全文获取类型
收费全文 | 212篇 |
免费 | 10篇 |
专业分类
化学 | 130篇 |
晶体学 | 1篇 |
力学 | 2篇 |
数学 | 70篇 |
物理学 | 19篇 |
出版年
2023年 | 1篇 |
2022年 | 10篇 |
2021年 | 11篇 |
2020年 | 7篇 |
2019年 | 5篇 |
2018年 | 2篇 |
2017年 | 7篇 |
2016年 | 8篇 |
2015年 | 14篇 |
2014年 | 13篇 |
2013年 | 23篇 |
2012年 | 19篇 |
2011年 | 18篇 |
2010年 | 11篇 |
2009年 | 12篇 |
2008年 | 15篇 |
2007年 | 6篇 |
2006年 | 9篇 |
2005年 | 3篇 |
2004年 | 6篇 |
2003年 | 7篇 |
2002年 | 4篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1998年 | 1篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1993年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1982年 | 1篇 |
排序方式: 共有222条查询结果,搜索用时 15 毫秒
111.
Flavia Bonomo Guillermo Durán Luciano N. Grippo Martín D. Safe 《Discrete Applied Mathematics》2011,159(16):1699-1706
A circle graph is the intersection graph of a family of chords on a circle. There is no known characterization of circle graphs by forbidden induced subgraphs that do not involve the notions of local equivalence or pivoting operations. We characterize circle graphs by a list of minimal forbidden induced subgraphs when the graph belongs to one of the following classes: linear domino graphs, P4-tidy graphs, and tree-cographs. We also completely characterize by minimal forbidden induced subgraphs the class of unit Helly circle graphs, which are those circle graphs having a model whose chords have all the same length, are pairwise different, and satisfy the Helly property. 相似文献
112.
Paulo F.C. TillesFernando F. Ferreira Gerson FranciscoCarlos de B. Pereira Flavia M. Sarti 《Physica A》2011,390(13):2562-2570
In this work we study an agent based model to investigate the role of asymmetric information degrees for market evolution. This model is quite simple and may be treated analytically since the consumers evaluate the quality of a certain good taking into account only the quality of the last good purchased plus her perceptive capacity β. As a consequence, the system evolves according to a stationary Markov chain. The value of a good offered by the firms increases along with quality according to an exponent α, which is a measure of the technology. It incorporates all the technological capacity of the production systems such as education, scientific development and techniques that change the productivity rates. The technological level plays an important role to explain how the asymmetry of information may affect the market evolution in this model. We observe that, for high technological levels, the market can detect adverse selection. The model allows us to compute the maximum asymmetric information degree before the market collapses. Below this critical point the market evolves during a limited period of time and then dies out completely. When β is closer to 1 (symmetric information), the market becomes more profitable for high quality goods, although high and low quality markets coexist. The maximum asymmetric information level is a consequence of an ergodicity breakdown in the process of quality evaluation. 相似文献
113.
Flavia Coelho de Souza Henrique Olival-Costa Leonardo da Silva Paulo A. Pontes Carmen Lúcia Penteado Lancellotti 《Journal of voice》2011,25(6):765-769
Hypothesis
The use of a material made of bacterial cellulose with the aim of obtaining vocal fold medialization has not hitherto been fully investigated. Although the material has been tested in other animal models, the evaluation did not include the larynx; hence, situations, such as tissue reaction, material absorption, and extrusion, need to be addressed to evaluate its usefulness as a material for laryngeal reconstruction.Objective
To evaluate the medialization, tissue response, and healing of rabbit vocal folds, after the implantation of a membrane of bacterial cellulose.Study Design
Experimental study.Methods
A total of 32 rabbits were used, two of which were used to check out the adequacy of the implant location. The animals were followed for 4 months and grouped according to follow-up times of 2, 4, and 16 weeks. All test animals received an implant of bacterial cellulose in one vocal fold and the injection of distilled water in the other, both performed by videoendoscopic cervicotomy. At the end of the follow-up, the presence of inflammatory and medial displacement was evaluated.Results
No statistically significant difference in the inflammatory parameters between the study and control vocal folds or among follow-up times was found. All animals receiving cellulose presented medial displacement of vocal folds, and all retained this material at the implant site up to study endpoint.Conclusion
Bacterial cellulose is a useful material for laryngeal medialization, showing no signs of rejection or absorption. 相似文献114.
Cappellin L Biasioli F Schuhfried E Soukoulis C Märk TD Gasperi F 《Rapid communications in mass spectrometry : RCM》2011,25(1):179-183
Proton transfer reaction time-of-flight mass spectrometry (PTR-TOF-MS) allows for very fast simultaneous monitoring of volatile organic compounds (VOCs) in complex environments. In several applications, food science and food technology in particular, peaks with very different intensities are present in a single spectrum. For VOCs, the concentrations range from the sub-ppt all the way up to the ppm level. Thus, a large dynamic range is necessary. In particular, high intensity peaks are a problem because for them the linear dependency of the detector signal on VOC concentration is distorted. In this paper we present, test with real data, and discuss a novel method which extends the linearity of PTR-TOF-MS for high intensity peaks far beyond the limit allowed by the usual analytical correction methods such as the so-called Poisson correction. Usually, raw data can be used directly without corrections with an intensity of up to about 0.1 ions/pulse, and the Poisson correction allows the use of peaks with intensities of a few ions/pulse. Our method further extends the linear range by at least one order of magnitude. Although this work originated from the necessity to extend the dynamic range of PTR-TOF-MS instruments in agro-industrial applications, it is by no means limited to this area, and can be implemented wherever dead time corrections are an issue. 相似文献
115.
