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121.
Filippo Bianchi Falk K. Wittel Marcel Thielmann Pavel Trtik Hans J. Herrmann 《Transport in Porous Media》2018,122(1):169-184
In particle-laden flows through porous media, porosity and permeability are significantly affected by the deposition and erosion of particles. Experiments show that the permeability evolution of a porous medium with respect to a particle suspension is not smooth, but rather exhibits significant jumps followed by longer periods of continuous permeability decrease. Their origin seems to be related to internal flow path reorganization by avalanches of deposited material due to erosion inside the porous medium. We apply neutron tomography to resolve the spatiotemporal evolution of the pore space during clogging and unclogging to prove the hypothesis of flow path reorganization behind the permeability jumps. This mechanistic understanding of clogging phenomena is relevant for a number of applications from oil production to filters or suffosion as the mechanisms behind sinkhole formation. 相似文献
122.
123.
Pavone M Cimino P De Angelis F Barone V 《Journal of the American Chemical Society》2006,128(13):4338-4347
The nitrogen isotropic hyperfine coupling constant (hcc) and the g tensor of a prototypical spin probe (di-tert-butyl nitroxide, DTBN) in aqueous solution have been investigated by means of an integrated computational approach including Car-Parrinello molecular dynamics and quantum mechanical calculations involving a discrete-continuum embedding. The quantitative agreement between computed and experimental parameters fully validates our integrated approach. Decoupling of the structural, dynamical, and environmental contributions acting onto the spectral observables allows an unbiased judgment of the role played by different effects in determining the overall experimental observables and highlights the importance of finite-temperature vibrational averaging. Together with their intrinsic interest, our results pave the route toward more reliable interpretations of EPR parameters of complex systems of biological and technological relevance. 相似文献
124.
Murgia S Portesani F Ninham BW Monduzzi M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(30):7889-7898
The thermodynamically stable microemulsion and lamellar phases in the didodecyldimethylammonium bromide/water/n-decane ternary system were explored in the presence of NaBr to gain information on sodium ion-interface interactions. Experimental results, obtained by different NMR techniques, strongly suggest accumulation of sodium ions at the cationic interface. This apparently counterintuitive result is explained by invoking the dispersion potential experienced by the ions near the interface. A mechanism is proposed that can account for the dramatic shrinkage of the microemulsion phase region when an electrolyte is added. 相似文献
125.
Capriati V Florio S Luisi R Perna FM Salomone A 《The Journal of organic chemistry》2006,71(10):3984-3987
A general method for the synthesis of hydroxyalkyl 1,3-dihydrobenzo[c]furans from ortho-lithiated aryloxiranes and carbonyl compounds is described. 相似文献
126.
Filippo Ubertini 《Meccanica》2013,48(5):1031-1051
The paper discusses the application of dynamic methods for damage detection in the main cables of suspension bridges, using data continuously recorded under wind excitation through permanent monitoring systems and automated operational modal analysis. A continuum model for predicting the vertical aeroelastic response of wind-excited damaged suspension bridges is formulated and presented at first. The model shows that, for a real sample bridge, typical variations of mean wind speed produce variations of natural frequencies, due to aeroelastic effects, that are more significant than those produced by a small damage. A possible solution to this issue, proposed in the paper, consists of removing the dependence on the excitation source by calculating frequency shifts considering frequencies, in reference and damaged states, associated to approximately the same mean wind speed. This task and the necessary estimation of frequency shifts through a statistical analysis of identified natural frequencies outline the need for a continuous dynamic monitoring. The analytical model is finally employed for generating dynamic wind response data that are successively processed by means of an advanced automated modal identification tool. Although based on the simplifications inherently contained in the analytical model, the results show that frequency shifts caused by a relatively small damage can be accurately estimated from response data recorded under wind excitation with a reasonable number of data sets. 相似文献
127.
128.
Ottaviani MF Retini G Cangiotti M Mangani F Segre U 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2002,58(6):1129-1141
Electron paramagnetic resonance (EPR) has been used to investigate the adsorption capability and the surface interacting ability towards Cu(II) solutions (CuCl2, Cu(NO3)2, CuSO4 in water or ethanol) of various carbon blacks, both graphitized and ungraphitized, selected on the basis of the surface area, namely, Carbograph1 (area = 100 m2/g), Carbograph4 (area = 210 m2/g), and Carbograph5 (area = 560 m2/g), which were indicated as C1g, C4g, C5g (g = graphitized), and C1ng, C4ng, C5ng (ng = ungraphitized). The EPR analysis was supported by surface analysis, for evaluating the surface area, the pore volume and the porosity, and by atomic absorption to obtain the adsorbed Cu(II) amounts. Graphitization provokes a decrease in surface area, but C1g, at low surface area, showed a unexpected increase of the adsorption ability ascribed to the formation of new surface porosity closed by graphite layers. The carbon samples showed a broad unresolved EPR signal due to mobile unpaired electrons in the carbon matrix. Graphitized samples presented a narrower signal than ungraphitized samples, which increases in width with the increase in surface area (with the exception of C5ng due to the high exposition of the wide surface to oxydizing external agents) and upon prolonged thermal treatment. The signal intensity of the carbon paramagnetic centers decreases upon Cu(II) adsorption. Computer aided analysis of the EPR spectra of the solids after Cu(II) adsorption allowed to extract structural information on the Cu-surface site complexes. The Cu2+ ions coordinated with surface polar sites, mainly oxygenated. Adsorption depends on the different Cu(II) salts, caused by the salt solubility and the interacting ability of the counter-ion. In several cases the solutions concentrated in the carbon porosity leading to precipitation of the salt. Ethanol solutions are more adsorbed at the carbon surface than water solutions; Cu(II) partially retains its solvation shell and partially presents electron transfer to the carbon surface. Adsorption is favored to ungraphitized carbons with respect to the graphitized ones due to both the higher surface area, and the higher hydrophilicity of the surface. In summary, these carbon powders, widely used for chromatographic applications, show an adsorption capability towards Cu(II) solutions higher than expected due to both a definite porosity, and the presence of polar groups which are not eliminated with chemical surface treatments. 相似文献
129.
Atzei D De Filippo D Rossi A Porcelli M 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2001,57(5):1073-1083
Metal complexes of general formula M(ttz)2X2 (with M= Pd(II) or Pt(II); X = Cl or Br; ttz = 1,3-thiazolidine-2-thione) have been synthetized as crystalline compounds and studied by means of X-ray Photoelectron Spectroscopy (XPS). The chemical shift of core level signals showed that ttz is bonded to the metal through the thioketonic sulphur atom and that electronic charge redistribution in the ligand takes place after complexation. No metal-nitrogen bonds are present. This is consistent with the results of all the quantum mechanical models according to which hydrogen is bound to nitrogen, even in the hydrogen bonded complex, making the latter rather unavailable to coordination 相似文献
130.
Darses B Michaelides IN Sladojevich F Ward JW Rzepa PR Dixon DJ 《Organic letters》2012,14(7):1684-1687
A synthetic strategy for the construction of the [7-5-5] all-carbon tricyclic core of numerous calyciphylline A-type Daphniphyllum alkaloids has been developed using a key intramolecular Pauson-Khand reaction. A subsequent base-mediated double-bond migration and a regio- and stereoselective radical late stage allylic oxygenation provide access to the substitution patterns of daphnilongeranin B and daphniyunnine D. 相似文献