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481.
Valentina MerliniSylvain Gaillard Alessio PortaGiuseppe Zanoni Giovanni Vidari Steven P. Nolan 《Tetrahedron letters》2011,52(10):1124-1127
A simple and convenient synthesis of α-ionone, an important component of flowers and fragrances, is reported. The key step in the formation of the α,β-unsaturated ketone moiety involves an NHC-AuI catalyzed Meyer-Schuster-like rearrangement of readily prepared propargylic esters. The complex [{Au(IPr)}2(μ-OH)][BF4] proved to be the most efficient catalyst leading to α-ionone in 70% yield from a propargylic benzoate. This optimized procedure represents a valuable and attractive alternative to classical methods leading to α,β-unsaturated ketones, such as the Wittig or aldol reactions. 相似文献
482.
Alessio Cardillo Massimiliano Zanin Jesús Gómez-Gardeñes Miguel Romance Alejandro J. García del Amo Stefano Boccaletti 《The European physical journal. Special topics》2013,215(1):23-33
We study the dynamics of the European Air Transport Network by using a multiplex network formalism. We will consider the set of flights of each airline as an interdependent network and we analyze the resilience of the system against random flight failures in the passenger’s rescheduling problem. A comparison between the single-plex approach and the corresponding multiplex one is presented illustrating that the multiplexity strongly affects the robustness of the European Air Network. 相似文献
483.
Damiano Monticelli Gabriele Carugati Alessio Castelletti Sandro Recchia Carlo Dossi 《Microchemical Journal》2010,95(2):158-163
A low cost, high performance ultraviolet digester was developed and tested in our laboratory. Its main features include limited costs (around 600 € for all the parts) and high efficiency toward total organic carbon (TOC) abatement. As a result the TOC of typical natural waters is reduced to less than 10% of its initial value with half an hour treatment. Easiness of use, temperature control and flexibility in sample size (up to 25 mL) and number (up to twelve 12 mL test tube) are other important characteristics of the developed UV digester.This apparatus was tested as a pretreatment method for the determination of the total content of trace elements such as copper, uranium and platinum in natural waters by cathodic adsorptive stripping voltammetry. The voltammetric technique was chosen because it is strongly interfered by the presence of even low levels of natural organic complexing molecules. As a result, a 30 minute UV treatment yielded results non distinguishable from ICP-MS data. 相似文献
484.
Given a compact Riemannian manifold, we study the regularity of the optimal transport map between two probability measures with cost given by the squared Riemannian distance. Our strategy is to define a new form of the so‐called Ma‐Trudinger‐Wang condition and to show that this condition, together with the strict convexity on the nonfocal domains, implies the continuity of the optimal transport map. Moreover, our new condition, again combined with the strict convexity of the nonfocal domains, allows us to prove that all injectivity domains are strictly convex too. These results apply, for instance, on any small C4‐deformation of the 2‐sphere. © 2009 Wiley Periodicals, Inc. 相似文献
485.
Lopez M Vu H Wang CK Wolf MG Groenhof G Innocenti A Supuran CT Poulsen SA 《Journal of the American Chemical Society》2011,133(45):18452-18462
Carbonic anhydrases (CAs) are enzymes whose endogenous reaction is the reversible hydration of CO(2) to give HCO(3)(-) and a proton. CA are also known to exhibit weak and promiscuous esterase activity toward activated esters. Here, we report a series of findings obtained with a set of CA inhibitors that showed quite unexpectedly that the compounds were both inhibitors of CO(2) hydration and substrates for the esterase activity of CA. The compounds comprised a monosaccharide core with the C-6 primary hydroxyl group derivatized as a sulfamate (for CA recognition). The remaining four sugar hydroxyl groups were acylated. Using protein X-ray crystallography, the crystal structures of human CA II in complex with four of the sulfamate inhibitors were obtained. As expected, the four structures displayed the canonical CA protein-sulfamate interactions. Unexpectedly, a free hydroxyl group was observed at the anomeric center (C-1) rather than the parent C-1 acyl group. In addition, this hydroxyl group is observed axial to the carbohydrate ring while in the parent structure it is equatorial. A mechanism is proposed that accounts for this inversion of stereochemistry. For three of the inhibitors, the acyl groups at C-2 or at C-2 and C-3 were also absent with hydroxyl groups observed in their place and retention of stereochemistry. With the use of electrospray ionization-Fourier transform ion cyclotron resonance-mass spectrometry (ESI-FTICR-MS), we observed directly the sequential loss of all four acyl groups from one of the carbohydrate-based sulfamates. For this compound, the inhibitor and substrate binding mode were further analyzed using free energy calculations. These calculations suggested that the parent compound binds almost exclusively as a substrate. To conclude, we have demonstrated that acylated carbohydrate-based sulfamates are simultaneously inhibitor and substrate of human CA II. Our results suggest that, initially, the substrate binding mode dominates, but following hydrolysis, the ligand can also bind as a pure inhibitor thereby competing with the substrate binding mode. 相似文献
486.
