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581.
Prélot B Villiéras F Pelletier M Razafitianamaharavo A Thomas F Poinsignon C 《Journal of colloid and interface science》2003,264(2):343-353
Relationships between structural parameters of MnO2 and their surface properties at the solid-gas interface were investigated. The studied series ranged from ramsdellite to pyrolusite and encompassed disordered gamma-MnO2 samples. The structural model used takes into account structural defects: Pr (rate of pyrolusite intergrowth in the ramsdellite network) and Tw (rate of microtwinning). Analysis of the N2 adsorption isotherm evidenced positive correlations between specific surface area and Tw for gamma-MnO2 only and between the energetic constant C and (1-Pr). No microporosity is evidenced. Water adsorption isotherms evidenced the dependence of the H2O monolayer volume on Tw and showed a positive correlation between the cross-section area of water molecules adsorbed in the first monolayer and Pr, ranging from 13.5 A2 for Pr=1 to 6.3 A2 for Pr=0.2 (12 sites/nm2). Energetic heterogeneity is quantified from Ar and N2 low-pressure adsorption isotherms with the DIS procedure and correlated with H2O adsorption. High-energy adsorption domains are quantified and assigned to the different crystal faces: (110) faces with a common 1 x 1 octahedra layer of pyrolusite and ramsdellite and the (001) face of ramsdellite with 2 x 2 octahedra on which channels and plateaus are differentiated. The specific surface area ratio of ramsdellite high-energy sites to total ramsdellite content is shown to depend on Tw. The dependence on microtwinning of low cross-sectional area of N2 and much lower cross-sectional of residual H2O molecules leads us to assume that their adsorption sites on grain boundaries are represented by the twin planes between the structured nanocrystals generated by oxygen evolution during MD synthesis. 相似文献
582.
Herv Casabianca Jean-Bernard Graff Patrick Jame Christiane Perrucchietti Maurice Chastrette 《Journal of separation science》1995,18(5):279-285
This work presents two techniques for testing for the adulteration of flavors. One uses multidimensional gas chromatography on cyclodextrin derivatives to separate chiral compounds, the other uses isotope ratio mass spectrometry coupled with gas chromatography to determine stable isotope ratios. Applications to fruits and plants for the food and perfume industry are introduced. 相似文献
583.
Bernd?HuberEmail author Hubert?Gnaser Christiane?Ziegler 《Analytical and bioanalytical chemistry》2003,375(7):917-923
Nanoporous thin films were deposited onto glass substrates by painting with a solution of nanocrystalline anatase TiO(2) particles (with a size of either 6 nm or 16 nm) suspended in an organic solvent. Upon drying in air for about 1 day, the films were tempered at 450 degrees C in air for 1 h. This procedure results in stoichiometric TiO(2) films with a thickness of several micro m and a milky whitish appearance. Scanning force microscopy of the surface revealed that the nanoparticles of the films agglomerated into structures with lateral dimensions of some 100 nm. Transmission electron microscopy was utilized to investigate the structural arrangement of the crystallites in the films. High-resolution electron diffraction and X-ray diffraction analyses demonstrated, furthermore, that the material consists exclusively of a single TiO(2) phase, namely anatase, and that the films do not exhibit any preferential texture. The elemental stoichiometry and the possible presence of impurities were monitored throughout the films by means of secondary-ion mass spectrometry depth profiling. Electrical measurements have been carried out as a function of both the sample temperature T and the ambient oxygen partial pressure p(O(2)). From these data the electrical conductivity sigma of the porous films was determined in dependence of those parameters. 相似文献
584.
Christiane Fernandes Eduardo Stadler Valderes Drago Carlos Jorge da Cunha Izaura Hiroko Kuwabara 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》1996,52(14):1815-1821
In this study we have investigated eight complexes of the general composition [Fe3O(OOCCH3)6(L)3]NO3, where L is a heterocyclic ligand, viz. a 4-substituted pyridine. The Mössbauer spectra of the complexes showed isomer shifts and quadrupole splittings that are characteristic of iron(III) high-spin complexes. The Mössbauer quadrupolar doublets showed asymmetries that are attributed principally to the Goldanskii-Karyagin effect. A correlation is proposed between the Mössbauer parameters, and between the energy of the charge transfer band spectra, and the pKa values of the N-heterocyclic ligands. 相似文献
585.
We report the synthesis of novel anticancer compounds based on bioreductive and DNA-alkylating properties. The strategy was to combine a benzoquinone annelated pyrrole with bioreductive properties with a set
of DNA-alkylating functionalities, thus resulting in bifunctional anticancer compounds. The biological activity of all compounds
was evaluated against a number of cancer cell lines. One of the compounds should be emphasized. 相似文献
586.
