全文获取类型
收费全文 | 877篇 |
免费 | 13篇 |
国内免费 | 2篇 |
专业分类
化学 | 512篇 |
晶体学 | 4篇 |
力学 | 34篇 |
综合类 | 1篇 |
数学 | 114篇 |
物理学 | 227篇 |
出版年
2023年 | 10篇 |
2022年 | 21篇 |
2021年 | 22篇 |
2020年 | 21篇 |
2019年 | 12篇 |
2018年 | 13篇 |
2017年 | 20篇 |
2016年 | 26篇 |
2015年 | 23篇 |
2014年 | 35篇 |
2013年 | 57篇 |
2012年 | 58篇 |
2011年 | 61篇 |
2010年 | 34篇 |
2009年 | 34篇 |
2008年 | 52篇 |
2007年 | 43篇 |
2006年 | 45篇 |
2005年 | 41篇 |
2004年 | 37篇 |
2003年 | 24篇 |
2002年 | 22篇 |
2001年 | 11篇 |
2000年 | 8篇 |
1999年 | 15篇 |
1998年 | 2篇 |
1997年 | 9篇 |
1996年 | 8篇 |
1995年 | 16篇 |
1994年 | 13篇 |
1993年 | 12篇 |
1992年 | 14篇 |
1991年 | 7篇 |
1990年 | 5篇 |
1989年 | 2篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 6篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1970年 | 4篇 |
1906年 | 3篇 |
1905年 | 3篇 |
排序方式: 共有892条查询结果,搜索用时 24 毫秒
71.
Angelamaria Maia Dario LandiniBoguslawa Leska Grzegorz Schroeder 《Tetrahedron letters》2003,44(21):4149-4151
Silicon polypodands 5-7 are found to be powerful complexing agents of alkali metal salts in low polarity solvents and very efficient catalysts in anion-promoted reactions under solid-liquid PTC conditions. The catalytic activity is comparable with that of the cyclic polyether PHDB18C6 8. 相似文献
72.
Low-energy (5-15 eV) electron- and photon-stimulated desorption of KI(100) yields I2P3/2 and 2P1/2 with hyperthermal (0.3 eV) and thermal velocity components. The desorption threshold for both components is 5.3 eV and is correlated with the gamma3/2-exciton long-wavelength edge. Exciton decay at the surface directly produces I2P3/2 and 2P1/2 with hyperthermal velocity and is in competition with self-trapping. Spin memory of the gamma-exciton hole-component is also evident in the hyperthermal channel. An exciton mediated desorption mechanism is presented which is general in alkali halides. 相似文献
73.
The Bootstrap Methodology in Statistics of Extremes—Choice of the Optimal Sample Fraction 总被引:2,自引:0,他引:2
The main objective of statistics of extremes is the prediction of rare events, and its primary problem has been the estimation of the tail index , usually performed on the basis of the largest k order statistics in the sample or on the excesses over a high level u. The question that has been often addressed in practical applications of extreme value theory is the choice of either k or u, and an adaptive estimation of . We shall be here mainly interested in the use of the bootstrap methodology to estimate adaptively, and although the methods provided may be applied, with adequate modifications, to the general domain of attraction of G, , we shall here illustrate the methods for heavy right tails, i.e. for > 0. Special relevance will be given to the use of an auxiliary statistic that is merely the difference of two estimators with the same functional form as the estimator under study, computed at two different levels. We shall also compare, through Monte Carlo simulation, these bootstrap methodologies with other data-driven choices of the optimal sample fraction available in the literature. 相似文献
74.
Aline Lima de Oliveira Carlos Henrique Alves de Oliveira Laura Maia Mairink Francine Pazini Ricardo Menegatti Luciano Morais Lião 《Magnetic resonance in chemistry : MRC》2011,49(8):537-542
Complete assignment of 1H and 13C NMR chemical shifts and J(1H/1H and 1H/19F) coupling constants for 22 1‐phenyl‐1H‐pyrazoles' derivates were performed using the concerted application of 1H 1D and 1H, 13C 2D gs‐HSQC and gs‐HMBC experiments. All 1‐phenyl‐1H‐pyrazoles' derivatives were synthesized as described by Finar and co‐workers. The formylated 1‐phenyl‐1H‐pyrazoles' derivatives were performed under Duff's conditions. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
75.
