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The free metal ion concentration and the dynamic features of the metal species are recognized as key to predict metal bioavailability and toxicity to aquatic organisms. Quantification of the former is, however, still challenging. In this paper, it is shown for the first time that the concentration of free copper (Cu2+) can be quantified by applying AGNES (Absence of Gradients and Nernstian equilibrium stripping) at a solid gold electrode. It was found that: i) the amount of deposited Cu follows a Nernstian relationship with the applied deposition potential, and ii) the stripping signal is linearly related with the free metal ion concentration. The performance of AGNES at the vibrating gold microwire electrode (VGME) was assessed for two labile systems: Cu-malonic acid and Cu-iminodiacetic acid at ionic strength 0.01 M and a range of pH values from 4.0 to 6.0. The free Cu concentrations and conditional stability constants obtained by AGNES were in good agreement with stripping scanned voltammetry and thermodynamic theoretical predictions obtained by Visual MinteQ. This work highlights the suitability of gold electrodes for the quantification of free metal ion concentrations by AGNES. It also strongly suggests that other solid electrodes may be well appropriate for such task. This new application of AGNES is a first step towards a range of applications for a number of metals in speciation, toxicological and environmental studies for the direct determination of the key parameter that is the free metal ion concentration.  相似文献   
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Absence of gradients and Nernstian equilibrium stripping (AGNES) is a recently developed electroanalytical technique specifically designed for the direct determination of free concentrations of metal ions. AGNES is applied here to the determination of free Zn concentration in a river water sample. The method has been validated with synthetic solutions of low ionic strengths containing Zn and 2,6-pyridinedicarboxylic acid and then applied to synthetic river waters and to a natural sample collected from Besòs River in Montcada i Reixac (Catalonia, North-Eastern Spain). In the river sample, an average free Zn concentration of 12.8(4) nM was obtained, while the total dissolved Zn concentration was 0.51(8)?μM. To control and maintain pH and pCO2 constant during AGNES measurements, a novel device for N2/CO2 mixed purging has been developed.  相似文献   
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Two in‐line enrichment procedures (large volume sample stacking (LVSS) and field amplified sample injection (FASI)) have been evaluated for the CZE analysis of haloacetic acids (HAAs) in drinking water. For LVSS, separation on normal polarity using 20 mM acetic acid–ammonium acetate (pH 5.5) containing 20% ACN as BGE was required. For FASI, the optimum conditions were 25 s hydrodynamic injection (3.5 kPa) of a water plug followed by 25 s electrokinetic injection (?10 kV) of the sample, and 200 mM formic acid–ammonium formate buffer at pH 3.0 as BGE. For both FASI and LVSS methods, linear calibration curves (r2>0.992), limit of detection on standards prepared in Milli‐Q water (49.1–200 μg/L for LVSS and 4.2–48 μg/L for FASI), and both run‐to‐run and day‐to‐day precisions (RSD values up to 15.8% for concentration) were established. Due to the higher sensitive enhancement (up to 310‐fold) achieved with FASI‐CZE, this method was selected for the analysis of HAAs in drinking water. However, for an optimal FASI application sample salinity was removed by SPE using Oasis WAX cartridges. With SPE‐FASI‐CZE, method detection limits in the range 0.05–0.8 μg/L were obtained, with recoveries, in general, higher than 90% (around 65% for monochloroacetic and monobromoacetic acids). The applicability of the SPE‐FASI‐CZE method was evaluated by analyzing drinking tap water from Barcelona where seven HAAs were found at concentration levels between 3 and 13 μg/L.  相似文献   
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The influence of ion size and surface charge model in titrations of ionizable polyelectrolytes is studied by means of the Semi Grand Canonical Monte Carlo simulation method in the context of the primitive model. Three models describing a discrete distribution of charged functional groups on the polyelectrolyte and different values for the radius of the background electrolyte spanning from ionic to hydrated radii values were analyzed. The polyelectrolyte titrations were simulated by calculating the degree of ionization versus pH curves at two ionic strengths. The results allow us to quantify the impact of the sizes of the background salt ions and surface functional groups of the polyelectrolyte on the dissociation degree. This influence is explained in terms of the effectiveness of the screening of the charged surface sites. Finally, by comparison with the Non-Linear Poisson–Boltzmann model, the influence of ionic correlations and finite size of the solution ions is assessed.  相似文献   
