全文获取类型
收费全文 | 50607篇 |
免费 | 1732篇 |
国内免费 | 1689篇 |
专业分类
化学 | 15576篇 |
晶体学 | 468篇 |
力学 | 1081篇 |
综合类 | 117篇 |
数学 | 24929篇 |
物理学 | 11857篇 |
出版年
2023年 | 468篇 |
2022年 | 458篇 |
2021年 | 420篇 |
2020年 | 621篇 |
2019年 | 1194篇 |
2018年 | 945篇 |
2017年 | 739篇 |
2016年 | 701篇 |
2015年 | 768篇 |
2014年 | 1147篇 |
2013年 | 2619篇 |
2012年 | 1418篇 |
2011年 | 2640篇 |
2010年 | 1857篇 |
2009年 | 2636篇 |
2008年 | 3070篇 |
2007年 | 2970篇 |
2006年 | 2460篇 |
2005年 | 1832篇 |
2004年 | 2079篇 |
2003年 | 2075篇 |
2002年 | 2739篇 |
2001年 | 2242篇 |
2000年 | 2079篇 |
1999年 | 2220篇 |
1998年 | 1896篇 |
1997年 | 1288篇 |
1996年 | 989篇 |
1995年 | 756篇 |
1994年 | 676篇 |
1993年 | 460篇 |
1992年 | 414篇 |
1991年 | 315篇 |
1990年 | 377篇 |
1989年 | 367篇 |
1988年 | 265篇 |
1987年 | 287篇 |
1986年 | 296篇 |
1985年 | 429篇 |
1984年 | 342篇 |
1983年 | 188篇 |
1982年 | 332篇 |
1981年 | 412篇 |
1980年 | 344篇 |
1979年 | 186篇 |
1978年 | 269篇 |
1977年 | 202篇 |
1976年 | 163篇 |
1975年 | 96篇 |
1974年 | 87篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
Chuanming Zong 《Monatshefte für Mathematik》2002,134(3):247-255
In this article we study the simultaneous packing and covering constants of two-dimensional centrally symmetric convex domains.
Besides an identity result between translative case and lattice case and a general upper bound, exact values for some special
domains are determined. Similar to Mahler and Reinhardt’s result about packing densities, we show that the simultaneous packing
and covering constant of an octagon is larger than that of a circle.
(Received 17 January 2001; in revised form 13 July 2001) 相似文献
32.
Kunyu Guo 《Journal of Functional Analysis》2004,213(2):380-411
This paper mainly concerns defect operators and defect functions of Hardy submodules, Bergman submodules over the unit ball, and Hardy submodules over the polydisk. The defect operator (function) carries key information about operator theory (function theory) and structure of analytic submodules. The problem when a submodule has finite defect is attacked for both Hardy submodules and Bergman submodules. Our interest will be in submodules generated by polynomials. The reason for choosing such submodules is to understand the interaction of operator theory, function theory and algebraic geometry. 相似文献
33.
Sauer, Shelah, Vapnik and Chervonenkis proved that if a set system on n vertices contains many sets, then the set system has full trace on a large set. Although the restriction on the size of the
groundset cannot be lifted, Frankl and Pach found a trace structure that is guaranteed to occur in uniform set systems even
if we do not bound the size of the groundset. In this note we shall give three sequences of structures such that every set
system consisting of sufficiently many sets contains at least one of these structures with many sets. 相似文献
34.
The graph-theoretic operation of rooted subtree prune and regraft is increasingly being used as a tool for understanding and modelling reticulation events in evolutionary biology. In this paper, we show that computing the rooted subtree prune and regraft distance between two rooted binary phylogenetic trees on the same label set is NP-hard. This resolves a longstanding open problem. Furthermore, we show that this distance is fixed parameter tractable when parameterised by the distance between the two trees.Received March 16, 2004 相似文献
35.
We extend the matrix version of Cochran's statistical theorem to outer inverses of a matrix. As applications, we investigate the Wishartness and independence of matrix quadratic forms for Kronecker product covariance structures. 相似文献
36.
Andrei K. Lerner 《Archiv der Mathematik》2005,85(6):538-543
We show that the Hardy-Littlewood maximal operator and a class of Calderón-Zygmund singular integrals satisfy the strong type
modular inequality in variable Lp spaces if and only if the variable exponent p(x) ∼ const.
Received: 15 September 2004 相似文献
37.
In this paper we show that for a given 3-manifold and a given Heegaard splitting there are finitely many preferred decomposing systems of 3g−3 disjoint essential disks. These are characterized by a combinatorial criterion which is a slight strengthening of Casson-Gordon's rectangle condition. This is in contrast to fact that in general there can exist infinitely many such systems of disks which satisfy just the Casson-Gordon rectangle condition. 相似文献
38.
39.
40.
R. Pizzoferrato L. Lagonigro T. Ziller A. Di Carlo R. Paolesse F. Mandoj A. Ricci C. Lo Sterzo 《Chemical physics》2004,300(1-3):217-225
We study the infrared emission at 1.54 μm of an organolanthanide complex, Er(III)-tetraphenylporphyrin [Er(TPP)acac], both as a result of direct optical excitation and via energy transfer from host π-conjugate polymers of type poly(arylene–ethynylene) [PAE]. In the first case, the emission of the neat complex is characterized in inert transparent materials and a value of the quantum yield at 1.54 μm φIR=4×10−4 is measured. Then, fluorescence resonance transfer is investigated in blends of Er(TPP)acac with PAEs by monitoring the quenching of the polymer fluorescence along with the enhancement of both the visible emission of the ligand and the near-infrared band of Er3+. These different procedures allow a detailed analysis of the transfer efficiency within a specific implementation of the Förster model for polymeric donors. The experimental values of the critical radius R0, ranging from 1.3 to 2.5 nm for the different blends, are in good agreement with theory for a wide interval of the physical and spectroscopic parameters. This suggests that other mechanisms for excitation transfer do not play a significant role in these materials. 相似文献