76.
Manuel Maia 《Discrete Mathematics》2008,308(23):5407-5427
We introduce two new binary operations on combinatorial species; the arithmetic product and the modified arithmetic product. The arithmetic product gives combinatorial meaning to the product of Dirichlet series and to the Lambert series in the context of species. It allows us to introduce the notion of multiplicative species, a lifting to the combinatorial level of the classical notion of multiplicative arithmetic function. Interesting combinatorial constructions are introduced; cloned assemblies of structures, hyper-cloned trees, enriched rectangles, etc. Recent research of Cameron, Gewurz and Merola, about the product action in the context of oligomorphic groups, motivated the introduction of the modified arithmetic product. By using the modified arithmetic product we obtain new enumerative results. We also generalize and simplify some results of Canfield, and Pittel, related to the enumerations of tuples of partitions with the restrictions met. 相似文献
77.
Andre Silva Pimentel Geoffrey S. Tyndall John J. Orlando Michale D. Hurley Timothy J. Wallington Mads P. Sulbaek Andersen Paul Marshall Theodore S. Dibble 《国际化学动力学杂志》2010,42(8):479-498
Formates are produced in the atmosphere as a result of the oxidation of a number of species, notably dialkyl ethers and vinyl ethers. This work describes experiments to define the oxidation mechanisms of isopropyl formate, HC(O)OCH(CH3)2, and tert‐butyl formate, HC(O)OC(CH3)3. Product distributions are reported from both Cl‐ and OH‐initiated oxidation, and reaction mechanisms are proposed to account for the observed products. The proposed mechanisms include examples of the α‐ester rearrangement reaction, novel isomerization pathways, and chemically activated intermediates. The atmospheric oxidation of isopropyl formate by OH radicals gives the following products (molar yields): acetic formic anhydride (43%), acetone (43%), and HCOOH (15–20%). The OH radical initiated oxidation of tert‐butyl formate gives acetone, formaldehyde, and CO2 as major products. IR absorption cross sections were derived for two acylperoxy nitrates derived from the title compounds. Rate coefficients are derived for the kinetics of the reactions of isopropyl formate with OH (2.4 ± 0.6) × 10?12, and with Cl (1.75 ± 0.35) × 10?11, and for tert‐butyl formate with Cl (1.45 ± 0.30) × 10?11 cm3 molecule?1 s?1. Simple group additivity rules fail to explain the observed distribution of sites of H‐atom abstraction for simple formates. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 479–498, 2010 相似文献
78.
Šárka Brodinová Maia Zaharieva Peter Filzmoser Thomas Ortner Christian Breiteneder 《Advances in Data Analysis and Classification》2018,12(2):261-284
Media content in large repositories usually exhibits multiple groups of strongly varying sizes. Media of potential interest often form notably smaller groups. Such media groups differ so much from the remaining data that it may be worthy to look at them in more detail. In contrast, media with popular content appear in larger groups. Identifying groups of varying sizes is addressed by clustering of imbalanced data. Clustering highly imbalanced media groups is additionally challenged by the high dimensionality of the underlying features. In this paper, we present the imbalanced clustering (IClust) algorithm designed to reveal group structures in high-dimensional media data. IClust employs an existing clustering method in order to find an initial set of a large number of potentially highly pure clusters which are then successively merged. The main advantage of IClust is that the number of clusters does not have to be pre-specified and that no specific assumptions about the cluster or data characteristics need to be made. Experiments on real-world media data demonstrate that in comparison to existing methods, IClust is able to better identify media groups, especially groups of small sizes. 相似文献
79.
For an accurate simulation of forming processes, it is of paramount importance to model the different lubrication regimes that can develop at the contact interface. These might vary from zone to zone of the forming piece, and from one regime to another, resulting in forces of different nature and magnitude. In these cases, the use of the classical Coulomb friction law will be clearly not sufficient to capture, in a suitable manner, the variety of forces applied on the forming piece. 相似文献
80.