全文获取类型
收费全文 | 293篇 |
免费 | 19篇 |
专业分类
化学 | 176篇 |
晶体学 | 2篇 |
力学 | 34篇 |
数学 | 27篇 |
物理学 | 73篇 |
出版年
2024年 | 3篇 |
2023年 | 1篇 |
2022年 | 17篇 |
2021年 | 23篇 |
2020年 | 14篇 |
2019年 | 10篇 |
2018年 | 7篇 |
2017年 | 7篇 |
2016年 | 15篇 |
2015年 | 24篇 |
2014年 | 21篇 |
2013年 | 21篇 |
2012年 | 25篇 |
2011年 | 30篇 |
2010年 | 24篇 |
2009年 | 17篇 |
2008年 | 9篇 |
2007年 | 10篇 |
2006年 | 3篇 |
2005年 | 4篇 |
2004年 | 9篇 |
2003年 | 4篇 |
2002年 | 3篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1996年 | 1篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1985年 | 1篇 |
1938年 | 1篇 |
排序方式: 共有312条查询结果,搜索用时 15 毫秒
61.
MUHAMMAD Nadeem Arshad HASSAN M.Faidallah ABDULLAH M.Asiri OSMAN I.Osman FAISAL M.S.Aqlan 《结构化学》2019,(3)
Pyridinone derivatives are of great interest in medicinal chemistry where they were found to be potent to various diseases. Their metal complexes added more value to their applications. Here, we have synthesized two 2-pyridinone derivatives(3-cyano-4-(4-hydroxy-3-methoxyphenyl)-6-phenyl-2(1 H)-pyridinone and 3-cyano-4-chlorophenyl-6-(4-tolyl)-2(1 H)-pyridinone) using one-pot multicomponent system. They were well characterized using spectroscopic techniques like nuclear magnetic resonance(NMR-1 H 13 C), Fourier transform infrared(FT-IR) and UV/Vis spectroscopy. The final structures were determined using single-crystal X-ray diffraction technique which helps us to determine their geometries. Density functional theory(DFT) and time-dependent density functional theory(TD-DFT) with suitable basis-sets of calculations have correctly simulated these spectroscopic parameters. The intramolecular charge transfer(ICT) of both substrates has been discussed using natural bond orbital(NBO) technique. Molecular electrostatic potential(MEP) surfaces showed their reactive locations for intermolecular charge transfer. Compared to p-nitroaniline(pNA), both substrates were shown to have substantial molecular hyperpolarizability. 相似文献
62.
63.
The kinetic parameters of photoinduced electron transfer reaction of two phenothiazine dyes, methylene blue and methylene green with titanium trichloride, were determined in water and different aqueous-alcoholic solvents at different acidities by using a specially designed optical system. The rate of photoinduced electron transfer reaction was measured by determining the quantum yield of the reaction. The methylene green had a higher reactivity as compared to methylene blue with titanium trichloride. The graphical analysis showed that the reaction of dye with titanium trichloride follows pseudo–first-order kinetics. A reaction mechanism was proposed by considering the different excited states of dye and their possible interaction with the solvent and titanium trichloride. The different steps in the reaction mechanism were taken into consideration for deriving rate equations, which were used to determine the different rate constants in the reaction mechanism in different solvents. 相似文献
64.
Roheena Abdullah Wajeeha Zafar Muhammad Nadeem Mehwish Iqtedar Shagufta Naz Quratulain Syed 《Natural product research》2015,29(12):1133-1138
This study deals with optimisation of cultural conditions for enhanced production of cellulase by Bacillus PC-BC6 and its mutant derivative Bacillus N3. Influence of different variables including incubation time, temperature, inoculum size, pH, nitrogen sources and metal ions has been studied. The optimum conditions for cellulase production were incubation period of 72 h, inoculum size 4% incubation temperature 37°C, pH 7, 0.25% ammonium sulphate, 0.2% peptone as inorganic and organic nitrogen source in case of Bacillus PC-BC6. In case of mutant Bacillus N3, optimal conditions were incubation period of 48 h, incubation temperature 37°C, inoculum size 3%, pH 7, 0.2% ammonium chloride and 0.15% yeast extract. Presence of MnSO4 and CaCl2 enhances the enzyme production by Bacillus PC-BC6 and mutant Bacillus N3, respectively. This study was innovative and successful in producing cellulase economically by using cheap indigenous substrate Saccharum spontaneum. 相似文献
65.
