全文获取类型
收费全文 | 68416篇 |
免费 | 2549篇 |
国内免费 | 185篇 |
专业分类
化学 | 44093篇 |
晶体学 | 388篇 |
力学 | 1934篇 |
综合类 | 4篇 |
数学 | 11218篇 |
物理学 | 13513篇 |
出版年
2023年 | 491篇 |
2022年 | 556篇 |
2021年 | 925篇 |
2020年 | 997篇 |
2019年 | 1009篇 |
2018年 | 1320篇 |
2017年 | 1133篇 |
2016年 | 2176篇 |
2015年 | 1921篇 |
2014年 | 1988篇 |
2013年 | 3997篇 |
2012年 | 4517篇 |
2011年 | 4790篇 |
2010年 | 2942篇 |
2009年 | 2559篇 |
2008年 | 4125篇 |
2007年 | 4091篇 |
2006年 | 3697篇 |
2005年 | 3512篇 |
2004年 | 2977篇 |
2003年 | 2436篇 |
2002年 | 2125篇 |
2001年 | 1329篇 |
2000年 | 1136篇 |
1999年 | 847篇 |
1998年 | 660篇 |
1997年 | 630篇 |
1996年 | 758篇 |
1995年 | 521篇 |
1994年 | 579篇 |
1993年 | 563篇 |
1992年 | 571篇 |
1991年 | 489篇 |
1990年 | 461篇 |
1989年 | 424篇 |
1988年 | 363篇 |
1987年 | 362篇 |
1986年 | 329篇 |
1985年 | 509篇 |
1984年 | 486篇 |
1983年 | 329篇 |
1982年 | 438篇 |
1981年 | 399篇 |
1980年 | 368篇 |
1979年 | 331篇 |
1978年 | 310篇 |
1976年 | 318篇 |
1975年 | 281篇 |
1974年 | 274篇 |
1973年 | 288篇 |
排序方式: 共有10000条查询结果,搜索用时 976 毫秒
121.
C Guéret N Jussien O Lhomme C Pavageau C Prins 《The Journal of the Operational Research Society》2003,54(5):458-465
In this paper, we describe an aircraft loading problem submitted by the French military agency (DGA) as part of a more general military airlift planning problem. It can be viewed as a kind of bi-dimensional bin-packing problem, with heterogeneous bins and several additional constraints. We introduce two-phase methods for solving this NP-hard problem. The first phase consists in building good initial solutions, thanks to two fast algorithms: a list-based heuristic and a loading pattern generation method. Both algorithms call a constraint-based subroutine, able to determine quickly if the items already loaded can be reshuffled to accommodate a new object. The second phase improves these preliminary solutions using local search techniques. Results obtained on real data sets are presented. 相似文献
122.
Julien Ferrari Christian Terreaux Tibor Kurtn Attila Szikszai‐Kiss Sndor Antus JeromeD. Msonthi Kurt Hostettmann 《Helvetica chimica acta》2003,86(8):2768-2778
Investigation of the methanol extract of the roots of Gnidia involucrata (Thymelaeaceae) led to the isolation and characterization of two new 3,8″‐biflavonoid diastereoisomers, named GB‐4 ( 6a ) and GB‐4a ( 6b ). Their absolute configurations were determined in mixture by on‐line LC/CD measurements, which also allowed the revision of absolute configurations of the biflavanoids GB‐1 and GB‐2, and the configurational assignment of GB‐3. 相似文献
123.
Let K be ? or an imaginary quadratic number field, and q ∈ K an integer with ¦q¦ > 1. We give a quantitative version of Σn≥1 an/(qn ? 1) ? K for non-zero periodic sequences (an) in K of period length ≤ 2. As a corollary, we get a quantitative version of the linear independence over K of 1, the q-harmonic series, and a q-analogue of log 2. A similar result on 1, the q-harmonic series, and a q-analogue of ζ(2) is also proved. Mathematics Subject Classification (2000): 11J72, 11J82 相似文献
124.
125.
