全文获取类型
收费全文 | 243801篇 |
免费 | 3516篇 |
国内免费 | 1471篇 |
专业分类
化学 | 137979篇 |
晶体学 | 3414篇 |
力学 | 9487篇 |
综合类 | 62篇 |
数学 | 28578篇 |
物理学 | 69268篇 |
出版年
2020年 | 1941篇 |
2019年 | 2147篇 |
2018年 | 2686篇 |
2017年 | 2720篇 |
2016年 | 4043篇 |
2015年 | 2729篇 |
2014年 | 3958篇 |
2013年 | 10092篇 |
2012年 | 8729篇 |
2011年 | 10712篇 |
2010年 | 7345篇 |
2009年 | 7011篇 |
2008年 | 9982篇 |
2007年 | 10147篇 |
2006年 | 9613篇 |
2005年 | 8937篇 |
2004年 | 7967篇 |
2003年 | 6961篇 |
2002年 | 6877篇 |
2001年 | 7021篇 |
2000年 | 5330篇 |
1999年 | 3894篇 |
1998年 | 3296篇 |
1997年 | 3291篇 |
1996年 | 3365篇 |
1995年 | 2880篇 |
1994年 | 2967篇 |
1993年 | 2841篇 |
1992年 | 3064篇 |
1991年 | 3105篇 |
1990年 | 2911篇 |
1989年 | 2838篇 |
1988年 | 2803篇 |
1987年 | 2719篇 |
1986年 | 2738篇 |
1985年 | 3648篇 |
1984年 | 3736篇 |
1983年 | 3081篇 |
1982年 | 3420篇 |
1981年 | 3177篇 |
1980年 | 2908篇 |
1979年 | 3092篇 |
1978年 | 3311篇 |
1977年 | 3330篇 |
1976年 | 3312篇 |
1975年 | 3035篇 |
1974年 | 3140篇 |
1973年 | 3175篇 |
1972年 | 2451篇 |
1971年 | 1953篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
V. Tokranov S. L. Rumyantsev M. S. Shur R. Gaska S. Oktyabrsky R. Jain N. Pala 《固体物理学:研究快报》2007,1(5):199-201
We show that HfO2/AlGaN/GaN structures with HfO2 layer deposited using an e‐beam in ultra high vacuum are suitable for field effect transistors. The dielectric constant of the HfO2 was found εHfO > 23–24, which is close to the highest re‐ ported values for this material. The leakage current did not exceed 10–4 A/cm2 at the threshold voltage. The comparison of the losses in the samples with and without HfO2 indicates low concentration of the interface traps. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
992.
Those who have worked in the Royal Institution of Great Britain have, since its foundation in 1799, made significant contributions
to scientific knowledge, to its practical application, and to its communication to a wide variety of audiences. Such work
cannot be carried out in an architectural vacuum, and in this paper we examine how the buildings of the Royal Institution,
20 and 21 Albemarle Street in central London, have shaped the work undertaken within its walls and how, on a number of occasions,
the buildings have been reconfigured to take account of the evolving needs of scientific research and communication.
This paper is based on the Conservation Plan of the Royal Institution that we wrote during 2003. The Conservation Plan did
not examine the land owned by the Royal Institution to the north (i.e., 22 and 23 Albemarle Street; for this area see Richard Garnier, “Grafton Street, Mayfair,” Georgian Group Journal 13 (2003), 210–272), but it did discuss 18 and 19 Albemarle Street. In this paper we concentrate on the core Royal Institution
buildings at 20 and 21 Albemarle Street. Other studies of the relationship of architecture,space, and science include Crosbie
Smith and Jon Agar, ed., Making Space for Science: Territorial Themes in the Shaping of Knowledge (Basingstoke: Macmillan, 1997); Peter Galison and Emily Thompson, ed., The Architecture of Science (Cambridge, Mass.: MIT Press, 1999); and Sophie Forgan,“The architecture of science and the idea of a university,” Studies in History and Philosophy of Science 20 (1989), 405–434.
