首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   108篇
  免费   5篇
化学   72篇
力学   5篇
数学   7篇
物理学   29篇
  2023年   1篇
  2022年   1篇
  2020年   2篇
  2019年   6篇
  2017年   6篇
  2016年   10篇
  2015年   4篇
  2014年   6篇
  2013年   8篇
  2012年   11篇
  2011年   7篇
  2010年   6篇
  2009年   1篇
  2008年   7篇
  2007年   5篇
  2006年   3篇
  2005年   3篇
  2004年   2篇
  2003年   4篇
  2002年   5篇
  2000年   3篇
  1999年   1篇
  1998年   1篇
  1995年   1篇
  1987年   2篇
  1986年   1篇
  1983年   1篇
  1979年   2篇
  1978年   1篇
  1973年   2篇
排序方式: 共有113条查询结果,搜索用时 78 毫秒
1.
Healthcare Operational Research (OR) has had limited success in achieving a sufficient level of stakeholder acceptance to lead to implementation of results. This research study is aimed at combining OR methodologies to achieve greater acceptance of results for organizational change. Patient flow delays in the Paediatric intensive care unit (PICU) at Children's Hospital of Wisconsin were identified using case studies. Patient flow was modelled using hard OR (simulation) using case study findings, with active stakeholder participation, and enhanced with outcomes research. Outcomes research allowed achieving greater clinical relevance of OR findings. Results from hard OR, particularly for politically sensitive issues, were persuasive but inadequate to result in change. Soft OR (cognitive mapping) was used to identify new issues and enhance results. Consequently, the planned PICU expansion was deferred, and resources focused on improving staffing strategies identified independently from both hard and soft OR. These findings suggest that: (1) Outcomes research can play a unique role to enhance results in healthcare OR. (2) After obtaining a holistic understanding of the system using hard and soft OR, stakeholders are willing to implement results from each independently, supporting the development of a common form of knowledge, which is consistent with Mixed-Mode Modelling. (3) Hard OR, enhanced with outcomes research, with active stakeholder participation, and combined with soft OR, results in greater acceptance and sustained organizational change.  相似文献   
2.
2,4-Dinitrophenylhydrazine has been suggested as a new reagent for the flow-injection spectrophotometric determination of residual chlorine based on its oxidation to 2,4-dinitrophenyldiazonium ion. The measurement of the decrease in colour intensity under reversed flow-injection (reagent injection) conditions has been used for the determination of 0.1–10 mg/l Cl present as free or combined chlorine, and for its speciation. The limit of detection was 0.05 mg/l Cl. Copper (II), iron (III) and many other ions have been found not to vitiate the results.  相似文献   
3.
The complex generated from 1/2[Ir(OMe)(cod)]2 and 4,4'-di-tert-butyl-2,2'-bipyridine catalyzes the regioselective borylation of ferrocenes, CpMn(CO)3 and CpMo(CO)3CH3 with a stoichiometric amount of B2pin2.  相似文献   
4.
A series of new dicationic dihydrogen complexes of ruthenium of the type cis-[(dppm)(2)Ru(eta(2)-H(2))(L)][BF(4)](2) (dppm = Ph(2)PCH(2)PPh(2); L = P(OMe)(3), P(OEt)(3), PF(O(i)Pr)(2)) have been prepared by protonating the precursor hydride complexes cis-[(dppm)(2)Ru(H)(L)][BF(4)] (L = P(OMe)(3), P(OEt)(3), P(O(i)Pr)(3)) using HBF(4).Et(2)O. The cis-[(dppm)(2)Ru(H)(L)][BF(4)] complexes were obtained from the trans hydrides via an isomerization reaction that is acid-accelerated. This isomerization reaction gives mixtures of cis and trans hydride complexes, the ratios of which depend on the cone angles of the phosphite ligands: the greater the cone angle, the greater is the amount of the cis isomer. The eta(2)-H(2) ligand in the dihydrogen complexes is labile, and the loss of H(2) was found to be reversible. The protonation reactions of the starting hydrides with trans PMe(3) or PMe(2)Ph yield mixtures of the cis and the trans hydride complexes; further addition of the acid, however, give trans-[(dppm)(2)Ru(BF(4))Cl]. The roles of the bite angles of the dppm ligand as well as the steric and the electronic properties of the monodentate phosphorus ligands in this series of complexes are discussed. X-ray crystal structures of trans-[(dppm)(2)Ru(H)(P(OMe)(3))][BF(4)], cis-[(dppm)(2)Ru(H)(P(OMe)(3))][BF(4)], and cis-[(dppm)(2)Ru(H)(P(O(i)Pr)(3))][BF(4)] complexes have been determined.  相似文献   
5.
