全文获取类型
收费全文 | 8103篇 |
免费 | 248篇 |
国内免费 | 28篇 |
专业分类
化学 | 5613篇 |
晶体学 | 90篇 |
力学 | 264篇 |
数学 | 763篇 |
物理学 | 1649篇 |
出版年
2022年 | 76篇 |
2021年 | 105篇 |
2020年 | 147篇 |
2019年 | 119篇 |
2018年 | 96篇 |
2017年 | 87篇 |
2016年 | 181篇 |
2015年 | 172篇 |
2014年 | 159篇 |
2013年 | 416篇 |
2012年 | 414篇 |
2011年 | 475篇 |
2010年 | 233篇 |
2009年 | 210篇 |
2008年 | 378篇 |
2007年 | 411篇 |
2006年 | 406篇 |
2005年 | 367篇 |
2004年 | 309篇 |
2003年 | 245篇 |
2002年 | 247篇 |
2001年 | 148篇 |
2000年 | 134篇 |
1999年 | 96篇 |
1998年 | 92篇 |
1997年 | 135篇 |
1996年 | 131篇 |
1995年 | 104篇 |
1994年 | 118篇 |
1993年 | 137篇 |
1992年 | 124篇 |
1991年 | 74篇 |
1990年 | 71篇 |
1989年 | 103篇 |
1988年 | 91篇 |
1987年 | 82篇 |
1986年 | 79篇 |
1985年 | 105篇 |
1984年 | 108篇 |
1983年 | 78篇 |
1982年 | 82篇 |
1981年 | 83篇 |
1980年 | 75篇 |
1979年 | 75篇 |
1978年 | 69篇 |
1977年 | 73篇 |
1976年 | 58篇 |
1975年 | 81篇 |
1974年 | 72篇 |
1973年 | 59篇 |
排序方式: 共有8379条查询结果,搜索用时 15 毫秒
901.
The waving wing experiment is a fully three-dimensional simplification of the flapping wing motion observed in nature. The
spanwise velocity gradient and wing starting and stopping acceleration that exist on an insect-like flapping wing are generated
by rotational motion of a finite span wing. The flow development around a waving wing at Reynolds number between 10,000 and
60,000 has been studied using flow visualization and high-speed PIV to capture the unsteady velocity field. Lift and drag
forces have been measured over a range of angles of attack, and the lift curve shape was similar in all cases. A transient
high-lift peak approximately 1.5 times the quasi-steady value occurred in the first chord length of travel, caused by the
formation of a strong attached leading edge vortex. This vortex appears to develop and shed more quickly at lower Reynolds
numbers. The circulation of the leading edge vortex has been measured and agrees well with force data. 相似文献
902.
903.
Sarah Plosker Christopher Ramsey 《Journal of Mathematical Analysis and Applications》2019,469(1):117-125
We generalize Lyapunov's convexity theorem for classical (scalar-valued) measures to quantum (operator-valued) measures. In particular, we show that the range of a nonatomic quantum probability measure is a weak?-closed convex set of quantum effects (positive operators bounded above by the identity operator) under a sufficient condition on the non-injectivity of integration. To prove the operator-valued version of Lyapunov's theorem, we must first define the notions of essentially bounded, essential support, and essential range for quantum random variables (Borel measurable functions from a set to the bounded linear operators acting on a Hilbert space). 相似文献
904.
Experimental Mechanics - Using a thin-walled tube torsion test to characterize a material’s shear response is a well-known technique; however, the thin walled specimen tends to buckle before... 相似文献
905.
The proton spin-lattice relaxation time, T 1, has been measured for aqueous solutions of sodium, potassium, rubidium and magnesium chlorides up to a concentration of about 4N at 25°c. The sodium and the magnesium chloride solutions were also measured at 60°c and 100°c. The variation of 1/T 1 is not linear with concentration, at least above about ¼N, in contrast with previous reports [1, 2]. The behaviour depends markedly on the nature of the salt and on the temperature. It is shown that almost the whole of the variation of T 1 as compared with that of water can be directly and simply related to the corresponding changes in the shear viscosity of the solutions. It is noted that the viscosity correction is better the higher the temperature of the solution. 相似文献
906.
The intensity distributions in the ‘d-d’ spectra of three planar CuCl2- 4 chromophores are reproduced quantitatively within the theoretical model described in the preceding paper. Intensity for these species, namely bis(1-methyl-4-oxo-3,3-diphenylhexyldimethylammonium)tetrachlorocopper(II), bis(2-iminol-1-methy-4-imidazolidinium)tetrachlorocopper(II) and bis(N-methylphenylethylammonium)-tetrachlorocopper(II), is deemed to arise dynamically via the bending vibrations. Fair reproduction of experimental absorbances is achieved using the b 2u mode alone, this being known to be the softest vibration in these systems. The roles of spin-orbit coupling and small departures from D 4h symmetry are discussed. Nearly perfect reproduction of experiment is obtained with addition of small contributions from the eu bend. The intensity distribution in the ‘d-d’ spectrum of the pseudo-tetrahedral chromophore, bis(N-benzylpiper-azinium)tetrachlorocopper(II), is reproduced quantitatively within the ‘static’ model described in part I of this series. Comparisons between the parameter values obtained from the ‘static’ analysis with those from the ‘dynamic’ analysis for the planar chromophores suggest that dynamic modelling with both b 2u and eu modes is the more physically persuasive. The efficacy of the model in part IV is critically reviewed in this first application. 相似文献
907.
Dr D.G.C. Jones 《Contemporary Physics》2013,54(2):169-170
This short paper, presented to the British Association at Guildford in September 1975, summarizes the exploration, engineering and environmental problems involved in the discovery and development of North Sea oil. The discovery of the oil and gas fields, with a notably high success ratio, depended on the development of highly sophisticated methods of seismic survey and data analysis. The subsequent engineering operations have involved technology well beyond previous practice as regards the use of equipment, the water depth and a highly adverse environment. 相似文献
908.
Derry Jones 《Contemporary Physics》2013,54(5):455-458
Many of the oxides and chalcogenides formed by the 3d transition metals and 4f rare-earth metals are antiferro-, ferri-and ferromagnetic semiconductors. In this review, several theoretical aspects of these materials are discussed, including electron correlation in narrow bands and the formation of electrostatic and magnetic polarons. The problems of crystal growth and physical measurement are briefly considered, together with recent studies on the conduction mechanism in typical compounds like NiO, MnO, ferrites, garnets, CdCr2Se4 and EuS. Finally, we comment on possible applications. 相似文献
909.
910.
Abstract We have determined the solidus for mantle peridotite with excess water. The solidus is important for prediction of temperature and depth of melting. Our results give slightly higher temperatures than predicted by extrapolation from lower pressure piston cylinder data. Melting may be restricted to shallower depths than previously expected. 相似文献