Daniele Fabbri Alessio Adamiano Cristian Torri 《Analytical and bioanalytical chemistry》2010,397(1):309-317
A method for the determination of polycyclic aromatic hydrocarbons (PAHs) in liquid pyrolysate of biomass (bio-oil) was developed
with attention to greenness along with accuracy. Bio-oil obtained from preparative pyrolysis at 500 °C of poplar wood as representative
biomass matrix was dissolved into acetonitrile (ACN). An aliquot of the ACN solution (0.1 mg bio-oil) was added with water
(20% v/v) and spiked with perdeuterated standards, then PAHs were extracted with n-hexane and separated from phenolic interferents by silica gel solid-phase extraction (SPE). All 16 priority PAHs were detected
at concentrations between 7.7 μg g−1 (naphthalene) and 0.1 μg g−1 (benz[a]anthracene) with RSD in the 6–23% range. Recovery of perdeuterated acenaphthene, phenanthrene and chrysene was 84, 93 and
90%, respectively. Results obtained from the analysis of bio-oil were used to evaluate the performance of analytical pyrolysis
conducted with a heated platinum filament in off-line configuration. Two sampling procedures were compared: (1) sorption onto
silica gel followed by elution with n-hexane (Py-SPE), (2) dynamic solid-phase micro-extraction followed by fibre cleanup with aqueous ammonia (Py-SPME). Emission
levels of priority PAHs could be determined by Py-SPE with RSD in the 13–45% range, while Py-SPME was unsatisfactory for quantitation.
Emission levels determined by Py-SPE fell in the 6.4–0.1 μg g−1 range slightly higher than those calculated from bio-oil analysis. Both Py methods were adequate for screening purposes to
assess the effect of catalysts on PAH formation. In particular, they agreed to show that the content of PAHs expected in bio-oil
increased dramatically when pyrolysis was conducted over HZSM-5 zeolite. 相似文献
487.
488.
In this paper we prove that a strictly convex Alexandrov solution u of the Monge–Ampère equation, with right-hand side bounded away from zero and infinity, is $W^{2,1}_{\mathrm{loc}}$ . This is obtained by showing higher integrability a priori estimates for D 2 u, namely D 2 u∈Llog k L for any k∈?. 相似文献
489.
Chiara Saggese Alessio Frassoldati Alberto Cuoci Tiziano Faravelli Eliseo Ranzi 《Proceedings of the Combustion Institute》2013,34(1):427-434
The aim of this work is to discuss a lumped approach to the kinetic modeling of the pyrolysis and oxidation of biodiesel fuels, i.e. rapeseed and soybean methyl esters. The lumped model is the natural extension of the kinetic scheme of methyl butanoate and methyl decanoate and takes also a great advantage from the detailed kinetic scheme of biodiesel fuels [Westbrook et al. Combustion and Flame 158 (2011) 742–755]. The combustion of methyl palmitate and methyl stearate is very similar to the one of methyl decanoate, while large unsaturated methyl esters are significantly less reactive at low and intermediate temperatures. The formation of resonantly stabilized allylic radicals from unsaturated methyl esters constitutes a critical element very useful to characterize the reactivity of the different fuels. The extension of the previous kinetic model of hydrocarbon and oxygenated fuel combustion to the methyl esters required the introduction of ~60 lumped species and ~2000 reactions. The dimension of the overall kinetic scheme (~420 species involved in ~13,000 reactions) allows a more flexible and direct application of the model without the need of kinetic reductions. The comparison of model predictions and different sets of experimental data from one side allows to verify the reliability of the proposed model, from the other side calls for further experimental and theoretical work on this subject. 相似文献
490.