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51.
52.
[reaction: see text] Redox-active dinuclear ruthenium complexes with various 1,2-dicarbonylhydrazido (DCH) ligands are designed and prepared to have intense absorption in the near-infrared region for potential optical sensing in aqueous media, as demonstrated for sensing hydrogen peroxide in this study. 相似文献
53.
The evolution of nickel speciation during the successive preparation steps of Ni-SiO(2) catalysts is studied by UV-Vis-NIR, FT-IR, DTG, TPR and TEM. The study focuses on the effect of the number of chelating ligands in the precursor complexes [Ni(en)(x)(H(2)O)((6-2x))](2+) (en = ethylenediamine, x = 1, 2, 3) on the adsorption on silica, and on nickel speciation after thermal treatment. When the en:Ni ratio in solution increases from 1 to 3, the most abundant complex is [Ni(en)(H(2)O)(4)](2+) (64% of all Ni complexes), [Ni(en)(2)(H(2)O)(2)](2+) (81%) and [Ni(en)(3)](2+) (61%), respectively. Equilibrium adsorption of [Ni(en)(x)(H(2)O)((6-2x))](2+) on SiO(2) results in the selective grafting of [Ni(en)(H(2)O)(4)](2+) and [Ni(en)(2)(H(2)O)(2)](2+), through the substitution of two labile H(2)O ligands by two surface SiO(-) groups. The surface [Ni(en)(H(2)O)(2)(SiO)(2)] complex formed by the grafting of [Ni(en)(H(2)O)(4)](2+) onto silica tends to transform into NiO and nickel phyllosilicate after calcination, which consequently leads to large and heterogeneously distributed metallic Ni particles upon reduction. In contrast, [Ni(en)(2)(SiO)(2)], resulting from the grafting of [Ni(en)(2)(H(2)O)(2)](2+) onto silica, no longer has aqua ligands able to react with other nickel complexes or silicium-containing species. Calcination transforms these complexes into isolated Ni(2+) ions, which are reduced into small metallic Ni particles with a more homogeneous size distribution, even at higher Ni loading. 相似文献
54.
Fluorescence characterization of the natural organic matter in deep ground waters from the Canadian Shield,Ontario, Canada 总被引:1,自引:0,他引:1
François Caron Karen Sharp-King Stefan Siemann D. Scott Smith 《Journal of Radioanalytical and Nuclear Chemistry》2010,286(3):699-705
Deep groundwater samples from a deep borehole in the Canadian Shield, Ontario, Canada, have been analyzed by fluorometry,
to determine the difference in character of the natural organic matter (NOM) with depth. This work was done to obtain a set
of geochemical characteristics of deep groundwaters at the site. The fluorescence signal is a complex signature of excitation
and emission of light from fluorescent molecules which are part of all natural waters. Fluorescent components have characteristic
excitation/emission components, defined as a humic-like (C1), fulvic-like (C2), and protein-like (C3); these are found in
various proportions in natural samples. Changes in relative fluorescence intensities of these components have been used in
the past to determine the origin and/or processes of the NOM between sampling locations. In this work, six samples were taken
at different depths, from ~108 to 650 m below the surface in the borehole. The fluorescence signals of the samples showed
three main patterns: (1) the shallower samples (~108, 139 and 285 m) had a pattern similar to that of surface groundwaters,
dominated by components C1 and C2; (2) the samples in deep groundwaters (~620 and 650 m) had a weak overall signal, dominated
by component C3; finally (3) the mid-depth sample (~503 m) had a component pattern intermediate between the shallower and
deeper zones. This set of data is consistent with other data for the groundwaters from this borehole, such as chlorinity,
suggesting that the three sampling intervals represent three different types of groundwaters. 相似文献
55.
Vicente Rodríguez-Gonzlez Eric Marceau Michel Che Claude Pepe 《Journal of solid state chemistry》2007,180(12):3469-3478
Synthesis of neutral complexes of Ni2+ with amino acids has often been reported on a qualitative basis, with a lack of information on the parameters involved in the dissolution of the nickel-containing solid precursor. This paper reports on a systematic study of the reactivity of Ni(OH)2 toward glycine in aqueous solution. The crystallinity and size of hydroxide particles are found to be key parameters in the rapid glycine-promoted dissolution of the hydroxide and synthesis of [Ni(glycinate)2(H2O)2]. These parameters derive from the nature of the salt used to prepare the hydroxide. Ni(II) chloride leads to the most reactive solid precursor, because of the presence of defects in the Ni(OH)2 sheets arrangements, assigned to the substitution of Cl− ions to OH− ions at the edges of the particles. The reaction between this hydroxide and glycine at 80 °C is quantitative after 7 min and similar rates of dissolution are obtained with other amino acids, alanine or histidine, the reaction with serine being slower. When the hydroxide contains nitrate or carbonate ions, a glycinato complex with composition similar to [Ni(glycinate)2(H2O)2], but with a different crystal structure, is also formed. Spectroscopic results may suggest a structure involving bridging ligands. 相似文献
56.
