全文获取类型
收费全文 | 387篇 |
免费 | 30篇 |
国内免费 | 5篇 |
专业分类
化学 | 324篇 |
力学 | 5篇 |
数学 | 30篇 |
物理学 | 63篇 |
出版年
2023年 | 5篇 |
2022年 | 16篇 |
2021年 | 16篇 |
2020年 | 29篇 |
2019年 | 33篇 |
2018年 | 31篇 |
2017年 | 29篇 |
2016年 | 36篇 |
2015年 | 22篇 |
2014年 | 30篇 |
2013年 | 45篇 |
2012年 | 20篇 |
2011年 | 18篇 |
2010年 | 14篇 |
2009年 | 8篇 |
2008年 | 18篇 |
2007年 | 17篇 |
2006年 | 9篇 |
2005年 | 2篇 |
2004年 | 5篇 |
2003年 | 5篇 |
2002年 | 6篇 |
2001年 | 2篇 |
1996年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1991年 | 1篇 |
1987年 | 1篇 |
1985年 | 1篇 |
排序方式: 共有422条查询结果,搜索用时 15 毫秒
121.
Majid M. Heravi Vahideh Zadsirjan Elham Kouhestanian Behnoush AlimadadiJani 《Chemical record (New York, N.Y.)》2020,20(4):273-331
One of the most important name reactions in organic chemistry, is the Diels‐Alder cycloaddition reaction. It is a chemical reaction between a conjugated diene and a substituted alkene, commonly termed the dienophile to construct a substituted cyclohexene derivative. It is the stereotypical example of a pericyclic reaction with a concerted mechanism. In synthesis, the use of electricity instead of stoichiometric amounts of oxidant or reducing agents is definitely appealing for economic, ecological and selective, reasons. In this review, we try to underscore the combination of the electrosynthesis with Diels‐Alder cycloaddition reaction to establish of a powerful synthetic tool which may encourage synthetic organic chemists to use it in the future. 相似文献
122.
Selective extraction of clonazepam from human plasma and urine samples by molecularly imprinted polymeric beads
下载免费PDF全文
![点击此处可从《Journal of separation science》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Homayon Ahmad Panahi Ali Mehramizi Somayeh Ghassemi Elham Moniri 《Journal of separation science》2014,37(6):691-695
A molecularly imprinted polymer (MIP) based on free‐radical polymerization was prepared with 1‐(N,N‐biscarboxymethyl)amino‐3‐allylglycerol and N,N‐dimethylacrylamide as functional monomers, N,N‐methylene diacrylamide as the cross‐linker, copper ion‐clonazepam as the template and 2,2‐azobis(2‐methylbutyronitrile) as the initiator. The imprinted polymer was characterized by Fourier transform infrared spectroscopy, elemental analysis, thermogravimetric analysis, and SEM. The MIP of agglomerated microparticles with multipores was used for SPE. The imprinted polymer sorbent was selective for clonazepam. The optimum pH and sorption capacity were 5 and 0.18 mg/g at 20°C, respectively. The profile of the drug uptake by the sorbent reflects good accessibility of the active sites in the imprinted polymer sorbent. The MIP‐SPE was the most feasible technique for the extraction of clonazepam with a high recovery from human plasma and urine samples. 相似文献
123.
An effective route to novel 2,6‐dioxohexahydropyrimidines is described. This involves reaction of alkyl isocyanides and dialkyl acetylenedicarboxylates in the presence of N,N′‐dimethylurea in 1M aq. glucose. 相似文献
124.
Elham Keshavarz Yadollah Ordokhani 《Mathematical Methods in the Applied Sciences》2019,42(13):4427-4443
In this paper, a fast numerical algorithm based on the Taylor wavelets is proposed for finding the numerical solutions of the fractional integro‐differential equations with weakly singular kernels. The properties of Taylor wavelets are given, and the operational matrix of fractional integration is constructed. These wavelets are utilized to reduce the solution of the given fractional integro‐differential equation to the solution of a linear system of algebraic equations. Also, convergence of the proposed method is studied. Illustrative examples are included to demonstrate the validity and applicability of the technique. 相似文献
125.
Kamal A. Idriss Magda S. Saleh Mohamed M. Seleim Elham Y. Hashem 《Journal of solution chemistry》1993,22(5):469-481
The reaction of 2-mercaptonicotinic-copper (II) complex (Cu2+-MENA, 1 3n 1) with thiosalicylic acid (TSA) has been investigated spectrophotometrically in ethanol-water solution (50%, v/v) at I=O.IM (NaClO4) and 25°C. Under the acidic conditions encountered in this study, there are competing equilibria between protonation of the Cu2+-MENA binary chelate, the formation of the Cu(MENA)(TSA) ternary complex and protonation of the second ligand (TSA). The equilibrium constants for the complexation reactions and the stability of the mixed-ligand complex are determined. The optimum conditions for the predominance of the ternary complex are established and the enhancement of this complex over binary complex formation is evaluated. Complex-forming equilibria have also been examined by potentiometric-pH titrations and the experimental data are discussed in relation to various equilibria existing in solution. Structural and bonding features of the mixed-ligand complex are illustrated from considerations of the IR spectral data. 相似文献
126.
