全文获取类型
收费全文 | 353675篇 |
免费 | 2471篇 |
国内免费 | 997篇 |
专业分类
化学 | 158829篇 |
晶体学 | 5225篇 |
力学 | 19567篇 |
综合类 | 4篇 |
数学 | 68880篇 |
物理学 | 104638篇 |
出版年
2018年 | 18369篇 |
2017年 | 19002篇 |
2016年 | 11035篇 |
2015年 | 3264篇 |
2014年 | 2784篇 |
2013年 | 8241篇 |
2012年 | 12265篇 |
2011年 | 26810篇 |
2010年 | 15980篇 |
2009年 | 16330篇 |
2008年 | 21592篇 |
2007年 | 26755篇 |
2006年 | 6307篇 |
2005年 | 13630篇 |
2004年 | 9805篇 |
2003年 | 9444篇 |
2002年 | 6526篇 |
2001年 | 6149篇 |
2000年 | 4935篇 |
1999年 | 3690篇 |
1998年 | 2962篇 |
1997年 | 2927篇 |
1996年 | 3031篇 |
1995年 | 2708篇 |
1994年 | 2536篇 |
1993年 | 2445篇 |
1992年 | 2888篇 |
1991年 | 2789篇 |
1990年 | 2731篇 |
1989年 | 2762篇 |
1988年 | 2715篇 |
1987年 | 2714篇 |
1986年 | 2525篇 |
1985年 | 3391篇 |
1984年 | 3413篇 |
1983年 | 2843篇 |
1982年 | 3033篇 |
1981年 | 2961篇 |
1980年 | 2876篇 |
1979年 | 3028篇 |
1978年 | 3277篇 |
1977年 | 3009篇 |
1976年 | 2965篇 |
1975年 | 2811篇 |
1974年 | 2754篇 |
1973年 | 2806篇 |
1972年 | 1807篇 |
1968年 | 2035篇 |
1967年 | 2173篇 |
1966年 | 1980篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
901.
Vibsanin O, isolated from the leaves and twigs of Viburnum awabuki, is an unprecedented bicyclic diterpenoid. The structures of vibsanin O was established by extensive analysis of spectroscopic data. 相似文献
902.
Andrea Grosso Marco Locatelli Fabio Schoen 《Computational Optimization and Applications》2007,38(3):351-370
In this paper we perform a computational analysis of a population based approach for global optimization, Population Basin
Hopping (PBH), which was proven to be very efficient on very challenging global optimization problems by the authors (see
). The experimental analysis aims at understanding more deeply how the approach works and why it is successful on challenging
problems. 相似文献
903.
A. V. Koshelkin 《Journal of Experimental and Theoretical Physics》2003,96(4):653-657
On the basis of diagram formalism for two-particle Green functions, the bremsstrahlung of charged particles interacting in a dense medium is investigated. In the case of production of soft photons, exact expressions for two-particle Green functions corresponding to the process of particle bremsstrahlung in the substance are obtained. The Green functions found are fully determined by the set of closed irreducible diagrams. It is shown that, in the case of radiation in a sufficiently dense medium in a far long-wave region of the spectrum, the coherent multiple particle scattering results in an additional (as compared that reported earlier in [1–13]) suppression of the bremsstrahlung photon yield. 相似文献
904.
L. A. Falkovsky 《Journal of Experimental and Theoretical Physics》2003,96(2):335-339
The effect of free carriers on the dispersion and damping of coupled phonon-plasmon modes is considered in the long-wave approximation. The electron and phonon scattering rate, as well as Landau damping, is taken into account. 相似文献
905.
Homogeneously prepared tosylcelluloses (TC) with degrees of substitution (DS) of DSTos 0.1–1.8 were used as intermediates for the synthesis of methylaminocelluloses (MAC) by nucleophilic substitution with methylamine. TC with DSTos up to 1.1 were shown to be valuable intermediates for selective synthesis of MAC with DSMA varying from 0.1 to approximately 1. No nucleophilic substitution was observed at higher DSTos. At the chosen reaction conditions (60 °C, 48 h) residual tosyl moieties remained unchanged and little hydrolysis took place. The samples obtained were characterized by means of elemental analysis, FTIR and 13C CP/MAS NMR spectroscopy. 13C CP/MAS NMR spectroscopy was found to be an efficient tool for quantification of DSMA. Furthermore, the swelling behaviour in water was investigated and preliminary tests concerning the bilirubin adsorption capacity of MAC were carried out. 相似文献
906.
A simple procedure for the synthesis of an important standard, isotopically enriched methylmercury, which is not commercially available, has been established successfully. The isotopically enriched standard synthesized is utilized in conventional isotope dilution mass spectrometry (IDMS), as well as in speciated IDMS (SIDMS), for determination of the true concentration of methylmercury in environmental samples. The CH3201Hg+ standard has been synthesized from commercially available 201HgO and tetramethyltin. The synthesis time required is 1 h at 60°C. The product is highly pure, yielding more than 90% as 201Hg in CH3201Hg+. Hazardous dimethylmercury does not occur during this synthesis procedure. The product synthesized was analyzed using high‐performance liquid chromatography coupled with inductively coupled plasma mass spectrometry (ICP‐MS) and ICP‐MS alone in order to determine its concentration, isotopic composition and purity. The stability of the product was also evaluated for over 6 months and found to be stable at 4°C in the dark. The isotopically enriched methylmercury synthesized can be used in SIDMS and IDMS analyses as a standard. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
907.
A series of optically active main chain polyesters were synthesized by high temperature polycondensation from biphenolic azo chromophores with azobenzene-4,4'-dicarbonylchloride and 1,4:3,6-dianhydro-D-sorbitol ([!]D25=+42.5°). The second harmonic generation of the polyesters is studied in thin films. The polar order in films is determined from the UV-visible absorption spectra. The variation in SHG intensity with chiral monomer concentration is explained as a function of polar order. The polymers with chiral units showed good second harmonic efficiency. The intensity of second harmonic light (532 nm) increased with angle of incidence and indicated the polar order in the plane of the film. The SH signal also showed good temporal stability. 相似文献
908.
H. -Q. Liu 《manuscripta mathematica》1995,87(1):159-166
This article was processed by the author using the IATEX style filecljourl from Springer-Verlag. 相似文献
909.
910.
This paper deals with a computational analysis of the influence of the pressing method and part geometry on the final density
distribution in the cold compaction process of ceramic alumina powders. The analysis is based on the explicit finite-element
model proposed and validated in a previous study. The mechanical behavior of the processing material is described using a
multisurface elastoplastic model, the modified Drucker-Prager/Cap model
Published in Prikladnaya Mekhanika, Vol. 43, No. 10, pp. 129–134, October 2007. 相似文献