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101.
Guillaume Guérin Norbert Mercier Roger Nathan Grzegorz Adamiec Yannick Lefrais 《Radiation measurements》2012,47(9):778-785
The infinite matrix assumption is commonly used to derive dose rates in the field of paleodosimetric dating methods. The update of nuclear data allowed calculating new dose rate conversion factors and attenuation factors for taking account of grain size. The relevance of the infinite matrix assumption was found to be limited to specific cases and a discussion of potential errors in estimating dose rates to natural dosimeters in sedimentary media is proposed. A new set of geometric features is shown to be of paramount importance for estimating dose rates in sedimentary media. To quantify these effects, Monte Carlo modelling was applied and the architecture of the programmes is described. It is also shown that proper characterization of sediment samples, coupled to the modelling of radioactivity in these sediments may provide more accurate dose rates to quartz grains, down to the single grain scale. 相似文献
102.
Lotfi Boudjema Dr. Jérôme Long Dr. Fabrice Salles Prof. Joulia Larionova Dr. Yannick Guari Prof. Philippe Trens 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(2):479-484
Porous coordination polymers are molecule-based materials presenting a high degree of tunability, which offer many advantages for targeted applications over conventional inorganic materials. This work demonstrates that the hydrophilic/hydrophobic character of Prussian blue analogues having a lipophilic feature may be tuned to optimize the gas adsorption properties. The role of the coordinatively unsaturated metal sites is emphasized through a combination of theoretical and experimental study of water, ethanol, and n-hexane adsorption. 相似文献
103.
Dr. Aurélien Béthegnies Dr. Yannick Escudié Dr. Nelson Nuñez-Dallos Dr. Laure Vendier John Hurtado Iker del Rosal Dr. Laurent Maron Dr. Sébastien Bontemps 《ChemCatChem》2019,11(2):760-765
To use carbon dioxide as a source of carbon, recent progress has been made toward the synthesis of higher value chemicals and in particular toward Cn compounds. In this context, we report here the synthesis of a borylated C3-carbohydrate from CO2 as the only source of carbon. This result corresponds to the unprecedented formation of a polyol chain and of asymmetric carbon atoms from CO2. The adopted strategy involves the Fe-catalysed selective 4e− reduction of CO2 into bis(boryl)acetal followed in one-pot by a carbene-mediated C−C coupling reaction. Boron is shown to play a key role in the coupling step enabling to observe the first diastereoselective formose-type reaction. This result is in addition obtained under mild reaction conditions (T<80 °C, 1 atm of CO2) and short reaction time (t<2 h). 相似文献
104.
105.
Jérémy Vuilleumier Geoffrey Gaulier Raphaël De Matos Yannick Mugnier Gabriel Campargue Jean-Pierre Wolf Luigi Bonacina Sandrine Gerber-Lemaire 《Helvetica chimica acta》2020,103(1):e1900251
While chemotherapy is one of the most used treatments in oncology, the systemic administration of chemotherapeutics generally results in undesired damages to healthy tissues and cells, side effects such as severe nausea and leukopenia, and reduced efficacy due to multidrug resistance and poor target accessibility. The limitations of conventional chemotherapy formulation have prompted the development of alternative nanomaterials-based strategies to achieve targeted and stimuli sensitive payload delivery to reach optimal local drug concentration at tumor sites. In this study, the anticancer drug chlorambucil (Clb) was conjugated to the surface of silica coated lithium niobate (LNO) harmonic nanoparticles (HNPs) using a photocaging tether based on coumarin-4-yl methyl derivative. Upon laser pulsed femtosecond irradiation at 790 nm, the second harmonic emission from the metal oxide core induced the efficient release of Clb, with concomitant contribution from the nonlinear absorption of the coumarin (CM)-based moiety. 相似文献
106.
Dr. Alberto Palazzolo Dr. Timothée Naret Dr. Marion Daniel-Bertrand David-Alexandre Buisson Dr. Simon Tricard Dr. Philippe Lesot Dr. Yannick Coppel Dr. Bruno Chaudret Dr. Sophie Feuillastre Dr. Grégory Pieters 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(47):21065-21070
We report the dramatic impact of the addition of N-heterocyclic carbenes (NHCs) on the reactivity and selectivity of heterogeneous Ru catalysts in the context of C−H activation reactions. Using a simple and robust method, we prepared a series of new air-stable catalysts starting from commercially available Ru on carbon (Ru/C) and differently substituted NHCs. Associated with C−H deuteration processes, depending on Ru/C-NHC ratios, the chemical outcome can be controlled to a large extent. Indeed, tuning the reactivity of the Ru catalyst with NHC enabled: 1) increased chemoselectivity and the regioselectivity for the deuteration of alcohols in organic media; 2) the synthesis of fragile pharmaceutically relevant deuterated heterocycles (azine, purine) that are otherwise completely reduced using unmodified commercial catalysts; 3) the discovery of a novel reactivity for such heterogeneous Ru catalysts, namely the selective C-1 deuteration of aldehydes. 相似文献
107.
