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71.
The analytical performance of an on-line sequential injection lab-on-valve (SI-LOV) system using chelating Sepharose beads as sorbent material for the determination of ultra-trace levels of Cd(II), Pb(II) and Ni(II) by electrothermal atomic absorption spectrometry (ETAAS) is described and discussed. The samples are adjusted to pH 5.0 on-line in the system for optimum operation. The target ions are adsorbed by chelation on the surface of the beads, contained in a 20 μl microcolumn within the LOV, and following elution by 50 μl 2 M nitric acid, the eluate is, as sandwiched by air segments, introduced into the ETAAS. Based on the consumption of 1.8 ml sample solution, retention efficiencies of 95, 75 and 90%, enrichment factors of 34, 27 and 32, and determination limits of 0.001, 0.07 and 0.02 μg l−1 were obtained for Cd(II), Pb(II) and Ni(II), respectively. The beads can be used repeatedly for at least 20 times without decrease of performance, yet can be replaced at will if the circumstances should so dictate. The optimized procedural parameters showed that 12 samples per hour could be prepared and successfully analyzed. The results obtained for three standard reference materials agreed very well with the certified values. 相似文献
72.
Monge D Martín-Zamora E Vazquez J Alcarazo M Alvarez E Fernandez R Lassaletta JM 《Organic letters》2007,9(15):2867-2870
The activation of alpha-hydroxy enones by the Zn(OTf)2/tBuBOX catalyst enables the enantioselective conjugate addition of 1-methyleneaminopyrrolidine as a neutral d1 synthon. Experimental evidence supports a stereochemical model where a triflate ligand controls the geometry of the catalyst-substrate complex by means of a OH-OTf hydrogen bond. The synthesis of beta-cyano acids illustrates the potential of the methodology. 相似文献
73.
Fernando Chacón-Gómez M. Eugenia Cornejo Jesús Medina Eloísa Ramírez-Poussa 《Mathematical Methods in the Applied Sciences》2023,46(2):1631-1650
In Rough Set Theory, the notion of bireduct allows to simultaneously reduce the sets of objects and attributes contained in a dataset. In addition, value reducts are used to remove some unnecessary values of certain attributes for a specific object. Therefore, the combination of both notions provides a higher reduction of unnecessary data. This paper is focused on the study of bireducts and value reducts of information and decision tables. We present theoretical results capturing different aspects about the relationship between bireducts and reducts, offering new insights at a conceptual level. We also analyze the relationship between bireducts and value reducts. The studied connections among these notions provide important profits for the efficient information analysis, as well as for the detection of unnecessary or redundant information. 相似文献
74.
Eloísa A. M. Kronka Ana Paula S. Paim B. F. Reis José L. F. Costa Lima Rui A. Lapa 《Fresenius' Journal of Analytical Chemistry》1999,364(4):358-361
A flow system based on a multicommutation approach was developed for the determination of glucose and sucrose employing enzymatic
reactions. The determination was based on the reaction with D-glucose generating hydrogen peroxide catalyzed by glucose-oxidase
(GOD). Subsequently, the H2O2 generated reacts with 4-aminefenazone plus phenol to form 4-(p-benzoquinone-mono-imine) fenazone detected at 510 nm. This
reaction is catalyzed by the peroxidase enzyme (POD). The flow network comprised a set of three-way solenoid valves and was
controlled by means of a microcomputer furnished with an electronic interface and running a software written in Quick BASIC
4.5. The flow network and control software were designed to implement the multicommutation approach providing facilities to
handle sample and reagent solutions, so that, sample dilution could be easily performed on line. Accuracy was assessed by
comparison with results obtained by known procedures and no significant difference at the 95% confidence level was observed.
Other advantageous features were a linear response ranging from 0.05 to 0.20% (w/v) glucose without prior dilution, a reagent
consumption of 336 μL per determination, an analytical throughput of 30 samples per hour.
Received: 24 August 1998 / Revised: 13 November 1998 / Accepted: 19 December 1998 相似文献
75.
Eloísa A. M. Kronka Ana Paula S. Paim B. F. Reis José L. F. Costa Lima Rui A. Lapa 《Analytical and bioanalytical chemistry》1999,364(4):358-361
A flow system based on a multicommutation approach was developed for the determination of glucose and sucrose employing enzymatic reactions. The determination was based on the reaction with D-glucose generating hydrogen peroxide catalyzed by glucose-oxidase (GOD). Subsequently, the H2O2 generated reacts with 4-aminefenazone plus phenol to form 4-(p-benzoquinone-mono-imine) fenazone detected at 510 nm. This reaction is catalyzed by the peroxidase enzyme (POD). The flow network comprised a set of three-way solenoid valves and was controlled by means of a microcomputer furnished with an electronic interface and running a software written in Quick BASIC 4.5. The flow network and control software were designed to implement the multicommutation approach providing facilities to handle sample and reagent solutions, so that, sample dilution could be easily performed on line. Accuracy was assessed by comparison with results obtained by known procedures and no significant difference at the 95% confidence level was observed. Other advantageous features were a linear response ranging from 0.05 to 0.20% (w/v) glucose without prior dilution, a reagent consumption of 336 μL per determination, an analytical throughput of 30 samples per hour. 相似文献
76.
Schön P Bonod N Devaux E Wenger J Rigneault H Ebbesen TW Brasselet S 《Optics letters》2010,35(23):4063-4065
We demonstrate the ability of single-subwavelength-size nanoapertures fabricated in a gold metal thin film to enhance second-harmonic generation (SHG) as compared to a bare metal film. Nonlinear microscopy imaging with polarization resolution is used to quantify the SHG enhancement in circular and triangular nanoaperture shapes. The dependence of the measured SHG enhancement on circular aperture diameters is seen to originate from both phase retardation effects and field enhancements at the nanoaperture edge. Triangular nanoapertures exhibit superior SHG enhancement compared with circular ones, as expected from their noncentrosymmetric shape. 相似文献
77.