Goswami A  Singh AK 《Talanta》2002,58(4):669-678
A new chelating matrix has been prepared by immobilizing 1,8-dihydroxyanthraquinone (DHAQ) on silica gel modified with (3-aminopropyl)triethoxysilane. After characterizing the matrix with thermogravimetric analysis (TGA), cross polarization magic angle spinning (CPMAS) NMR and diffuse reflectance infrared fourier transformation (DRIFT) spectroscopy, it has been used to preconcentrate Pb(II), Cd(II) and Zn(II) prior to their determination by flame atomic absorption spectrometry. The optimum pH ranges for quantitative sorption are 6.0-7.5, 7.0-8.0 and 6.0-8.0 for Pb, Zn, and Cd, respectively. All the metal ions can be desorbed with 2 mol l(-1) HCl/HNO(3). The sorption capacity of the matrix has been found to be 76.0, 180.0 and 70.2 mumol g(-1) for Pb, Zn and Cd, respectively, with the preconcentration factor of approximately 200. The limits upto which electrolytes NaNO(3), NaCl, NaBr, Na(2)SO(4), Na(3)PO(4) sodium citrate, EDTA, glycine and humic acid and cations Ca(II), Mg(II), Cu(II), Co(II), Ni(II), Mn(II) Al(III), Cr(III) and Fe(III) can co-exist with the metal ions during their sorption without any adverse effect are reported. The lowest concentration of metal ions for quantitative recovery is 5.0 ng ml(-1) The simultaneous enrichment and determination of all the metals is possible if total load of metal ions is less than sorption capacity. The flame AAS was used to determine these metal ions in underground, tap and river water samples (relative standard deviation (R.S.D.)相似文献   
6.
Two simple and sensitive spectrophotometric methods have been developed for analysis of the antipsychotic drug olanzapine in pharmaceuticals. Method A is based on liberation of iodine by reaction between the drug and potassium iodate, followed by reaction with leuco crystal violet (LCV), the color of oxidized LCV being measured at 598 nm. Method B is based on oxidation of olanzapine with chloramine-T (CAT) in acidic medium, the unconsumed CAT being determined with rhodamine B, measuring the absorbance at 550 nm. Calibration graphs were linear over the ranges of 0.05–2.0 and 0.1–1.6 μg mL?1 olanzapine for method A and B, respectively. The molar absorptivity, Sandell’s sensitivity, detection limit, and quantitation limit were found to be 1.59 × 105, 0.00132, 0.038, and 0.117, respectively, for method A and 0.953 × 105, 0.00221, 0.064, and 0.192, respectively, for method B. The optimum conditions and other analytical parameters were evaluated. The proposed methods have been applied successfully for analysis of olanzapine in pure form and its dosage forms, and no interference was observed from common excipients present in pharmaceutical formulations.  相似文献   
7.
Mononuclear divalent complexes of Co, Ni, Cu and Zn derived from a benzofuran‐based novel hydrazone tridentate ligand were synthesized and characterized using various spectroscopic methods. Elemental analysis reveals that the metal‐to‐ligand ratio is 1:2 which is supported by mass spectrometry results. Conductivity measurements suggest that all the complexes are non‐electrolytic in nature. The ligand and complexes were evaluated for their antimicrobial potency. Bioassay of all hydrazone chelates shows enhanced activity as compared to that of the ligand. The complex with cobalt ion as the metal centre shows better activity against fungi than the standard. Also, ligand and complexes were screened for antituberculosis activity; some analogues (Ni, Cu, Zn) are eight times more active than the standard. Both ligand and complexes show moderate ability to cleave calf thymus DNA. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
8.
