全文获取类型
收费全文 | 359篇 |
免费 | 18篇 |
国内免费 | 4篇 |
专业分类
化学 | 284篇 |
晶体学 | 3篇 |
力学 | 15篇 |
数学 | 33篇 |
物理学 | 46篇 |
出版年
2024年 | 1篇 |
2023年 | 4篇 |
2022年 | 8篇 |
2021年 | 9篇 |
2020年 | 19篇 |
2019年 | 16篇 |
2018年 | 28篇 |
2017年 | 18篇 |
2016年 | 28篇 |
2015年 | 12篇 |
2014年 | 23篇 |
2013年 | 30篇 |
2012年 | 26篇 |
2011年 | 28篇 |
2010年 | 22篇 |
2009年 | 26篇 |
2008年 | 13篇 |
2007年 | 21篇 |
2006年 | 8篇 |
2005年 | 8篇 |
2004年 | 3篇 |
2003年 | 8篇 |
2002年 | 2篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1998年 | 1篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1989年 | 1篇 |
1984年 | 1篇 |
1982年 | 3篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有381条查询结果,搜索用时 15 毫秒
61.
62.
Hübner J Taheri R Melchior D Kling HW Gäb S Schmitz OJ 《Analytical and bioanalytical chemistry》2007,388(8):1755-1762
Multidimensional gas-chromatographical analysis of various tensides of natural or synthetic origin in cosmetic products is
demonstrated. Comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry allows the qualitative
and quantitative determination of alkyl polyglucosides (AG), fatty alcohol ethoxylates (FAEO), fatty alcohol sulfates (FAS),
fatty alcohol ether sulfates (FAES) and cocamidopropyl betaines (CAPB) in shower gel and cleaning agents. The samples were
aliquoted in two parts. The first part was silylated, diluted and analysed; then, in order to detect anionic tensides (FAES,
FAS) too, the second aliquot was hydrolysed before being silylated for analysis. Because of their amphoteric character, the
betaines can only be analysed by gas chromatography after thermal decomposition in the injector, which leads to the corresponding
amidoamines among other products. 相似文献
63.
M. Mozaffari M. Taheri J. Amighian 《Journal of magnetism and magnetic materials》2009,321(9):1285-1289
A series of barium hexaferrite nanoparticles (BaO·nFe2O3) with different n values were prepared by the sol-gel method, using goethite and Ba carbonate as raw materials. Phase identification of the samples was investigated by X-ray diffraction (XRD). XRD investigations show that the samples with n=5 and calcined at temperatures higher than 875 °C are single-phase Ba ferrite. An average crystallite size of 22 nm was obtained for the single-phase sample with minimum calcining temperature of 875 °C, using the Scherrer's formula. The morphology of the samples was checked by transmission electron microscope (TEM) and magnetic properties were measured by a sensitive permeameter. The results show that the samples have nonzero coercivities, which shows the particle size are not less than the critical size of Ba ferrite and then are not superparamagnet. 相似文献
64.
K. Taheri M. Chamsaz G. H. Rounaghi M. Ansari Fard 《Journal of inclusion phenomena and macrocyclic chemistry》2009,63(1-2):43-52
The complexation reactions between some rare earth metal cations (Ln; Y3+, La3+ and Ce3+) with 18-crown-6 (18C6), dicyclohexyl-18-crown-6 (DC18C6), benzo-18-crown-6 (B18C6) and decyl-18-crown-6 (Dec18C6), have been studied in methanol–acetonitrile (MeOH–AN) and methanol–water (MeOH–H2O) binary mixtures using a competitive spectrophotometric method. 2-(2-thiazolylazo)-4-methyl phenol (TAC or L) was used as colorimetric complexant. It was found that the selectivity order of TAC for Ln cations is highly changed with changing the composition of the mixed solvents. Moreover, as the concentration of acetonitrile increases in MeOH–AN binary mixture, the stability of Ln–TAC complexes increases and passes through a maximum at a certain mole fraction of acetonitrile. In addition, the stability of Ln–crown ether complexes increases with increasing the concentration of methanol in MeOH–H2O and acetonitrile in MeOH–AN binary solutions. A non linear behaviour was observed for variation of stability constants of all complexes versus the composition of the mixed solvents. The results show that 18C6 generally forms more stable complexes with La3+ and Ce3+ cations than DC18C6 in methanol and MeOH–H2O binary mixtures, while this sequence is reversed in the methanol-acetonitrile binary mixtures which are rich with respect to acetonitrile. 相似文献
65.