Nardello V Caron L Aubry JM Bouttemy S Wirth T Saha-Möller Chantu R Adam W 《Journal of the American Chemical Society》2004,126(34):10692-10700
The chiral allylic alcohols 1a-d and their acetate (1e) and silyl ether (1f) derivatives have been oxidized by the H2O2/MoO4(2)- system, a convenient and efficient chemical source of singlet oxygen. This chemical peroxidation (formation of the allylic hydroperoxides 2) has been conducted in various media, which include aqueous solutions, organic solvents, and microemulsions. The reactivity, chemoselectivity, and diastereoselectivity of this chemical oxidation are compared to those of the sensitized photooxygenation, with the emphasis on preparative applications in microemulsion media. While a similar threo diastereoselectivity is observed for both modes of peroxidation, the chemoselectivity differs significantly, since in the chemical oxidation with the H2O2/MoO4(2)- system the undesirable epoxidation by the intermediary peroxomolybdate competes efficiently with the desirable peroxidation by the in situ generated singlet oxygen. A proper choice of the type of microemulsion and the reaction conditions furnishes a high chemoselectivity (up to 97%) in favor of threo-diastereoselective (up to 92%) peroxidation. 相似文献
57.
Low-level radioactive waste leachates were analyzed for volatile fatty acids by gas chromatography as part of the continuing waste management program at the Chalk River Laboratories. An existing method was optimized whereby carboxylic acids were detected at the mg/1 level with a precision of 5% or better for C2---C7 acids and an accuracy of 3% or better for acetic acid. Parameters such as sample handling, calibration and accuracy are discussed. 相似文献
58.
Summary The chromatographic properties of five columns packed with phenyl-bonded phases were characterized by an approach based on
Tanaka's method for column to column comparisons in order to develop an LC analysis of partially methylated β-cyclodextrins.
The retention behaviour of β-cyclodextrin, heptakis(2,6-di-O-methyl)-β-cyclodextrin and heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin
was examined in order to evaluate the different interactions between phenyl stationary phase and this family of compound.
Chromatograms show that the residual silanol activity of the packing materials plays a beneficial role in the partially methylated
β-cyclodextrins separation process. It is concluded that knowledge of the interactions involved allows one to make a reasoned
choice of the stationary phase in order to obtain the best possible analysis of three different commercial samples of partially
methylated β-cyclodextrins. 相似文献
59.
Giulia Caron Guillaume Steyaert Alessandra Pagliara Frdric Reymond Patrizia Crivori Patrick Gaillard Pierre-Alain Carrupt Alex Avdeef John Comer KarlJ. Box HubertH. Girault Bernard Testa 《Helvetica chimica acta》1999,82(8):1211-1222
The objectives of this study were to validate new experimental techniques used to measure the log P of protonated drugs, and to investigate the inter- and intramolecular forces influencing the partitioning behavior of β-blockers in isotropic biphasic solvent systems. The lipophilicity parameters of a number of β-blockers were measured by two-phase titration, centrifugal partition chromatography (CPC), and cyclic voltammetry (CV) in one or more of the following solvent systems: octanol/water, 1,2-dichloroethane/water, and dibutyl ether/water. CV proved to be a promising technique for measuring the lipophilicity of protonated β-blockers. Derived parameters such as Δlog P (difference between log P in two different solvent systems, a parameter valid for a given solute in a given electrical form) and diff (difference between log P of two different electrical forms of a given solute, in the same system) yielded insights into inter- and intramolecular interactions characteristic of β-blockers. The relevance of these parameters in structure-permeation relationships is explored. 相似文献
60.
Giulia Caron Giuseppe Ermondi Donatella Boschi Pierre-Alain Carrupt Roberta Fruttero Bernard Testa Alberto Gasco 《Helvetica chimica acta》1999,82(10):1630-1639
Homologous N,N-dimethyl-phenylalkylamine oxides and N,N-dimethyl-diphenylalkylamine oxides were prepared. Their basicity and lipophilicity (octan-1-ol/H2O) were compared to those of the parent amines. In contrast to the amines, the basicity of all N,N-dimethyl-arylalkylamine oxides showed very limited pKa variations (range 4.65 – 5.01) with increasing chain length and number of Ph groups. The N-oxides in their neutral form had a log PN value lower by 2.77±0.34 (n=9) units than that of the parent amine. The log PC of the cationic N,N-dimethyl-diphenylalkylamines was lower than that of their neutral form, with a decrement diff(log PN−C) that increased from 3.25 to 4.21 in the homologous series. Unexpectedly, the decrement diff(log PN−C) for the N-oxides was much smaller than for the tertiary amines, being 0.23 for the aliphatic N,N-dimethyl-pentylamine oxide, 0.47±0.13 for the phenylalkylamine oxides, and 0.80±0.07 for the diphenylalkylamine oxides. In fact, the protonated N-oxides had log PC values that were quite comparable to those of the protonated parent amines. Because of the differences in basicity, the difference in distribution coefficients at physiological pH (log D7.4) between a tertiary arylalkylamine and its N-oxide was 0.82±0.66 (n=9). The pharmacokinetic implication is that N-oxygenation may have a smaller effect on the urinary excretion of tertiary amines than usually assumed. 相似文献