全文获取类型
收费全文 | 81篇 |
免费 | 19篇 |
国内免费 | 4篇 |
专业分类
化学 | 18篇 |
力学 | 2篇 |
综合类 | 4篇 |
数学 | 27篇 |
物理学 | 22篇 |
无线电 | 31篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2022年 | 5篇 |
2021年 | 5篇 |
2020年 | 2篇 |
2019年 | 5篇 |
2018年 | 1篇 |
2017年 | 6篇 |
2016年 | 6篇 |
2015年 | 5篇 |
2014年 | 7篇 |
2013年 | 7篇 |
2012年 | 5篇 |
2011年 | 7篇 |
2010年 | 3篇 |
2009年 | 4篇 |
2008年 | 1篇 |
2007年 | 9篇 |
2006年 | 7篇 |
2005年 | 3篇 |
2004年 | 1篇 |
2003年 | 1篇 |
2002年 | 3篇 |
2000年 | 1篇 |
1999年 | 4篇 |
1998年 | 1篇 |
1992年 | 1篇 |
排序方式: 共有104条查询结果,搜索用时 156 毫秒
81.
Enumerating Constrained Non-crossing Minimally Rigid Frameworks 总被引:2,自引:1,他引:1
David Avis Naoki Katoh Makoto Ohsaki Ileana Streinu Shin-ichi Tanigawa 《Discrete and Computational Geometry》2008,40(1):31-46
In this paper we present an algorithm for enumerating without repetitions all the non-crossing generically minimally rigid
bar-and-joint frameworks under edge constraints, which we call constrained non-crossing Laman frameworks, on a given set of
n points in the plane. Our algorithm is based on the reverse search paradigm of Avis and Fukuda. It generates each output graph
in O(n
4) time and O(n) space, or, with a slightly different implementation, in O(n
3) time and O(n
2) space. In particular, we obtain that the set of all the constrained non-crossing Laman frameworks on a given point set is
connected by flips which preserve the Laman property.
D. Avis’s research was supported by NSERC and FQRNT grants.
N. Katoh’s, M. Ohsaki’s and S.-i. Tanigawa’s research was supported by NEXT Grant-in-Aid for Scientific Research on priority
areas of New Horizons in Computing.
I. Streinu’s research was supported by NSF grant CCF-0430990 and NSF-DARPA CARGO CCR-0310661. 相似文献
82.
83.
Posterior mode estimators are proposed, which arise from simply expressed prior opinion about expected outcomes, roughly as follows: a conjugate family of prior distributions is determined by a given variance function. Using a conjugate prior, a posterior mode estimator and its estimated (co-)variances are obtained through conventional maximum likelihood computations, by means of small alterations to the observed outcomes and/or to the modelled variance function. Within the conjugate family, for purposes of inference about the regression vector, a reference prior is proposed for a given choice of linear design of the canonical link. The resulting approximate reference inferences approximate the Bayesian inferences which arise from a minimally informative reference prior. A set of subjective prior upper and lower percentage points for the expected outcomes can be used to determine a conjugate family member. Alternatively, a set of subjective prior means and standard deviations determines a member. The subfamily of priors determinable by percentage points either includes or approximates the proposed reference prior.The research of the first-named author was funded in part by a Natural Sciences and Engineering Research Council grant.The second named author gratefully acknowledges the support of the National Science Foundation, grant #DMS-8901494 and of the Kansas Geological Survey where he visited during the term of the majority of this research. 相似文献
84.
Catia Clementi Witold Nowik Aldo Romani Dominique Cardon Marek Trojanowicz Athénaïs Davantès Pierre Chaminade 《Analytica chimica acta》2016
In this paper, partial least square (PLS) regression is innovatively applied for a semi-quantitative non invasive study of the most precious dye of Antiquity: Tyrian purple. This original approach for the study of organic dyes in the cultural heritage field, is based on the correlation of spectrophotometric (UV–Visible) and chromatographic (Fast-HT-HPLC-PDA) data from an extensive set of textiles prepared with different snail species according to historical recipes. A cross-validated PLS model, based on the quantity of 6,6′-dibromoindigotin, displays an excellent correlation factor (R2Y = 0.987) between values determined by chromatography and those predicted from reflectance spectra. This indicates that the spectral features of Tyrian purple on textile fibre is strictly related to the amount of this indigoid component whose content may be non invasively predicted from reflectance spectrum. The studied correlation also highlights that, independently of the dyeing method and nature of the textile fibre used, the relative content of 6,6′-dibromindigotin may be used as a parameter to distinguish samples prepared with Hexaplex trunculus L. snails from those prepared with further mollusc species. To validate this model, archaeological textile fragments dating from the Roman period were successfully examined. The results achieved open an absolutely new way in Tyrian purple analysis in cultural heritage by non invasive spectroscopic techniques attesting their convergence with HPLC and giving them a semi-quantitative value. 相似文献
85.
