全文获取类型
收费全文 | 177篇 |
免费 | 4篇 |
国内免费 | 5篇 |
专业分类
系统科学 | 14篇 |
教育与普及 | 1篇 |
理论与方法论 | 5篇 |
现状及发展 | 45篇 |
研究方法 | 27篇 |
综合类 | 85篇 |
自然研究 | 9篇 |
出版年
2022年 | 2篇 |
2021年 | 3篇 |
2020年 | 3篇 |
2019年 | 3篇 |
2018年 | 2篇 |
2017年 | 3篇 |
2016年 | 13篇 |
2015年 | 5篇 |
2014年 | 3篇 |
2013年 | 6篇 |
2012年 | 15篇 |
2011年 | 19篇 |
2010年 | 8篇 |
2009年 | 7篇 |
2008年 | 10篇 |
2007年 | 15篇 |
2006年 | 13篇 |
2005年 | 11篇 |
2004年 | 10篇 |
2003年 | 10篇 |
2002年 | 15篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1996年 | 1篇 |
1991年 | 2篇 |
1967年 | 3篇 |
1946年 | 1篇 |
排序方式: 共有186条查询结果,搜索用时 171 毫秒
1.
In agglomerative hierarchical clustering, pair-group methods suffer from a problem of non-uniqueness when two or more distances
between different clusters coincide during the amalgamation process. The traditional approach for solving this drawback has
been to take any arbitrary criterion in order to break ties between distances, which results in different hierarchical classifications
depending on the criterion followed. In this article we propose a variable-group algorithm that consists in grouping more
than two clusters at the same time when ties occur. We give a tree representation for the results of the algorithm, which
we call a multidendrogram, as well as a generalization of the Lance andWilliams’ formula which enables the implementation of the algorithm in a recursive
way.
The authors thank A. Arenas for discussion and helpful comments. This work was partially supported by DGES of the Spanish
Government Project No. FIS2006–13321–C02–02 and by a grant of Universitat Rovira i Virgili. 相似文献
2.
PERUGINI Carlo Alberto ARZILLI Gilberto TORLUCCIO Antonio BLUMRICH Reinhar WAGNER Andreas 《同济大学学报(自然科学版)》2021,49(S1):20-27
为了优化车辆开发过程的有效性,数值气动声学分析法的实施和应用对汽车制造商来说变得越来越重要。提出了一种结合延迟分离涡流模拟和基于Lighthill方程及声学扰动方程的有限元模型混合数值工具,应用OpenFOAM和Actran软件实现了基于声学有限元法的近场声源区提取及声学压力脉动计算,并尝试应用于车顶扰流板及后视镜区域的气动噪声计算及分析。在兰博基尼Urus车型上,研究了不同车顶扰流板设计的气动声学行为,将仿真结果与斯图加特大学气动声学全尺寸风洞的实验结果进行比较,发现了令人信服的相关性。此外,探讨了扰流板上的主要噪声产生机制,研究了汽车表面压力波动水平随几何形状改变的变化情况。 相似文献
3.
4.
Giovanni Barone‐Adesi Marinela Adriana Finta Chiara Legnazzi Carlo Sala 《Journal of forecasting》2019,38(6):552-563
Using option market data we derive naturally forward‐looking, nonparametric and model‐free risk estimates, three desired characteristics hardly obtainable using historical returns. The option‐implied measures are only based on the first derivative of the option price with respect to the strike price, bypassing the difficult task of estimating the tail of the return distribution. We estimate and backtest the 1%, 2.5%, and 5% WTI crude oil futures option‐implied value at risk and conditional value at risk for the turbulent years 2011–2016 and for both tails of the distribution. Compared with risk estimations based on the filtered historical simulation methodology, our results show that the option‐implied risk metrics are valid alternatives to the statistically based historical models. 相似文献
5.
6.
Piccioni G Drossart P Sanchez-Lavega A Hueso R Taylor FW Wilson CF Grassi D Zasova L Moriconi M Adriani A Lebonnois S Coradini A Bézard B Angrilli F Arnold G Baines KH Bellucci G Benkhoff J Bibring JP Blanco A Blecka MI Carlson RW Di Lellis A Encrenaz T Erard S Fonti S Formisano V Fouchet T Garcia R Haus R Helbert J Ignatiev NI Irwin PG Langevin Y Lopez-Valverde MA Luz D Marinangeli L Orofino V Rodin AV Roos-Serote MC Saggin B Stam DM Titov D Visconti G 《Nature》2007,450(7170):637-640
Venus has no seasons, slow rotation and a very massive atmosphere, which is mainly carbon dioxide with clouds primarily of sulphuric acid droplets. Infrared observations by previous missions to Venus revealed a bright 'dipole' feature surrounded by a cold 'collar' at its north pole. The polar dipole is a 'double-eye' feature at the centre of a vast vortex that rotates around the pole, and is possibly associated with rapid downwelling. The polar cold collar is a wide, shallow river of cold air that circulates around the polar vortex. One outstanding question has been whether the global circulation was symmetric, such that a dipole feature existed at the south pole. Here we report observations of Venus' south-polar region, where we have seen clouds with morphology much like those around the north pole, but rotating somewhat faster than the northern dipole. The vortex may extend down to the lower cloud layers that lie at about 50 km height and perhaps deeper. The spectroscopic properties of the clouds around the south pole are compatible with a sulphuric acid composition. 相似文献
7.
8.
Gout AM;ADPKD Gene Variant Consortium Ravine D Harris PC Rossetti S Peters D Breuning M Henske EP Koizumi A Inoue S Shimizu Y Thongnoppakhun W Yenchitsomanus PT Deltas C Sandford R Torra R Turco AE Jeffery S Fontes M Somlo S Furu LM Smulders YM Mercier B Ferec C Burtey S Pei Y Kalaydjieva L Bogdanova N McCluskey M Geon LJ Wouters CH Reiterova J Stekrová J San Millan JL Aguiari G Del Senno L 《Nature genetics》2007,39(4):427-428
9.
In 1873, W. K. Clifford introduced a notion of parallelism in the three-dimensional elliptic space that, quite surprisingly, exhibits almost all properties of Euclidean parallelism in ordinary space. The purpose of this paper is to describe the genesis of this notion in Clifford’s works and to provide a historical analysis of its reception in the investigations of F. Klein, L. Bianchi, G. Fubini, and E. Bortolotti. Special emphasis is placed upon the important role that Clifford’s parallelism played in the development of the theory of connections. 相似文献
10.
Beryl?Royer-Bertrand Carlo?RivoltaEmail author 《Cellular and molecular life sciences : CMLS》2015,72(8):1463-1471
The past decade has seen the emergence of next-generation sequencing (NGS) technologies, which have revolutionized the field of human molecular genetics. With NGS, significant portions of the human genome can now be assessed by direct sequence analysis, highlighting normal and pathological variants of our DNA. Recent advances have also allowed the sequencing of complete genomes, by a method referred to as whole genome sequencing (WGS). In this work, we review the use of WGS in medical genetics, with specific emphasis on the benefits and the disadvantages of this technique for detecting genomic alterations leading to Mendelian human diseases and to cancer. 相似文献