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91.
Following the recent discussion on the puzzling nature of the interactions in the nanotubular system Na(2)V(3)O(7), we present a detailed ab initio microscopic analysis of its electronic and magnetic properties. By means of a nontrivial downfolding study we propose an effective model in terms of tubes of nine-site rings with the geometry of a spin-diamond necklace with frustrated inter-ring interactions. We show that this model provides a quantitative account of the observed magnetic behavior. 相似文献
92.
Bibiana Moreno-Valle Milagros Aguilar-Martínez Marisela Martínez-Quiroz Valentín Miranda-Soto José García-Elías 《Supramolecular chemistry》2018,30(1):9-19
A new group of ureylbenzamide-based receptors (1–4) has been synthesized; its binding affinity and capacity to form supramolecular complexes in solution with different anions have been investigated. For designing these receptors, it was considered a combination of the positions of the urea and amide groups (ortho and meta), and the chromophore groups naphthyl and nitrophenyl, yielding four receptors. The position and chromophore structure affected the acidity of the urea and amide hydrogens in the order 4>3>2>1. All the spectroscopic studies showed a significant change of 1 and 2 compared with 3 and 4 in the presence of different TBAX salts in acetonitrile. The 1H-NMR spectra show a preferential interaction of the anions with the urea group in receptors 1 and 2 due to the less steric hindrance, while there is a cooperative interaction of amide group in receptors 3 and 4 due to the closeness of both groups. 相似文献
93.
Dynamic Kinetic Resolution of Heterobiaryl Ketones by Zinc‐Catalyzed Asymmetric Hydrosilylation 下载免费PDF全文
Dr. Valentín Hornillos José A. Carmona Dr. Abel Ros Dr. Javier Iglesias‐Sigüenza Dr. Joaquín López‐Serrano Prof. Rosario Fernández Prof. José M. Lassaletta 《Angewandte Chemie (International ed. in English)》2018,57(14):3777-3781
A diastereo‐ and highly enantioselective dynamic kinetic resolution (DKR) of configurationally labile heterobiaryl ketones is described. The DKR proceeds by zinc‐catalyzed hydrosilylation of the carbonyl group, thus leading to secondary alcohols bearing axial and central chirality. The strategy relies on the labilization of the stereogenic axis that takes place thanks to a Lewis acid–base interaction between a nitrogen atom in the heterocycle and the ketone carbonyl group. The synthetic utility of the methodology is demonstrated through stereospecific transformations into either N,N‐ligands or appealing axially chiral, bifunctional thiourea organocatalysts. 相似文献
94.
Amaral JS Ferreres F Andrade PB Valentão P Pinheiro C Santos A Seabra R 《Natural product research》2005,19(2):157-163
In this study, phenolic compounds of hazelnut leaves of 10 different cultivars with the same cultural, geographical, geological and climatic conditions were analyzed by HPLC/DAD and HPLC/DAD/MS/MS - ESI. Eight phenolic compounds (3-caffeoylquinic acid, 5-caffeoylquinic acid, caffeoyltartaric acid, p-coumaroyltartaric acid, myricetin 3-rhamnoside, quercetin 3-glycoside, quercetin 3-rhamnoside and kaempferol 3-rhamnoside) were identified and quantified. All of the analyzed samples showed a similar phenolic profile, in which myricetin 3-rhamnoside and quercetin 3-rhamnoside were the major compounds and caffeoyltartaric and p-coumaroyltartaric acids were present in vestigial amounts. 相似文献
95.
D. Sa R. Valentí C. Gros 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(2):301-305
We develop a generalized Ginzburg-Landau theory for second harmonic generation (SHG) in magnets by expanding the free energy
in terms of the order parameter in the magnetic phase and the susceptibility tensor in the corresponding high-temperature
phase. The non-zero components of the SHG susceptibility in the ordered phase are derived from the symmetries of the susceptibility
tensor in the high-temperature phase and the symmetry of the order parameter. In this derivation, the dependence of the SHG
susceptibility on the order parameter follows naturally, and therefore its nonreciprocal optical properties. We examine this
phenomenology for the magnetoelectric compound Cr2O3 as well as for the ferroelectromagnet YMnO3.
