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排序方式: 共有327条查询结果,搜索用时 15 毫秒
321.
Che Abd Rahim Mohamed Asnor Azrin Sabuti Nor Affizah Saili 《Journal of Radioanalytical and Nuclear Chemistry》2013,297(2):257-263
Biogenic burning as forest fire phenomena occurring from April to August each year in the Sumatra and Borneo islands are major sources of biogenic uranium–thorium decay series in marine systems. 30 samples were collected during the Ekspedisi Pelayaran Saintifik Perdana 2009 cruise (EPSP 2009 cruise) between 12th June and 1st August 2009 from the Straits of Malacca to the Sulu and Sulawesi Seas to study the effect of haze and the monsoon season on the deposition rate of 210Po and 210Pb in Malaysian waters. All samples were spiked with 1 ml of lead [Pb(NO3)2; 25 mg ml?1] and 0.05 ml of Polonium-209 tracer (26.08 dpm ml?1). 210Po activity was determined by auto plating onto silver foil and counting using an alpha spectrometry system (Canberra model Alpha Analyst with a silicon-surface barrier detector). Lead that was collected via electrodeposition, formed lead sulphate (PbSO4) precipitation. This precipitate was wrapped onto plastic discs and counted for 210Pb beta activity using a gross alpha–beta counting system (Tennelec model LB-5100 low background gas-flowing anti-coincidence alpha/beta counter) after 1 month to allow bismuth ingrowths. The range of 210Po activities varied between 51.08 ± 15.1 and 742.08 ± 220.34 Bq/kg, whereas the activity of 210Pb ranged from 31.10 ± 4.20 to 880.23 ± 123.86 Bq/kg and 210Po/210Pb ratio value varied between sampling stations from 0.19 to 13.77. The contents of 210Po were also statistically positively correlated with the amount of total suspended particulate especially those recorded during heavy haze period events. 相似文献
322.
Rahim Hekmatshoar Sanaz Souri Mahshid Rahimifard Farnoosh Faridbod 《Phosphorus, sulfur, and silicon and the related elements》2013,188(12):2827-2833
Protonation of the highly reactive 1:1 intermediates produced in the reaction between triphenylphosphine and dimethyl acetylenedicarboxylate(DMAD) by substituted phenols lead to vinyl triphenylphosphonium salts, which undergo aromatic electrophilic substitution reaction with a phenolate conjugate base to produce 4-carboxymethyl coumarins in fairly highly yields. 相似文献
323.
Majid M. Heravi Fatemeh Derikvand Hossein A. Oskooie Rahim Hekmat Shoar Mahmood Tajbakhsh 《合成通讯》2013,43(3):513-517
An efficient and convenient method for the oxidation of thiols mediated by silica‐supported bis (trimethylsilyl) chromate (BTSC) in acetonitrile is reported. 相似文献
324.
Rahim Hekmatshoar Sodeh Sadjadi Samaheh Sadjadi Majid M. Heravi Yahya S. Beheshtiha Fatemeh F. Bamoharram 《合成通讯》2013,43(11):1708-1716
An efficient synthetic method of six- and five-member nitrogen heterocyclic compounds was developed. Nitrogen heterocyclic compounds were prepared by condensation of the β-dicarbonyl compounds with the corresponding β- or γ-amino alcohols, subsequent cyclization, and spontaneous aromatization in the presence of a catalytic amount of Keggin-type heteropoly acids under very mild conditions. 相似文献
325.
Rahim Hekmatshoar Ghodsieh Nanva Kenary Sodeh Sadjadi Yahya S. Beheshtiha 《合成通讯》2013,43(13):2007-2013
An efficient method for the synthesis of 4-amino-5-pyrimidinecarbonitriles by three-component reaction of malononitrile, aldehydes, and N-unsubstituted amidines, under aqueous conditions, using ZnO nanoparticles as catalyst is reported. The catalyst exhibited remarkable activity and is recyclable. 相似文献
326.
