全文获取类型
收费全文 | 2242篇 |
免费 | 67篇 |
国内免费 | 28篇 |
专业分类
化学 | 1281篇 |
晶体学 | 35篇 |
力学 | 34篇 |
数学 | 436篇 |
物理学 | 551篇 |
出版年
2022年 | 22篇 |
2021年 | 29篇 |
2020年 | 29篇 |
2019年 | 32篇 |
2018年 | 15篇 |
2017年 | 23篇 |
2016年 | 40篇 |
2015年 | 45篇 |
2014年 | 38篇 |
2013年 | 145篇 |
2012年 | 118篇 |
2011年 | 103篇 |
2010年 | 69篇 |
2009年 | 59篇 |
2008年 | 103篇 |
2007年 | 125篇 |
2006年 | 134篇 |
2005年 | 124篇 |
2004年 | 97篇 |
2003年 | 78篇 |
2002年 | 89篇 |
2001年 | 37篇 |
2000年 | 49篇 |
1999年 | 36篇 |
1998年 | 30篇 |
1997年 | 32篇 |
1996年 | 45篇 |
1995年 | 32篇 |
1994年 | 50篇 |
1993年 | 43篇 |
1992年 | 39篇 |
1991年 | 24篇 |
1990年 | 30篇 |
1989年 | 29篇 |
1988年 | 16篇 |
1987年 | 18篇 |
1986年 | 19篇 |
1985年 | 26篇 |
1984年 | 17篇 |
1983年 | 17篇 |
1982年 | 13篇 |
1981年 | 17篇 |
1980年 | 22篇 |
1979年 | 19篇 |
1978年 | 23篇 |
1977年 | 14篇 |
1976年 | 21篇 |
1975年 | 16篇 |
1973年 | 16篇 |
1972年 | 9篇 |
排序方式: 共有2337条查询结果,搜索用时 15 毫秒
1.
2.
Anna Arkhireeva John N. Hay Jackie M. Lane Miguel Manzano Helen Masters Wilberforce Oware Steve J. Shaw 《Journal of Sol-Gel Science and Technology》2004,31(1-3):31-36
The synthesis of ORganically MOdified SILica (ORMOSIL) particles has been carried out using both the hydrolytic and non-hydrolytic sol-gel routes. The hybrid (nano)composites are organically modified with an alkyl or aryl group covalently bonded to silicon. Hybrids have been synthesised in an aqueous sol-gel process by a modified Stöber route, producing spherical nanoparticles with diameters in the range 50–300 nm. The size of the particles can be controlled by control of certain reaction parameters. Smaller ormosil nanoparticles can be synthesised by a base-catalysed emulsion polymerisation route, by varying the type and concentration of surfactant and precursor feed rate. In this case, particles in the size range 3.5–10 nm can be obtained. Hybrids have been synthesised from hyperbranched polyesters by encapsulation in a silica matrix using the hydrolytic sol-gel route. Optimisation of the reaction conditions allows the hybrids to be produced as isolated sub-micron spherical particles. Ormosil particles have also been synthesised using the non-hydrolytic sol-gel route, which may lead to products of different morphologies because of the different polarity of the reaction medium. Different reaction conditions were studied in order to optimise the size and shape of the particles, including choice of solvent, use of surfactants and addition of polystyrene. Dimethylsulfoxide acts as a novel oxygen donor for the catalyst-free formation of colourless silsesquioxanes. 相似文献
3.
4.
This report focuses on a theoretical study of the cobalt-cabon bond activation mechanism in Vitamin B12, its co enzyme complexes, and model compounds such as cobalamins (Cbl), cobaloximes and cobalt porphyrins. In particular, emphasis is placed on the nucleotide loop and its role in the base on and base off mechanism. 相似文献
5.
The regression problem in learning theory is investigated with least square Tikhonov regularization schemes in reproducing
kernel Hilbert spaces (RKHS). We follow our previous work and apply the sampling operator to the error analysis in both the
RKHS norm and the L2 norm. The tool for estimating the sample error is a Bennet inequality for random variables with values in Hilbert spaces.
By taking the Hilbert space to be the one consisting of Hilbert-Schmidt operators in the RKHS, we improve the error bounds
in the L2 metric, motivated by an idea of Caponnetto and de Vito. The error bounds we derive in the RKHS norm, together with a Tsybakov
function we discuss here, yield interesting applications to the error analysis of the (binary) classification problem, since
the RKHS metric controls the one for the uniform convergence. 相似文献
6.
The q-Catalan numbers studied by Carlitz and Riordan are polynomials in q with nonnegative coefficients. They evaluate, at q = 1, to the Catalan numbers: 1, 1, 2, 5, 14,…, a log-convex sequence. We use a combinatorial interpretation of these polynomials
to prove a q-log-convexity result. The sequence of q-Catalan numbers is not q-log-convex in the narrow sense used by other authors, so our work suggests a more flexible definition of q-log convex be adopted.
Received January 2, 2007 相似文献
7.
Ian R. Butler Alfonso G. Callabero Jennifer R. Amey Dafydd A. Thomas Thomas Gelbrich 《Tetrahedron letters》2004,45(3):467-472
The synthesis of a range of ferrocene-substituted ethynylanthracenes and 1,1′-(bis-(2-ethenylanthraquinoyl)ferrocene has been achieved. The synthesis relies on the production of ferrocenylanthraquinones as key precursors. The products were obtained in the reactions of ferrocenylanthraquinones with phenylethynyllithium or trimethylsilylethynyllithium followed by reduction with tin chloride. The key products such as 1- and 2-ferrocenyl(9,10-bis-phenylethynyl)anthracenes have been characterised by X-ray single crystal diffraction. 相似文献
8.
9.
Thin films of polystyrene (PS), poly(methyl methacrylate) (PMMA) and polystyrene-polyacrylonitrile copolymer (PS-AN), containing various embedded transition-metal complexes, have been studied by FTIR microscopy. The spatial distributions of the transition-metal carbonyl complexes throughout the thin organic polymer films have been determined by a two-dimensional IR mapping procedure. The spectral variations observed in the distribution of the metal carbonyls throughout the different polymer films are discussed. The IR data show that the technique used to prepare the organometallic-embedded thin films (viz. freeze-drying of solutions followed by hot mechanical pressing of the residues) does in general lead to homogeneous films which may eventually find industrial application, e.g. as membrane sensors for small molecules. 相似文献
10.