Roseli M. de Souza Andr L. Saraceno Christiane Duyck Carmem Lúcia P. da Silveira Ricardo Q. Auclio 《Microchemical Journal》2007,87(2):99-103
A simple procedure for the extraction of Fe, Ni and V from asphaltene into acid solutions prior to the ICP OES determination is proposed. Either sonication or vortex agitation was used to disperse the organic sample into concentrated nitric acid, achieving efficient analyte extraction into the aqueous acid solution. Both procedures were compared and the advantage of the ultrasound-assisted procedure was evaluated. In both cases, pre-heating of sample–acid mixtures was necessary to enable quantitative extractions. Optimized conditions for the ultrasonic bath were established: 1 L of water at room-temperature, 20 min of sonication and tubes (maximum of eight) in vertical position. By using the vortex, 50 min of vigorous mechanical agitation was needed for each one of the tubes containing samples. The acid solution obtained after extraction was directly aspirated into the ICP in order to perform quantification by optical emission. Calibration was made with aqueous analyte standards containing Sc as internal standard. The procedures were tested using certified fuel oil (SRM NIST 1634c) and the method was applied for the determination of Fe, V and Ni in one asphaltene sample obtained by the fractionation of the SRM NIST 1634c. Recoveries above 90% were achieved and limits of quantification in the asphaltene sample were 1.5, 15 and 1.0 μg g− 1 estimated for Fe, Ni and V, respectively. 相似文献
587.
Marc Lang Alain Lacroix Christiane Pont Jean-Pierre Fleury 《Helvetica chimica acta》1986,69(5):1025-1033
2-Aza-1,3-dienes. Synthesis and Properties of 1-Alkylpyrazone-imines and their Tautomers Treatment of 5-dialkylamino-1,1-dicyano-2-aza-1,3-dienes (or their 1-methoxycarbonyl analogoues) with primary amines gives substituted 1-alkyl-3-cyano-(or methoxycarbonyl-)pyrazoneimines. Tautomeric behaviour, nucleophilic addition to imino function and spectroscopic data of these isomers are examined. 相似文献
588.
Erben MF Della Védova CO Boese R Willner H Leibold C Oberhammer H 《Inorganic chemistry》2003,42(22):7297-7303
The geometric structure and conformational properties of trifluoromethyl chlorosulfonate (chlorosulfuric acid trifluoromethyl ester), CF(3)OSO(2)Cl, have been determined by X-ray crystallography, gas electron diffraction (GED), and vibrational spectroscopy (IR(gas), IR(matrix), and Raman(liquid)). These experimental investigations were supplemented by quantum chemical calculations (B3LYP with 6-311G* and 6-311+G(3df) basis sets). All experimental methods result in a single conformer with gauche orientation of the CF(3) group relative to the S[bond]Cl. The dihedral angle delta(COSCl) is determined to be 91.7(3) degrees in the crystal and 94(3) degrees in the gas phase. This dihedral angle corresponds to a near-eclipsed orientation of the O[bond]C relative to one of the S[double bond]O bonds (delta(CO[bond]SO) = -23.0(3) degrees and -21(3) degrees in the crystal and gas phase, respectively). 相似文献
589.
Groger H Trauthwein H Buchholz S Drauz K Sacherer C Godfrin S Werner H 《Organic & biomolecular chemistry》2004,2(14):1977-1978
The first aminoacylase-catalyzed enantioselective synthesis of aromatic beta-amino acids is reported. The presence of an N-chloroacetyl group as acyl group in the substrate as well as the use of porcine kidney acylase I as a suitable enzyme component are prerequisites for this resolution process whereby optically active beta-amino acids are formed with high enantioselectivities of >98% ee. 相似文献
590.
Neureiter Markus Danner Herbert Thomasser Christiane Saidi Bamusi Braun Rudolf 《Applied biochemistry and biotechnology》2002,98(1-9):49-58
Sugarcane bagasse, a byproduct of the cane sugar industry, is an abundant source of hemicellulose that could be hydrolyzed
to yield a fermentation feedstock for the production of fuel ethanol and chemicals. The effects of sulfuric acid concentration,
temperature, time, and dry matter concentration on hemicellulose hydrolysis were studied with a 20-L batch hydrolysis reactor
using a statistical experimental design. Even at less severe conditions considerable amounts (>29%) of the hemicellulose fraction
could be extracted. The percentage of soluble oligosaccharides becomes very low in experiments with high yields in monosaccharides,
which indicates that the cellulose fraction is only slightly affected. For the sugar yields, acid concentration appears to
be the most important parameter, while for the formation of sugar degradation products, temperature shows the highest impact.
It could be demonstrated that the dry matter concentration in the reaction slurry has a negative effect on the xylose yield
that can be compensated by higher concentrations of sulfuric acid owing to a positive interaction between acid concentration
and dry matter contents. 相似文献