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排序方式: 共有192条查询结果,搜索用时 17 毫秒
1.
Leila Torkian Mostafa M. Amini Tayebeh Gorji Omid Sadeghi 《Arabian Journal of Chemistry》2019,12(7):1315-1321
In this study, multiwalled carbon nanotube (MWCNT) was modified by the pyridine group using a silane agent and characterized by infrared spectroscopy (IR), thermal analysis (TG/DTA), and elemental analysis (CHN) and scanning electron microscopy (SEM). The application of this sorbent was investigated in determination of lead ions in aqueous samples, using flame atomic absorption spectrometry (FAAS). Through this study, different parameters such as pH and sample flow rate on adsorption process and eluent concentration, volume and flow rate were optimized. The limit of detection (LOD), the relative standard deviation and the recovery of the method were 2 ng mL?1, 1.3% and 99.7%, respectively. Two standard reference materials (NIST 1571 and NIST 1572) were used to verify accuracy of this method. Finally, the sorbent was successfully applied for extraction and determination of low levels of Pb(II) ions in aqueous samples. 相似文献
2.
MySQL安全机制及应对措施探讨 总被引:2,自引:0,他引:2
探讨作为一种最主要的网络数据库系统MySQL的基于授权表的安全机制,以及如何在应用中就文件系统保护、口令保护、权限表设置和运行选项的采用来提高安全性能的问题。 相似文献
3.
Debora Di Caprio 《Topology and its Applications》2006,153(14):2680-2702
We introduce and study some completeness properties for systems of open coverings of a given topological space. A Hausdorff space admitting a system of cardinality κ satisfying one of these properties is of type Gκ. Hence, we define several new variants of the ?ech number and use elementary submodels to determine further results. We introduce M-hulls and M-networks, for M elementary submodel. As an application, we give estimates for both the tightness and the Lindelöf number of a generic upper hyperspace. Two recent results of Costantini, Holá and Vitolo on the tightness of co-compact hyperspaces follow from ours as corollaries. 相似文献
4.
Pentacoordinate complex cations of the general formula [(C6F5)2SbL3]3+ stabilized as solid salts in combination with tetraphenylborate (BPh4), tetrafluorobroate (BF4) anions, where L=DMSO, Ph3AsO, PyO, DMF, α-, β- and γ-picoline have been isolated. The newly formed complexes were characterized by elemental analysis, molar conductance measurements, solid-state IR and and NMR. From these results, a five-fold coordination around antimony was required. 相似文献
5.
Geometries and stabilization energies of various simple H-bonded complexes (water dimer, hydrogen fluoride dimer, formamide
dimer, formic acid dimer) have been determined by a gradient optimization that eliminates the basis set superposition error
(BSSE) by the counterpoise (CP) method in each gradient cycle as well as by the standard gradient optimization. Both optimization
methods lead to different potential energy surfaces (PES). The difference depends on the theoretical level used and is larger
if correlation energy is considered. Intermolecular distances from the CP-corrected PES are consistently longer, and this
difference might be significant (∼0.1 ?); also angular characteristics determined from both surfaces differ significantly.
Different geometries were obtained even when passing to larger basis sets (aug-cc-pVDZ). The standard optimization procedure
can result in a completely wrong structure. For example, the “quasi-linear” structure of the (HF)2 (global minimum) does not exist at the standard MP2/ 6-31G** PES (where only cyclic structure was detected) and is found
only at the CP-corrected PES. Stabilization energies obtained from the CP-corrected PES are always larger than these from
the standard PES where the BSSE is added only a posteriori for the final optimized structure; both energies converge only
when passing to a larger basis set (aug-cc-pVDZ).
Received: 11 March 1998 / Accepted: 19 June 1998 / Published online: 4 September 1998
RID="
ID=" <E6>Acknowledgements.</E6> The project was supported by the Grant Agency of the Czech Republic (Grant No. 203/98/1166).
RID="
ID=" <E5>Correspondence to</E5>: P. Hobza 相似文献
6.
In an effort to develop an efficient synthetic method of highly diastereoselective (2′R)- and (2′S)-2′-deoxy[2′-2H]guanosines, chemoenzymatic conversion was investigated. The synthesis of (2′R > 98% de)-2′-deoxy[2′-2H]guanosine was achieved by biological transdeoxyribosylation using (2′R > 98% de)-2′-deoxy[2′-2H]uridine, 2,6-diaminopurine, and Enterobacter aerogenes AJ-11125, followed by treatment with adenosine deaminase. (2′S > 98% de)-2′-Deoxy[2′-2H]guanosine was synthesized from (2′S > 98% de)-2′-deoxy[2′-2H]uridine and 2,6-diaminopurine using thymidine phosphorylase and purine nucleoside phosphorylase instead of E. aerogenes AJ-11125. 相似文献
7.
基于MSComm控件的串行通信方法及实现 总被引:7,自引:0,他引:7
串行接口由于其具有连接简单、使用方便、数据传递可靠等优点,在工业实时控制系统中得到了广泛应用。本文探讨了基于Windows98平台上利用Microsoft Communica-tions Control控件编写串行通信程序的方法,并结合开发实践,阐述了用C Builder5语言实现了基于ActiveX技术的串行通信编程的一般步骤。实践表明,该方法简单、可靠,从而大大缩短实时控制软件的开发周期,减少程序员的工作量。 相似文献
8.
9.
Iwona E. Głowacka Dorota G. Piotrowska Andrzej E. Wróblewski Aleksandra Trocha 《Tetrahedron: Asymmetry》2017,28(11):1602-1607
A simple and efficient synthetic strategy to all four enantiomerically pure diethyl 1,2-di(N-Boc-amino)propylphosphonates has been elaborated starting from the corresponding N-[(R)-(1-phenylethyl)]aziridine-(2S)- and N-[(S)-(1-phenylethyl)]aziridine-(2R)-carboxaldehydes, employing a one-pot three-components Kabachnik-Fields reaction followed by the hydrogenolytic removal of the chiral auxiliary and aziridine ring opening with simultaneous protection of the amino groups as the N-Boc derivatives. 相似文献
10.
Michelle Cutajar Robert A. Stockman Susan Braovac Calin Constantin Steindal Angeliki Zisi Stephen E. Harding 《Molecules (Basel, Switzerland)》2022,27(7)
Butvar B-98 and PDMS-OH both have a demonstrable ability as consolidants for archaeological wood. This makes them both potential treatment options for the Oseberg collection, which is one of the most important archaeological finds from the Viking era. Both Butvar B-98 and PDMS-OH are soluble in organic solvents, offering a useful alternative to aqueous-based consolidants. Extensive characterisation studies were carried out on both of these polymers, with the use of analytical ultracentrifugation and viscometry, for the benefit of conservators wanting to know more about the physical properties of these materials. Short column sedimentation equilibrium analysis using SEDFIT-MSTAR revealed a weight-average molar mass (weight-average molecular weight) Mw of (54.0 ± 1.5) kDa (kg · mol−1) for Butvar B-98, while four samples of PDMS-OH siloxanes (each with a different molar mass) had an Mw of (52.5 ± 3.0) kDa, (38.8 ± 1.5) kDa, (6.2 ± 0.7) kDa and (1.6 ± 0.1) kDa. Sedimentation velocity confirmed that all polymers were heterogeneous, with a wide range of molar masses. All molecular species showed considerable conformational asymmetry from measurements of intrinsic viscosity, which would facilitate networking interactions as consolidants. It is anticipated that the accumulated data on these two consolidants will enable conservators to make a more informed decision when it comes to choosing which treatment to administer to archaeological artefacts. 相似文献