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31.
The thermodynamics and kinetics of the binding of Ga(III) and In(III) to two hydroxamic acids, C6H5-C(O)N(OH)H (BHA) and C6H5-C(O)N(OH)C6H5 (PBHA), have been investigated in acidic media. Spectrophotometric titrations in the UV region reveal that, with excess metal, only the chelate ML forms, whereas the concentration of the protonated species, MHL, is negligible. The thermodynamic parameters indicate that the driving force for formation of ML from MOH2+ and HL is mainly enthalpic, with entropic contributions favoring InL2+ and disfavoring GaL2+ formation. The kinetic (stopped-flow) experiments are interpreted on the basis of two parallel reaction paths both involving reaction of the undissociated ligand (HL): (a) M + HL <==> MHL <==> ML + H where MHL is in a steady state and (b) MOH + HL <==> ML + H2O. Whereas gallium binding to BHA and PBHA proceeds mainly through path b, indium binding to PBHA proceeds through both a and b paths. The rates of both the a and b steps are ligand dependent. Two alternative mechanisms are proposed. The first is based on the electronic characteristics of the ligands and is of the Ia type. The second, of the Id type, assumes that a considerable fraction of the ligand is unreactive owing to intramolecular hydrogen bonding (possibly including a water molecule) which blocks the reaction site. The reasons for preferring the former mechanism are discussed. 相似文献
32.
33.
Begoña Cano Adolfo González‐Pachón 《Numerical Methods for Partial Differential Equations》2015,31(1):78-104
In this article, it is proved that explicit Lawson methods, when projected onto one of the invariants of nonlinear Schrödinger equation (norm) are also automatically projected onto another invariant (momentum) for many solutions. As this procedure is very cheap and geometric because two invariants are conserved, it offers an efficient tool to integrate some solutions of this equation till long times. On the other hand, we show a detailed study on the numerical performance of these methods against splitting ones, with fixed and variable stepsize implementation. © 2014 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq31: 78–104, 2015 相似文献
34.
Marta Maria Pereira da Silva Neves Maria Begoña González-Garcia Hendrikus Petrus Antonius Nouws Cristina Delerue-Matos Alice Santos-Silva Agustín Costa-García 《Analytical and bioanalytical chemistry》2010,397(5):1743-1753
Celiac disease (CD) is an autoimmune enteropathy, characterized by an inappropriate T-cell-mediated immune response to the
ingestion of certain dietary cereal proteins in genetically susceptible individuals. This disorder presents environmental,
genetic, and immunological components. CD presents a prevalence of up to 1% in populations of European ancestry, yet a high
percentage of cases remain underdiagnosed. The diagnosis and treatment should be made early since untreated disease causes
growth retardation and atypical symptoms, like infertility or neurological disorders. The diagnostic criteria for CD, which
requires endoscopy with small bowel biopsy, have been changing over the last few decades, especially due to the advent of
serological tests with higher sensitivity and specificity. The use of serological markers can be very useful to rule out clinical
suspicious cases and also to help monitor the patients, after adherence to a gluten-free diet. Since the current treatment
consists of a life-long gluten-free diet, which leads to significant clinical and histological improvement, the standardization
of an assay to assess in an unequivocal way gluten in gluten-free foodstuff is of major importance. 相似文献
35.
Fustero S Catalan S Piera J Sanz-Cervera JF Fernandez B Aceña JL 《The Journal of organic chemistry》2006,71(10):4010-4013
Two families of bicyclic fluorinated uracils have been prepared starting from a gem-difluorinated unsaturated nitrile, by means of a ring-closing metathesis reaction to form the new ring, which is fused at the C-5/C-6 or N-1/C-6 positions of the uracil moiety. The selective formation of olefin regioisomers in the metathesis process can be controlled according to the reaction conditions (catalyst, solvent, and temperature). The acaricidal activities of the resulting compounds have also been investigated. 相似文献
36.
