全文获取类型
收费全文 | 457116篇 |
免费 | 5216篇 |
国内免费 | 1597篇 |
专业分类
化学 | 252282篇 |
晶体学 | 6840篇 |
力学 | 18981篇 |
综合类 | 11篇 |
数学 | 51586篇 |
物理学 | 134229篇 |
出版年
2018年 | 2974篇 |
2016年 | 5681篇 |
2015年 | 4525篇 |
2014年 | 6255篇 |
2013年 | 19932篇 |
2012年 | 14374篇 |
2011年 | 17996篇 |
2010年 | 11467篇 |
2009年 | 11329篇 |
2008年 | 16531篇 |
2007年 | 16885篇 |
2006年 | 16218篇 |
2005年 | 14816篇 |
2004年 | 13401篇 |
2003年 | 11888篇 |
2002年 | 11698篇 |
2001年 | 13832篇 |
2000年 | 10614篇 |
1999年 | 8504篇 |
1998年 | 6792篇 |
1997年 | 6664篇 |
1996年 | 6695篇 |
1995年 | 6118篇 |
1994年 | 5863篇 |
1993年 | 5564篇 |
1992年 | 6414篇 |
1991年 | 6162篇 |
1990年 | 5855篇 |
1989年 | 5746篇 |
1988年 | 5939篇 |
1987年 | 5687篇 |
1986年 | 5435篇 |
1985年 | 7666篇 |
1984年 | 7774篇 |
1983年 | 6379篇 |
1982年 | 6819篇 |
1981年 | 6829篇 |
1980年 | 6480篇 |
1979年 | 6751篇 |
1978年 | 6931篇 |
1977年 | 6820篇 |
1976年 | 6710篇 |
1975年 | 6491篇 |
1974年 | 6291篇 |
1973年 | 6470篇 |
1972年 | 3916篇 |
1971年 | 3035篇 |
1968年 | 3375篇 |
1967年 | 3278篇 |
1966年 | 2990篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
D. Amutha Rani Y. Yamamoto S. Mohri M. Sivakumar Y. Tsujita H. Yoshimizu 《Journal of Polymer Science.Polymer Physics》2003,41(3):269-273
In this study, a novel stepwise extraction method has been examined. The guest molecules housed between the helices of the clathrate δ form of syndiotactic polystyrene can be removed completely with this method. A systematic study of the preparation of a solvent‐free mesophase (emptied clathrate) membrane, its helical and residual solvent contents, and its structural transformations has been performed. In this first attempt, an enhancement in the TTGG helical content has been observed in the extracted membrane, and a conceptual mechanism is proposed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 269–273, 2003 相似文献
152.
153.
154.
J. Stankowski 《Applied magnetic resonance》2004,27(1-2):251-258
Microwave nonresonant dissipation observed around zero field makes a powerful method in characterizing superconducting state (to determineT C,H C1,H CJ parameters). This review shows several successful applications of magnetically modulated microwave absorption (MMMA). MMMA enables to study MgB2 superconducting nanoregions embedded in the Mg host structure. Application of MMMA to study intercalation of fullerence enabled the observation of a new superconducting phase. The pressure effect dT C/dp has been studied below the percolation threshold in YBaCuO/PST composites. The local temperature of the Josephson junction measured by the MMMA technique showed that a granular superconductor consists of two phases: host phase and Josephson junction system. MMMA has been applied lately to separate the giant magnetoresistance from the magnetization effect in differential hysteresis loops. 相似文献
155.
Fundamentals of the direct measurement of sound intensity and practical applications 总被引:1,自引:0,他引:1
Sound intensity is a measure of the magnitude and direction of the flow of sound energy. Developments in sound intensity measurement capabilities in the last quarter century have occurred because of several reasons. The main ones include the derivation of the cross-spectral formulation for sound intensity and developments in digital signal processing. This paper begins with a brief historical introduction of sound intensity measurements. Then elementary theory for sound intensity is presented. A section on sound intensity measurements is then included. The next section of the paper discusses sources of measurement error; the major sources of error are described in some detail. The paper continues with a discussion of the main applications of sound intensity measurements: sound power determination, noise source identification, and transmission loss measurements. The paper concludes with a discussion of ISO and ANSI intensity related standards and relevant references. 相似文献
156.
H.L. Xu A. Persson S. Svanberg 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(2):233-236
New radiative lifetime measurements based on time-resolved laser-induced fluorescence techniques are reported for 18 even-parity
levels belonging to the 4f5d26p and 4f
25d
2 configurations of Ce I and 6 even-parity levels belonging to the 5d26s, 4f5d6p, and 4f6s6p configurations of Ce II. Free neutral and singly ionized cerium atoms were produced by laser ablation. The Ce I and Ce II
levels range in energy from 26 545 to 29 102 cm-1, and 42 573 to 48 152 cm-1, respectively.
Received 25 September 2002 Published online 4 March 2003 相似文献
157.
Pascher W. Den Besten J. H. Caprioli D. Leijtens X. Smit M. van Dijk R. 《Optical and Quantum Electronics》2003,35(4-5):453-464
Based on a rigorous vectorial analysis, a fast travelling-wave Mach–Zehnder modulator is modelled and designed. The cross-section of the semiconductor layer stack and the lossy electrodes are carefully modelled using the method of lines in order to investigate propagation characteristics, velocity and losses. This yields an accurate microwave and optical field distribution to explain the behaviour of the component. In order to enhance the modulation efficiency, design curves are derived and the cross-sectional dimensions for minimum microwave loss are determined. The loss of the optimized modulator agrees very well with small-signal measurements up to 40 GHz and HFSS simulations. The layerstack of the fabricated device is suitable for integration with InP multi-wavelength lasers. 相似文献
158.
Mrio J. Edmundo 《Mathematical Logic Quarterly》2005,51(6):639-641
We show that if G is a definably compact, definably connected definable group defined in an arbitrary o‐minimal structure, then G is divisible. Furthermore, if G is defined in an o‐minimal expansion of a field, k ∈ ? and pk : G → G is the definable map given by pk (x ) = xk for all x ∈ G , then we have |(pk )–1(x )| ≥ kr for all x ∈ G , where r > 0 is the maximal dimension of abelian definable subgroups of G . (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
159.
R. Hefelmann P. Mann A. Aignan F. Filsinger und H. Amsel 《Fresenius' Journal of Analytical Chemistry》1902,41(1):66-68
Ohne Zusammenfassung 相似文献
160.
A parallel method for time discretization of parabolic equations based on Laplace transformation and quadrature 总被引:5,自引:0,他引:5
We consider the discretization in time of an inhomogeneous parabolicequation in a Banach space setting, using a representation ofthe solution as an integral along a smooth curve in the complexleft half-plane which, after transformation to a finite interval,is then evaluated to high accuracy by a quadrature rule. Thisreduces the problem to a finite set of elliptic equations withcomplex coefficients, which may be solved in parallel. The paperis a further development of earlier work by the authors, wherewe treated the homogeneous equation in a Hilbert space framework.Special attention is given here to the treatment of the forcingterm. The method is combined with finite-element discretizationin spatial variables. 相似文献