全文获取类型
收费全文 | 325篇 |
免费 | 5篇 |
国内免费 | 1篇 |
专业分类
化学 | 189篇 |
晶体学 | 2篇 |
力学 | 8篇 |
数学 | 66篇 |
物理学 | 66篇 |
出版年
2023年 | 2篇 |
2022年 | 2篇 |
2021年 | 10篇 |
2020年 | 4篇 |
2019年 | 6篇 |
2018年 | 2篇 |
2017年 | 6篇 |
2016年 | 12篇 |
2015年 | 5篇 |
2014年 | 10篇 |
2013年 | 17篇 |
2012年 | 20篇 |
2011年 | 14篇 |
2010年 | 9篇 |
2009年 | 7篇 |
2008年 | 14篇 |
2007年 | 11篇 |
2006年 | 12篇 |
2005年 | 19篇 |
2004年 | 6篇 |
2003年 | 9篇 |
2002年 | 21篇 |
2001年 | 18篇 |
2000年 | 6篇 |
1999年 | 7篇 |
1998年 | 6篇 |
1997年 | 7篇 |
1996年 | 6篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 7篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1986年 | 2篇 |
1983年 | 3篇 |
1980年 | 4篇 |
1974年 | 4篇 |
1969年 | 1篇 |
1966年 | 2篇 |
1962年 | 1篇 |
1947年 | 1篇 |
1908年 | 1篇 |
1907年 | 1篇 |
1899年 | 1篇 |
1885年 | 2篇 |
1883年 | 2篇 |
1869年 | 1篇 |
排序方式: 共有331条查询结果,搜索用时 15 毫秒
31.
Adolfo Ballester-Bolinches Ramón Esteban-Romero Luis M. Ezquerro 《Israel Journal of Mathematics》2014,204(1):359-371
The main aim of this paper is to give structural information of a finite group of minimal order belonging to a subgroup-closed class of finite groups and whose p-length is greater than 1, p a prime number. Alternative proofs and improvements of recent results about the influence of minimal p-subgroups on the p-nilpotence and p-length of a finite group arise as consequences of our study. 相似文献
32.
We consider the problem of finding the spectrum of an n × n matrix which arises in the study of a certain model of long-range interactions in a one-dimensional statistical mechanics
system. Our analysis exhibits a curious resemblance of the suitably normalized distribution of eigenvalues to the Marčenko–Pastur
law in the limit n → ∞. 相似文献
33.
A simple method to evaluate the performance of transparent optical networks (TON) that takes into account the incoherent homodyne crosstalk, signal distortion, inter-symbol interference (ISI), amplified spontaneous emission (ASE) noise, and arbitrary optical and electrical filters is proposed. This method combines the effect of the incoherent homodyne crosstalk with an exhaustive Gaussian approximation for the influence of ASE noise, signal distortion, and ISI. It is shown that the incoherent homodyne crosstalk penalty depends on the ASE noise accumulated in the TON, ISI, and extinction ratio. The proposed method estimates are compared with experimental results published by other authors. Good agreement is observed for one, two, and four incoherent homodyne crosstalk signals, revealing that the proposed method provides accurate estimates even when the methods based on a Gaussian approximation for the incoherent homodyne crosstalk fail. The proposed method is used to assess the performance of a TON composed by optical add-drop multiplexers based on arrayed waveguide gratings. Results reveal that incoherent homodyne crosstalk, ASE noise, and ISI impair the TON performance and, therefore, none can be neglected in the TON design. 相似文献
34.
Diego Adolfo Santamaría Razo Luca Pallavidino Edoardo Garrone Francesco Geobaldo Emiliano Descrovi Angelica Chiodoni Fabrizio Giorgis 《Journal of nanoparticle research》2008,10(7):1225-1229
A sol-gel synthesis procedure based on the method proposed by Stöber et al. (J Colloid Interface Sci 26:302–315, 1968) has been adopted for the one-step preparation of mono-dispersed silica nanospheres. An excellent control of the particle diameter over a wide range is obtained by varying the amount of silicon alkoxide only, while the concentration of all other components is kept fixed: this allows the fabrication of artificial opals with a finely tuned and precisely predictable lattice parameter. 相似文献
35.
Adolfo Zavelani-Rossi 《Meccanica》1974,9(4):312-324
Summary Limit analysis of plane structures is formulated by applying a finite element linear programming technique that was previously proposed by the same author.Three different element models are considered: the constant stress compatible model, the linear stress equilibrium model, the quadratic stress equilibrium model. Some notes are devoted to the construction of the stress fields with reference to the adopted method.Some suitably chosen numerical applications are then proposed in order to compare the different approaches as far as numerical efficiency and result accuracy are concerned. The possibility of improving the linear programming procedure is also discussed, and in particular a method is proposed to find out an initial feasible vector on the basis of mechanical considerations, in order to overcome the necessity of the so-called M-phase of the simplex method.Numerical results are given together with the comments.