F. Toutounian J. Saberi-Nadjafi S. H. Taheri 《Journal of Mathematical Modelling and Algorithms》2009,8(4):425-443
Solving systems of nonlinear equations is perhaps one of the most difficult problems in all numerical computation. Although
numerous methods have been developed to attack this class of numerical problems, one of the simplest and oldest methods, Newton’s
method is arguably the most commonly used. As is well known, the convergence and performance characteristics of Newton’s method
can be highly sensitive to the initial guess of the solution supplied to the method. In this paper a hybrid scheme is proposed,
in which the Electromagnetic Meta-Heuristic method (EM) is used to supply a good initial guess of the solution to the finite
difference version of the Newton-GMRES method (NG) for solving a system of nonlinear equations. Numerical examples are given
in order to compare the performance of the hybrid of the EM and NG methods. Empirical results show that the proposed method
is an efficient approach for solving systems of nonlinear equations. 相似文献
66.
Davarani SS Najafi NM Ramyar S Masoumi L Shamsipur M 《Chemical & pharmaceutical bulletin》2006,54(7):959-962
Electrochemical oxidation of catechol and some 3-substituted catechols (1a--c) has been studied in the presence of 2-chloro-5,5-dimethyl-1,3-cyclohexanedione (3) in aqueous solution using cyclic voltammetry and controlled-potential coulometry. The results indicate that the quinones derived from catechols (1a--c) participate in a Michael addition reaction with 2-chloro-5,5-dimethyl-1,3-cyclohexanedione (3) with consumption of only two electrons per molecule of (1a--c) to from the corresponding benzoforans (10a--c). The electrochemical synthesis of benzofurans has been successfully performed at a carbon rod electrode and in an undivided cell with high yields and purity. 相似文献
67.
Some 1-(6-chloroquinoxalin-2-yl)-2-[4-(trifluoromethyl)-2,6-dinitrophenyl] hydrazine derivatives have been synthesized via both conventional and microwave assisted organic synthesis(MAOS) methods. The MAOS method is more effective on synthesizing these compounds than the conventional method in regard to the higher chemical yields of products(76%-98%) and the shorter reaction time(1-15 min). 相似文献
68.
Ali Asghar Mohammadi Salman Taheri Arman Amini Reza Ahdenov 《Molecular diversity》2018,22(4):999-1006
Triamide derivatives have been synthesized in good yields in a novel, one-pot, five-component, and efficient process by the reaction of Z-oxazolone, water, primary amines, aldehydes, isocyanides, in the presence of catalytic amount of KAl(SO4)2·12H2O (alum) as a non-toxic, reusable, inexpensive, and easily available reagent via Ugi reaction in aqueous solution. 相似文献
69.
A shock control bump (SCB) is a flow control method that uses local small deformations in a flexible wing surface to considerably reduce the strength of shock waves and the resulting wave drag in transonic flows. Most of the reported research is devoted to optimization in a single flow condition. Here, we have used a multi-point adjoint optimization scheme to optimize shape and location of the SCB. Practically, this introduces transonic airfoils equipped with the SCB that are simultaneously optimized for different off-design transonic flight conditions. Here, we use this optimization algorithm to enhance and optimize the performance of SCBs in two benchmark airfoils, i.e., RAE-2822 and NACA-64-A010, over a wide range of off-design Mach numbers. All results are compared with the usual single-point optimization. We use numerical simulation of the turbulent viscous flow and a gradient-based adjoint algorithm to find the optimum location and shape of the SCB. We show that the application of SCBs may increase the aerodynamic performance of an RAE-2822 airfoil by 21.9 and by 22.8 % for a NACA-64-A010 airfoil compared to the no-bump design in a particular flight condition. We have also investigated the simultaneous usage of two bumps for the upper and the lower surfaces of the airfoil. This has resulted in a 26.1 % improvement for the RAE-2822 compared to the clean airfoil in one flight condition. 相似文献
70.
In continuation of our investigation of characteristics and thermodynamic properties of the i‐motif 5′‐d[(CCCTAA)3CCCT)] upon insertion of intercalating nucleotides into the cytosine‐rich oligonucleotide, this article evaluates the stabilities of i‐motif oligonucleotides upon insertion of naphthalimide (1H‐benzo[de]isoquinoline‐1,3(2H)‐dione) as the intercalating nucleic acid. The stabilities of i‐motif structures with inserted naphthalimide intercalating nucleotides were studied using UV melting temperatures (Tm) and circular dichroism spectra at different pH values and conditions (crowding and non‐crowding). This study indicated a positive effect of the naphthalimide intercalating nucleotides on the stabilities of the i‐motif structures compared to the wild‐type structure which is in contrast to a previous observation for a pyrene‐intercalating nucleotide showing a decrease in Tm values. 相似文献