Yvette Lock Toy Ki Armelle Garcia Franck Pelissier Tomasz K. Olszewski Alicja Babst-Kostecka Yves-Marie Legrand Claude Grison 《Molecules (Basel, Switzerland)》2022,27(10)
The Michael addition reaction was revisited with a full focus on sustainability combined with efficiency, using mechanochemistry in mild conditions. First, the synthesis of cyclopentenone derivatives was chosen as a model reaction to find optimal conditions in mechanochemistry while using classical but weak bases. The reaction was efficient (84–95% yields), fast (2–6 h), solvent free, and required 0.1 equivalent of base. Aiming to reach greener conditions, classical bases were then replaced using new bio-sourced bases, called Eco-bases, that were easily prepared from plants and led to heterogeneous catalysts. The composition and structure of Eco-bases were characterized by MP-AES, XRPD, EBSD/EDS, HRTEM/EDX and ion chromatography. Interestingly, a high ratio of potassium was observed with the presence of K2Ca(CO3)2 for the most effective Eco-base. The new Eco-bases were used for the mechanical-assisted construction of functionalized alkenone derivatives. The versatility of the method has been successfully applied with good to excellent yields to different Michael donors and acceptors. Eco-bases were recycled and reused four times with the same performances. Combining Eco-bases and mechanochemistry in Michael addition reactions allowed reaching a maximum degree of sustainability (efficient, rapid, low catalyst loading, solvent-free reactions with bio-sourced catalysts) and participating in the development of mechanochemistry in sustainable chemistry. 相似文献
86.
Xesús Fes Carmen Vidal M. Pilar Vzquez-Tato Julio A. Seijas 《Molecules (Basel, Switzerland)》2022,27(1)
The yellow-legged Asian hornet (Vespa velutina Lepeletier 1836 (Hymenoptera: Vespidae)) is naturally distributed in China, Southeast Asia, and India; however, recently it has been detected outside of its native area, confirmed as being established in South Korea, Europe, and Japan. Health risks and deaths caused by the invasive Vespa velutina stings have become a public health concern, being the most common cause of anaphylaxis due to hymenopterans in some European regions. This in turn has led to increased demand from medical practitioners and researchers for Vespa velutina venom for diagnostic and therapeutic purposes. In this study, a straightforward, quick, and inexpensive method for obtaining Vespa velutina venom by electric stimulation is described. The venom extracts were analyzed by nuclear magnetic resonance spectroscopy (1H-NMR). The availability of Vespa velutina venom will lead to improved diagnostic and therapeutic methods, mainly by venom immunotherapy (VIT), in patients allergic to this invasive species. 相似文献
87.
Maria Ponticelli Ludovica Lela Daniela Russo Immacolata Faraone Chiara Sinisgalli Mayssa Ben Mustapha Germana Esposito Hichem Ben Jannet Valeria Costantino Luigi Milella 《Molecules (Basel, Switzerland)》2022,27(3)
Dittrichia graveolens L. Greuter belonging to the Asteraceae family, is an aromatic herbaceous plant native to the Mediterranean region. This plant species has been extensively studied for its biological activities, including antioxidant, antitumor, antimicrobial, antifungal, anti-inflammatory, anticholinesterase, and antityrosinase, and for its peculiar metabolic profile. In particular, bioactivities are related to terpenes and flavonoids metabolites, such as borneol (40), tomentosin (189), inuviscolide (204). However, D. graveolens is also well known for causing health problems both in animals and humans. Moreover, the species is currently undergoing a dramatic northward expansion of its native range related to climate change, now including North Europe, California, and Australia. This review represents an updated overview of the 52 literature papers published in Scopus and PubMed dealing with expansion, chemistry (262 different compounds), pharmacological effects, and toxicology of D. graveolens up to October 2021. The review is intended to boost further studies to determine the molecular pathways involved in the observed activities, bioavailability, and clinical studies to explore new potential applications. 相似文献
88.
Moritz F. Richter Andrea Smirne Walter T. Strunz Dario Egloff 《Annalen der Physik》2024,536(4):2300304
In classical stochastic theory, the joint probability distributions of a stochastic process obey by definition the Kolmogorov consistency conditions. Interpreting such a process as a sequence of physical measurements with probabilistic outcomes, these conditions reflect that the measurements do not alter the state of the underlying physical system. Prominently, this assumption has to be abandoned in the context of quantum mechanics, yet there are also classical processes in which measurements influence the measured system. Here, conditions that characterize uniquely classical processes that are probed by a reasonable class of such invasive measurements are derived. We then analyze under what circumstances such classical processes can simulate the statistics arising from quantum processes associated with informationally-complete measurements. It is expected that this investigation will help build a bridge between two fundamental traits of non-classicality, namely, coherence and contextuality. 相似文献
89.
Abstract A nondestructive method employing Fourier transform infrared (FTIR) microspectroscopy coupled with attenuated total reflectance (ATR) objective for the analysis of histopathological specimens is described. Malignant breast tissue specimens have been analyzed to demonstrate the hypothesis that chemical changes taking place in biological tissue can be reliably and reproducibly identified. This study is the first report to elucidate clear spectral differences between different ductal carcinoma in situ (DCIS) grades. Sixty individual cases of breast carcinoma including DCIS and invasive ductal carcinoma (IDC) and seven cases of normal breast tissues were studied using the FTIR-ATR spectroscopic technique. FTIR analysis of tissue sections has provided distinct spectra that can be used to distinguish between the nuclear grades of DCIS and IDC of the breast. It was concluded that FTIR could objectively and reproducibly discriminate between DCIS and IDC grades without sample destruction. In the future, applications of FTIR approaches should become feasible in the nondestructive express classification of grades and diagnosis of breast carcinoma. 相似文献
90.