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151.
Favaro D. I. T. Rocha F. R. Angelini M. A Henriques H. R. Soares J. S. Silva P. S. C. Oliveira S. M. B. 《Journal of Radioanalytical and Nuclear Chemistry》2018,316(2):805-818
Journal of Radioanalytical and Nuclear Chemistry - Concentration of metals in 15 bottom sediment samples from Tietê River, a significantly polluted river, were assessed. Total and partial... 相似文献
152.
A. J. A. Aquino L. A. Soares II A. B. F. Da Silva M. Trsic 《Journal of Molecular Structure》1986,139(3-4):327-332
Semiempirical MNDO calculations are performed on various models for the polythiazyl polymer with increasing chain sizes. Population analysis, geometry optimization and the evolution of the frontier orbital energies are discussed. A low-lying broken symmetry structure with (SN)2 repeating units is detected. 相似文献
153.
Cleide M. F. Soares Onelia A. dos Santos Heizir F. de Castro Flavio F. de Moraes Gisella M. Zanin 《Applied biochemistry and biotechnology》2004,113(1-3):307-319
The hydrolysis of tetraethoxysilane using the sol-gel process was used to produce silica matrices, and these were tested for the immobilization of lipase from Candida rugosa by three methods: physical adsorption, covalent binding, and gel entrapment in the presence and absence of polyethylene glycol (PEG-1450). The silica matrices and their derivatives were characterized regarding particle size distribution, specific surface area, pore size distribution (Brunauer, Emmett, and Teller [B.E.T.] method), yield of grafting (thermogravimetric analyzer [TGA]), and chemical composition (Fourier transform infrared). Immobilization yields based on recovered lipase activity varied from 3.0 to 32.0%, and the highest efficiency was attained when lipase was encapsulated in the presence of PEG. 相似文献
154.
155.
Patricia Kaori Soares Gustavo Galo Marcheafave Adriano de Araújo Gomes Ieda Spacino Scarminio Roy Edward Bruns 《Chromatographia》2018,81(8):1189-1200
HPLC-DAD analysis of statistical mixture design extracts of Erythrina speciosa Andrews leaves provided chromatographic and UV–visible profiles of their basic and organic fractions that were treated with the PARAFAC multivariate method. The design extracts provided greater varieties and amounts of metabolites than could be obtained by classical extraction methods. Fractionation provided more diverse fingerprint information than obtained previously from only the crude extract. The two largest chromatographic peaks, one with a 4.8 min elution time having an intense spectral band at 235 nm and the other a 5.8 min peak with an intense 238 nm band for the basic fraction were obtained with the ternary 1:1:1 ethanol–dichloromethane–hexane mixture. These can be assigned to diene-type and lactonic alkaloids. Peaks with the same retention times are also found in the organic fraction but are extracted with different mixtures and have distinct spectral behavior in the 235 nm region, probably being aromatic alkaloids. The above strategy permits a more unambiguous assignment of metabolic groups to specific chromatographic peaks. This can be expected to provide higher quality chromatographic fingerprints for natural products’ chemistry. 相似文献
156.
157.
158.
Pinho e Melo TM Soares MI Gonsalves AM Paixão JA Beja AM Silva MR 《The Journal of organic chemistry》2005,70(17):6629-6638
1-Azafulvenium methides, generated from pyrrolo[1,2-c]thiazole-2,2-dioxides' thermal extrusion of sulfur dioxide, led to the synthesis of functionalized pyrroles. The intramolecular trapping of these transient 8pi 1,7-dipoles in pericyclic reactions, namely sigmatropic [1,8]H shifts and 1,7-electrocyclization, allowed the synthesis of N-vinylpyrroles and C-vinylpyrroles which, under flash vacuum pyrolysis conditions, are converted into 5-oxo-5H-pyrrolizines or 4-oxo-1,4-dihydro-1-aza-benzo[f]azulenes, respectively. These heterocycles can also be obtained directly from FVP of pyrrolo[1,2-c]thiazole 2,2-dioxides. The synthesis and X-ray structure of a new 6-oxocyclopenta[b]pyrrole derivative is also reported. 相似文献
159.
The influence of [(2-hydroxy-1,1-bis(hydroxymethyl)ethyl)amino]-1-propanesulfonic acid (TAPS) on solutions containing lead(II) was studied by direct current polarography (DCP) and glass electrode potentiometry (GEP). The readings were taken at fixed total TAPS to total lead(II) concentration ratios and various pH values, at 25.0 ± 0.1 °C and ionic strength 0.1 M KNO3.Due to the basic pKa of the ligand, which occurs in the pH range where large amount of lead polynuclear species are formed, and the occurrence of ligand adsorption, that disabled the use of high concentrations of TAPS on DCP experiments, GEP and DCP experimental conditions were put to the limit in order to provide the correct Pb-TAPS-OH model and reliable stability constants.The proposed final model is: PbL, PbL2, PbL2(OH) and PbL2(OH)2 with overall stability constants values, as log β, 3.27 ± 0.06, 6.5 ± 0.1, 12.7 ± 0.1 and 17.27 ± 0.06, respectively.A comparative analysis of the strength of complexation of TAPS and a structural related buffer, 2-hydroxy-3-[tris(hydroxymethyl)methylamino]-1-propanesulfonic acid (TAPSO), with lead is also discussed. 相似文献
160.
CarinaM.M. Machado Ignacy Cukrowski HelenaM.V.M. Soares 《Helvetica chimica acta》2003,86(10):3288-3304
The influence of 2‐hydroxy‐3‐[(2‐hydroxy‐1,1‐dimethylethyl)amino]propane‐1‐sulfonic acid (AMPSO=HL) on systems containing copper(II) was studied by glass‐electrode potentiometry (GEP) and direct‐current polarography (DCP), at fixed total‐ligand‐to‐total‐metal‐concentration ratios and various pH values (25°, 0.1M KNO3 medium). The predicted model ([CuL]+, [CuL(OH)], [CuL2], [CuL2(OH)]?, [CuL2(OH)2]2?, and [CuL3]?) and the overall stability constants for species found were obtained by combining results from both electrochemical techniques. The last five complexes are reported for the first time. For the species [CuL]+, [CuL2], [CuL3]?, and [CuL2(OH)2]2?, it was possible to determine stability constants with reasonable certainty and their values, as log β, were found to be 4.62±0.04, 9.5±0.1, 13.4±0.1, and 21.2±0.1, respectively. For the species [CuL(OH)] and [CuL2(OH)]?, stability constants 11.7±0.2 and 15.6±0.2, respectively, are presented as indicative values. It was demonstrated that AMPSO buffer may decrease the Cu2+ concentration by ten orders of magnitude by forming complexes with Cu2+. For the first time, the correction in DCP waves for the adsorption of the ligand and quasi‐reversibility of the metal allowed to determine stability‐constant values that are in good agreement with the values obtained by GEP. The importance of graphic analysis of data and significance of employing two analytical techniques was demonstrated; neither GEP nor DCP would be able to provide the correct M/L/OH? model and reliable stability constants when used independently. 相似文献