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   136篇
  免费   14篇
化学   116篇
力学   2篇
数学   22篇
物理学   10篇
  2023年   3篇
  2022年   6篇
  2021年   5篇
  2020年   6篇
  2019年   24篇
  2018年   10篇
  2017年   4篇
  2016年   19篇
  2015年   12篇
  2014年   11篇
  2013年   10篇
  2012年   10篇
  2011年   5篇
  2010年   5篇
  2009年   5篇
  2008年   6篇
  2007年   3篇
  2006年   3篇
  2003年   1篇
  2002年   1篇
  1998年   1篇
排序方式: 共有150条查询结果,搜索用时 31 毫秒
141.
142.
Project portfolio selection problems are inherently complex problems with multiple and often conflicting objectives. Numerous analytical techniques ranging from simple weighted scoring to complex mathematical programming approaches have been proposed to solve these problems with precise data. However, the project data in real-world problems are often imprecise or ambiguous. We propose a fuzzy Multidimensional Multiple-choice Knapsack Problem (MMKP) formulation for project portfolio selection. The proposed model is composed of an Efficient Epsilon-Constraint (EEC) method and a customized multi-objective evolutionary algorithm. A Data Envelopment Analysis (DEA) model is used to prune the generated solutions into a limited and manageable set of implementable alternatives. Statistical analysis is performed to investigate the effectiveness of the proposed approach in comparison with the competing methods in the literature. A case study is presented to demonstrate the applicability of the proposed model and exhibit the efficacy of the procedures and algorithms.  相似文献   
143.
In the present study, adsorption of Bismarck Brown (BB) dye onto iron oxide nanospheres (IONs) and modified IONs by HCl from aqueous solution was investigated. The IONs was synthesized by solvothermal method and then modified by HCl. The high magnetic properties of both adsorbents lead to facial separation from aqueous solution by an external magnet. The results show that the modification of adsorbent cause higher adsorption capacity for removal of BB from aqueous solution. The prepared adsorbents were characterized by SEM, XRD, FTIR, and ATR-IR techniques. The adsorption kinetic and equilibrium data were fitted with different models. The results show that the equilibrium and kinetic data were best fitted with Langmuir–Freundlich isotherm and fractal-like pseudo-second-order kinetic model, respectively. The effects of pH and temperature have also been investigated.  相似文献   
144.
In the present study, the photo-generation of silver nanoparticles in ethanolic solution and in the presence of F127 block copolymer using UV irradiation have been investigated. The aim of the present study is preparing the green, facile and much faster method than previous studies. The kinetics of silver nanoparticles formation has been investigated by using UV-vis spectroscopy. The two-dimensioanl map technique has been used to estimate the switching time between the nucleation and growth of Ag nanoparticles. The results show that the dispersed Ag nanoparticle in ethanol can be formed by high intensity ultraviolet exposure within few minutes.  相似文献   
145.
Graphene oxide (GO), an up‐and‐coming material rich in oxygenated groups, shows much promise in pollution management. GO is synthesised using several synthetic routes, and the adsorption behaviour of GO is investigated to establish its ability to remove the heavy‐metal pollutants of lead and cadmium ions. The GO is synthesised by Hummers’ (HU), Hofmann’s (HO) and Staudenmaier’s (ST) methodologies. Characterisation of GO is performed before and after adsorption experiments to investigate the structure–function relationship by using Fourier‐transform infrared spectroscopy and X‐ray photoelectron spectroscopy. Scanning electron microscopy coupled with elemental detection spectroscopy is used to investigate morphological changes and heavy‐metal content in the adsorbed GO. The filtrate, collected after adsorption, is analysed by inductively coupled plasma mass spectrometry, through which the efficiency and adsorption capacity of each GO for heavy‐metal‐ion removal is obtained. Spectroscopic analysis and characterisation reveal that the three types of GO have different compositions of oxygenated carbon functionalities. The trend in the affinity towards both PbII and CdII is HU GO>HO GO>ST GO. A direct correlation between the number of carboxyl groups present and the amount of heavy‐metal ions adsorbed is established. The highest efficiency and highest adsorption capacity of heavy‐metal ions is achieved with HU, in which the relative abundance of carboxyl groups is highest. The embedded systematic study reveals that carboxyl groups are the principal functionality responsible for heavy‐metal‐ion removal in GO. The choice of synthesis methodology for GO has a profound influence on heavy‐metal‐ion adsorption. A further enrichment of the carboxyl groups in GO will serve to enhance the role of GO as an adsorbent for environmental clean‐up.  相似文献   
146.
