全文获取类型
收费全文 | 15175篇 |
免费 | 633篇 |
国内免费 | 67篇 |
专业分类
化学 | 10466篇 |
晶体学 | 106篇 |
力学 | 440篇 |
数学 | 2479篇 |
物理学 | 2384篇 |
出版年
2023年 | 111篇 |
2022年 | 92篇 |
2021年 | 270篇 |
2020年 | 291篇 |
2019年 | 285篇 |
2018年 | 291篇 |
2017年 | 243篇 |
2016年 | 582篇 |
2015年 | 483篇 |
2014年 | 483篇 |
2013年 | 982篇 |
2012年 | 1026篇 |
2011年 | 1133篇 |
2010年 | 618篇 |
2009年 | 571篇 |
2008年 | 1012篇 |
2007年 | 970篇 |
2006年 | 883篇 |
2005年 | 791篇 |
2004年 | 642篇 |
2003年 | 562篇 |
2002年 | 554篇 |
2001年 | 279篇 |
2000年 | 251篇 |
1999年 | 180篇 |
1998年 | 157篇 |
1997年 | 160篇 |
1996年 | 185篇 |
1995年 | 119篇 |
1994年 | 139篇 |
1993年 | 141篇 |
1992年 | 118篇 |
1991年 | 82篇 |
1990年 | 83篇 |
1989年 | 77篇 |
1988年 | 65篇 |
1987年 | 65篇 |
1986年 | 51篇 |
1985年 | 102篇 |
1984年 | 116篇 |
1983年 | 74篇 |
1982年 | 79篇 |
1981年 | 58篇 |
1980年 | 62篇 |
1979年 | 38篇 |
1978年 | 52篇 |
1977年 | 43篇 |
1976年 | 25篇 |
1975年 | 28篇 |
1974年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 406 毫秒
81.
We exhibit a probabilistic algorithm which computes a rational point of an absolutely irreducible variety over a finite field defined by a reduced regular sequence. Its time-space complexity is roughly quadratic in the logarithm of the cardinality of the field and a geometric invariant of the input system. This invariant, called the degree, is bounded by the Bézout number of the system. Our algorithm works for fields of any characteristic, but requires the cardinality of the field to be greater than a quantity which is roughly the fourth power of the degree of the input variety.
82.
83.
Magnetic after-effects in vacancy-doped magnetite at room temperature are considered on the basis of a statistical thermodynamic treatment. In this paper we study the kinetics of a very small vacancy concentration distributed on the four non-equivalent octahedral sites of the inverse spinel structure. It is to be noted that satisfactory agreement is found between recent experimental results and the theoretical model. 相似文献
84.
Francisco-Javier Muñoz-Delgado Victoriano Ramirez-González Paul Sablonnière 《分析论及其应用》1995,11(1):62-71
In this work we study linear polynomial operators preserving some consecutive i-convexities and leaving invariant the polynomials
up to a certain degree. First, we study the existence of an incom patibility between the conservation of certain i-convexities
and the invariance of a space of polynomials. Interpolation properties are obtained and a theorem by Berens and DeVore about
the Bernstein's operator is extended. Finally, from these results a generalized Bernstein's operator is obtained.
This work was supported by Junta de Andalucia. Grupo de investigación: Matemática Aplicada. Código: 1107 相似文献
85.
In this note we treat some open problems of Heinrich on ultrapowers of locally convex spaces. In section 1 we investigate the localization of bounded sets in the full ultrapower of a locally convex space, in particular the coincidence of the full and the bounded ultrapower, mainly concentrating in the case of (DF)-spaces. In section 2 we provide a partial answer to a question of Heinrich on commutativity of strict inductive limits and ultrapowers. In section 3 we analyze the relation between some natural candidates for the notion of superreflexivity in the setting of Fréchet spaces. We give an example of a Fréchet-Schwartz space which is not the projective limit of a sequence of superreflexive Banach spaces. 相似文献
86.
Let X be a complex connected projective nonsingular algebraic surface endowed with an ample line bundle L, which is spanned by its global sections. Pairs (X, L) as above, with sectional genus g(X, L)=1+(L·(K
X
L))/2=3 are classified by means of the main techniques of adjunction theory. 相似文献
87.
Antonio Pasini 《Geometriae Dedicata》1988,25(1-3):317-337
Let be a finite thick geometry of type Cn (n 4) or F4. We prove that is a building iff Aut() is flag-transitive. 相似文献
88.
Alvarez-Muñoz D Sáez M Lara-Martin PA Gómez-Parra A González-Mazo E 《Journal of chromatography. A》2004,1052(1-2):33-38
A new method has been developed for the determination of linear alkylbenzene sulfonates (LAS) from various marine organisms, and compared with Soxhlet extraction. The technique applied includes the use of pressurized liquid extraction (PLE) for the extraction stage, preconcentration of the samples, purification by solid-phase extraction (SPE) and analysis by liquid chromatography with fluorescence detection. The spiked concentrations were added to the samples (wet mass of the organisms: Solea senegalensis and Ruditapes semidecussatus), which were homogenized and agitated continuously for 25 h. The samples were extracted by pressurized hot solvent extraction using two different extraction temperatures (100 and 150 degrees C) and by traditional Soxhlet extraction. The best recoveries were obtained employing pressurized hot solvent extraction at 100 degrees C and varied in the range from 66.1 to 101.3% with a standard deviation of between 2 and 13. Detection limit was between 5 and 15 microg kg(-1) wet mass using HPLC-fluorescence detection. The analytical method developed in this paper has been applied for LAS determination in samples from a Flow-through exposure system with the objective of measuring the bioconcentration of this surfactant. 相似文献
89.
Antonio Tiripicchio Marisa Tiripicchio Camellini Mauro Ghedini Giuliano Dolcetti 《Transition Metal Chemistry》1980,5(1):102-105
Summary The structure of [Ir(NO)(phen)(PPh3)2][PF6]2 has been determined from x-ray diffractometer data. The compound crystallizes in space groupPnam with four molecules in a unit cell witha = 19.924(12),b = 14.793(9) andc = 16.348(9) A. Full-matrix least-squares refinement has led to a final R value of 0.061 for the 4796 observed reflections. The structure consists of well-separated ions, and the geometry around the metal is trigonal bipyramidal with nitrosyl and bidentate 1,10-phenanthroline (in spite of the very narrow bite angle of 75.8°) ligands occupying the equatorial positions and the triphenylphosphine ligands the axial positions. The cation has an imposed crystallographicm symmetry. Important bond lengths are as follows: Ir-P, 2.391(3): Ir-N (nitrosyl) 1.700(12): Ir-N (1,10-phenanthroline) 2.103(12) and 2.142(11): N-O, 1.201(18)A. The nitrosyl ligand is linear [Ir-N-O = 179.9(9)°] so that this complex can be formulated as an NO+ complex of iridium(I). 相似文献
90.
The synthesis and properties of perchlorobi-9-fluorenylidene, a highly twisted ethylene, are reported. It is a diamagnetic chlorocarbon. 相似文献