Grégory Duby 《Archive for Mathematical Logic》2003,42(5):435-447
This paper generalizes results of F. K?rner from [4] where she established the existence of maximal automorphisms (i.e. automorphisms
moving all non-algebraic elements). An ω-maximal automorphism is an automorphism whose powers are maximal automorphisms. We
prove that any structure has an elementary extension with an ω-maximal automorphism. We also show the existence of ω-maximal
automorphisms in all countable arithmetically saturated structures. Further we describe the pairs of tuples (ˉa,ˉb) for which there is an ω-maximal automorphism mapping ˉa to ˉb.
Received: 12 December 2001 /
Published online: 10 October 2002
Supported by the ``Fonds pour la Formation à la Recherche dans l'Industrie et dans l'Agriculture'
Mathematics Subject Classification (2000): Primary: 03C50; Secondary: 03C57
Key words or phrases: Automorphism – Recursively saturated structure 相似文献
126.
Various physical systems of dispersive waves admit solutions in the form of generalized solitary waves. Such waves result from the resonance between a long localized wave and short periodic oscillations. Many estimates (rigorous and numerical) have been given for the amplitude of the ripples in the tail of the generalized solitary wave when its central part has a sech2 shape. This Note provides estimates (not yet rigorous) for the ripple amplitude when the central part is flat and wide. To cite this article: C. Fochesato, F. Dias, C. R. Acad. Sci. Paris, Ser. I 337 (2003). 相似文献
127.
Mattias Edn Jekabs Grins Zhijian Shen Zheng Weng 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2004,169(2):1
Using enhancement of the 27Al central-transition magnetization by applying RAPT prior to 27Al → 29Si cross-polarization, we demonstrate fast acquisition of 29Si one-dimensional MAS and two-dimensional 27Al–29Si HETCOR spectra on a new sialon phase Ba2Al3Si9N13O5. 相似文献
128.
Recent mass measurements of proton-rich nuclei close to the N=Z line were used for the calculation of the interaction strength δV pn between valence protons and neutrons. When compared with δV pn values calculated from mass values of the AME’95 mass tables, the breaking down of the SU(4) symmetry is verified at Z=32,33,34. 相似文献
129.
Christophe Roussel Loc Dayon Henrik Jensen Hubert H. Girault 《Journal of Electroanalytical Chemistry》2004,570(2):187-199
A series of electrogenerated selective electrophiles based on substituted benzoquinones has been characterized as tags for l-cysteine and cysteine residues in proteins. The electrophiles are generated electrochemically from the corresponding hydroquinones. It is shown from mass spectrometry analysis that the electrogenerated benzoquinone can tag the biomolecules. The rate constants pertaining to the addition of l-cysteine onto the electrogenerated benzoquinones have been determined using electrochemical techniques. The substitution patterns have been unraveled leading to the assessment of site-specific rate constants. It is shown that the rate constants are primarily dependent on the electronic nature of the substituents as expressed by the Hammett substitution constant. The apparent tagging yields observed for l-cysteine in nanospray mass spectrometry experiments do not correspond to the yields expected from the electrochemical study, as the ionisation efficiencies are highly dependent on the tag. Finally, the on-line tagging has been tested using β-lactoglobulin A and myoglobin. Based on these results, it is concluded that the tagging reaction is selective towards cysteine when it takes place in the nanospray interface. The results show that the methodology presented can be used for a rapid characterization and identification of reactive sites in biomolecules. 相似文献
130.
Bou-Huot Phe Véronique Bounor-Legare Laurent David Alain Michel 《Journal of Sol-Gel Science and Technology》2004,31(1-3):47-50
We study the synthesis of organic-inorganic hybrids in the molten state of the polymer without solvent, by reactive processing. The synthesis is based in a first step upon the crosslinking of ethylene vinyl acetate copolymer (EVA) through an exchange reaction between the pendant ester groups of EVA and tetrapropoxysilane (TPOS) in presence of dibutyltin oxide (DBTO) as an indispensable catalyst. Then in a second step the hydrolysis-condensation reactions of residual alkoxide groups results in silica network formation, which is covalently bonded with the organic network. An original approach was developed to correlate the evolution of the hydrolysis-condensation reactions through the assessment of propanol by gas chromatography and the evolution of the morphology through SAXS and TEM analysis. Silica-rich domains with a diameter close to 5 nm are obtained. 相似文献