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排序方式: 共有159条查询结果,搜索用时 31 毫秒
41.
Liquid phase microextraction with back extraction (LPME-BE) combined with liquid chromatography-ultra violet (LC-UV) was applied for the extraction and determination of methadone in biological fluids. At the optimized conditions, an enrichment factor of 386 and detection limit (LOD) of 0.2 μg L?1 were obtained. The calibration curve was linear (r 2 = 0.989) in the concentration range of 0.6–1,000 μg L?1. Within-day relative standard deviation RSD (S/N = 3) and between-day RSD were 2.7 and 5.9%, respectively. The feasibility of the proposed method was evaluated by extraction and determination of methadone in plasma and urine samples and satisfactory results were obtained. 相似文献
42.
Behrooz Alizadeh Esmaeil Afrashteh Fahimeh Baroughi 《Journal of Optimization Theory and Applications》2018,178(3):914-934
This paper concerns with some variants of the inverse obnoxious median location problem on tree networks, where the aim is either to augment or to reduce the edge lengths at the minimum total cost such that a prespecified subset of vertices becomes an obnoxious multi-facility median location with respect to the perturbed edge lengths. For both augmentation and reduction models, under the rectilinear norm and the sum-type Hamming distance, we develop novel combinatorial algorithms with polynomial time complexities. Particularly, if the underlying tree is an extended star graph, then the problems can be solved in linear time. 相似文献
43.
In this paper, we generalize the concept of codismantlable graphs to hypergraphs and show that some special vertex decomposable hypergraphs are codismantlable. Then we generalize the concept of bouquet in graphs to hypergraphs to extend some combinatorial invariants of graphs about disjointness of a set of bouquets. We use these invariants to characterize the projective dimension of Stanley–Reisner ring of special hypergraphs in some sense. 相似文献
44.
Fahimeh Khosh-Ahang 《Archiv der Mathematik》2009,93(4):315-317
In this note, we provide a short argument which corrects flaws in the mentioned article. 相似文献
45.
A solid uncharged complex produced from 2‐aminocyclopentene‐1‐dithiocarboxylic acid (synthetic reagent) on naphthalene provides a very sensitive, selective and economical method for the preconcentration and determination of trace amounts of copper in drug and alloy samples. The 2‐aminocyclopentene‐1‐dithiocarboxylate of copper is retained quantitatively on microcrystalline naphthalene in the pH range 2.8–3.3. After filtration the solid mass consisting of copper complex‐naphthalene is dissolved with 4 mL of dimethylformamide (DMF). The absorbance is measured at 462 nm with a spectrophotometer against the reagent blank and molar absorptivity found to be 2.8 × 105 liter mol?1 cm?1. Beer's law is obeyed over the concentration range of 0.1–16.0 μg of copper in 4 mL of the dimethylformamide solution. Detection limit is 3 ng mL?1 [signal to noise ratio = 2]. Ten replicate determinations on a sample containing 1 μg of copper gave a relative standard deviation of 0.76%. The interference of a large number of anions and cations have been studied and the optimized conditions developed were utilized for determination of copper in various real samples. 相似文献
46.
Fahimeh Khosh-Ahang 《Archiv der Mathematik》2008,90(1):18-23
In this paper, we compare Krull dimension, Gorenstein injective dimension and injective dimension of a module in several cases.
In fact, we establish some generalizations of the Bass formula. To this end, we generalize the Grothendieck non-vanishing
theorem to a class of modules larger than finitely generated modules.
Received: 21 May 2007 相似文献
47.
48.
Beigoli Sima Hekmat Azadeh Farzanegan Fahimeh Darroudi Majid 《Journal of Sol-Gel Science and Technology》2021,98(3):508-516
Journal of Sol-Gel Science and Technology - Considering the existing various sources that can supply the nano-biomaterials that are related to the Amorphous Calcium Phosphate (ACP) family, Aloe... 相似文献
49.
Hamid Reza Shaterian Fahimeh Khorami Razieh Doostmohammadi Azita Amirzadeh Majid Ghashang 《Phosphorus, sulfur, and silicon and the related elements》2013,188(9):2227-2237
Silica-supported zinc chloride (SiO2-ZnCl2) and novel alumina-supported sodium hydrogensulfate (NaHSO4-Al2O3) as recyclable heterogeneous catalysts have been used for the mild trimethylsilylation of hydroxyl groups under ambient conditions. This procedure also allows for the selective protection of primary and secondary alcohols in the presence of tertiary alcohols. 相似文献
50.
Hamid Reza Shaterian Asghar Hosseinian Majid Ghashang Fahimeh Khorami 《Phosphorus, sulfur, and silicon and the related elements》2013,188(10):2490-2501
Carbonyl compounds have been successfully converted into their corresponding dithiolanes and dithianes derivatives with 1,2-ethanedithiol and 1,3-propanedithiol in excellent yield at room temperature and short reaction times using a catalytic amount of magnesium hydrogensulfate. The synthetic simple procedures reported in this paper constitute an exceptionally mild procedure for carbonyl protection in ambient conditions. 相似文献