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排序方式: 共有421条查询结果,搜索用时 15 毫秒
71.
Michal?Landa Petr?Sedlák Hanu??Seiner Luděk?Heller Lucie?Bicanová Petr??ittner Václav?Novák 《Applied Physics A: Materials Science & Processing》2009,96(3):557-567
Recent experimental and theoretical improvements of resonant ultrasound spectroscopy (RUS) are summarized to investigate elastic
constants of phases in shape memory alloys. The proposed inversion procedure, described in this work, is particularly suitable
to reliable evaluation of the temperature dependence of elastic constants of low-symmetry ferroelastic materials which may
be strongly elastically anisotropic and tend to exist in twinned forms. The method is applicable even for the evaluation of
single-crystal elastic constants from RUS measurements on microtwinned crystals, since it involves a homogenization algorithm
based on the macroscopic deformation response of the layered structure. This potentially allows performing meaningful acoustic
studies on samples with a general submicron-size layered structure. 相似文献
72.
Phi Minh Do Alexander Angerhofer Ivan Hrdy Lucie Bardonova Lonnie O. Ingram K. T. Shanmugam 《Applied biochemistry and biotechnology》2009,153(1-3):21-33
Trichomonas vaginalis generates reduced ferredoxin within a unique subcellular organelle, hydrogenosome that is used as a reductant for H2 production. Pyruvate ferredoxin oxidoreductase and NADH dehydrogenase (NADH-DH) are the two enzymes catalyzing the production of reduced ferredoxin. The genes encoding the two subunits of NADH-DH were cloned and expressed in Escherichia coli. Kinetic properties of the recombinant heterodimer were similar to that of the native enzyme from the hydrogenosome. The recombinant holoenzyme contained 2.15 non-heme iron and 1.95 acid-labile sulfur atoms per heterodimer. The EPR spectrum of the dithionite-reduced protein revealed a [2Fe–2S] cluster with a rhombic symmetry of g xyz?=?1.917, 1.951, and 2.009 corresponding to cluster N1a of the respiratory complex I. Based on the Fe content, absorption spectrum, and the EPR spectrum of the purified small subunit, the [2Fe–2S] cluster was located in the small subunit of the holoenzyme. This recombinant NADH-DH oxidized NADH and reduced low redox potential electron carriers, such as viologen dyes as well as Clostridium ferredoxin that can couple to hydrogenase for H2 production from NADH. These results show that this unique hydrogenosome NADH dehydrogenase with a critical role in H2 evolution in the hydrogenosome can be produced with near-native properties in E. coli for metabolic engineering of the bacterium towards developing a dark fermentation process for conversion of biomass-derived sugars to H2 as an energy source. 相似文献
73.
Thomas C. T. Michaels Lucie X. Liu Samo Curk Peter G. Bolhuis 《Molecular physics》2018,116(21-22):3055-3065
ABSTRACTProbing reaction mechanisms of supramolecular processes in soft and biological matter, such as protein aggregation, is inherently challenging. This is because these processes involve multiple molecular mechanisms that are associated with the rearrangement of large numbers of weak bonds, resulting in complex free energy landscapes with many kinetic barriers. Reaction rate measurements at different temperatures can offer unprecedented insights into the underlying molecular mechanisms. However, to be able to interpret such measurements, a key challenge is to establish which properties of the complex free energy landscapes are probed by the reaction rate. Here, we present a reaction rate theory for supramolecular kinetics based on Kramers theory of diffusive reactions over multiple kinetic barriers. We find that reaction rates for protein aggregation are of the Arrhenius–Eyring type and that the associated activation energies probe only one relevant barrier along the respective free energy landscapes. We apply this advancement to interpret, in experiments and in coarse-grained computer simulations, reaction rates of amyloid aggregation in terms of molecular mechanisms and associated thermodynamic signatures. These results suggest a practical extension of the concept of rate-determining steps for complex supramolecular processes and establish a general platform for probing the underlying energy landscape using kinetic measurements. 相似文献
74.