In this paper, we have analyzed the Jeffrey fluid with pressure‐dependent viscosity. The equations of Jeffrey fluid model have been modelled when viscosity is a function of pressure. Two types of flow problem, namely, Poiseulle flow and Couette flow have been solved numerically for Jeffrey fluid. The velocity field for different physical parameters has been discussed through graphs. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
66.
67.
68.
Xiao-Jing Liu Chun-Hua Cui Hui-Hui Li Yong Lei Tao-Tao Zhuang Meng Sun Muhammad Nadeem Arshad Hassan A. Albar Tariq R. Sobahi Shu-Hong Yu 《Chemical science》2015,6(5):3038-3043
Hollow alloyed nanoparticles (NPs) represent one kind of promising fuel cell electrocatalyst. However, the formation of single-cavity hollow structures by a dealloying process is quite challenging owing to the random leaching/dissolution of transition metals, surface passivation and the limited diffusion distance of the noble metals. Here we present a facile method to prepare hollow PtPdCu NPs derived from monodisperse alloy NPs by an acetic acid-assisted dealloying process. Here, acetic acid not only acts as a chemical etching agent but also plays an important role in the removal of the residual surfactants for colloidal NPs. Our findings rectify the current knowledge that hollow alloyed NPs cannot be prepared by a dealloying strategy and provide further understanding of the dealloying process in a ternary system. Such unique hollow ternary PtPdCu NPs exhibit outstanding durability and improved catalytic activity toward the oxygen reduction reaction. 相似文献
69.
Shafqat Nadeem Muhammad Khawar Rauf Michael Bolte Saeed Ahmad Syed Ahmed Tirmizi Maliha Asma Abdul Hameed 《Transition Metal Chemistry》2010,35(5):555-561
Palladium(II) bromide complexes of thioamides having the general formulae [PdL2Br2] and [PdL4]Br2 where L = Thiourea (Tu), Methylthiourea (Metu), Dimethylthiourea (Dmtu), Tetramethylthiourea (Tmtu), Imidazolidine-2-thione
(Imt), Mercaptopyridine (Mpy), Mercaptopyrimidine (Mpm) and Thionicotinamide (Tna) were prepared by reacting K2[PdCl4] with KBr and the corresponding thioamides. The complexes were characterized by elemental analysis, IR and NMR spectroscopy,
and one of them, [Pd(Tmtu)4]Br2 (1) by X-ray crystallography. The crystal structure of 1 shows a square-planar coordination environment around the Pd(II) atoms with the average cis and trans S–Pd–S bond angles of 90.0° and 180.0°, respectively. The synthesized complexes were screened for antibacterial effects,
and the results showed that the complexes exhibit significant activities against both gram positive and gram negative bacteria. 相似文献
70.
Iain Coldham Prof. Sophie Raimbault Dr. David T. E. Whittaker Dr. Praful T. Chovatia Dr. Daniele Leonori Jignesh J. Patel Dr. Nadeem S. Sheikh Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(13):4082-4090
Proton abstraction of N‐tert‐butoxycarbonyl‐piperidine (N‐Boc‐piperidine) with sBuLi and TMEDA provides a racemic organolithium that can be resolved using a chiral ligand. The enantiomeric organolithiums can interconvert so that a dynamic resolution occurs. Two mechanisms for promoting enantioselectivity in the products are possible. Slow addition of an electrophile such as trimethylsilyl chloride allows dynamic resolution under kinetic control (DKR). This process occurs with high enantioselectivity and is successful by catalysis with substoichiometric chiral ligand (catalytic dynamic kinetic resolution). Alternatively, the two enantiomers of this organolithium can be resolved under thermodynamic control with good enantioselectivity (dynamic thermodynamic resolution, DTR). The best ligands found are based on chiral diamino‐alkoxides. Using DTR, a variety of electrophiles can be used to provide an asymmetric synthesis of enantiomerically enriched 2‐substituted piperidines, including (after Boc deprotection) the alkaloid (+)‐β‐conhydrine. The chemistry was extended, albeit with lower yields, to the corresponding 2‐substituted seven‐membered azepine ring derivatives. 相似文献