全文获取类型
收费全文 | 1590篇 |
免费 | 58篇 |
国内免费 | 26篇 |
专业分类
化学 | 903篇 |
晶体学 | 23篇 |
力学 | 28篇 |
数学 | 410篇 |
物理学 | 310篇 |
出版年
2022年 | 20篇 |
2021年 | 21篇 |
2020年 | 24篇 |
2019年 | 31篇 |
2018年 | 16篇 |
2017年 | 19篇 |
2016年 | 34篇 |
2015年 | 35篇 |
2014年 | 37篇 |
2013年 | 84篇 |
2012年 | 95篇 |
2011年 | 81篇 |
2010年 | 58篇 |
2009年 | 48篇 |
2008年 | 87篇 |
2007年 | 98篇 |
2006年 | 104篇 |
2005年 | 98篇 |
2004年 | 83篇 |
2003年 | 61篇 |
2002年 | 74篇 |
2001年 | 20篇 |
2000年 | 32篇 |
1999年 | 22篇 |
1998年 | 25篇 |
1997年 | 23篇 |
1996年 | 25篇 |
1995年 | 17篇 |
1994年 | 29篇 |
1993年 | 26篇 |
1992年 | 25篇 |
1991年 | 16篇 |
1990年 | 17篇 |
1989年 | 13篇 |
1988年 | 6篇 |
1987年 | 9篇 |
1986年 | 15篇 |
1985年 | 9篇 |
1984年 | 8篇 |
1983年 | 10篇 |
1982年 | 12篇 |
1981年 | 8篇 |
1980年 | 12篇 |
1978年 | 12篇 |
1977年 | 9篇 |
1976年 | 8篇 |
1975年 | 11篇 |
1974年 | 7篇 |
1973年 | 7篇 |
1968年 | 6篇 |
排序方式: 共有1674条查询结果,搜索用时 15 毫秒
1.
Michael S. Donovan Andrew B. Lowe Taylor A. Sanford Charles L. McCormick 《Journal of polymer science. Part A, Polymer chemistry》2003,41(9):1262-1281
A novel bifunctional acrylamido‐based reversible addition–fragmentation chain transfer (RAFT) chain‐transfer agent (CTA), N,N′‐ethylenebis[2‐(thiobenzoylthio)propionamide] (CTA2), has been synthesized and used for the controlled free‐radical polymerization of N,N‐dimethylacrylamide (DMA). A comparative study of CTA2 and the monofunctional CTA N,N‐dimethyl‐s‐thiobenzoylthiopropionamide (CTA1) has been conducted. Polymerizations mediated by CTA1 result in poly(N,N‐dimethylacrylamide) (PDMA) homopolymers with unimodal molecular weight distributions, whereas CTA2 yields unimodal, bimodal, and trimodal distributions according to the extent of conversion. The multimodal nature of the PDMAs has been attributed to termination events and/or chains initiated by primary radicals. The RAFT polymerization of DMA with CTA2 also results in a prolonged induction period that may be attributed to the higher local concentration of dithioester functionalities early in the polymerization. A series of ω‐ and α,ω‐dithioester‐capped PDMAs have been prepared in organic media and subsequently employed as macro‐CTAs for the synthesis of diblock and triblock copolymers in aqueous media with the zwitterionic monomer 3‐[2‐(N‐methylacrylamido)‐ethyldimethylammonio] propane sulfonate (MAEDAPS). Additionally, an ω‐dithioester‐capped MAEDAPS homopolymer has been used as a macro‐CTA for the block polymerization of DMA. To our knowledge, this is the first example of a near‐monodisperse, sulfobetaine‐containing block copolymer prepared entirely in aqueous media. The diblock and triblock copolymers form aggregates in pure water that can be dissociated by the addition of salt, as determined by 1H NMR spectroscopy and dynamic light scattering. In pure water, highly uniform, micellelike aggregates with hydrodynamic diameters of 71–93 nm are formed. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1262–1281, 2003 相似文献
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.
7.
8.
Steve Tisserand Célia Billaud J.R. Falck Charles Mioskowski 《Tetrahedron letters》2006,47(29):5177-5180
CrCl2-mediated condensation of γ-chloro-gem-trichloroalkanes with aldehyde generates homoallylic alcohols through a hydride rearrangement followed by a Nozaki-Hiyama allylation. 相似文献
9.
10.