Dr. Yannick Mathieu Dr. Juan D. Vidal Dr. Lourdes Arribas Martínez Dr. Nerea Abad Fernández Prof. Sara Iborra Prof. Avelino Corma 《ChemSusChem》2020,13(17):4743-4758
During oxidative depolymerization of lignin in aqueous alkaline medium using molecular oxygen as oxidant, the highly functionalized primary phenolic monomers are not stable products, owing to various not fully identified secondary reaction mechanisms. However, better understanding of the mechanisms responsible for the instability of the main part of the products of interest derived from lignin is of much interest. Evaluation of their individual reactivities under oxidative conditions should significantly help to find a better way to valorize the lignin polymer and to maximize the yields of target value-added products. Consequently, the main objective of this study is to assess the individual stabilities of some selected lignin-based phenolic compounds, such as vanillin, vanillic acid, and acetovanillone, together with some other pure chemical compounds such as phenol and anisole to give an insight into the mechanisms responsible for the simultaneous formation and repolymerization of those products and the influence of the oxidation conditions. Various complementary strategies of stabilization are proposed, discussed, and applied for the oxidative depolymerization reactions of a technical lignin extracted from pinewood with a high content of β-O-4 interconnecting bonds to try to obtain enhanced yields of value-added products. 相似文献
108.
Yannick Geiger Thierry Achard Aline Maisse-Franois Stphane Bellemin-Laponnaz 《Chemical science》2020,11(46):12453
The chiral ligand N-methylephedrine (NME) was found to catalyse the addition of dimethylzinc to benzaldehyde in an enantiodivergent way, with a monomeric and a homochiral dimeric complex both catalysing the reaction at a steady state and giving opposite product enantiomers. A change in the sign of the enantiomeric product was thus possible by simply varying the catalyst loading or the ligand ee, giving rise to an enantiodivergent non-linear effect. Simulations using a mathematical model confirmed the possibility of such behaviour and showed that this can lead to situations where a reaction gives racemic products, although the system is composed only of highly enantioselective individual catalysts. Furthermore, depending on the dimer''s degree of participation in the catalytic conversion, enantiodivergence may or may not be observed experimentally, which raises questions about the possibility of enantiodivergence in other monomer/dimer-catalysed systems. Simulations of the reaction kinetics showed that the observed kinetic constant kobs is highly dependent on user-controlled parameters, such as the catalyst concentration and the ligand ee, and may thus vary in a distinct way from one experimental setup to another. This unusual dependency of kobs allowed us to confirm that a previously observed U-shaped catalyst order vs. catalyst loading-plot is linked to the simultaneous catalytic activity of both monomeric and dimeric complexes.An asymmetric reaction consisting of competing monomeric and dimeric catalysts may explain enantiodivergent non-linear effects. 相似文献
109.
Yannick Privat Emmanuel Trlat Enrique Zuazua 《ZAMM - Journal of Applied Mathematics and Mechanics / Zeitschrift für Angewandte Mathematik und Mechanik》2016,96(5):538-549
The problems of observing, controlling and stabilizing wave processes arise in many different contexts ranging from structural mechanics to seismic waves. In a suitable functional setting, they are closely interconnected and sometimes completely equivalent. In a series of previous articles we have addressed the problem of the optimal design of sensors for purely conservative wave models. We analyzed a relaxed version of the optimal observation problem, considering the expectation of solutions under a randomisation procedure, rather than that where all possible solutions are considered in a purely deterministic setting. From an analytical point of view, this randomisation procedure had the advantage of leading to a spectral diagonalisation of the observations. In this way, using fine asymptotic spectral properties of the Laplacian, we disclosed the links between the geometric properties of the domain where waves propagate and the existence of optimal locations for the sensors or, by the contrary, the emergence of relaxation phenomena. Here we show that spectral randomised observability is equivalent to the property of spectral controllability by means of a discrete set of lumped controls acting everywhere on the domain, and distributed according to the shape of the eigenfunctions. Our results on optimal observation then find natural equivalents on the problem of optimal spectral control. We also give an interpretation of these results in terms of a feedback stabilization property, ensuring the exponential decay of the energy of solutions as time tends to infinity. 相似文献
110.
Cis-2,4- and cis-cis-2,4,5-substituted tetrahydrofurans have been prepared stereoselectively using electrophile-mediated cyclization of β-hydroxyhomoallylsilanes, readily available from α-silylacetic esters. 相似文献