Malkov AV Barłóg M Miller-Potucká L Kabeshov MA Farrugia LJ Kočovský P 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(22):6873-6884
Enantiopure, Boc-protected alkoxyamines 12 and 13, derived from the readily available homoallylic alcohols 4 via a reaction that involves either inversion or retention of configuration, undergo a diastereoselective Pd-catalyzed ring-closing carbonylative amidation to produce isoxazolidines 16/17 (≤50:1 diastereoisomer ratio (d.r.)) that can be readily converted into the N-Boc-protected esters of β-amino-δ-hydroxy acids and their γ-substituted homologues 37. The key carbonylative cyclization proceeds through an unusual syn addition of the palladium and the nitrogen nucleophile across the C=C bond (19→21), as revealed by the reaction of 15, which afforded isoxazolidine 18 with high diastereoselectivity. 相似文献
75.
Dr. Yvonne Schmidt Dipl.‐Chem. Konrad Lehr Lucie Colas Prof. Dr. Bernhard Breit 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(23):7071-7081
The determination of the relative configuration of 1,3‐dimethyl‐substituted alkyl chains is possible by interpretation of 1H NMR shift differences. Additionally, assignments are feasible in a variety of deuterated solvents, because the corresponding shift differences are not significantly influenced by the solvent. The trends for Δδ values depending on functional groups adjacent to the stereogenic centers are shown. Based on a thorough comparison with literature data, the relative configuration of natural products can be predicted. For this purpose, we derived an empirical rule for the ranges in which Δδ values usually occur. Furthermore, we were able to proof the validity of our method by the successful prediction of the relative configuration for the polyketide natural product xylarinic acid A, which was confirmed by the asymmetric total synthesis of its enantiomer. Based on the proposed simple analysis of published 1H NMR data and the determination of the relevant chemical‐shift differences, we predicted the relative configurations of several previously unassigned natural products. 相似文献
76.
Antiplatelet therapy is a cornerstone of cardiovascular treatment in patients with coronary artery disease and after myocardial infarction. Clopidogrel has become a popular antiplatelet agent due to its fast action and low frequency of adverse effects. Kinetics of clopidogrel metabolism is driven by enzymatic activity of the Cytochrome P450 system. Genotyping of CYP2C19 and CYP2C9 polymorphisms allows to identify slow metabolizers showing resistance to clopidogrel therapy. Today, a number of PCR-based techniques for single nucleotide polymorphism genotyping directed at clopidogrel resistance polymorphisms are in use. Here, we describe a new alternative genotyping approach combining the separation power of denaturing capillary electrophoresis with the analysis speed and ease of use of Bioanalyzer chipCE platform. Using an upgraded heater control, we present an optimization for allele separation of CYP2C19 I331V, CYP2C9 R144C, and CYP2C9 I359L polymorphisms employing run temperatures of up to 55°C. We demonstrate rapid and accessible approach to reproducible clopidogrel resistance with feasibility and low cost. 相似文献
77.
Karolína Salvadori Alena Krupkov Lucie ervenkov astn Monika Müllerov Vclav Eigner Tom Strak Petra Cuínov 《Molecules (Basel, Switzerland)》2021,26(18)
The repetition of urea-based binding units within the receptor structure does not only lead to monomer properties multiplication. As confirmed by spectroscopic studies, UV-Vis and 1H-NMR in classical or competitive titration mode, the attachment to a carrier allocates the active moieties to mutual positions predetermining the function of the whole receptor molecule. Bivalent receptors form self-aggregates. Dendritic receptors with low dihydrogen phosphate loadings offer a cooperative complexation mode associated with a positive dendritic effect. In higher dihydrogen phosphate concentrations, the dendritic branches act independently and the binding mode changes to 1:1 anion: complexation site. Despite the anchoring, the dendritic receptors retain the superior efficiency and selectivity of a monomer, paving the way to recyclable receptors, desirable for economic and ecological reasons. 相似文献
78.
79.
Christophe O. Soulage Lucie Grand Alain Géloën Stéphane Chambert 《Tetrahedron letters》2012,53(5):480-483
A straightforward procedure leading to the flavone cirsimaritin and its 4′-O-β-d-glycosylation to afford cirsimarin, its corresponding flavone glucopyranoside, is described. The biological properties of cirsimarin, measured on human adipocytes, showed potent effects on both lipolysis and lipogenesis. Cirsimarin could therefore be considered as an efficient tool in the struggle against excessive adipose tissue deposition and as a potential candidate in the treatment of obesity. 相似文献