全文获取类型
收费全文 | 322263篇 |
免费 | 5070篇 |
国内免费 | 922篇 |
专业分类
化学 | 159585篇 |
晶体学 | 4110篇 |
力学 | 15552篇 |
综合类 | 4篇 |
数学 | 63348篇 |
物理学 | 85656篇 |
出版年
2021年 | 2047篇 |
2020年 | 2506篇 |
2019年 | 2602篇 |
2018年 | 13183篇 |
2017年 | 12886篇 |
2016年 | 11411篇 |
2015年 | 4966篇 |
2014年 | 5701篇 |
2013年 | 13014篇 |
2012年 | 14332篇 |
2011年 | 21538篇 |
2010年 | 13305篇 |
2009年 | 13122篇 |
2008年 | 16940篇 |
2007年 | 18719篇 |
2006年 | 10173篇 |
2005年 | 10429篇 |
2004年 | 9742篇 |
2003年 | 9033篇 |
2002年 | 7701篇 |
2001年 | 6947篇 |
2000年 | 5537篇 |
1999年 | 4082篇 |
1998年 | 3444篇 |
1997年 | 3198篇 |
1996年 | 3329篇 |
1995年 | 2835篇 |
1994年 | 2899篇 |
1993年 | 2810篇 |
1992年 | 3087篇 |
1991年 | 2911篇 |
1990年 | 2886篇 |
1989年 | 2748篇 |
1988年 | 2720篇 |
1987年 | 2686篇 |
1986年 | 2551篇 |
1985年 | 3381篇 |
1984年 | 3383篇 |
1983年 | 2909篇 |
1982年 | 3107篇 |
1981年 | 2912篇 |
1980年 | 2812篇 |
1979年 | 2943篇 |
1978年 | 2952篇 |
1977年 | 2821篇 |
1976年 | 2921篇 |
1975年 | 2786篇 |
1974年 | 2764篇 |
1973年 | 2936篇 |
1972年 | 1858篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
We obtain asymptotic lower bounds for the spectral function of the Laplacian and for the remainder in local Weyl’s law on
manifolds. In the negatively curved case, thermodynamic formalism is applied to improve the estimates. Key ingredients of
the proof include the wave equation parametrix, a pretrace formula and the Dirichlet box principle. Our results develop and
extend the unpublished thesis of A. Karnaukh [Ka].
The first author was supported by NSERC, FQRNT, Alfred P. Sloan Foundation Fellowship and Dawson Fellowship. The second author
was supported by NSERC and FQRNT.
Received: April 2006 Revision: October 2006 Accepted: October 2006 相似文献
992.
G. A. Baranov A. A. Belyaev A. V. Zemlyanoĭ S. B. Onikienko S. A. Smirnov V. V. Khukharev 《Technical Physics》2007,52(7):927-933
A cavitation flow in an expanding nozzle is numerically simulated. The cavitation activation of cells is studied experimentally. 相似文献
993.
A group of machines for processing a set of jobs in a manufacturing system is often located in a serial line. An efficient strategy for locating these machines such that the total travel distance or the cost of transporting the jobs is minimized is desired. In this research, the assumption of a linear line with equally spaced machine location is relaxed. This research addressed problems of locating unique machines. It is found that the machine distances possess unique properties in this type of a problem. Utilizing these properties, heuristic strategies are proposed to obtain efficient solution where optimal methods are expected to be computationally prohibitive. A lower bound for the optimum solution is also proposed. Results are encouraging. 相似文献
994.
B. Velázquez-Martí C. Gracia-López 《International Journal of Infrared and Millimeter Waves》2004,25(7):1109-1122
The thermal treatment by millimeter waves for the soil disinfection can be one possible alternative to chemical treatments. This physical method is based on incrementing the soil temperature and its pathogens irradiating with high frequency electromagnetic waves. So the previous knowledge of the temperature distribution in the irradiated soil is essential for achieving an effective bad microorganism and weed seeds elimination. This report analyse the heating kinetic and spatial distribution of the maximum temperatures reached by the soil. It is presented a mathematic model about how are distributed the reached temperatures in the depth of the irradiated soil. This model concludes that when an orchard soil is irradiated superficially by microwaves, the microwaves have a big attenuation due to the soil dielectric properties and the water located in the pores of the most superficial layer. This fact causes a shield effect blocking the waves penetration in few centimetres. The heating by radiation is reduced to the superficial layer. The heating propagation in the depth is occurred by conduction following the Fourier equations. 相似文献
995.
996.
Martin I. Karakhanyan 《Journal of Contemporary Mathematical Analysis (Armenian Academy of Sciences)》2007,42(3):146-150
The paper proves some general facts on commutators that refer to Fuglede-Putnam classical theorem in the spectral theory of not necessarily selfadjoint operators. 相似文献
997.
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
998.
G. Bouwmans B. Ségard P. Glorieux P. A. Khandokhin N. D. Milovsky E. Yu. Shirokov 《Radiophysics and Quantum Electronics》2004,47(10-11):729-742
This paper is devoted to the polarization dynamics of a longitudinally monomode bipolarized Nd:YAG laser: the low-frequency polarization dynamics of a microchip laser is studied experimentally and theoretically. The intensities and the relaxation oscillation spectrum of orthogonally polarized modes versus the direction of pump polarization is observed. A phase-sensitive model of a longitudinally monomode bipolarized solid-state laser with linear polarized diode laser pump is developed to account for the experimental observations. 相似文献
999.
François Loiseau Jean-Mary Simone David Carcache Pavel Bobal Reinhard Neier 《Monatshefte für Chemie / Chemical Monthly》2007,138(2):121-129
Summary. Free radical couplings from furan, as cheap starting material, were studied in view of developing a rapid strategy en route to the synthesis of derivatives of nonactin. The chain containing the alcohol function was introduced in one or two steps
in 86% yield. For the introduction of the second chain with the ester function two different coupling methods were tested.
Starting from the advanced intermediates obtained nonactin derivatives can be prepared by catalytic hydrogenation of the furan
ring. 相似文献
1000.
Katharina Habermann Lutz Habermann Paul Rosenthal 《Calculus of Variations and Partial Differential Equations》2007,30(2):137-152
A Yang–Mills theory in a purely symplectic framework is developed. The corresponding Euler–Lagrange equations are derived
and first integrals are given. We relate the results to the work of Bourgeois and Cahen on preferred symplectic connections. 相似文献