全文获取类型
收费全文 | 16028篇 |
免费 | 437篇 |
国内免费 | 327篇 |
专业分类
化学 | 10016篇 |
晶体学 | 100篇 |
力学 | 446篇 |
综合类 | 30篇 |
数学 | 2211篇 |
物理学 | 3989篇 |
出版年
2022年 | 169篇 |
2021年 | 199篇 |
2020年 | 184篇 |
2019年 | 196篇 |
2018年 | 186篇 |
2017年 | 153篇 |
2016年 | 358篇 |
2015年 | 337篇 |
2014年 | 404篇 |
2013年 | 873篇 |
2012年 | 710篇 |
2011年 | 839篇 |
2010年 | 583篇 |
2009年 | 559篇 |
2008年 | 769篇 |
2007年 | 781篇 |
2006年 | 638篇 |
2005年 | 647篇 |
2004年 | 660篇 |
2003年 | 621篇 |
2002年 | 658篇 |
2001年 | 456篇 |
2000年 | 422篇 |
1999年 | 327篇 |
1998年 | 241篇 |
1997年 | 213篇 |
1996年 | 233篇 |
1995年 | 247篇 |
1994年 | 240篇 |
1993年 | 187篇 |
1992年 | 174篇 |
1991年 | 185篇 |
1990年 | 202篇 |
1989年 | 160篇 |
1988年 | 146篇 |
1987年 | 136篇 |
1986年 | 128篇 |
1985年 | 227篇 |
1984年 | 250篇 |
1983年 | 163篇 |
1982年 | 184篇 |
1981年 | 155篇 |
1980年 | 158篇 |
1979年 | 148篇 |
1978年 | 132篇 |
1977年 | 166篇 |
1976年 | 148篇 |
1975年 | 125篇 |
1974年 | 116篇 |
1973年 | 121篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
A variational approach is proposed to study some properties of the adiabatic Holstein–Hubbard model which describes an assembly of fermionic charges interacting with a static atomic lattice. The sum of the electronic energy and the lattice elastic energy is proved to have minima with a many-polaron structure in a certain domain of model parameters. Our analytical work consists in expanding these energy minima from the zero electronic transfer limit which remarkably holds for a finite amplitude of the onsite Hubbard repulsion and for an unbounded lattice size. 相似文献
2.
3.
Zuo LIU Zhen De WU 《数学学报(英文版)》2005,21(5):997-1000
Let κ be non-negative integer. The unoriented bordism classes, which can be represented as [RP(ξ^κ)] where ξ^κ is a k-plane bundle, form an ideal of the unoriented bordism ring MO.. A group of generators of this ideal expressed by a base of MO. and a necessary and sufficient condition for a bordism class to belong to this ideal are given. 相似文献
4.
In this paper we obtain a number of Maharam-type slice integral representations, with respect to scalar measures, for positive
projections in Dedekind complete vector lattices and f-algebras.
AMS Classification: 47B65, 46A40, 06F25 相似文献
5.
Michael De Castro 《Tetrahedron letters》2004,45(34):6501-6504
2-Deoxy-2-iodo-glycosylamides have been prepared from a variety of protected d-glucals by their reaction with N-iodosuccinimide and amides. Benzyl protected 2-iodoamides, when treated with sodium hydride and 15-crown-5, gave stable C1 N-linked 2-glycooxazolines as the major products. Silyl protected 2-iodoamides afforded the C1 O-linked 2-glycooxazolines; presumably by the rearrangement of unstable N-acylaziridine intermediates. 相似文献
6.
Ashish Goel Monika R. Henzinger Serge Plotkin Eva Tardos 《Journal of Algorithms in Cognition, Informatics and Logic》2003,48(2):314-332
In this paper we consider the online ftp problem. The goal is to service a sequence of file transfer requests given bandwidth constraints of the underlying communication network. The main result of the paper is a technique that leads to algorithms that optimize several natural metrics, such as max-stretch, total flow time, max flow time, and total completion time. In particular, we show how to achieve optimum total flow time and optimum max-stretch if we increase the capacity of the underlying network by a logarithmic factor. We show that the resource augmentation is necessary by proving polynomial lower bounds on the max-stretch and total flow time for the case where online and offline algorithms are using same-capacity edges. Moreover, we also give polylogarithmic lower bounds on the resource augmentation factor necessary in order to keep the total flow time and max-stretch within a constant factor of optimum. 相似文献
7.
8.
Jocelyn Sabatier Serge Poullain Patrick Latteux Jean Luc Thomas Alain Oustaloup 《Nonlinear dynamics》2004,38(1-2):383-400
Robust speed control of a low damped electromechanical system with backlash is studied, controlled load angular speed being not measured. The proposed control strategy combines a Luenberger observer (load angular speed and load torque disturbance estimations) and a robust CRONE controller. The observer provides estimation of the load angular speed and of the disturbance torque applied on the load. Through the computation of only three independent parameters (as many as a PID controller), the CRONE controller permits to ensure the robust speed control of the load in spite of plant parametric variations and speed observation errors. The proposed control strategy is applied to a four mass experimental test bench. 相似文献
9.
Peixiang Xing Gilles P. Robertson Michael D. Guiver Serguei D. Mikhailenko Serge Kaliaguine 《Journal of polymer science. Part A, Polymer chemistry》2004,42(12):2866-2876
A series of sulfonated poly(aryl ether ketone)s (SPAEKs) were prepared by aromatic nucleophilic polycondensation of 2,6‐dihydroxynaphthalene with 5,5′‐carbonyl‐bis(2‐fluorobenzenesulfonate) and 4,4′‐difluorobenzophenone. The structure and degree of sulfonation (DS) of the SPAEKs were characterized using 1H NMR spectroscopy. The experimentally observed DS values were close to the expected values derived from the starting material ratios. The thermal stabilities of the SPAEKs were characterized by thermogravimetric analysis, which showed that in acid and sodium salt forms they were thermally stable in air up to about 240 and 380 °C, respectively. Transparent membranes cast from the directly polymerized SPAEKs exhibited good mechanical properties in both dry and hydrated states. The dependence of water uptake and of membrane swelling on the DS at different temperatures was studied. SPAEK membranes with a DS from 0.72 to 1.60 maintained adequate mechanical properties after immersion in water at 80 °C for 24 h. The proton conductivity of SPAEK membranes with different degrees of sulfonation was measured as a function of temperature. The proton conductivity of the SPAEK films increased with increased DS, and the highest room temperature conductivity (4.2 × 10?2 S/cm) was recorded for a SPAEK membrane with a DS of 1.60, which further increased to 1.1 × 10?1 S/cm at 80 °C. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2866–2876, 2004 相似文献
10.
The basic features of a chemical measurement 总被引:2,自引:0,他引:2