Received 27 August 1999 相似文献
96.
We characterize the orthogonal polynomials in a class of polynomials defined through their generating functions. This led to three new systems of orthogonal polynomials whose generating functions and orthogonality relations involve elliptic functions. The Hamburger moment problems associated with these polynomials are indeterminate. We give infinite families of weight functions in each case. The different polynomials treated in this work are also polynomials in a parameter and as functions of this parameter they are orthogonal with respect to unique measures, which we find explicitly. Through a quadratic transformation we find a new exactly solvable birth and death process with quartic birth and death rates. 相似文献
97.
Dolnik M Bánsági T Ansari S Valent I Epstein IR 《Physical chemistry chemical physics : PCCP》2011,13(27):12578-12583
We use the photosensitive chlorine dioxide-iodine-malonic acid reaction-diffusion system to study wavenumber locking of Turing patterns with spatial periodic forcing. Wavenumber-locked stripe patterns are the typical resonant structures that labyrinthine patterns exhibit in response to one-dimensional forcing by illumination when images of stripes are projected on a working medium. Our experimental results reveal that segmented oblique, hexagonal and rectangular patterns can also be obtained. However, these two-dimensional resonant structures only develop in a relatively narrow range of forcing parameters, where the unforced stripe pattern is in close proximity to the domain of hexagonal patterns. Numerical simulations based on a model that incorporates the forcing by illumination using an additive term reproduce well the experimental observations. These findings confirm that additive one-dimensional forcing can generate a two-dimensional resonant response. However, such a response is considerably less robust than the effect of multiplicative forcing. 相似文献
98.
Dorus Heijnen Dr. Jean‐Baptiste Gualtierotti Dr. Valentín Hornillos Prof. Dr. Ben L. Feringa 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(12):3991-3995
Nickel‐catalyzed selective cross‐coupling of aromatic electrophiles (bromides, chlorides, fluorides and methyl ethers) with organolithium reagents is presented. The use of a commercially available nickel N‐heterocyclic carbene (NHC) complex allows the reaction with a variety of (hetero)aryllithium compounds, including those prepared via metal‐halogen exchange or direct metallation, whereas a commercially available electron‐rich nickel‐bisphosphine complex smoothly converts alkyllithium species into the corresponding coupled product. These reactions proceed rapidly (1 h) under mild conditions (room temperature) while avoiding the undesired formation of reduced or homocoupled products. 相似文献
99.
Galliano Valent 《Letters in Mathematical Physics》2014,104(9):1121-1135
Matveev and Shevchishin have constructed a family of superintegrable models, involving a linear and a cubic integral. Their metrics, when defined on a closed manifold, have the remarkable property of being Zoll metrics. Using the explicit form of the metrics defined on \({\mathbb{S}^2}\) , which we obtained in a recent paper, we reduce them to a canonical form which displays their Zoll property. For the same class of models several metrics are defined on Tannery’s orbifold and we show, by the same procedure, that in this case we are led either to Zoll or to Tannery surfaces. 相似文献
100.
Ferreres F Gil-Izquierdo A Valentão P Andrade PB 《Rapid communications in mass spectrometry : RCM》2011,25(22):3441-3446
The metabolite profiling of Gomphrena globosa inflorescences was performed by high-performance liquid chromatography-diode array detection/electrospray ionization multi-stage mass spectrometry (HPLC-DAD/ESI-MS(n)). Based on the fragmentation patterns, 24 phenolic compounds were characterized. The identified phenolics include p-coumaric and ferulic acids, quercetin, kaempferol, isorhamnetin, and hydroxylated 6,7-methylenedioxyflavone derivatives, as well as their aglycones, none of them reported before in the species. This is also the first time that tetrahydroxy-methylenedioxyflavone derivatives and acetylglycosides are described in nature. Betacyanins were also found. This study significantly extends the knowledge of the G. globosa metabolome, by providing further insights into its phenolic composition. 相似文献