Research supported by the C.N.R. (Italian National Research Council). 相似文献
Sommario Si formula il problema dell'analisi limite di strutture piane secondo un metodo degli elementi finiti già proposto dall'autore.Nel presente lavoro vengono considerati tre diversi modelli di elementi e precisamente: il modello congruente a sforzo costante e quelli equilibrati a campi di sforzo lineare e quadratico. La costruzione dei tre modelli viene presentata in dettaglio nell'ambito del metodo adottato.Vengono quindi presentati alcuni esempi di applicazione opportunamente scelti, con lo scopo di confrontare l'efficienza numerica e l'accuratezza di risultati ottenuti con l'impiego dei tre modelli. Si discute inoltre la possibilità di migliorare l'efficacia dell'algoritmo matematico ed in particolare si suggerisce un metodo che, individuando una soluzione ammissibile di partenza sulla scorta di considerazioni meccaniche, permette di evitare la cosiddetta fase M della programmazione lineare.I commenti sono accompagnati dai risultati numerici.
Research supported by the C.N.R. (Italian National Research Council). 相似文献
36.
Rafael A. García Victoria Morales Sergio Martín Estela Vilches Adolfo Toledano 《Chromatographia》2014,77(5-6):501-509
Exhaled breath contains thousands of gaseous volatile organic compounds (VOCs) that may be used as non-invasive markers of head and neck epidermoid cancer. We hypothesized that solid phase micro-extraction coupled to gas chromatography–mass spectrometry can discriminate patients with epidermoid head and neck cancer from healthy controls by analyzing the gaseous volatile organic compounds, VOC-profile, in exhaled breath, thus identifying some non-invasive biomarkers to be used in early detection. Twenty healthy subjects participated in a cross-sectional study plus 11 patients with epidermoid supraglottic laryngeal cancer. VOCs from T3 supraglottic cancer were clustered distinctly from those of T1 and healthy subjects. Up to seven VOCs were detected differently from healthy volunteers, mainly 2-butanone and ethanol. Thus VOC-patterns of exhaled breath may discriminate patients with epidermoid head and neck cancer from healthy controls. 相似文献
37.
Finite groups G=AB factorized by two subgroups A and B such that every subgroup of A permutes with every subgroup of B are studied in this paper. The behaviour of such products with respect to the class of finite groups in which Sylow-permutability is transitive is analyzed. 相似文献
38.
We present and study a procedure for testing the null hypothesis of multivariate elliptical symmetry. The procedure is based on the averages of some spherical harmonics over the projections of the scaled residual (1978, N. J. H. Small, Biometrika65, 657–658) of the d-dimensional data on the unit sphere of
d. We find, under mild hypothesis, the limiting null distribution of the statistic presented, showing that, for an appropriate choice of the spherical harmonics included in the statistic, this distribution does not depend on the parameters that characterize the underlying elliptically symmetric law. We describe a bivariate simulation study that shows that the finite sample quantiles of our statistic converge fairly rapidly, with sample size, to the theoretical limiting quantiles and that our procedure enjoys good power against several alternatives. 相似文献
39.
The limit behavior of the conditional probability of error of linear and quadratic discriminant analyses is studied under wide assumptions on the class conditional distributions. Results obtained may help to explain analytically the behavior in applications of linear and quadratic discrimination techniques. 相似文献
40.
Simona Lai Emanuela Locci Giuseppe Saba Ivan Husu Giancarlo Masci Vittorio Crescenzi Adolfo Lai 《Journal of polymer science. Part A, Polymer chemistry》2003,41(20):3123-3131
Dry and hydrated poly(vinyl alcohol) (PVA) gels with 55% (a‐PVA) and 61% (s‐PVA) syndiotacticity and related PVA/lactyl chitosan (LC) blends have been investigated with 129Xe and cross‐polarization/magic‐angle‐spinning 13C NMR techniques. Although the dry gels exhibit two broad 129Xe resonances in the slow‐to‐intermediate exchange limit, both hydrated gels show three resonances. The corresponding dry blends exhibit two signals, the chemical shifts and line widths of which change with respect to those of pure PVA, whereas one (a‐PVA/LC) or two (s‐PVA/LC) signals appear in the spectra of the hydrated blends. A comparative analysis of the data demonstrates that LC rearranges the domains of the polymeric matrix in both the dry and hydrated blends according to the syndiotacticity of the PVA chains. Information on the molecular motions of the amorphous and swollen polymeric domains in the kilohertz range has been obtained from an analysis of the spin‐lattice relaxation times. These data indicate that the dynamics and arrangement of the PVA chains in the gels are strongly affected by their tacticity and the addition of the copolymer LC. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3123–3131, 2003 相似文献