全文获取类型
收费全文 | 15528篇 |
免费 | 399篇 |
国内免费 | 253篇 |
专业分类
化学 | 1008篇 |
晶体学 | 24篇 |
力学 | 214篇 |
综合类 | 25篇 |
数学 | 13813篇 |
物理学 | 1096篇 |
出版年
2023年 | 30篇 |
2022年 | 71篇 |
2021年 | 58篇 |
2020年 | 72篇 |
2019年 | 414篇 |
2018年 | 488篇 |
2017年 | 249篇 |
2016年 | 166篇 |
2015年 | 191篇 |
2014年 | 483篇 |
2013年 | 988篇 |
2012年 | 552篇 |
2011年 | 919篇 |
2010年 | 843篇 |
2009年 | 1162篇 |
2008年 | 1217篇 |
2007年 | 1160篇 |
2006年 | 901篇 |
2005年 | 560篇 |
2004年 | 501篇 |
2003年 | 465篇 |
2002年 | 357篇 |
2001年 | 325篇 |
2000年 | 281篇 |
1999年 | 378篇 |
1998年 | 316篇 |
1997年 | 248篇 |
1996年 | 328篇 |
1995年 | 322篇 |
1994年 | 350篇 |
1993年 | 249篇 |
1992年 | 181篇 |
1991年 | 141篇 |
1990年 | 101篇 |
1989年 | 118篇 |
1988年 | 75篇 |
1987年 | 73篇 |
1986年 | 76篇 |
1985年 | 118篇 |
1984年 | 94篇 |
1983年 | 64篇 |
1982年 | 102篇 |
1981年 | 92篇 |
1980年 | 69篇 |
1979年 | 37篇 |
1978年 | 48篇 |
1977年 | 42篇 |
1976年 | 51篇 |
1974年 | 18篇 |
1973年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
锰结核中硅,铝,铁,镁,磷,钾,锰,钛的XRFA 总被引:1,自引:0,他引:1
本文叙述了用XRF分析锰结核中Si、Al、Fe、Mg、P、K、Mn和Ti的方法。按照通常锰结核的主次成分制备6个人工合成标准,根据Sherman方程计算了已知成分(二元系统)的相对强度。用L-T方求得了互致元素校正的理论α系数(基本的、混合的、修正的),用DATAFLEX151B计算机以BASIC语言汇了“PRA,APU”计算机程序。然后进行非线性回归分析了锰结核样品得到了满意的结果。 相似文献
62.
Sans résumé
相似文献
相似文献
63.
Summary We prove convergence and error estimates in Sobolev spaces for the collocation method with tensor product splines for strongly elliptic pseudodifferential equations on the torus. Examples of applications include elliptic partial differential equations with periodic boundary conditions but also the classical boundary integral operators of potential theory on torus-shaped domains in three or more dimensions. For odd-degree splines, we prove convergence of nodal collocation for any strongly elliptic operator. For even-degree splines and midpoint collocation, we find an additional condition for the convergence which is satisfied for the classical boundary integral operators. Our analysis is a generalization to higher dimensions of the corresponding analysis of Arnold and Wendland [4]. 相似文献
64.
Pascal Cherrier 《Bulletin des Sciences Mathématiques》2007,131(4):375-396
We study a parabolic version of a system of Von Karman type on a compact Kähler manifold of arbitrary dimension. We provide local in time regular solutions, which can be extended to global bounded ones if the data of the problem are small. 相似文献
65.
Daisuke Kishimoto 《Topology and its Applications》2007,154(7):1465-1469
By calculating certain generalized cohomology theory, lower bounds for the L-S category of quaternionic Stiefel manifolds are given. 相似文献
66.
Helly and Hadwiger type theorems for transversal m-flats to families of flats and, respectively, convex sets of dimension n are proved in the case of general position. The proofs rely on Helly type theorems for “linear partitions” and “convex partitions,” so that a general theory of Helly numbers is also developed. 相似文献
67.
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
68.
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
69.
70.
Marilyn Breen 《Journal of Geometry》1989,36(1-2):8-16
LetS be a compact, simply connected set inR
2. If every boundary point ofS is clearly visible viaS from at least one of the three pointsa, b, c, thenS is a union of three starshaped sets whose kernels containa, b, c, respectively. The result fails when the number three is replaced by four.As a partial converse, ifS is a union of three starshaped sets whose kernels containa, b, c, respectively, then the set of points in the boundary ofS clearly visible from at least one ofa, b, orc is dense in the boundary ofS.Supported in part by NSF grant DMS-8705336. 相似文献