Frank A.J.L. James is Professor of the History of Science at the Royal Institution; he has written widely on the history of
nineteenth-century science in its social and cultural contexts and is editor of the Correspondence of Michael Faraday. He is President of the British Society for the History of Science. Anthony Peers is an Associate of Rodney Melville and
Partners where he works in the field of building conservation as an architectural historian. He is a Council member of the
Ancient Monument Society. 相似文献
993.
Results are presented on the production of purified myocardial proteins from two-dimensional (2-D) gels. Proteins were fixed in a native condition using potassium acetate and then eluted into an aqueous solution. Homogeneous tropomyosin and myosin light chain fractions and a number of nonidentified myocardial proteins present on 2-D gels were obtained. 相似文献
994.
L. A. Bondar' L. M. Kustov I. P. Beletskii A. Yu. Stakheev A. A. Chuiko V. B. Kazanskii 《Russian Chemical Bulletin》1991,40(10):1940-1943
Microporous silica gels containing small amounts of titanium ions are synthesized. Addition of Ti ions to the silica gels during the sol-forming step is demonstrated to increase the specific surface area and decrease the volume of sorptive pores. Spectral results indicate that Ti ions uniformly distribute in the silica gel matrix and isomorphously replace Si.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2217–2222, October, 1991. 相似文献
995.
L.E. Payne 《Journal of Mathematical Analysis and Applications》2007,335(1):371-376
In this paper we consider two different initial-boundary value problems in temperature dependent viscous flow when the temperature equation has a nonlinear heat source term. When blow-up occurs we derive lower bounds for the blow-up time in each case. 相似文献
996.
K. Olimov K. G. Gulamov V. V. Lugovoi S. L. Lutpullaev Kh. K. Olimov V. I. Petrov 《Physics of Atomic Nuclei》2007,70(11):1977-1979
997.
L. Bartosch P. Kopietz 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(1):29-36
We consider the effect of Coulomb interactions on the average density of states (DOS) of disordered low-dimensional metals
for temperatures T and frequencies ω smaller than the inverse elastic life-time 1/τ. Using the fact that long-range Coulomb interactions in two dimensions (2d) generate ln2-singularities in the DOS ν(ω) but only ln-singularities in the conductivity σ(ω), we can re-sum the most singular contributions
to the average DOS via a simple gauge-transformation. If σ(ω) > 0, then a metallic Coulomb gapν(ω) ∝ |ω|/e
4 appears in the DOS at T = 0 for frequencies below a certain crossover frequency Ω
2 which depends on the value of the DC conductivity σ(0). Here, - e is the charge of the electron. Naively adopting the same procedure to calculate the DOS in quasi 1d metals, we find ν(ω) ∝ (|ω|/Ω
1)1/2exp(- Ω
1/|ω|) at T = 0, where Ω
1 is some interaction-dependent frequency scale. However, we argue that in quasi 1d the above gauge-transformation method is on less firm grounds than in 2d. We also discuss the behavior of the DOS at finite temperatures and give numerical results for the expected tunneling conductance
that can be compared with experiments.
Received 28 August 2001 / Received in final form 28 January 2002 Published online 9 July 2002 相似文献
998.
L. Sriramkumar 《General Relativity and Gravitation》2003,35(9):1699-1705
We consider the response of a uniformly accelerated monopole detector that is coupled to a superposition of an odd and an even power of a quantized, massless scalar field in flat spacetime in arbitrary dimensions. We show that, when the field is assumed to be in the Minkowski vacuum, the response of the detector is characterized by a Bose-Einstein factor in even spacetime dimensions, whereas a Bose-Einstein as well as a Fermi-Dirac factor appear in the detector response when the dimension of spacetime is odd. Moreover, we find that, it is possible to interpolate between the Bose-Einstein and the Fermi-Dirac distributions in odd spacetime dimensions by suitably adjusting the relative strengths of the detector's coupling to the odd and the even powers of the scalar field. We point out that the response of the detector is always thermal and we, finally, close by stressing the apparent nature of the appearance of the Fermi-Dirac factor in the detector response. 相似文献
999.
1000.
This paper deals with a model of time-dependent double diffusive convection in Darcy flow. In particular it is concerned with the spatial decay of solutions when the flow is confined to a semi-infinite cylinder. Decay bounds for an energy expression are derived. 相似文献