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Drugs that are used as medicines and also as growth promoters in veterinary care are considered as emerging environmental contaminants and in recent years concern about their potential risk to ecosystems and human health has risen. In this paper we used a method based on liquid chromatography/electrospray tandem mass spectrometry to analyze eight coccidiostatic compounds: diclazuril, dinitrocarbanilide (the main metabolite of nicarbazin), robenidine, lasalocid, monensin, salinomycin, maduramicin and nasarin. Multiple‐stage mass spectrometry (MSn) based on the precursor ions [M+Na]+ (polyether ionophores), [M+H]+ (robenidine) and [M–H]? (diclazuril and dinitrocarbanilide) was used to study the fragmentation of these compounds. MSn data and genealogical relationships were used to propose a tentative assignment of the different fragment ions. Loss of water, decarboxylations, ketone β‐cleavages and rearrangement of cyclic ethers and amide groups were some of the fragmentations observed for these compounds. Liquid chromatography with a sub‐2 µm particle size column was coupled to tandem mass spectrometry (LC/MS/MS) allowing the separation of these compounds in less than 7 min. Method detection limits ranging from 11 to 71 ng L?1 and run‐to‐run values in terms of relative standard deviation (RSD) (up to 12%) were obtained. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   
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Background  

Spt7 is an integral component of the multi-subunit SAGA complex that is required for the expression of ~10% of yeast genes. Two forms of Spt7 have been identified, the second of which is truncated at its C-terminus and found in the SAGA-like (SLIK) complex.  相似文献   
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Electrospray ionization mass spectrometry was applied to the study of the amines IQ, Trp-P-1, Trp-P-2, PhIP and AC and the co-mutagens harman and norharman. The results obtained on a triple quadrupole mass spectrometer equipped with a pneumatically assisted electrospray source are reported. The chromatographic conditions were optimized with a reversed-phase column (1 mm I.D.) using acetonitrile-5 mM ammonium acetate (pH 6.7) (50:50) as the mobile phase at a flow-rate of 50 μl min−1. Different parameters influencing the mass spectra were investigated. For these compounds [M + H]+ in the positive-ion mode and also some fragments produced through collisionally activated decomposition in the interface were observed. Detection limits of 5.4–44 pg were obtained for standard solutions of these amines. Analysis of a meat extract was performed by HPLC-MS using single-ion monitoring after a solid-phase extraction clean-up.  相似文献   
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A fast and reliable method using solid-phase extraction and ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) has been developed for the simultaneous detection, identification and quantification of several central nervous system depressor drugs of abuse such as cannabinoids (Delta9-tetrahydrocannabinol, THC) and opiates (morphine, codeine, heroin, methadone, fentanyl) and their metabolites in water samples. Compounds were extracted from water by using Oasis HLB cartridges. After SPE enrichment, the selected depressor drugs, under UPLC optimized conditions, were separated in less than 8 min. Electrospray (ESI) tandem MS in positive ion mode and selected reaction monitoring was used for quantification. ESI-MS/MS conditions such as capillary and cone voltages, source and desolvation temperatures and cone and desolvation gas flow rates have been optimized and MS and MS/MS spectra of the studied compounds were obtained. At the working conditions four identification points were obtained as required by European Union guidelines for analysis by LC-MS/MS. Quality parameters (intra-day and inter-day precisions) for each analyte have been established in three different matrixes (purified, surface and waste waters). Recoveries were generally higher than 70% and instrumental quantification limits and limits of quantification were in the low pg and ng/l range, respectively. Finally, the method has been applied to the analysis of influent and effluents wastewaters and natural water samples from Catalonia (NE Spain) where the presence of several opiates such as morphine, codeine, norcodeine 2-ethylene-1,5-dimethyl-3,3-diphenylpyrrolidine and methadone and cannnabinoids such as THC and 11-nor-carboxy-Delta9-tetrahydrocannabinol has been demonstrated.  相似文献   
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