全文获取类型
收费全文 | 4844篇 |
免费 | 152篇 |
国内免费 | 13篇 |
专业分类
化学 | 2672篇 |
晶体学 | 47篇 |
力学 | 149篇 |
数学 | 495篇 |
物理学 | 1646篇 |
出版年
2023年 | 38篇 |
2022年 | 78篇 |
2021年 | 81篇 |
2020年 | 97篇 |
2019年 | 97篇 |
2018年 | 97篇 |
2017年 | 74篇 |
2016年 | 132篇 |
2015年 | 89篇 |
2014年 | 127篇 |
2013年 | 289篇 |
2012年 | 253篇 |
2011年 | 299篇 |
2010年 | 185篇 |
2009年 | 168篇 |
2008年 | 241篇 |
2007年 | 239篇 |
2006年 | 252篇 |
2005年 | 210篇 |
2004年 | 155篇 |
2003年 | 137篇 |
2002年 | 112篇 |
2001年 | 93篇 |
2000年 | 87篇 |
1999年 | 59篇 |
1998年 | 46篇 |
1997年 | 45篇 |
1996年 | 52篇 |
1995年 | 54篇 |
1994年 | 49篇 |
1993年 | 62篇 |
1992年 | 50篇 |
1991年 | 42篇 |
1990年 | 56篇 |
1989年 | 43篇 |
1988年 | 43篇 |
1987年 | 42篇 |
1985年 | 53篇 |
1984年 | 48篇 |
1983年 | 43篇 |
1982年 | 40篇 |
1981年 | 46篇 |
1980年 | 51篇 |
1979年 | 35篇 |
1978年 | 44篇 |
1977年 | 38篇 |
1976年 | 40篇 |
1975年 | 33篇 |
1974年 | 40篇 |
1973年 | 40篇 |
排序方式: 共有5009条查询结果,搜索用时 15 毫秒
11.
A. M. Yakunin A. Yu. Silov P. M. Koenraad W. Van Roy J. De Boeck J. H. Wolter 《Superlattices and Microstructures》2003,34(3-6):539
An individual Mn acceptor in GaAs is mapped by cross-sectional scanning tunneling microscopy (X-STM) at room temperature and a strongly anisotropic shape of the acceptor state is observed. An acceptor state manifests itself as a cross-like feature which we attribute to a valence hole weakly bound to the Mn ion forming the (Mn2+3d5+hole) complex. We propose that the observed anisotropy of the Mn acceptor wavefunction is due to the d-wave present in the acceptor ground state. 相似文献
12.
Samit Mandal T. Madhusoodhanan Subinit Roy S. Ray H. Majumdar S. Datta S. S. Ghugre S. Ghosh A. Mandal D. K. Avasthi S. K. Datta 《Nuclear Physics A》2003,720(3-4):222-244
Angular distributions of elastic scattering and inelastic scattering from 2+1 state are measured for 16O+142,144,146Nd systems at several energies in the vicinity of the Coulomb barrier. The angular distributions are systematically analyzed in coupled channel framework. Renormalized double folded real optical and coupling potentials with DDM3Y interaction have been used in the calculation. Relevant nuclear densities needed to generate the potentials are derived from shell model wavefunctions. A truncated shell model calculation has been performed and the calculated energy levels are compared with the experimental ones. To simulate the absorption, a ‘hybrid’ approach is adopted. The contribution to the imaginary potential of couplings to the inelastic channels, other than the 2+1 target excitation channel, is calculated in the Feshbach formalism. This calculated imaginary potential along with a short ranged volume Woods–Saxon potential to simulate the absorption in fusion channel reproduces the angular distributions for 16O+146Nd quite well. But for 16O+142,144Nd systems additional surface absorption is found to be necessary to fit the angular distribution data. The variations of this additional absorption term with incident energy and the mass of the target are explored. 相似文献
13.
For an innovative product characterized by short product lifecycle and high demand uncertainty, investment in capacity buildup has to be done cautiously. Otherwise either the product’s market diffusion is impeded or the manufacturer is left with unutilized capacity. Using the right information for making capacity augmentation decisions is critical in facing this challenge. In this paper, we propose a method for identifying critical information flows using the system dynamics model of a two-echelon supply chain. The fundamental premise of system dynamics methodology is that (system) structure determines (its) behavior. Using loop dominance analysis method we study the feedback loop structure of the supply chain system. The outcome is a set of dominant loops that determine the dynamics of capacity growth. It is revealed that the delivery delay information has little effect while the loop that connects retail sales with production order affects the dynamics significantly. Modifying this loop yields appropriate capacity augmentation decisions resulting in higher performance. What-if analyses bring out effects of modifying other structural elements. In conclusion, we claim that the information feedback based methodology is general enough to be useful in designing decision support systems for capacity augmentation. The limitations of the model are also discussed and possible extensions identified. 相似文献
14.
Summary A new tri-cavity decaaza macrocycle (TCM) has been synthesised by the condensation of tetra(aminopropyl)-cyclam with diethanolamine. The new macrocyclic ligand forms tri-nuclear complexes, [Cu3(TCM)(H2O)2]-(ClO4)6 and [Ni3(TCM)(H2O)2](ClO4)6. 相似文献
15.
16.
The decision problem for positively quantified formulae in the theory of linearly ordered Heyting algebras is known, as a special case of work of Kreisel, to be solvable; a simple solution is here presented, inspired by related ideas in Gödel-Dummett logic. 相似文献
17.
P. C. Roy 《等离子体物理论文集》1992,32(2):101-107
By using the two-point space correlation function an equation for the power spectral density for a random Langmuir field has been derived. The dispersion relation for a monochromatic wave is regained for a delta spectrum. For a Gaussian spectrum, the maximum growth rate is less than that for a monochromatic wave. For a “meander spectrum”, the growth rate is increased with the width of the spectrum in the first stage then decreased for further increase of the width. 相似文献
18.
The complexification of a semi-algebraic set is the smallest complex algebraic set containing S. Let S be defined by s polynomials of degrees less than d. We prove that the geometric degree of the complexification is less than .
Received: 9 January 1997; in final form: 11 August 2000 / Published online: 17 May 2001 相似文献
19.
The analysis in this paper looks at two important elements in modelling the market for timber in the United States. First, the issue of directional causality between price and quantity and its implications in a modelling effort is investigated. Second, the extent of the geographic market for timber is discussed and a method of detecting it is suggested. The method for detecting the extent of the geographical market is tractable and can be applied in a straightforward way. Both considerations are applied to the softwood lumber market in the United States. 相似文献
20.
This paper presents an algorithm and the supporting theory for solving a class of nonlinear multiple criteria optimization problems using Zionts—Wallenius type of interaction. The Zionts—Wallenius method, as extended in this paper, can be used for solving multiple criteria problems with concave objective and (implicit) value functions and convex feasible regions. Modifications of the method to handle nonconvex feasible regions and general nonlinear objective functions are also discussed.This research was supported, in part, by a Faculty Research Development Award and by a Council of 100 Research Grant from Arizona State University (Roy), and by a grant from Y. Jahnsson Foundation, Finland (Wallenius). The research was performed while the second author was a Visiting Professor at Arizona State University. 相似文献