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排序方式: 共有157条查询结果,搜索用时 15 毫秒
71.
A. Cesana A. Nava A. Teatini T. Tenconi M. Terrani S. Terrani 《Journal of Radioanalytical and Nuclear Chemistry》1978,42(2):435-445
A method of estimating total body calcium and sodium in rats by in vivo neutron activation analysis is described. The subjects
were exposed to an integrated flux of about 1.6·1011 thermal neutrons and activity was determined by counting with a 3″×3″ NaI(Tl) detector. The growth of the subjects was followed
for about 75 days. The values of total body concentrations obtained are 0.83–0.90% for Ca and 0.128% for Na. Consideration
is given to the accuracy attainable and to the effects on the blood and the hematopoietic tissues of the radiation doses imparted. 相似文献
72.
Mutter R Campbell IB Martin De La Nava EM Merritt AT Wills M 《The Journal of organic chemistry》2001,66(10):3284-3290
The palladium-catalyzed reaction of pinacolone with tert-butyldimethyl(3-(2-bromophenyl)allyloxy)silane results in direct formation of 1-vinyl-3-tert-butyl-1H-isochromene. This is the result of a ketone arylation followed by an intramolecular cyclization of the enolate with the allylic system. The use of a lithium diamide base appears to be essential for success. The tert-butyldimethylsilyl protecting group is also an essential choice as it furnishes the appropriate reactivity to promote allylic substitution after the aryl coupling process. The use of more effective leaving groups, such as acetate, results in reaction of the allylic group, and no aryl coupling is observed. Through the appropriate selection of phosphine ligand and solvent, either the cyclized isochromene product or the noncyclized intermediate may be formed selectively. A short combinatorial study of the scope and limitations of the reaction, involving 24 ketones, is described. 相似文献
73.
74.
Vittorio Bertacche Natascia Lorenzi Donatella Nava Elena Pini Chiara Sinico 《Journal of inclusion phenomena and macrocyclic chemistry》2006,55(3-4):279-287
The aim of this work is to increase the stability and water solubility of resveratrol by complexation with different cyclodextrins. Furthermore, physical–chemical properties of each inclusion compound were investigated. Complexes of resveratrol with cyclodextrins both native (α, β, γ) and modified (2-hydroxypropyl-β-cyclodextrin, dimethyl-β-cyclodextrin) were obtained by using the suspension method. An inclusion complex with β-cyclodextrin was also prepared by using the microwave. Solid state characterization of the products was carried out using Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), X-ray diffraction (DRX); solution studies were performed by UV–Vis spectrophotometry and 1H-NMR spectroscopy. Phase solubility profiles with all cyclodextrins employed were classified as AN type, indicating the formation of 1:1 stoichiometric inclusion complexes. Stability constants (K
c) from the phase solubility diagrams were calculated. Stability studies in the solid state and in solution were performed; the photodegradation by UV–Vis spectrophotometry was monitored. The isomerization rate trans to cis, in ethanol solution, decreased with inclusion. The dissolution studies revealed that resveratrol dissolution rate was improved by the formation of inclusion complexes. 相似文献
75.
N. Nava J. P. Jacobs A. García J. J. W. M. Rosink M. A. Valenzuela L. J. Van Ijzendoorn H. H. Brongersma 《Journal of Radioanalytical and Nuclear Chemistry》1996,212(6):431-443
ZnxMg1-xFe2O4 mixed oxide spinels (x=0.0, 0.2, 0.4, 0.6, 0.8, and 1.0) were prepared by conventional solid state reaction method. Bulk and surface characterization of these ferrites were carried out by different techniques. The ratios Zn/Fe and Mg/Fe determined by PIXE and AAS were nearly as expected from the synthesis mixture, i.e. following the substitution model. XRD shows only a spinel structure (fcc) with increasing lattice parameter as x increases from 0 to 1. The bulk ratios of tetrahedral to octahedral sites occupied by Fe cations measured by NGR are in good agreement with the theoretical bulk stoichiometry. LEIS results indicate a Mg substitution by Fe cations at the surface. Only octahedral sites are proposed at the surface. The transition from inverse to normal spinel was follow through NGR-spectra occurring at x=0.4. 相似文献
76.
