.3 nm. The influence of solution concentration, spin speed and annealing temperature on the fluorescence intensity was studied. Optimum results were obtained with a solution whose concentration was 2.5 M. It was found that lower spin speed resulted in higher fluorescence intensity. Moreover, the fluorescence intensity decreased as the annealing temperature was increased. The durability of the films over a period of 30 days was also investigated, and films annealed at higher temperatures were found to be less degraded with time. 相似文献
109.
110.
GAO Jing ZHOU Xiaohua CHEN Xun Chongqing University Chemical Engineering Department Chongqing China 《Chinese Journal of Reactive Polymers》2006,(2)
1. INTRODUCTION In the process of coking plant, about 30%~35% sulfur is transformed to H2S and some other sulfide, which form impurity in coal gas together with NH3 and HCN. Only 0.1% H2S containing in air can lead to die, so it is very important to carry on desulphurization and decyanation with coal gas [1~3]. Currently desulphurization and decyanation craft technique have Dry Oxidation Technology, Wet Oxidation Technology and Liquid Absorption Technology [2] three main kinds. The… 相似文献