Ylenia Pieracci Roberta Ascrizzi Valentina Terreni Luisa Pistelli Guido Flamini Laura Bassolino Flavia Fulvio Massimo Montanari Roberta Paris 《Molecules (Basel, Switzerland)》2021,26(13)
Cannabis sativa L. is an annual species cultivated since antiquity for different purposes. While, in the past, hemp inflorescences were considered crop residues, at present, they are regarded as valuable raw materials with different applications, among which extraction of the essential oil (EO) has gained increasing interest in many fields. The aim of the present study is the evaluation of the yield and the chemical composition of the EO obtained by hydrodistillation from eleven hemp genotypes, cultivated in the same location for two consecutive growing seasons. The composition of the EOs was analyzed by GC–MS, and then subjected to multivariate statistical analysis. Sesquiterpenes represented the main class of compounds in all the EOs, both in their hydrocarbon and oxygenated forms, with relative abundances ranging from 47.1 to 78.5%; the only exception was the Felina 32 sample collected in 2019, in which cannabinoids predominated. Cannabinoids were the second most abundant class of compounds, of which cannabidiol was the main one, with relative abundances between 11.8 and 51.5%. The statistical distribution of the samples, performed on the complete chemical composition of the EOs, evidenced a partition based on the year of cultivation, rather than on the genotype, with the exception of Uso-31. Regarding the extraction yield, a significant variation was evidenced among both the genotypes and the years of cultivation. 相似文献
116.
A result by Van de Ven characterizes linear subspaces as the only closed submanifolds X ? ? N for which the normal bundle exact sequence splits. We show that X is linear assuming only the splitting of the same exact sequence when restricted to some curve contained in X . 相似文献
117.
Cohen Joel M. Colonna Flavia Picardello Massimo A. Singman David 《Potential Analysis》2020,52(1):41-67
Potential Analysis - In Cohen et al. (Potential Anal. 44(4), 745–766, 2016), we introduced several classes of Carleson-type measures with respect to a radial reference measure σ on a... 相似文献
118.
Bin Zhou Flavia M.Zimbres Joshua H.Butler Cheng-Hui Xu Reagan S.Haney Yan Wu Maria B.Cassera Jian-Min Yue 《中国科学:化学(英文版)》2022,65(1):82-86
In our long-term efforts searching for antimalarial agents from Chinese medicinal plants,seven novel dimeric sesquiterpenoids(1–7)with significant antimalarial activity were isolated and characterized from the whole plants of Sarcandra glabra subsp.brachystachys by solid data acquired by diverse methods.Among them,compound 3 with an EC50 value of 4.3 pM against the chloroquine-resistant Plasmodium falciparum is the most potent antimalarial agent reported hitherto,about 1,000-fold stronger than artemisinin.This article further consolidates and refines our previously delineated structure-activity relationship for this antimalarial compound class. 相似文献
119.
Anna M. Kaczmarek Ying‐Ya Liu Mariusz K. Kaczmarek Hengshuo Liu Flavia Artizzu Luís D. Carlos Pascal Van Der Voort 《Angewandte Chemie (International ed. in English)》2020,59(5):1932-1940
Covalent Organic Frameworks (COFs), an emerging class of crystalline porous materials, are proposed as a new type of support for grafting lanthanide ions (Ln3+) and employing these hybrid materials as ratiometric luminescent thermometers. A TpBpy‐COF—prepared from 1,3,5‐triformylphloroglucinol (Tp) and 2,2′‐bipyridine‐5,5′‐diamine (Bpy) grafted with Eu/Tb and Dy acetylacetone (acac) complexes can be successfully used as a luminescent thermometer in the 10–360 K (Eu) and 280–440 K (Tb) ranges with good sensing properties (thermal sensitivity up to 1.403 % K?1, temperature uncertainty δT<1 K above 110 K). For the Eu/Tb systems, we observe an unusual and rarely reported behavior, that is, no thermal quenching of the Tb3+ emission, a result of the absence of ion‐to‐ligand/host energy back‐transfer. The LnCOF materials proposed here could be a new class of materials employed for temperature‐sensing applications following up on the well‐known luminescent metal–organic framework thermometers. 相似文献
120.
Paola Deplano Luciano Marchiò Flavia Artizzu Maria Laura Mercuri Luca Pilia Gloria Pintus Angela Serpe Eduard B. Yagubskii 《Monatshefte für Chemie / Chemical Monthly》2009,17(3):775-781