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941.
Leandro Rodrigues de LemosPamela da Rocha Patrício Guilherme Dias RodriguesRaquel Moreira Maduro de Carvalho Maria C. Hespanhol da SilvaLuis Henrique Mendes da Silva 《Fluid Phase Equilibria》2011,305(1):19-24
Phase diagrams of aqueous two-phase systems composed of PEO1500 + salt (di-potassium phosphate + potassium hydroxide or ammonium sulfate or zinc sulfate) + water were determined at (283.15, 298.15, and 313.15) K. All systems produce a large two-phase region; however the influence of temperature on the binodal position seems to be very small. By analyzing the effects of ammonium sulfate or zinc sulfate, it was observed that zinc was more effective in promoting phase separation than ammonium. The consistency of the tie-line data was ascertained by applying the Othmer-Tobias correlation. In this paper, aqueous two-phase systems data for nine ternary systems are correlated by using the NRTL model and UNIFAC for the activity coefficient. The results are very satisfactory, with root mean square deviations between experimental and calculated compositions as low as 0.99 and 1.21%, respectively. However the NRTL model better represents the systems in study, when compared with UNIFAC. 相似文献
942.
Pamela da Rocha PatrícioAparecida Barbosa Mageste Leandro Rodrigues de LemosRaquel Moreira Maduro de Carvalho Luis Henrique Mendes da SilvaMaria C. Hespanhol da Silva 《Fluid Phase Equilibria》2011,305(1):1-8
The phase diagrams of PEO1500 + sodium tartrate + water, PPO400 + sodium tartrate + water, PEO1500 + sodium succinate + water, PPO400 + sodium succinate + water, PEO1500 + sodium citrate + water, PPO400 + sodium citrate + water and PPO400 + sodium acetate + water aqueous two-phase systems were determined at (283.15, 298.15, and 313.15) K. Both equilibrium phases composition were analyzed by conductimetry and refractive index. In this paper, the influences of polymer hydrophobicity, salt nature and temperature on the phase diagram were analyzed. The phase separation processes was endothermic and the hydrophobic increase make easier the phase splitting, while the electrolyte capacity to induce phase separation follow the order: citrate > tartrate > succinate. The consistency of the tie-line data was ascertained by applying the Othmer-Tobias correlation. The experimental data were correlated with the NRTL model for the activity coefficient, with estimation of new interaction energy parameters. The results, analyzed in terms of root mean square deviations between experimental and calculated compositions, were considered satisfactory. 相似文献
943.
In this work, we show that nanoparticles (NPs) dispersed in compressible hydrofluoroalkanes (HFAs) at small volume fractions are capable of stabilizing micrometer-sized particle colloids, which otherwise flocculate due to strong van der Waals forces. Water-soluble, biodegradable NPs with a chitosan (CS) core, grafted with highly HFA-philic moieties, can be readily dispersed in the low dielectric HFAs and are capable of imparting stability to a wide range of therapeutic particles having different chemistries (polar or hydrophobic; small and large molecular weight, including peptides and proteins) and morphologies (micronized crystals or amorphous). These NP systems thus serve as a broadly applicable platform for the noninvasive delivery of therapeutics to and through the lungs using propellant-based, portable inhalers, and are also of potential relevance in other industries where HFAs are employed as solvents or propellants. This concept may also be applicable to other compressible solvents. 相似文献
944.
Martines Marco Antonio Utrera do Carmo Devaney Ribeiro de Castro Gustavo Rocha Caetano Laércio 《Journal of Sol-Gel Science and Technology》2011,59(1):188-193
This paper reports an electrochemical study of ordered mesoporous silica impregnated with a cationic dye (o-toluidine blue),
prepared with a non-ionic surfactant as the structure-directing agent. O-toluidine blue was chosen because of its utility
as an electron transfer mediator (redox catalyst). O-toluidine blue impregnated mesoporous silica was characterized by nitrogen
sorption porosimetry, small angle X-ray scattering, infrared spectroscopy, scanning electron microscopy and cyclic voltammetry
using chemically modified carbon paste electrodes. Results indicate that the dye is located within the ordered mesopores of
micron-sized silica spheres. 相似文献
945.
Guilherme Post Sabin Werickson Fortunato de Carvalho Rocha Ronei Jesus Poppi 《Microchemical Journal》2011,99(2):542-547
Nowadays, near-infrared spectroscopy chemical imaging (NIR-CI) has been widely used in pharmaceutical analysis since it provides important surface information about the samples. In this work the information of NIR-CI at the pixel level was compared through calculation of the similarity between distribution maps of concentration obtained by different multivariate calibration approaches. The comparison was performed by using four different multivariate methods (MCR, MLR, CLS and PLS) in analysis of carbamazepine pharmaceutical formulations. For global determination, all models developed showed RMSEP below 1.9% (w/w) for active principal ingredient (API) and better than 4.6% (w/w) for excipients. Also, the distribution maps obtained by PLS, CLS and MCR showed great similarity for all compounds of the formulation as well with concentrations in the tablets. However, comparing the distribution maps obtained by MLR with those from the other chemometric tools, a lower similarity was observed. Thus, this fitted model does not ensure, by itself, that the images obtained are reliable or accurate. The paper also compares the distribution maps of concentrations obtained from all constituents present in the pharmaceutical formulation with their respective micrographs. 相似文献
946.