Ahmad Shaabani Elham Farhangi Abbas Rahmati 《Monatshefte für Chemie / Chemical Monthly》2008,139(8):905-908
1-Butyl-3-methylimidazolium bromide ([bmim]Br) as an ionic liquid promoted selectively the oxidation of alkyl arenes and alcohols to the corresponding carbonyl compounds
with NaBrO3 in excellent yields under neutral conditions at the 70°C. Among the various ionic liquids examined, the [bmim]Br exhibited the best performances with NaBrO3. The ionic liquid can be recycled and reused for several runs without any significant loss of activity.
Correspondence: Ahmad Shaabani, Department of Chemistry, Shahid Beheshti University, P.O. Box 19839-4716, Tehran, Iran. 相似文献
127.
Callus and suspension cultures of Linum album as an Iranian species for synthesis of aryltetralin lactone were used. After cultivation period; we can isolate and characterize podophyllotoxin as glycosides compounds. Maximal product yield is 0.5% of the dry weight in dark grown cultures. 相似文献
128.
This paper deals with the numerical solution of time fractional diffusion equation. In this work, we consider the fractional derivative in the sense of Riemann-Liouville. At first, the time fractional derivative is discretized by integrating both sides of the equation with respect to the time variable and we arrive at a semi–discrete scheme. The stability and convergence of time discretized scheme are proven by using the energy method. Also we show that the convergence order of this scheme is O(τ2?α). Then we use the sinc collocation method to approximate the solution of semi–discrete scheme and show that the problem is reduced to a Sylvester matrix equation. Besides by performing some theorems, the exponential convergence rate of sinc method is illustrated. The numerical experiments are presented to show the excellent behavior and high accuracy of the proposed hybrid method in comparison with some other well known methods. 相似文献
129.
Elham Mirmomtaz Ali Zirakbash Ali Asghar Ensafi 《Russian Journal of Electrochemistry》2016,52(4):320-329
In the present study, the electrochemical behavior of 6-Thioguanine (6-TG) and its interaction with double-strand DNA (ds-DNA) were investigated at the surface of hanging mercury drop electrode (HMDE) in neutral media. The interaction of 6-TG with ds-DNA in neutral buffer was clearly demonstrated by the elimination of 6-TG signal and the advent of a new reduction peak. To investigate the interaction, various parameters including accumulation time and potential as well as ds-DNA concentration were optimized using a combination of adsorptive stripping voltammetry (AdSV) and square wave voltammetry (SWV) techniques. As a consequence a low detection limit of 1.1 μM was obtained in a dynamic range of 16.0 to 360.0 μM. To better understand the interaction mechanism between 6-TG anti-cancer drug and ds-DNA, cyclic voltammetry and UV-Vis spectroscopy measurements were carried out and the intercalation of 6-TG into ds-DNA was proposed as the plausible mechanism. The application of this screening assay in real sample analysis was investigated by using the procedure for determination of 6-TG in 6-Thioguanine tablets and also in spiked 6-TG blood serum. Overall, the results were indicative of a DNA sensor which could be applied effectively in the analysis of 6-TG in vitro. 相似文献
130.
Electrocatalytic Activities of Graphene/Nile Blue Nanocomposite Toward Determination of Hydrogen Peroxide and Nitrite Ion
下载免费PDF全文
![点击此处可从《Electroanalysis》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Reza Karimi Shervedani Elham Ansarifar Marzieh Samiei Foroushani 《Electroanalysis》2016,28(9):1957-1969
Electrocatalytic activities of graphene nanosheets/Nile blue nanocomposite, synthesized and adsorbed simultaneously on the glassy carbon (GC?GNs?NB) electrode, are investigated. The nanocomposite was characterized by ATR?FTIR, FESEM and voltammetry. Activity of the electrode toward reduction of H2O2 and oxidation of NO2? was studied electrochemically. Values of 1.95 and 0.730 mM are found for the Michaelis?Menten constant of the electrode toward H2O2 and NO2?, respectively. Wide dynamic response ranges were observed for the electrode, with DLs of 0.22 μM H2O2 and 1.1 μM NO2?. Effect of interferences was studied. The sensor was successfully tested for H2O2 and NO2? contents in real samples, respectively. 相似文献