全文获取类型
收费全文 | 2186篇 |
免费 | 53篇 |
国内免费 | 11篇 |
专业分类
化学 | 1422篇 |
晶体学 | 23篇 |
力学 | 82篇 |
数学 | 396篇 |
物理学 | 327篇 |
出版年
2023年 | 15篇 |
2022年 | 21篇 |
2021年 | 33篇 |
2020年 | 32篇 |
2019年 | 30篇 |
2018年 | 24篇 |
2017年 | 26篇 |
2016年 | 57篇 |
2015年 | 47篇 |
2014年 | 52篇 |
2013年 | 109篇 |
2012年 | 97篇 |
2011年 | 143篇 |
2010年 | 77篇 |
2009年 | 71篇 |
2008年 | 111篇 |
2007年 | 128篇 |
2006年 | 106篇 |
2005年 | 102篇 |
2004年 | 89篇 |
2003年 | 85篇 |
2002年 | 70篇 |
2001年 | 40篇 |
2000年 | 38篇 |
1999年 | 34篇 |
1998年 | 24篇 |
1997年 | 25篇 |
1996年 | 29篇 |
1995年 | 24篇 |
1994年 | 34篇 |
1993年 | 28篇 |
1992年 | 30篇 |
1991年 | 25篇 |
1990年 | 21篇 |
1989年 | 25篇 |
1988年 | 20篇 |
1987年 | 17篇 |
1986年 | 14篇 |
1985年 | 32篇 |
1984年 | 33篇 |
1983年 | 24篇 |
1982年 | 20篇 |
1981年 | 17篇 |
1980年 | 22篇 |
1979年 | 20篇 |
1978年 | 14篇 |
1977年 | 15篇 |
1976年 | 14篇 |
1975年 | 10篇 |
1974年 | 16篇 |
排序方式: 共有2250条查询结果,搜索用时 46 毫秒
1.
P. González D. Fernández J. Pou E. García J. Serra B. León M. Pérez-Amor T. Szörényi 《Applied Physics A: Materials Science & Processing》1993,57(2):181-185
A study of the gas-phase parameters involved in ArF laser induced chemical vapour deposition of silicon-oxide thin films is presented. A complete set of experiments has been performed showing the influence of the concentration of the precursor gases, N2O and SiH4, and their influence on total and partial pressures on film growth and properties. In this paper we demonstrate the ability of this LCVD method to deposit silicon oxide films of different compositions and densities by appropriate control of gas composition and total pressure. Moreover, a material specific calibration plot comprising data obtained using different preparation techniques is presented, allowing determination of the stoichiometry of SiO
x
films by using FTIR spectroscopy independently of the deposition method. For the range of processing conditions examined, the experimental results suggest that chemical processes governing deposition take place mainly in the gas phase. 相似文献
2.
An analysis of the different philosophic and scientific visions of Henri Poincaré and Federigo Enriques relative to qualitative analysis provides us with a complex and interesting image of the “essential tension” between “tradition” and “innovation” within the history of science. In accordance with his scientific paradigm, Poincaré viewed qualitative analysis as a means for preserving the nucleus of the classical reductionist program, even though it meant “bending the rules” somewhat. To Enriques's mind, qualitative analysis represented the affirmation of a synthetic, geometrical vision that would supplant the analytical/quantitative conception characteristic of 19th-century mathematics and mathematical physics. Here, we examine the two different answers given at the turn of the century to the question of the relationship between geometry and analysis and between mathematics, on the one hand, and mechanics and physics, on the other.Copyright 1998 Academic Press.Un'analisi delle diverse posizioni filosofiche e scientifiche di Henri Poincaré e Federigo Enriques nei riguardi dell'analisi qualitativa fornisce un'immagine complessa e interessante della “tensione essenziale” tra “tradizione” e “innovazione” nell'ambito della storia della scienza. In linea con il proprio paradigma scientifico, Poincaré vedeva nell'analisi qualitativa un mezzo per preservare il nucleo del programma riduzionista calssico, anche se cio comportava una lieve “distorsione delle regole”. Nella mente di Enriques, l'analisi qualitativa rappresentava l'affermazione di un punto di vista sintetico e geometrico che avrebbe soppiantato la concezione analitico-quantitativa caratteristica della matematica e della fisica matematica del 19° secolo. Il nostro scopo principale è di esaminare due diverse risposte date a cavallo del secolo alla questione dei rapporti tra geometria e analisi e tra matematica da un lato e meccanica e fisica dall'altro.Copyright 1998 Academic Press.AMS subject classification: 01A55 相似文献
3.
