全文获取类型
收费全文 | 658篇 |
免费 | 33篇 |
国内免费 | 15篇 |
专业分类
化学 | 473篇 |
晶体学 | 2篇 |
力学 | 43篇 |
数学 | 76篇 |
物理学 | 112篇 |
出版年
2023年 | 2篇 |
2022年 | 7篇 |
2021年 | 12篇 |
2020年 | 27篇 |
2019年 | 26篇 |
2018年 | 35篇 |
2017年 | 34篇 |
2016年 | 61篇 |
2015年 | 38篇 |
2014年 | 41篇 |
2013年 | 100篇 |
2012年 | 52篇 |
2011年 | 73篇 |
2010年 | 28篇 |
2009年 | 35篇 |
2008年 | 26篇 |
2007年 | 24篇 |
2006年 | 11篇 |
2005年 | 15篇 |
2004年 | 11篇 |
2003年 | 18篇 |
2002年 | 11篇 |
2001年 | 4篇 |
2000年 | 2篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1984年 | 1篇 |
1976年 | 2篇 |
排序方式: 共有706条查询结果,搜索用时 375 毫秒
101.
Morteza Shiri Majid M. Heravi Hoda Hamidi Mohammad A. Zolfigol Zahra Tanbakouchian Atefeh Nejatinezhad-Arani Suhas A. Shintre Neil A. Koorbanally 《Journal of the Iranian Chemical Society》2016,13(12):2239-2246
2-(2-Chloroquinolin-3-yl)-3-(arylamino)-2,3-dihydroquinazolin-4(1H)-one was converted to quinolino[2′,3′:3,4]pyrazolo[5,1-b]quinazolin-8(6H)-ones in the presence of KOtBu in DMSO at room temperature. The present method has the advantages of easy conditions, construction of highly novel five heterocycles, transition metal-free conditions, cascade dehydrogenation and intramolecular N-arylation and good to high yield of products. 相似文献
102.
A new convenient colorimetric sensor for fructose based on anti-aggregation of citrate-capped gold nanoparticles(Au NPs) is presented. 4-Mercaptophenylboronic acid(MPBA) induces the aggregation of Au NPs, leading to a color change from red to blue. Fructose as a potent competitor has strong affinity for MPBA and a borate ester is formed between MPBA and fructose. There is an obvious color change from blue to red with increasing the concentration of fructose. The anti-aggregation effect of fructose on Au NPs was seen by the naked eye and monitored by UV–vis spectra. Our results showed that the absorbance ratio(A_(519)/A_(640)) was linear with fructose concentration in the range of 0.032–0.96 μmol/L(R~2= 0.996), with a low detection limit of 0.01 μmol/L(S/N = 3). Notably, a highly selective recognition of fructose was shown against other monosaccharide and disaccharide(glucose, mannose, galactose,lactose and saccharose). With anti-aggregation assays higher selectivity is achievable. The results of this work provide a rapid method for evaluating the quantitative analysis of fructose in human plasma at physiologically meaningful concentrations and at neutral pH. The proposed procedure can be used as an efficient method for the precise and accurate determination of fructose. 相似文献
103.
This work introduces a version of filter technique to produce an adaptive radius and then adds it into trust-region algorithm. This method uses advantages of the functions norm’s necessary information in order to produce a smaller radius of trust-region close to the optimizer and also a larger radius of trust-region far away from the optimizer using advantages of the filter technique (Fatemi and Mahdavi-Amiri, Comput. Optim. Appl. 52(1), 239–266 2012). Under some ordinary conditions, the global convergence of the proposed approach is proved. Numerical results are also presented. 相似文献
104.
Construction of Modified Carbon Paste Electrode for Highly Sensitive Simultaneous Electrochemical Determination of Trace Amounts of Copper (II) and Cadmium (II) 下载免费PDF全文
Abbas Afkhami Morteza Soltani‐Shahrivar Hamed Ghaedi Tayyebeh Madrakian 《Electroanalysis》2016,28(2):296-303
A chemically modified electrode was constructed for rapid, simple, accurate, selective and highly sensitive simultaneous determination of Cu(II) and Cd(II) using square wave anodic stripping voltammetry. The electrode was prepared by incorporation of SiO2 nanoparticles, coated with a newly synthesized Schiff base, in carbon paste electrode. The limit of detection was found to be 0.28 ng mL?1 and 0.54 ng mL?1 for Cu(II) and Cd(II), respectively. The proposed chemically modified electrode was used for the determination of copper and cadmium in several foodstuffs and water samples. 相似文献
105.
Abdol Reza Hajipour Morteza Karimzadeh Sirous Ghorbani Hossein Farrokhpour Alireza Najafi Chermahini 《Structural chemistry》2016,27(5):1345-1362
Electronic structures of allophanic acid were studied using MP2/6-311++G(d,p) level of theory. Five most stable tautomers were selected and stability of them was studied in detail. Obtained data showed that tautomer 1 having hydrogen atom in the central nitrogen N3 and also in a trans conformation of carbonyl and amino functional groups becomes the most stable one. Then, interconversion of these tautomers to each other was investigated step by step through internal rotation and proton transfer routes. Results indicated that movement of protons determines rate-determining step of all paths A–E. Effects of different solvents were carefully surveyed for each tautomer, and among investigated solvents, water made slight stabilization. Activation barrier for proton exchange assisted by one water molecule and one formic acid molecule was also studied, separately. Both molecules had a great influence on lowering barrier especially for proton transfer routes. Comparative MP2 study showed that the barrier will be lowered much more when acid-assisted proton exchange takes place. 相似文献
106.
