全文获取类型
收费全文 | 6216篇 |
免费 | 167篇 |
国内免费 | 44篇 |
专业分类
化学 | 4647篇 |
晶体学 | 67篇 |
力学 | 143篇 |
数学 | 641篇 |
物理学 | 929篇 |
出版年
2023年 | 26篇 |
2022年 | 48篇 |
2021年 | 50篇 |
2020年 | 76篇 |
2019年 | 94篇 |
2018年 | 65篇 |
2017年 | 45篇 |
2016年 | 128篇 |
2015年 | 107篇 |
2014年 | 119篇 |
2013年 | 274篇 |
2012年 | 372篇 |
2011年 | 464篇 |
2010年 | 220篇 |
2009年 | 190篇 |
2008年 | 396篇 |
2007年 | 446篇 |
2006年 | 442篇 |
2005年 | 434篇 |
2004年 | 397篇 |
2003年 | 314篇 |
2002年 | 280篇 |
2001年 | 92篇 |
2000年 | 72篇 |
1999年 | 73篇 |
1998年 | 84篇 |
1997年 | 57篇 |
1996年 | 83篇 |
1995年 | 62篇 |
1994年 | 58篇 |
1993年 | 43篇 |
1992年 | 42篇 |
1991年 | 48篇 |
1990年 | 41篇 |
1989年 | 36篇 |
1988年 | 36篇 |
1987年 | 30篇 |
1986年 | 30篇 |
1985年 | 54篇 |
1984年 | 52篇 |
1983年 | 48篇 |
1982年 | 46篇 |
1981年 | 48篇 |
1980年 | 44篇 |
1979年 | 43篇 |
1978年 | 52篇 |
1977年 | 40篇 |
1976年 | 37篇 |
1975年 | 24篇 |
1974年 | 23篇 |
排序方式: 共有6427条查询结果,搜索用时 31 毫秒
11.
Brian Lucena 《Discrete Applied Mathematics》2007,155(8):1055-1065
One consequence of the graph minor theorem is that for every k there exists a finite obstruction set Obs(TW?k). However, relatively little is known about these sets, and very few general obstructions are known. The ones that are known are the cliques, and graphs which are formed by removing a few edges from a clique. This paper gives several general constructions of minimal forbidden minors which are sparse in the sense that the ratio of the treewidth to the number of vertices n does not approach 1 as n approaches infinity. We accomplish this by a novel combination of using brambles to provide lower bounds and achievable sets to demonstrate upper bounds. Additionally, we determine the exact treewidth of other basic graph constructions which are not minimal forbidden minors. 相似文献
12.
13.
14.
Brian Jefferies 《Journal d'Analyse Mathématique》1995,65(1):125-144
Set functions which are unbounded on an algebra of sets arise naturally by taking the products of bounded operators and spectral
measures acting on a space of square integrable functions. The purpose of this note is to show that, provided a certain regularity
condition is satisfied, there is a natural integration structure associated with such a set function and an auxiliary measure,
so providing a complete space of integrable functions. Several examples illustrate the extent and limitations of the approach. 相似文献
15.
Brian Hartwig 《Linear algebra and its applications》2007,422(1):219-235
Recently Terwilliger and the present author found a presentation for the three-point sl2 loop algebra via generators and relations. To obtain this presentation we defined a Lie algebra ? by generators and relations and displayed an isomorphism from ? to the three-point sl2 loop algebra. In this paper we classify the finite-dimensional irreducible ?-modules. 相似文献
16.
Brian A. Hagler 《Linear algebra and its applications》2007,422(1):100-118
Definitions, theorems and examples are established for a general model of Laurent polynomial spaces and ordered orthogonal Laurent polynomial sequences, ordered with respect to ordered bases and orthogonal with respect to inner products ·=L°⊙ decomposed into transition functional ⊙ and strong moment functional, or, more generally, sample functional L couplings. Under this formulation that is shown to subsume those in the existing literature, new fundamental results are produced, including necessary and sufficient conditions for ordered OLPS to be sequences of nth numerators of continued fractions, in contrast to the classical result concerning nth denominators which is shown to hold only in special cases. 相似文献
17.
The intention of the research reported here was to seek explanations for low achievement in school mathematics, as conventionally assessed, that derive from broad understandings of mathematics as social. Such a broad social perspective can provide explanations for low achievement, which could lead to different understandings and hence to different teaching approaches. This study centered on 5- to 8-year-old children from a White working-class area in England. Data were collected during visits to the children in school, in their homes, and in the broader community over a 3-year period. Parents, teachers, and other professionals in the broad school context were interviewed, and data were also collected from school documents and policy statements. Interpretations of these data in terms of ways of understanding children's achievements in school mathematics are put forward. The potential effects of these factors on low schooled numeracy attainment are discussed, together with some possible strategic implications for practice and policy. 相似文献
18.
Roberto D. Galvão Luis Gonzalo Acosta Espejo Brian Boffey 《Annals of Operations Research》2006,143(1):31-44
A study has been carried out aimed at reducing perinatal mortality in the municipality of Rio de Janeiro through a better
distribution of health care facilities. The algorithmic aspects are detailed elsewhere and here the emphasis is on practical
issues and difficulties encountered.
A 3-level hierarchical model was developed. Both uncapacitated and capacitated versions are briefly described together with
some results based on actual data. The project brought to light many contradictions between OR theory and practice in developing
countries and, unfortunately, the models developed were not implemented by the municipality health authorities. Possible reasons
for this outcome are analysed. 相似文献
19.
20.
The thermolysis of dicarbonylcyclopentadienyliron dimer in a sealed tube at 300°C has been reported to produce ferrocene, carbon monoxide, carbon dioxide, cyclopentadiene and elemental iron. We observe in addition to these products the production of biferrocene and elemental carbon. Thermolysis of carbonylcyclopentadienyliron tetramer (produced from the dimer by thermolysis in refluxing xylene) produces ferrocene, iron and carbon monoxidre; no biferrocene, carbon dioxide or elemental carbon are produced. A scheme is proposed to account for these products. 相似文献