全文获取类型
收费全文 | 3155篇 |
免费 | 105篇 |
国内免费 | 37篇 |
专业分类
化学 | 1895篇 |
晶体学 | 30篇 |
力学 | 84篇 |
综合类 | 1篇 |
数学 | 552篇 |
物理学 | 735篇 |
出版年
2022年 | 24篇 |
2021年 | 32篇 |
2020年 | 37篇 |
2019年 | 41篇 |
2018年 | 20篇 |
2017年 | 39篇 |
2016年 | 66篇 |
2015年 | 54篇 |
2014年 | 59篇 |
2013年 | 154篇 |
2012年 | 166篇 |
2011年 | 172篇 |
2010年 | 93篇 |
2009年 | 97篇 |
2008年 | 160篇 |
2007年 | 175篇 |
2006年 | 178篇 |
2005年 | 161篇 |
2004年 | 151篇 |
2003年 | 109篇 |
2002年 | 112篇 |
2001年 | 50篇 |
2000年 | 67篇 |
1999年 | 61篇 |
1998年 | 43篇 |
1997年 | 35篇 |
1996年 | 43篇 |
1995年 | 52篇 |
1994年 | 58篇 |
1993年 | 55篇 |
1992年 | 63篇 |
1991年 | 33篇 |
1990年 | 31篇 |
1989年 | 29篇 |
1988年 | 23篇 |
1987年 | 23篇 |
1986年 | 23篇 |
1985年 | 39篇 |
1984年 | 18篇 |
1983年 | 26篇 |
1982年 | 33篇 |
1981年 | 28篇 |
1980年 | 24篇 |
1979年 | 28篇 |
1978年 | 34篇 |
1977年 | 30篇 |
1976年 | 24篇 |
1975年 | 27篇 |
1974年 | 31篇 |
1973年 | 30篇 |
排序方式: 共有3297条查询结果,搜索用时 78 毫秒
1.
A one-dimensional bulk reaction model for the oxidation of nickeltitanium is formulated, with preferential oxidation of titaniumbeing included. The modelling is directed at the better understandingof the dominant mechanisms involved in the oxidation processand their significance for the biocompatibility of the alloy.Two different regimes for the relative diffusivities of oxygenand the metals are investigated. By assuming fast bulk reactions,different asymptotic structures emerge in different parameterregimes and the resulting models take the form of moving boundaryproblems. Different profiles of nickel concentration are obtained:in particular a nickel-rich layer (observed in practice) ispresent below the oxide/metal interface for the case when oxygenand the metals diffuse at comparable rates. 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.
Cheriyan and Hagerup developed a randomized algorithm to compute the maximum flow in a graph with n nodes and m edges in O(mn + n2 log2n) expected time. The randomization is used to efficiently play a certain combinatorial game that arises during the computation. We give a version of their algorithm where a general version of their game arises. Then we give a strategy for the game that yields a deterministic algorithm for computing the maximum flow in a directed graph with n nodes and m edges that runs in time O(mn(logm/n log nn)). Our algorithm gives an O(mn) deterministic algorithm for all m/n = Ω(nε) for any positive constant ε, and is currently the fastest deterministic algorithm for computing maximum flow as long as m/n = ω(log n). 相似文献
4.
5.
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
6.
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
7.
Chris Rasmussen Michelle Zandieh Karen King Anne Teppo 《Mathematical Thinking and Learning》2005,7(1):51-73
The purpose of this article is to contribute to the dialogue about the notion of advanced mathematical thinking by offering an alternative characterization for this idea, namely advancing mathematical activity. We use the term advancing (versus advanced) because we emphasize the progression and evolution of students' reasoning in relation to their previous activity. We also use the term activity, rather than thinking. This shift in language reflects our characterization of progression in mathematical thinking as acts of participation in a variety of different socially or culturally situated mathematical practices. For these practices, we emphasize the changing nature of students' mathematical activity and frame the process of progression in terms of multiple layers of horizontal and vertical mathematizing. 相似文献
8.
9.
10.
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