Morteza?MoradiEmail author Ali?Aghakhani Mohammad?Javad?Eshraghi 《Structural chemistry》2016,27(2):535-542
Electrical sensitivity of a boron carbon nanotube (B2CNT) was examined toward carbon monoxide (CO) molecule by using dispersion-corrected density functional theory calculations. It was found that CO is weakly adsorbed on the tube, releasing energy of 3.5–4.1 kcal/mol, and electronic properties of the tube are not significantly changed. To overcome this problem, boron and carbon atoms of the tube were substituted by aluminum and silicon atoms, respectively. Although both Al and Si doping make the tube more reactive and sensitive to CO, Si doping seems to be a better strategy to manufacture CO chemical sensors due to the higher sensitivity without deformation of nanotube structure after adsorption procedure. Moreover, it was shown that some interference molecules such as H2O, H2S and NH3 cannot significantly change the electronic properties of B2CNT. Therefore, the Si-doped tube might convert the presence of CO molecules to electrical signal. 相似文献
107.
Kazem Barati William Clegg Mohammad Hossein Habibi Ross W. Harrington Arash Lalegani Morteza Montazerozohori 《Acta Crystallographica. Section C, Structural Chemistry》2016,72(3):239-242
Transition metal complexes of Schiff base ligands have been shown to have particular application in catalysis and magnetism. The chemistry of copper complexes is of interest owing to their importance in biological and industrial processes. The reaction of copper(I) chloride with the bidentate Schiff base N,N′‐bis(trans‐2‐nitrocinnamaldehyde)ethylenediamine {Nca2en, systematic name: (1E,1′E,2E,2′E)‐N,N′‐(ethane‐1,2‐diyl)bis[3‐(2‐nitrophenyl)prop‐2‐en‐1‐imine]} in a 1:1 molar ratio in dichloromethane without exclusion of air or moisture resulted in the formation of the title complex μ‐chlorido‐μ‐hydroxido‐bis(chlorido{(1E,1′E,2E,2′E)‐N,N′‐(ethane‐1,2‐diyl)bis[3‐(2‐nitrophenyl)prop‐2‐en‐1‐imine]‐κ2N,N′}copper(II)) dichloromethane sesquisolvate, [Cu2Cl3(OH)(C20H18N4O4)2]·1.5CH2Cl2. The dinuclear complex has a folded four‐membered ring in an unsymmetrical Cu2OCl3 core in which the approximate trigonal bipyramidal coordination displays different angular distortions in the equatorial planes of the two CuII atoms; the chloride bridge is asymmetric, but the hydroxide bridge is symmetric. The chelate rings of the two Nca2en ligands have different conformations, leading to a more marked bowing of one of the ligands compared with the other. This is the first reported dinuclear complex, and the first five‐coordinate complex, of the Nca2en Schiff base ligand. Molecules of the dimer are associated in pairs by ring‐stacking interactions supported by C—H…Cl interactions with solvent molecules; a further ring‐stacking interaction exists between the two Schiff base ligands of each molecule. 相似文献
108.
Morteza Hosseini Freshteh Khaki Ehsan Shokri Hossein Khabbaz Mehdi Dadmehr Mohammad Reza Ganjali Mina Feizabadi Davood Ajloo 《Journal of fluorescence》2017,27(6):2059-2068
A novel sensitive method for detection of DNA methylation was developed with thioglycollic acid (TGA)-capped CdTe quantum dots (QDs) as fluorescence probes. Recognition of methylated DNA sites would be useful strategy due to the important roles of methylation in disease occurrence and developmental processes. DNA methylation occurs most often at cytosine-guanine sites (CpG dinucleotides) of gene promoters. The QDs significantly interacted with hybridized unmethylated and methylated DNA. The interaction of CpG rich methylated and unmethylated DNA hybrid with quantum dots as an optical probe has been investigated by fluorescence spectroscopy and electrophoresis assay. The fluorescence intensity of QDs was highly dependent to unmethylated and methylated DNA. Specific site of CpG islands of Adenomatous polyposis coli (APC), a well-studied tumor suppressor gene, was used as the detection target. Under optimum conditions, upon the addition of unmethylated dsDNA, the fluorescence intensity increased in linear range from 1.0?×?10??10 to 1.0?×?10??6M with detection limit of 6.2?×?10??11 M and on the other hand, the intensity of QDs showed no changes with addition of methylated dsDNA. We also demonstrated that the unmethylated and methylated DNA and QDs complexes showed different mobility in electrophoresis assay. This easy and reliable method could distinguish between methylated and unmethylated DNA sequences. 相似文献
109.
Ali Ramazani Amir Tofangchi Mahyari Morteza Rouhani Aram Rezaei 《Tetrahedron letters》2009,50(40):5625-5627
Reaction of an isocyanide with an iminium ion intermediate, formed by reaction between an electron-poor 2-hydroxybenzaldehyde derivative and a secondary amine in the presence of silica gel proceeds smoothly at room temperature to afford benzo[b]furan derivatives in high yields. 相似文献
110.
Farough Nasiri Morteza Bidar Bahareh Atashkar 《Monatshefte für Chemie / Chemical Monthly》2009,140(4):463-466
Abstract The reaction between dibenzoylacetylene and enol systems, such as acetylaceton or cyclohexane-1,3-dione in the presence of
triphenylphosphine in THF/H2O, leads to 4-acetyl-3-benzoyl-1-phenyl-1,5-hexanedione and 2-hydroxy-3-(2-oxo-2-phenylethyl)-2-phenyl-3,5,6,7-tetrahydro-1-benzofuran-4(2H)-one. Subsequently, these compounds undergo cyclization and elemination reactions in acidic dichloromethane at room temperature
to produce known highly functionalized furan derivatives.
Graphical abstract
相似文献