Jun Fujii Giancarlo Panaccione Giorgio Rossi Giancarlo Trimarchi 《Surface science》2006,600(18):3884-3887
Bulk carbon impurities segregate at the Fe(1 0 0) surface and, upon thermal annealing, can form metastable surface phases with local and long range order and peculiar electronic properties. We present a surface science study of C-segregated Fe(1 0 0) with scanning tunneling microscopy, angle resolved photoemission, and ab initio calculations of the surface structure and electron states. In particular the c(3√2 × √2) structure, observed for 0.67 atomic layers of C segregated at the iron surface, is found to be due to self-organized carbon stripes made of zig-zag chains. The strong hybridization between C and Fe was observed in ARPES spectra. 相似文献
4.
Giorgio AbbiatiAntonio Arcadi Egle BeccalliElisabetta Rossi 《Tetrahedron letters》2003,44(28):5331-5334
Intramolecular cyclization of 2-acyl-1-propargyl-1H-indoles in the presence of ammonia provides an easy entry to pyrazino[1,2-a]indole nucleus. 相似文献
5.
We show that every arithmetically Cohen-Macaulay two-codimensional subscheme ofP
n can be deformed to a reduced union of two-codimensional linear subvarieties. This problem (classical for curves with the name of Zeuthen problem) was solved for curves by F.Gaeta. 相似文献
6.
A survey of the contributions of Aldo Cossu in finite geometry is given.
Dedicated to the memory of Professor Aldo Cossu 相似文献
7.
Demetrio Pitea Laura Bonati Elena Collina Ugo Cosentino Marina Lasagni Giorgio Moro Roberto Todeschini 《Fresenius' Journal of Analytical Chemistry》1994,348(1-2):111-120
Summary The role of multivariate analysis methods in evaluating, rationalizing, and working out complex environmental problems is discussed. The discussion is organized in two sections; a literature analysis of the application of chemometric methods to PCDD/PCDF data interpretation and source correlation and a review of the role of chemometric methods in analysing the results obtained by the Authors studying PCDD/PCDF formation and destruction mechanisms in MSW combustion processes. 相似文献
8.
Patrick Pruja Sauveur Bnet Bernard Claudet Olivier Faugeroux Jean-Jacques Serra 《Superlattices and Microstructures》2004,35(3-6):409
Modeling the behavior of a protective coating during a thermal shock not only requires the knowledge of its own thermophysical characteristics, but also those of the coating–substrate discontinuity. According to its nature, this discontinuity can be modeled as a zero-thickness interface (thermal contact resistance) or a finite thickness layer (thermal third body). This paper presents an experimental device and two associated thermal transfer models developed in view of the microscale characterization of such discontinuities. 相似文献
9.
In the general case of multilevel Toeplitz matrices, we recently proved that any multilevel circulant preconditioner is not superlinear (a cluster it may provide cannot be proper). The proof was based on the concept of quasi-equimodular matrices, although this concept does not apply, for example, to the sine-transform matrices. In this paper, with a new concept of partially equimodular matrices, we cover all trigonometric matrix algebras widely used in the literature. We propose a technique for proving the non-superlinearity of certain frequently used preconditioners for some representative sample multilevel matrices. At the same time, we show that these preconditioners are, in a certain sense, the best among the sublinear preconditioners (with only a general cluster) for multilevel Toeplitz matrices.
10.
The Fourier transform of orthogonal polynomials with respect to their own orthogonality measure defines the family of Fourier–Bessel
functions. We study the asymptotic behaviour of these functions and of their products, for large real values of the argument.
By employing a Mellin analysis we construct a general framework to exhibit the relation of the asymptotic decay laws to certain
dimensions of the orthogonality measure, that are defined via the divergence abscissas of suitable integrals. The unifying
r?le of Mellin transform techniques in deriving classical and new results is underlined.
Submitted: November 5, 2004. Accepted: January 6, 2006. 相似文献