全文获取类型
收费全文 | 7347篇 |
免费 | 335篇 |
国内免费 | 22篇 |
专业分类
化学 | 5165篇 |
晶体学 | 23篇 |
力学 | 143篇 |
数学 | 816篇 |
物理学 | 1557篇 |
出版年
2023年 | 61篇 |
2022年 | 63篇 |
2021年 | 98篇 |
2020年 | 136篇 |
2019年 | 131篇 |
2018年 | 81篇 |
2017年 | 76篇 |
2016年 | 261篇 |
2015年 | 220篇 |
2014年 | 221篇 |
2013年 | 376篇 |
2012年 | 445篇 |
2011年 | 459篇 |
2010年 | 296篇 |
2009年 | 266篇 |
2008年 | 419篇 |
2007年 | 357篇 |
2006年 | 382篇 |
2005年 | 370篇 |
2004年 | 322篇 |
2003年 | 224篇 |
2002年 | 234篇 |
2001年 | 145篇 |
2000年 | 123篇 |
1999年 | 99篇 |
1998年 | 88篇 |
1997年 | 121篇 |
1996年 | 109篇 |
1995年 | 98篇 |
1994年 | 87篇 |
1993年 | 106篇 |
1992年 | 81篇 |
1991年 | 49篇 |
1990年 | 56篇 |
1989年 | 46篇 |
1988年 | 39篇 |
1987年 | 55篇 |
1986年 | 47篇 |
1985年 | 46篇 |
1984年 | 49篇 |
1983年 | 30篇 |
1981年 | 31篇 |
1978年 | 41篇 |
1977年 | 47篇 |
1976年 | 40篇 |
1975年 | 35篇 |
1974年 | 33篇 |
1973年 | 49篇 |
1957年 | 30篇 |
1955年 | 30篇 |
排序方式: 共有7704条查询结果,搜索用时 125 毫秒
11.
Markus Szymik 《Topology and its Applications》2007,154(11):2323-2332
Let G be a finite group. For semi-free G-manifolds which are oriented in the sense of Waner [S. Waner, Equivariant RO(G)-graded bordism theories, Topology and its Applications 17 (1984) 1-26], the homotopy classes of G-equivariant maps into a G-sphere are described in terms of their degrees, and the degrees occurring are characterised in terms of congruences. This is first shown to be a stable problem, and then solved using methods of equivariant stable homotopy theory with respect to a semi-free G-universe. 相似文献
12.
C. Baumgarten B. Braun G. Court G. Ciullo P. Ferretti G. Graw W. Haeberli M. Henoch R. Hertenberger N. Koch H. Kolster P. Lenisa A. Nass S.P. Pod'yachev D. Reggiani K. Rith M.C. Simani E. Steffens J. Stewart T. Wise 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(1):37-49
The use of storage cells has become a standard technique for internal gas targets in conjunction with high energy storage
rings. In case of spin-polarized hydrogen and deuterium gas targets the interaction of the injected atoms with the walls of
the storage cell can lead to depolarization and recombination. Thus the number of wall collisions of the atoms in the target
gas is important for modeling the processes of spin relaxation and recombination. It is shown in this article that the diffusion
process of rarefied gases in long tubes or storage cells can be described with the help of the one-dimensional diffusion equation.
Mathematical methods are presented that allow one to calculate collision age distributions (CAD) and their moments analytically.
These methods provide a better understanding of the different aspects of diffusion than Monte Carlo calculations. Additionally
it is shown that measurements of the atomic density or polarization of a gas sample taken from the center of the tube allow
one to determine the possible range of the corresponding density weighted average values along the tube. The calculations
are applied to the storage cell geometry of the HERMES internal polarized hydrogen and deuterium gas target.
Received 9 July 2001 and Received in final form 18 September 2001 相似文献
13.
G.Biju Kumar Hetal.V Patel Amrish C Shah Markus Trenkle Christine J Cardin 《Tetrahedron: Asymmetry》1996,7(12):3391-3396
N-Arylsulfonamides of (R)- and (S)-2-amino-1-butanol, on condensation with aromatic aldehydes produced diastereomerically pure 2-aryl-3-arenesulfonyl 4-ethyl-1,3-oxazolidines. The absolute configurations of one enantiomeric pair have been determined from two fully refined X-ray structures, supplemented by nmr data. 相似文献
14.
15.
Markus Hegland Jochen Garcke Vivien Challis 《Linear algebra and its applications》2007,420(2-3):249-275
The combination technique has repeatedly been shown to be an effective tool for the approximation with sparse grid spaces. Little is known about the reasons of this effectiveness and in some cases the combination technique can even break down. It is known, however, that the combination technique produces an exact result in the case of a projection into a sparse grid space if the involved partial projections commute.
The performance of the combination technique is analysed using a projection framework and the C/S decomposition. Error bounds are given in terms of angles between the spanning subspaces or the projections onto these subspaces. Based on this analysis modified combination coefficients are derived which are optimal in a certain sense and which can substantially extend the applicability and performance of the combination technique. 相似文献
16.
D. Chiladze J. Carbonell S. Dymov V. Glagolev M. Hartmann V. Hejny A. Kacharava I. Keshelashvili A. Khoukaz H.R. Koch V. Komarov P. Kulessa A. Kulikov G. Macharashvili Y. Maeda T. Mersmann S. Merzliakov S. Mikirtytchiants A. Mussgiller M. Nioradze H. Ohm F. Rathmann R. Schleichert H.J. Stein H. Ströher Yu. Uzikov S. Yaschenko C. Wilkin 《Physics letters. [Part B]》2006
17.
18.
Matthias Heydenreich Andreas Koch E. Kleinpeter Thomas Zimmermann 《Fresenius' Journal of Analytical Chemistry》1997,357(5):517-521
Dynamic NMR investigations of a number of 2-amino-3-aroyl-4,6-diaryl-pyrylium salts were carried out. The barrier to rotation
of the partial C, N double bond was determined and proved to be in the range of 62 to 63 kJ/mol. Quantum chemical calculations
of bond orders and electron densities of the different atoms in the molecules show the distinct double bond character of the
exocyclic C, N bond. This is in agreement with the relatively high barrier to rotation. By quantum chemical ab initio 3-21G
calculations, the dynamic behaviour of this kind of compounds was simulated; two pairs (image and mirror image) of ground
state conformations, in coincidence with the experiment, were obtained.
Received: 10 May 1996 / Revised: 1 July 1996 / Accepted: 4 July 1996 相似文献
19.
20.