Fanjul-Bolado P González-García MB Costa-García A 《Analytical and bioanalytical chemistry》2006,385(7):1202-1208
p-Nitrophenyl phosphate is one of the most widely used substrates for alkaline phosphatase in ELISAs because its yellow, water-soluble
product, p-nitrophenol, absorbs strongly at 405 nm. p-Nitrophenol is also electroactive; an oxidative peak at 0.97 V (vs. an Ag pseudoreference electrode) is obtained when a bare
screen-printed carbon electrode is used. When an amperometric detector was coupled to a flow-injection analysis system the
detection limit achieved for p-nitrophenol was 2×10−8 mol L−1, almost two orders of magnitude lower than that obtained by measuring the absorbance of the compound. By use of this electrochemical
detection method, measurement of 7×10−14 mol L−1 alkaline phosphatase was achieved after incubation for 20 min. The feasibility of coupling immunoassay to screen-printed
carbon electrode amperometric detection has been demonstrated by performing an ELISA for detection of pneumolysin, a toxin
produced by Streptococcus pneumoniae, which causes respiratory infections. The method is simple, reproducible, and much more sensitive than traditional spectrophotometry. 相似文献
37.
de la Escosura-Muñiz A González-García MB Costa-García A 《Analytical and bioanalytical chemistry》2006,384(3):742-750
A new electroactive label has been used to monitor immunoassays in the determination of human serum albumin (HSA) using glassy-carbon
electrodes as supports for the immunological reactions. The label was a gold(I) complex, sodium aurothiomalate, which was
bound to rabbit IgG anti-human serum albumin (anti-HSA-Au). The HSA was adsorbed on the electrode surface and the immunological
reaction with gold-labelled anti-HSA was then performed for one hour by non-competitive or competitive procedures. The gold(I)
bound to the anti-HSA was electrodeposited in 0.1 mol L−1 HCl at −1.00 V for 5 min then oxidised in 0.1 mol L−1 H2SO4 solution at +1.40 V for 1 min. Silver electrodeposition at −0.14 V for 1 min followed by anodic stripping voltammetry were
then performed in aqueous 1.0 mol L−1 NH3–2.0×10−4 mol L−1 AgNO3. For both non-competitive and competitive formats, calibration plots in the ranges 5.0×10−10 to 1.0×10−8 mol L−1 and 1.0×10−10 to 1.0×10−9 mol L−1 HSA, respectively, with estimated detection limits of 1.5×10−10 mol L−1 (10 ng mL−1) and 1.0×10−10 mol L−1 (7 ng mL−1), respectively, were obtained. Levels of HSA in two healthy volunteer urine samples were also evaluated, using both immunoassay
formats. 相似文献
38.
Peñacoba IA García B Navarro AM Hoyuelos FJ Leal JM 《Journal of colloid and interface science》2010,352(2):465-469
The decomposition reaction of the purple dye murexide in acidic media is used as a probe indicator for protons in nonionic microemulsions. The reaction kinetics primarily rely on the proton concentration and permit assessment of the proton activity in the nonionic microemulsions of water/cyclohexane/Igepal and water/heptane/Igepal. The experiments performed in the two microemulsions covered a wide range of water-to-oil mass fraction for the two systems. The kinetic runs were monitored under pseudo-first order conditions by the stopped-flow technique. The equilibrium constants for the formation of purpuric acid and the kinetic constants for the ensuing decomposition reaction fulfill a trend consistent with the micro compartmentalized nature of the multicomponent medium, and support the use of murexide as an indicator of the proton activity in microemulsions. 相似文献
39.
40.
Goñi FM Basáñez G Begoña Ruiz-Argüello M Alonso A 《Faraday discussions》1998,(111):55-68; discussion 69-78
Previous studies from this laboratory have shown that the enzymic generation of diacylglycerol in bilayers by phospholipase C may lead to membrane fusion through the formation of transient non-lamellar lipidic intermediates. The present paper intends to explore the correlations existing among the three main processes involved, namely (a) the induction (or inhibition) of lamellar-to-non-lamellar phase transitions in lipid mixtures through the addition of small (< 5 mol%) proportions of other lipids, (b) the promotion, by the latter lipids, of fusion in otherwise stable phospholipid vesicles (large unilamellar liposomes) under conditions leading to inverted hexagonal/inverted cubic phase formation in bulk lipid systems, and (c) the modulation, by the same small proportions of lipids, of phospholipase C hydrolysis of phosphatidylcholine in liposome bilayers. It is concluded that phospholipase C may give rise to non-lamellar lipidic structures that in turn permit liposomal fusion to occur, but neither enzyme activity is directly modulated by non-lamellar phase formation, nor will whatever kind of enzyme-induced non-lamellar structure give rise to fusion. Moreover, only under certain kinetic conditions will the enzyme give rise to the organization of non-lamellar structures that are conducive to the fusion event. 相似文献