全文获取类型
收费全文 | 525篇 |
免费 | 25篇 |
国内免费 | 2篇 |
专业分类
化学 | 393篇 |
晶体学 | 4篇 |
力学 | 6篇 |
数学 | 62篇 |
物理学 | 87篇 |
出版年
2023年 | 13篇 |
2022年 | 9篇 |
2021年 | 28篇 |
2020年 | 25篇 |
2019年 | 31篇 |
2018年 | 33篇 |
2017年 | 19篇 |
2016年 | 24篇 |
2015年 | 22篇 |
2014年 | 19篇 |
2013年 | 37篇 |
2012年 | 40篇 |
2011年 | 54篇 |
2010年 | 34篇 |
2009年 | 24篇 |
2008年 | 30篇 |
2007年 | 20篇 |
2006年 | 32篇 |
2005年 | 17篇 |
2004年 | 18篇 |
2003年 | 6篇 |
2002年 | 9篇 |
2001年 | 2篇 |
2000年 | 3篇 |
1999年 | 1篇 |
1996年 | 2篇 |
排序方式: 共有552条查询结果,搜索用时 15 毫秒
41.
Nataliya Yu. Strutynska Vyacheslav N. Baumer Igor V. Zatovsky Artem A. Babaryk Nikolay S. Slobodyanik 《Acta Crystallographica. Section C, Structural Chemistry》2010,66(4):i39-i41
The complex phosphate tricaesium calcium iron bis(diphosphate), Cs3CaFe(P2O7)2, has been prepared by the flux method. Isolated [FeO5] and [CaO6] polyhedra are linked by two types of P2O7 groups into a three‐dimensional framework. The latter is penetrated by hexagonal channels along the a axis where three Cs atoms are located. Calculations of caesium Voronoi–Dirichlet polyhedra give coordination schemes for the three Cs atoms as [8 + 3], [9 + 1] and [9 + 4]. The structure includes features of both two‐ and three‐dimensional frameworks of caesium double pyrophosphates. 相似文献
42.
Sławomir Prucnal Marcin Turek Andrzej Drozdziel Krzysztof Pyszniak Artur Wójtowicz Sheng-Qiang Zhou Alohe Kanjilal Artem Shalimov Wolfgang Skorupa Jerzy Zuk 《Central European Journal of Physics》2011,9(2):338-343
The InAs quantum structures were formed in silicon by sequential ion implantation and subsequent thermal annealing. Two kinds of crystalline InAs nanostructures were successfully synthesized: nanodots (NDs) and nanopyramids (NPs). The peaks at 215 and 235 cm?1, corresponding to the transverse optical (TO) and longitudinal optical (LO) InAs single-phonon modes, respectively, are clearly visible in the Raman spectra. Moreover, the PL band at around 1.3 µm, due to light emission from InAs NDs with an average diameter 7±2 nm, was observed. The InAs NPs were found only in samples annealed for 20 ms at temperatures ranging from 1000 up to 1200°C. The crystallinity and pyramidal shape of InAs quantum structures were confirmed by HRTEM and XRD techniques. The average size of the NPs is 50 nm base and 50 nm height, and they are oriented parallel to the Si (001) planes. The lattice parameter of the NPs increases from 6.051 to 6.055 Å with the annealing temperature increasing from 1100 to 1200°C, due to lattice relaxation. Energy dispersive spectroscopy (EDS) shows almost stoichiometric composition of the InAs NPs. 相似文献
43.
The toughness of a (noncomplete) graph G is the minimum value of t for which there is a vertex cut A whose removal yields components. Determining toughness is an NP‐hard problem for general input graphs. The toughness conjecture of Chvátal, which states that there exists a constant t such that every graph on at least three vertices with toughness at least t is hamiltonian, is still open for general graphs. We extend some known toughness results for split graphs to the more general class of 2K2‐free graphs, that is, graphs that do not contain two vertex‐disjoint edges as an induced subgraph. We prove that the problem of determining toughness is polynomially solvable and that Chvátal's toughness conjecture is true for 2K2‐free graphs. 相似文献
44.
45.
In 1960, Dirac posed the conjecture that r‐connected 4‐critical graphs exist for every r ≥ 3. In 1989, Erd?s conjectured that for every r ≥ 3 there exist r‐regular 4‐critical graphs. In this paper, a technique of constructing r‐regular r‐connected vertex‐transitive 4‐critical graphs for even r ≥ 4 is presented. Such graphs are found for r = 6, 8, 10. © 2004 Wiley Periodicals, Inc. J Graph Theory 46: 103–130, 2004 相似文献
46.
47.
Using the Monte Carlo method, we address the influence of the Wiener and Poisson random noises on the behavior of oscillatory solutions to systems of stochastic differential equations (SDEs). For the linear and Van der Pol oscillators, we study the accuracy of estimates of the functionals of numerical solutions to SDEs obtained by the generalized explicit Euler method. For a linear oscillator, we obtain the exact analytical expressions for the mathematical expectation and the variance of the SDE solution. These expressions allow us to investigate the dependence of the accuracy of estimates of the solution moments on the values of SDE parameters, the size of meshsize, and the ensemble of simulated trajectories of the solution. For the Van der Pol oscillator, we study the dependence of the frequency and the damping rate of the oscillations of the mathematical expectation of SDE solution on the values of parameters of the Poisson component. The results of the numerical experiments are presented. 相似文献
48.
Artem N. Shevlyakov 《代数通讯》2017,45(9):3757-3767
A semigroup S is called an equational domain if any finite union of algebraic sets over S is algebraic. We give some necessary and su?cient conditions for a completely simple semigroup to be an equational domain. 相似文献
49.
Artem A. Zemtsov Marina I. Struchkova Vladimir A. Tartakovsky 《Journal of fluorine chemistry》2011,132(6):378-381
The interaction of 2-nitrocinnamates with silicon reagents Me3SiRf (Rf = CF3, C2F5, and C6F5) promoted either by sodium acetate in DMF or by tetrabutylammonium acetate in dichloromethane has been described. The reactions proceed as conjugate addition of fluorinated carbanion at the CC bond and afford 3-aryl-2-nitrobutanoates bearing a fluorinated substituent in good yields as diastereomeric mixtures in ratio from 1:1 to 1.6:1. 相似文献
50.
Mishchenko A Abdualla M Rudnev A Fu Y Pike AR Wandlowski T 《Chemical communications (Cambridge, England)》2011,47(35):9807-9809
As revealed for the first time by in situ scanning tunnelling spectroscopy (STS), ferrocene-modified Si(111) substrates show ambipolar field effect transistor (FET) behaviour upon electrolyte gating. 相似文献