Density functional theory calculations were carried out on the structurally characterized [(Cl(4)-cat)Mo(py)Fe(3)S(3) (CO)(4)(P(n)Pr(3))(3)], A, and (Cl(4)-cat)Mo(py)Fe(3)S(3)(CO)(6)(PEt(3))(2), B, and also on A(2)(-) and B(2+) clusters. The Fe-Fe distances in these molecules depend on the total number of valence electrons (60 e(-) in A and B(2)(+) and 62 e(-) in A(2)(-) and B) and undergo great structural changes upon addition or removal of electrons. The changes are consistent with known electron-counting rules in organometallic chemistry. The weak nature of the Fe-Fe bonding interactions in these clusters is apparent in the very similar energies of states with widely different Fe-Fe distances. 相似文献
77.
Hildeberto Nava Virgil Percec 《Journal of polymer science. Part A, Polymer chemistry》1986,24(5):965-990
A novel and convenient synthetic method for the preparation of α,ω-bis(2,6-dimethylphenol)–poly(2,6-dimethyl-1,4-phenylene oxide) (PPO-2OH) is presented. It is based on the oxidative copolymerization of 2,6-dimethylphenol (DMP) with 2,2′-di(4-hydroxy-3,5-dimethylphenyl propane) (TMBPA) in a mixture of water–methanol or chlorobenzene–methanol. By using a 4/1 mole ratio of DMP to TMBPA and different solvent mixtures, it was possible to obtain bifunctional PPO-2OHs with number average molecular weights between 1000 and 5000. A phase-transfer-catalyzed etherification of PPO-2OH chain ends with a mixture of m- and p-chloromethylstyrene was used to synthesize α,ω-bis(vinylbenzyl)-poly(2,6-dimethyl-1,4-phenylene oxide)s (PPO-2VBs). The thermal polymerization of the PPO-2VBs was studied by differential scanning calorimetry, and has demonstrated a very high thermal reactivity for this new class of reactive oligomers. 相似文献
78.
79.
Ultrasonic pulsed-echo patterns in AC-cut quartz crystals cooled to 4.2 K have been studied over the frequency range 0.2<f<0.6 [GHz]. The observed beats, superimposed on the exponential decay, have been identified as resulting from diffraction
of the waves in the finite-size crystals. Furthermore, it has been found that irradiation with 1 MeV γ-rays yields samples
with both a smaller attenuation constant and less pronounced beats. The significance of the reported results lies mainly in
the potential application of the procedure of γ-ray irradiation, and subsequent bleaching with ultraviolet light, in order
to obtain quartz crystals with improved acoustic patterns. 相似文献
80.
Daniela Kunkel Muenchen Janine Martinazzo Alexandra Nava Brezolin Alana Marie de Cezaro Aline Andressa Rigo Mateus Nava Mezarroba Alexandra Manzoli Fábio de Lima Leite Juliana Steffens Clarice Steffens 《Applied biochemistry and biotechnology》2018,184(4):1061-1072
A highly efficient process for reducing the fatty acid (FA) content of high-acid rice bran oil (RBO) was developed by immobilized partial glycerides-selective lipase SMG1-F278N-catalyzed esterification/transesterification using methanol as a novel acyl acceptor. Molecular docking simulation indicated that methanol was much closer to the catalytic serine (Ser-171) compared with ethanol and glycerol, which might be one of the reasons for its high efficiency in the deacidification of high-acid RBO. Additionally, the reaction parameters were optimized to minimize the FA content of high-acid RBO. Under the optimal conditions (substrate molar ratio of methanol to FAs of 1.8:1, enzyme loading of 40 U/g, and at 30 °C), FA content decreased from 25.14 to 0.03% after 6 h of reaction. Immobilized SMG1-F278N exhibited excellent methanol tolerance and retained almost 100% of its initial activity after being used for ten batches. After purification by molecular distillation, the final product contained 97.86% triacylglycerol, 2.10% diacylglycerol, and 0.04% FA. The acid value of the final product was 0.09 mg KOH/g, which reached the grade one standard of edible oil. Overall, methanol was a superior acyl acceptor for the deacidification of high-acid RBO and the high reusability of immobilized SMG1-F278N indicates an economically attractive process. 相似文献