Luis E. G. Armas Vitor M. Zamarion Luis T. Quispe Enrique P. U. Otero J. W. Menezes Lizandro B. R. Zegarra Abdur Rahim Koiti Araki Henrique E. Toma Carlos Jacinto Chiara Valsechi Antonio C. Seabra 《Brazilian Journal of Physics》2018,48(5):477-484
We report the effect of gold nanoparticles (AuNPs) and unwanted sodium citrate residues (UnR) left after deposition of AuNPs by drop-casting method on the Raman spectra of graphene sheets (GS). The AuNPs solution was deposited on three different substrates: 5.0 wt% Yb3+-doped (Q5) phosphate glass, silica glass (S1), and Si/SiO2-300 nm (S2) substrates. For Q5 substrate, a slight increase in intensity of the G peak was observed, mostly for thinner layers, which can be attributed to a weak SERS effect shielded by UnR. The combination of the following aspects: a blue shift of the G band position, a slight increase in the FWHM (Full Width at Half Maximum), and a slight increase of the Raman intensities of both G and 2D bands in other GS without UnR supports the argument of shielded SERS effect. On the other hand, the effects of UnR on the S1 and S2 substrates produce a decrease on the Raman intensities of G and 2D bands, opposite to the effect produced by the AuNPs; this result was found more intense for the S2 substrate in relation to S1. This is possibly caused by the greater amount of UnR accumulated on the Si/SiO2 substrate, due to its higher hydrophilicity in relation to other samples. Additional Raman measurements reveal that the Raman intensity of GS in all substrates is unaffected by the presence of a possible humidity on GS, revealing the effect of UnR. Hence, it is vital to understand how residues influence the salient features of GS/AuNPs. 相似文献
327.
Muhammad Arif Rahim Ullah Maaz Ahmad Ahmad Ali Zahid Ullah Mohammad Ali Fakhria A. Al-Joufi Muhammad Zahoor Hassan Sher 《Molecules (Basel, Switzerland)》2022,27(11)
Biologically synthesized silver nanoparticles are emerging as attractive alternatives to chemical pesticides due to the ease of their synthesis, safety and antimicrobial activities in lower possible concentrations. In the present study, we have synthesized silver nanoparticles (AgNPs) using the aqueous extract of the medicinal plant Euphorbia wallichii and tested them against the plant pathogenic bacterium Xanthomonas axonopodis, the causative agent of citrus canker, via an in vitro experiment. The synthesized silver nanoparticles were characterized by techniques such as UV-Vis spectroscopy, Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction analysis and transmission electron microscopy. Moreover, the plant species were investigated for phenolics, flavonoids and antioxidant activity. The antioxidant potential of the extract was determined against a DPPH radical. The extract was also evaluated for phenolic compounds using the HPLC technique. The results confirmed the synthesis of centered cubic, spherical-shaped and crystalline nanoparticles by employing standard characterization techniques. A qualitative and quantitative phytochemical analysis revealed the presence of phenolics (41.52 mg GAE/g), flavonoids (14.2 mg QE/g) and other metabolites of medicinal importance. Different concentrations (1000 µg/mL to 15.62 µg/mL—2 fold dilutions) of AgNPs and plant extract (PE) alone, and both in combination (AgNPs-PE), exhibited a differential inhibition of X. axanopodis in a high throughput antibacterial assay. Overall, AgNPs-PE was superior in terms of displaying significant antibacterial activity, followed by AgNPs alone. An appreciable antioxidant potential was recorded as well. The observed antibacterial and antioxidant potential may be attributed to eight phenolic compounds identified in the extract. The Euphorbia wallichii leaf-extract-induced synthesized AgNPs exhibited strong antibacterial activity against X. axanopodis, which could be exploited as effective alternative preparations against citrus canker in planta in a controlled environment. In addition, as a good source of phenolic compounds, the plant could be further exploited for potent antioxidants. 相似文献