全文获取类型
收费全文 | 2997篇 |
免费 | 9篇 |
国内免费 | 257篇 |
专业分类
化学 | 2822篇 |
力学 | 7篇 |
综合类 | 3篇 |
数学 | 13篇 |
物理学 | 418篇 |
出版年
2022年 | 6篇 |
2021年 | 4篇 |
2020年 | 2篇 |
2019年 | 2篇 |
2018年 | 3篇 |
2017年 | 3篇 |
2016年 | 5篇 |
2015年 | 6篇 |
2014年 | 9篇 |
2013年 | 1篇 |
2012年 | 260篇 |
2011年 | 324篇 |
2010年 | 41篇 |
2009年 | 125篇 |
2008年 | 430篇 |
2007年 | 303篇 |
2006年 | 355篇 |
2005年 | 349篇 |
2004年 | 252篇 |
2003年 | 196篇 |
2002年 | 147篇 |
2001年 | 97篇 |
2000年 | 113篇 |
1999年 | 42篇 |
1998年 | 13篇 |
1997年 | 8篇 |
1996年 | 37篇 |
1995年 | 19篇 |
1994年 | 21篇 |
1993年 | 46篇 |
1992年 | 25篇 |
1991年 | 6篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1979年 | 1篇 |
排序方式: 共有3263条查询结果,搜索用时 78 毫秒
991.
We model the QCD Dirac operator as a power-law random banded matrix (RBM) with the appropriate chiral symmetry. Our motivation is the form of the Dirac operator in a basis of instantonic zero modes with a corresponding gauge background of instantons. We compare the spectral correlations of this model to those of an instanton liquid model (ILM) and find agreement well beyond the Thouless energy. In the bulk of the spectrum the dimensionless Thouless energy of the RBM scales with the square root of system size in agreement with the ILM and chiral perturbation theory. Near the origin the scaling in the RBM remains the same as in the bulk which agrees with chiral perturbation theory but not with the ILM. Finally we discuss how this RBM should be modified in order to describe the spectral correlations of the QCD Dirac operator at the finite temperature chiral restoration transition. 相似文献
992.
Brewer WD Scherz A Sorg C Wende H Baberschke K Bencok P Frota-Pessôa S 《Physical review letters》2004,93(7):077205
We present x-ray magnetic circular dichroism determinations of the orbital/spin magnetic moment ratios of dilute 3d-series impurities in Au (and Cu) host matrices. This is the first direct measurement of considerable orbital moments in cubic symmetry for a localized impurity in a bulk metal host. It is shown that the unquenching of orbital magnetism depends on a delicate balance of hybridization effects between the local impurity with the host and the filling of the 3d states of the impurity. The results are accompanied by ab initio calculations that support our experimental findings. 相似文献
993.
We propose a method for generating shock waves in Bose-Einstein condensates by rapidly increasing the value of the nonlinear coefficient using Feshbach resonances. We show that in a cigar-shaped condensate there exist primary (transverse) and secondary (longitudinal) shock waves. We analyze how the shocks are generated in multidimensional scenarios and describe the related phenomenology. 相似文献
994.
We present an ab initio study of the relaxations introduced in TiO (2) when a Cd impurity substitutes a Ti atom and an experimental test of this calculation by a perturbed-angular-correlation (PAC) measurement of the orientation of the electric-field gradient (EFG) tensor at the Cd site. The ab initio calculation predicts strong anisotropic relaxations of the nearest oxygen neighbors of the impurity and a change of the orientation of the largest EFG tensor component, V(33 ), from the [001] to the [110] direction upon substitution of a Ti atom by a Cd impurity. The last prediction is confirmed by the PAC experiment that shows that V(33 ) at the Cd site is parallel to either the [110] or the [1 1;0] crystal axis. 相似文献
995.
Baragaña B Blackburn AG Breccia P Davis AP de Mendoza J Padrón-Carrillo JM Prados P Riedner J de Vries JG 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(13):2931-2936
The cationic steroidal receptors 9 and 11 have been synthesized from cholic acid 3. Receptor 9 extracts N-acetyl-alpha-amino acids from aqueous media into chloroform with enantioselectivities (L:D) of 7-10:1. The lipophilic variant 11 has been employed for the enantioselective transport of N-acetylphenylalanine, a) through dichloromethane (DCM) and dichloroethane (DCE) bulk liquid membranes (U-tube apparatus), and b) through 2.5% (v/v) octanol/hexane via hollow fibre membrane contactors. Significant enantioselectivities and multiple turnovers were observed for both types of apparatus. 相似文献
996.
Corma A Galletero MS García H Palomares E Rey F 《Chemical communications (Cambridge, England)》2002,(10):1100-1101
Pyrene as a fluorophore has been covalently anchored on a delaminated ITQ-2 zeolite having a large external surface area (730 m2 g-1) and the resulting solid found to have a selective response as a heterogeneous sensor for I- in the presence of other halides. 相似文献
997.
Corma A García H Moussaif A Sabater MJ Zniber R Redouane A 《Chemical communications (Cambridge, England)》2002,(10):1058-1059
Two solid catalysts in which a chiral copper(II) bisoxazoline has been covalently anchored on silica and MCM-41 have been prepared; the solids are enantioselective catalysts (up to 92% ee) for the Friedel-Crafts hydroxyalkylation of 1,3-dimethoxybenzene with 3,3,3-trifluoropyruvate. 相似文献
998.
Korybut-Daszkiewicz B Wieckowska A Bilewicz R Domagała S Woźniak K 《Journal of the American Chemical Society》2001,123(38):9356-9366
[2]Catenane systems containing copper(II) and nickel(II) as metal centers have been self-assembled using tetraazamacrocyclic complexes and benzo-24-crown-8 as building blocks. A variety of methods, including X-ray crystallography, ESI mass spectrometry, (13)C and (1)H NMR, and electrochemistry, were applied to characterize these new face-to-face bismacrocyclic systems. Weak pi...pi interactions introduced by interlocking transition metal complexes with benzocrown moieties were shown to increase the communication (cooperativity) of metal centers. Introduction of the benzocrown increases the stability of the mixed valence state of the macrocyclic complex, which is reflected in high values of conproportionation constants. Moreover, this effect was found to be stronger than that obtained by shortening the length of the spacer between the two tetraazamacrocyclic subunits in the parent bismacrocycles. The extent of communication is larger for the nickel catenane than for the copper one. 相似文献
999.
1000.
García-Ripoll JJ Molina-Terriza G Pérez-García VM Torner L 《Physical review letters》2001,87(14):140403
In this paper we study a gaseous Bose-Einstein condensate and show the following: (i) A minimum value of the interaction is needed for the existence of stable persistent currents. (ii) Vorticity is not a fundamental invariant of the system, as there exists a conservative mechanism which can destroy a vortex and change its sign. (iii) This mechanism is suppressed by strong interactions. 相似文献