Tramadol was found to exhibit weak fluorescence with a maximum emission at 300 nm when excited at 200 nm. Also, fluorescence spectra of the drug and its two main metabolites, O-desmethyltramadol and N-desmethyltramadol are not practically identical. Thus low and different sensitivities have been reported for the drug and its metabolites in previously published work. In the present method using 9-fluorenylmethyl chloroformate (FMOC-Cl) as labeling agent, equal and magnified fluorescence intensity were obtained for the analytes. The drug, its metabolites and an internal standard (oseltamivir phosphate) were extracted from serum by dichloromethane. Pre-column derivatization of the analytes was achieved using FMOC-Cl in the presence of borate buffer (0.1 M, pH 7.5). Liquid chromatography with a mobile phase consisting of a mixture of 0.05 M phosphate buffer containing triethylamine (2 ml L?1; pH = 3.0) and methanol (54:46; v/v) and a Shimpack CLC-ODS column were used for analytical separation of the analytes. The fluorescence of the column effluent was monitored at an excitation and emission wavelengths of 265 and 315 nm, respectively. The analytical method was linear over the concentration range of 1.0–1,280 ng mL?1 of the parent drug and its metabolites and limit of quantification of 1.0 ng mL?1 was obtained for the analytes using 10 μL injection. The method validation was studied and the validated method applied in a bioequivalence study of 2 different tramadol preparations in 24 healthy volunteers.  相似文献   
147.
C−H bond functionalization generates molecular complexity in single-step transformation. However, the activation of C−H bonds requires expensive metals or stoichiometric amounts of oxidizing/reducing species. In many cases, they often require pre-functionalization of starting molecules. Such pre-activating measures cause waste generation and their separation from the final product is also troublesome. In such a scenario, reactions activating elements generating from renewable energy resources such as electricity and light would be more efficient, green, and cost-effective. Further, incorporation of growing flow technology in chemical transformation processes will accelerate the safer accesses of valuable products. Arenes & heteroarenes are ubiquitous in pharmaceuticals, natural products, medicinal compounds, and other biologically important molecules. Herein, we discussed enabling tools and technologies used for the recent C−H bonds functionalization of arenes and heteroarenes.  相似文献   
148.
We introduce a dynamic range image compression technique for nonlinear deconvolution; the impulse response of the distortion function and the noisy distorted image are jointly transformed to pump a clean reference beam in a two-beam coupling arrangement. The Fourier transform of the pumped reference beam contains the deconvolved image and its conjugate. In contrast to standard deconvolution approaches, for which noise can be a limiting factor in the performance, this approach allows the retrieval of distorted signals embedded in a very high-noise environment.  相似文献   
149.
One-pot, three-component coupling reactions of indole, aromatic aldehydes, and heteroaryl amines under solvent-free conditions lead to the formation of the corresponding novel 3-[(N-heteroaryl)(aryl)methyl]indoles in moderate to high yields. The key features of this multi-component reaction are the simple reaction procedure, no organic solvent or acid catalyst, and easy product separation without further purification.  相似文献   
150.
As the most common cancer in women, efforts have been made to develop novel nanomedicine-based therapeutics for breast cancer. In the present study, the in silico curcumin (Cur) properties were investigated, and we found some important drawbacks of Cur. To enhance cancer therapeutics of Cur, three different nonionic surfactants (span 20, 60, and 80) were used to prepare various Cur-loaded niosomes (Nio-Cur). Then, fabricated Nio-Cur were decorated with folic acid (FA) and polyethylene glycol (PEG) for breast cancer suppression. For PEG-FA@Nio-Cur, the gene expression levels of Bax and p53 were higher compared to free drug and Nio-Cur. With PEG-FA-decorated Nio-Cur, levels of Bcl2 were lower than the free drug and Nio-Cur. When MCF7 and 4T1 cell uptake tests of PEG-FA@Nio-Cur and Nio-Cur were investigated, the results showed that the PEG-FA-modified niosomes exhibited the most preponderant endocytosis. In vitro experiments demonstrate that PEG-FA@Nio-Cur is a promising strategy for the delivery of Cur in breast cancer therapy. Breast cancer cells absorbed the prepared nanoformulations and exhibited sustained drug release characteristics.  相似文献   
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