The electrochemical behavior of dopamine was examined under redox cycling conditions in the presence and absence of a high concentration of the interferent ascorbic acid at a coplanar, microelectrode array where the area of the generator electrodes was larger than that of the collector electrodes. Redox cycling converts a redox species between its oxidized and reduced forms by application of suitable potentials on a set of closely located generator and collector electrodes. It allows signal amplification and discrimination between species that undergo reversible and irreversible electron transfer. Microfabrication was used to produce 18 individually addressable, 4-μm-wide gold band electrodes, 2 mm long, contained in an array having an interelectrode spacing of 4 μm. Because the array electrodes are individually addressable, each can be selectively biased to produce an overall optimal electrochemical response. Four adjacent microbands were shorted together to serve as the collector, and were flanked on each side by seven microbands shorted as the generator (a ratio of 1:3.5 of electroactive area, respectively). This configuration achieved a detection limit of 0.454?±?0.026 μM dopamine at the collector in the presence of 100 μM ascorbic acid in artificial cerebrospinal fluid buffer, concentrations that are consistent with physiological levels. Enhancement by surface modification of the microelectrode array to achieve this detection limit was unnecessary. The results suggest that the redox cycling method may be suitable for in vivo quantification of transients and basal levels of dopamine in the brain without background subtraction.
Figure 1
Microelectrode array chip design and assignment of electrodes used for determination of dopamine (DA) in the presence of large excess of ascorbic acid (AA) by redox cycling. Analytes (DA and AA) are oxidized at the generator electrodes to form dopamine-o-quinone (DAQ) and dehydroascorbic acid (AAo) which diffuse to the nearest collector electrodes. DA is selectively detected at the collector electrodes, because DAQ can be reduced there, but AAo hydrolyzes to a nonelectroactive form prior to arrival  相似文献   
9.
A simple sensitive extractive spectrophotometric method for determination of trichloroethylene is proposed. Trichloroethylene is treated with pyridine to form glutaconic aldehyde by heterolytic cleavage of the pyridine ring. Glutaconic aldehyde is further coupled with 4-aminoacetanilide to form an orange–red dye which is extractable in 3-methyl-1-butanol. The extracted dye shows absorption maximum at 520 nm. The system obeys Beer’s law in the range of 0.05–0.8 μg mL?1. Important analytical parameters such as time, temperature, reagent concentration, acidity etc. have been optimized for complete colour reaction. Sandell’s sensitivity and molar absorptivity for the system were found to be 0.001 μg cm?2 and 1.2 × 105 L mol?1 cm?1, respectively. The proposed method is satisfactorily applied to micro-level determination of trichloroethylene in various environmental and biological samples.  相似文献   
10.
This study is attempted to develop a green corrosion inhibitor from a waste material of Jack fruit (Artocarpus heterophyllus). This method is therefore quite valuable to health, environment, and economic point of view. Pectin is isolated from the jackfruit peel waste using 0.05 ?N oxalic acid and used as an inhibitor for mild steel corrosion in acidic environment as it is highly water soluble. 250–1000 ?ppm of pectin was used in this study at a temperature range of 303–323 ?K. The protection efficiency of jack fruit pectin (JP) in 0.5 ?M HCl was evaluated by conventional weight loss and electrochemical techniques. The potentiodynamic polarization results revealed that JP could effectively reduce the corrosion of mild steel in acidic medium at 1000 ?ppm concentration with an inhibition efficiency of 89.75% and corrosion rate of 2.392 mpy. The mixed type behavior of the inhibitor is identified from Tafel polarization studies. Electrochemical impedance spectroscopy (EIS) measurements suggest that the corrosion inhibition process is kinetically controlled. adsorption and kinetic behavior of the inhibitor also have been studied. Surface manifestations were followed using FESEM and AFM techniques. DFT calculations and Monte Carlo simulations were also carried out to corroborate the experimental results with theoretical outputs and succeeded to a great extent.  相似文献   
1 [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] 下一页 » 末  页»
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号