D. V. Demidov I. P. Prosvirin A. M. Sorokin T. Rocha A. Knop-Gericke V. I. Bukhtiyarov 《Kinetics and Catalysis》2011,52(6):855-861
The preparation of model silver catalysts supported on highly oriented pyrolytic graphite is described, and the effect of
the Ag particle size on the catalytic ethylene oxidation into ethylene oxide, studied by in situ XPS and mass spectrometry,
is considered. For a mean particle diameter of 8 nm, the adsorbed oxygen species characterized by an O 1s binding energy of 530.8 ± 0.2 eV (electrophilic oxygen) forms on the silver surface exposed to the ethylene-oxygen reaction
mixture. Larger silver particles with a mean diameter of 40 nm additionally contain the adsorbed oxygen species characterized
by an O 1s binding energy of 529.2 ± 0.2 eV (nucleophilic oxygen). The presence of both oxygen species on the surface of the larger
particles ensures the formation of ethylene oxide, while the sample with the smaller silver particles is inactive in the epoxidation
reaction. The O 1s signal at 530.8 eV is partly due to oxygen dissolved in the subsurface layers of silver. 相似文献
947.
The hydrothermal synthesis of a new metal-organic framework (MOF) formulated as Cu2(4,4′-bpy)2SO4·6(H2O), [abbreviation: (1); bpy or 4,4′-bpy=4,4′-bipyridine; SO42−=sulfate group] has been reported. The structure of this MOF consists of Cu+ nodes connected via 4,4′-bpy to form infinite chains, with two neighboring chains further bridged on the nodes by SO42−, resulting in a 1-D double chain network. Guest water molecules reside in between the chains and are hydrogen-bonded to the O and S atoms from the nearest sulfate groups, leading to the formation of a 3-D supramolecular framework. This MOF is good heterogeneous catalyst for the cyclopropanation of styrene, with high trans cyclopropane diastereoselectivity and was recycled and reused for three consecutive cycles without a significant loss of catalytic activity. 相似文献
948.
Chrysomya blowflies are originally from Africa and Australasia and were introduced in the American Continent, probably as a sheep parasite, in the 1970s. These flies are extremely important for medical-sanitary purposes and are useful to forensic entomology being used as an indicative of decomposition time in human corpses. The morphology of the larval and pupal stages of some species has been already studied by different authors demonstrating that it is possible to identify them in premature stages. In this study, Chrysomya megacephala egg ultramorphology was analyzed to describe its structure, generating data for further comparison between different species and genera. The blowflies were collected in Rio Claro city, SP, Brazil. Flies were attracted by fish carcasses and maintained in net cages; small portions of minced meat were placed in plastic pots for egg laying. Eggs were collected, fixed in alcoholic Bouin, prepared according to SEM routine and observed under Philips scanning electron microscope. C. megacephala eggs are oval with one flat face and another convex, measuring approximately 0.52 (+/-0.03) mm of length and 0.12 (+/-0.02) mm of width. The micropyle is circular in shape, with two perforations enclosed by countless small projections and is located in one of the extremities in the interface between the flat and convex faces. On the convex surface hexagonal imprints were observed, this surface is impermeable to water and gases. The flat surface has numerous round projections with different sizes, creating a permeable surface with a thinner chorion from which the larvae hatches. The larvae presents itself all wrinkled and with numerous cuticular projections with a thorn shape facing the posterior region. The cuticle projections with a thorn shape from C. megacephala larvae are probably a vestige of the thorns found in larvae of parasite Diptera. 相似文献
949.
M.S.F. da Rocha T.E.A. Santos V.R. Hering J.H. Vuolo V.P. Mammana 《Applied Surface Science》2008,254(6):1859-1869
A statistical data analysis methodology was developed to evaluate the field emission properties of many samples of copper oxide nanostructured field emitters. This analysis was largely done in terms of Seppen-Katamuki (SK) charts, field strength and emission current. Some physical and mathematical models were derived to describe the effect of small electric field perturbations in the Fowler-Nordheim (F-N) equation, and then to explain the trend of the data represented in the SK charts. The field enhancement factor and the emission area parameters showed to be very sensitive to variations in the electric field for most of the samples. We have found that the anode-cathode distance is critical in the field emission characterization of samples having a non-rigid nanostructure. 相似文献
950.
We consider classes of translationally invariant black hole solutions whose equations of state closely resemble that of QCD at zero chemical potential. We use these backgrounds to compute the ratio zeta/s of bulk viscosity to entropy density. For a class of black holes that exhibits a first-order transition, we observe a sharp rise in zeta/s near Tc. For constructions that exhibit a smooth crossover, like QCD does, the rise in zeta/s is more modest. We conjecture that divergences in zeta/s for black hole horizons are related to extrema of the entropy density as a function of temperature. 相似文献