全文获取类型
收费全文 | 73245篇 |
免费 | 6609篇 |
国内免费 | 4861篇 |
专业分类
化学 | 26287篇 |
晶体学 | 210篇 |
力学 | 5246篇 |
综合类 | 1346篇 |
数学 | 32184篇 |
物理学 | 19442篇 |
出版年
2023年 | 728篇 |
2022年 | 1476篇 |
2021年 | 2138篇 |
2020年 | 1617篇 |
2019年 | 1707篇 |
2018年 | 1503篇 |
2017年 | 1811篇 |
2016年 | 2058篇 |
2015年 | 1879篇 |
2014年 | 2969篇 |
2013年 | 4865篇 |
2012年 | 3206篇 |
2011年 | 3796篇 |
2010年 | 3409篇 |
2009年 | 4273篇 |
2008年 | 4632篇 |
2007年 | 4820篇 |
2006年 | 3899篇 |
2005年 | 2919篇 |
2004年 | 2704篇 |
2003年 | 2687篇 |
2002年 | 5044篇 |
2001年 | 2429篇 |
2000年 | 1890篇 |
1999年 | 1637篇 |
1998年 | 1555篇 |
1997年 | 1256篇 |
1996年 | 1166篇 |
1995年 | 1035篇 |
1994年 | 855篇 |
1993年 | 859篇 |
1992年 | 788篇 |
1991年 | 653篇 |
1990年 | 505篇 |
1989年 | 378篇 |
1988年 | 424篇 |
1987年 | 313篇 |
1986年 | 321篇 |
1985年 | 446篇 |
1984年 | 343篇 |
1983年 | 216篇 |
1982年 | 362篇 |
1981年 | 535篇 |
1980年 | 477篇 |
1979年 | 517篇 |
1978年 | 410篇 |
1977年 | 314篇 |
1976年 | 254篇 |
1974年 | 120篇 |
1973年 | 167篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
291.
Lévy processes in matrix Lie groups are studied. Subordination (random time change) is used to show that quasi-invariance of the Brownian motion in a Lie group induces absolute continuity of the laws of the corresponding pure jump processes. These results are applied to several examples which are discussed in detail. 相似文献
292.
当s∈ R,0,〈q, p〈∈∞,0,〈β≤∞且 max{-n/q,-nδ2/qδ1}〈a时,定义了加权Herz—type Triebel-Lizorkin空间kq^q,pF^s β(R^n,ω1,ω2)和Kq^a,pF^sβ(R^n,ω1,ω2),并给出这些空间的一些特征及在这些空间上的Hard—Littlewood极大算子不等式. 相似文献
293.
Roberto E. Madariaga-Garcia 《Topology and its Applications》2007,154(7):1470-1480
Tkachenko showed in 1990 the existence of a countably compact group topology on the free Abelian group of size c using CH. Koszmider, Tomita and Watson showed in 2000 the existence of a countably compact group topology on the free Abelian group of size c2 using a forcing model in which CH holds.Wallace's question from 1955, asks whether every both-sided cancellative countably compact semigroup is a topological group. A counterexample to Wallace's question has been called a Wallace semigroup. In 1996, Robbie and Svetlichny constructed a Wallace semigroup under CH. In the same year, Tomita constructed a Wallace semigroup from MAcountable.In this note, we show that the examples of Tkachenko, Robbie and Svetlichny, and Koszmider, Tomita and Watson can be obtained using a family of selective ultrafilters. As a corollary, the constructions presented here are compatible with the total failure of Martin's Axiom. 相似文献
294.
We construct cellular homotopy theories for categories of simplicial presheaves on small Grothendieck sites and discuss applications to the motivic homotopy category of Morel and Voevodsky. 相似文献
295.
屋顶绿化对提高城市空气质量、减少“热岛效应”、改善居住环境有积极的意义,但其灌溉环节与普通园林绿化灌溉相比有更高的要求.为了增强屋顶灌溉的科学性,根据其特点提出了建立自动灌溉系统的设想,并对灌溉过程建立了混杂自动机模型,从离散事件动态系统与连续变量动态系统的角度共同描述了自动灌溉的过程,最后给出了自动灌溉系统的工程设计方案,对屋顶绿化自动化、精细化程度的提高具有一定的启示意义. 相似文献
296.
The main results of the paper are as follows: covering characterizations of wQN-spaces, covering characterizations of QN-spaces and a theorem saying that Cp(X) has the Arkhangel'ski?ˇ property (α1) provided that X is a QN-space. The latter statement solves a problem posed by M. Scheepers [M. Scheepers, Cp(X) and Arhangel'ski?ˇ's αi-spaces, Topology Appl. 89 (1998) 265-275] and for Tychonoff spaces was independently proved by M. Sakai [M. Sakai, The sequence selection properties of Cp(X), Preprint, April 25, 2006]. As the most interesting result we consider the equivalence that a normal topological space X is a wQN-space if and only if X has the property S1(Γshr,Γ). Moreover we show that X is a QN-space if and only if Cp(X) has the property (α0), and for perfectly normal spaces, if and only if X has the covering property (β3). 相似文献
297.
298.
D.L. Skuratov Yu.L. Ratis I.A. Selezneva J. Pérez P. Fernández de Córdoba J.F. Urchueguía 《Applied Mathematical Modelling》2007
This paper deals with modelling the workpiece temperature field produced during the grinding process. The proposed model is given in terms of a two-dimensional boundary-value problem where the interdependence among the grinding wheel, the workpiece and the coolant is described by two variable functions in the boundary condition. An explicit integral form solution is constructed using the Laplace and Fourier transforms and the Green’s function method. 相似文献
299.
This paper deals with the small-angle neutron scattering (SANS) investigation on solution-quenched PH13-8 Mo stainless steel.
From the nature of the variation of the functionality of the profiles for varying specimen thickness and also from the transmission
electron microscopy (TEM), it has been established that the small-angle scattering signal predominantly originates from the
block-like metallic carbide precipitates in the specimen. The contribution due to double Bragg reflection is not significant
in the present case. The single scattering profile has been extracted from the experimental profiles corresponding to different
values of specimen thickness. In order to avoid complexity and non-uniqueness of the multi-parameter minimization for randomly
oriented polydisperse block-like precipitate model, the data have been analyzed assuming randomly oriented polydisperse cylindrical
particle model with a locked aspect ratio. 相似文献
300.