Elo Harald Hansen 《应用光谱学评论》2013,48(4):335-357
Abstract One of the current needs within the analytical spectrometric community is the development of straightforward and cost‐effective, yet rugged, sample processing procedures aimed at precluding both spectroscopic and nonspectroscopic matrix interferences while fostering concomitant sample enrichment. Illustrated via selected representative examples, this review presents and discusses the current state of the art in implementing miniaturised and automated sample treatments for environmental and biochemical assays via microfluidic systems exploiting the lab‐on‐valve (LOV) platform in hyphenation with syringe pump propelling devices as a front end to a plethora of spectroscopic detection schemes including ultraviolet‐visible (UV‐Vis) spectrometry, spectrofluorimetry, chemiluminescence, atomic absorption spectrometry (AAS), atomic flourescence spectrometry (AFS), and inductively coupled plasma‐atomic emission spectrometry/mass spectrometry (ICP‐AES/MS). In contrast to lab‐on‐a‐chip units, the versatile configuration of the micromachined LOV readily facilitates the implementation of on‐line unit operations at will encompassing not merely the introduction of minute, well‐defined volumes of sample followed by chemical derivatization, but the potential for accommodation of solid‐phase extraction, hydride/vapor generation, precipitation/coprecipitation, and bead injection protocols with no need for chip redesign. 相似文献
78.
The previously unassigned carbon-13 NMR resonances of the side-chain carbon atoms of the enzyme inhibitor dipropylglyoxal bis(amidinohydrazone) (DPGBG) have been unambiguously assigned with the aid of DEPT measurements and experiments involving the selective decoupling of the protons of one of the methylene groups. The chemical shifts of the side-chain carbon atoms of DPGBG decrease in a nearly linear fashion as a function of the position of the atom in the side chain, the terminal methyl groups having the lowest shift value. The carbon-13 shifts are positively correlated with the chemical shifts of the corresponding hydrogen atoms. 相似文献
79.
The first study on the 13C relaxation times of bis(amidinohydrazones) is reported. The spin-lattice relaxation times (T1) of the carbons of the free bases of methylglyoxal bis(amidinohydrazone) (MGBG) and of four dialkylglyoxal analogs thereof were determined with the aid of the inversion recovery method and using dimethyl sulfoxide as the solvent. In the series of compounds studied, one of the side chains was always a methyl group, while the other one was altered (hydrogen, methyl, ethyl, propyl, butyl). Remarkable differences were found to exist between the T1 values of the various carbons within each molecule. The T1 values were in the range 1.5 - 2 s for methyl carbons, 0.16 - 1.9 s for carbons of longer alkyl groups, 4.3 - 7.0 s for unprotonated carbons of the glyoxal moiety, 0.57 s for the protonated glyoxal carbon of MGBG, and 2.6 - 3.1 s for guanidino carbons. The bulk of the differences are explainable by assuming that the major relaxation mechanism for the protonated carbons is dipolar relaxation. In alkyl side chains, the T1 values increased in a very regular fashion down the chain. This effect made possible the assignment of two previously unassigned carbon resonances of the butyl group of BMGBG. T1 studies thus offer a facile and reliable method for the assignment of side-chain carbon resonances of bis(amidinohydrazones). Further, T1 measurements were found to offer a very good method for the individual assignment of the glyoxal carbons of unsymmetrical congeners, whose assignment has so far constituted a problem. The method, based on the finding that the one of the carbons bonded to the shorter alkyl chain has a longer relaxation time than does the other one, made possible the unambiguous assignment of several previously unassigned carbon resonances. The results obtained also offer a reliable method for unambiguously distinguishing between the resonances of glyoxal carbons and guanidino carbons that have been difficult to distinguish from each other because the separation of their chemical shifts is often extremely small. Correlations observed between T1 values and the degree of alkyl substitution in the molecule are discussed, as are also possible relaxation mechanisms. Somewhat unexpectedly, the results obtained suggest that dipolar relaxation through the hydrogens of neighboring carbon atoms may to a significant extent contribute to the relaxation of some unprotonated carbons in bis(amidinohydrazones). 相似文献
80.
Ground‐State Chemical Reactivity under Vibrational Coupling to the Vacuum Electromagnetic Field
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Dr. Anoop Thomas Dr. Jino George Dr. Atef Shalabney Dr. Marian Dryzhakov Sreejith J. Varma Dr. Joseph Moran Thibault Chervy Dr. Xiaolan Zhong Dr. Eloïse Devaux Dr. Cyriaque Genet Dr. James A. Hutchison Prof. Dr. Thomas W. Ebbesen 《Angewandte Chemie (International ed. in English)》2016,55(38):11462-11466
The ground‐state deprotection of a simple alkynylsilane is studied under vibrational strong coupling to the zero‐point fluctuations, or vacuum electromagnetic field, of a resonant IR microfluidic cavity. The reaction rate decreased by a factor of up to 5.5 when the Si?C vibrational stretching modes of the reactant were strongly coupled. The relative change in the reaction rate under strong coupling depends on the Rabi splitting energy. Product analysis by GC‐MS confirmed the kinetic results. Temperature dependence shows that the activation enthalpy and entropy change significantly, suggesting that the transition state is modified from an associative to a dissociative type. These findings show that vibrational strong coupling provides a powerful approach for modifying and controlling chemical landscapes and for understanding reaction mechanisms. 相似文献