全文获取类型
收费全文 | 80篇 |
免费 | 6篇 |
国内免费 | 5篇 |
专业分类
化学 | 68篇 |
晶体学 | 5篇 |
力学 | 1篇 |
综合类 | 1篇 |
数学 | 8篇 |
物理学 | 8篇 |
出版年
2022年 | 1篇 |
2020年 | 3篇 |
2019年 | 3篇 |
2018年 | 4篇 |
2017年 | 2篇 |
2016年 | 3篇 |
2015年 | 4篇 |
2014年 | 3篇 |
2013年 | 4篇 |
2012年 | 6篇 |
2011年 | 3篇 |
2010年 | 3篇 |
2008年 | 2篇 |
2007年 | 3篇 |
2006年 | 3篇 |
2005年 | 3篇 |
2004年 | 1篇 |
2003年 | 3篇 |
2002年 | 6篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1998年 | 1篇 |
1995年 | 1篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1990年 | 1篇 |
1989年 | 8篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1973年 | 1篇 |
1967年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有91条查询结果,搜索用时 31 毫秒
51.
本文定义了一个新的代数系{R×C×S}这是一个有环结构的自由R-模,并讨论了结构性质与R的性质. 相似文献
52.
The electrochemical oxidation of 3,4-ethylenedioxythiophene (EDOT) on platinum is studied in electrolyte solutions containing hydroxypropyl-β-cyclodextrin (HP-β-CD). HP-β-CD is found to increase the solubility of EDOT up to a concentration of 0.026 M in aqueous solutions. Addition of HP-β-CD (0.1 M) produces a slight red shift of the EDOT main absorption band from 254.9 to 257.7 nm and an increase of the HP-β-CD concentration decreases the absorption coefficient, max to 6150 l mol−1 cm−1 in the UV–vis region, indicating complex formation. The cyclic voltammetric response of EDOT in 0.1 M aqueous LiClO4 solutions consists of an ill-defined wave (P1) and an adsorption peak (P2). Contrary to the case of oxidation in acetonitrile medium, a post-peak is observed in the voltammograms of EDOT electro-oxidation in aqueous LiClO4 solutions due to the adsorption of the oxidized EDOT species. A gradual reduction of the peak current of P2 with increasing [HP-β-CD] and its total disappearance at high [HP-β-CD] suggest complex formation between HP-β-CD and EDOT√+ and also the peak P2 to be due to adsorption of EDOT√+ species. The experiments intended to show the effect of ‘pre-adsorbed’ HP-β-CD on EDOT oxidation led to the conclusion that adsorbed HP-β-CD also solubilizes EDOT at the electrode surface. The CV behaviour of EDOT in HP-β-CD is discussed in comparison with that in sodium dodecylsulfate micellar solutions. Addition of increasing amounts of HP-β-CD shifts P1 positively and P2 negatively while also suppressing P2 totally and reducing the peak current of P1 to a significant extent. At a higher concentration of HP-β-CD, viz. 0.05 M, a peak appears at 1.29 V as a result of the above two opposing effects of CD on the peak potentials of P1 and P2. This resultant peak (Pcomposite) is more positive relative to the position of P1 observed in the absence of HP-β-CD. The positive shift of the peak and peak current reduction indicate that EDOT (or an oxidized EDOT species) possibly interacts with the outer nucleophilic part of HP-β-CD. The electro-oxidation processes occurring at P1 and P2 are explained using an oligomeric approach, in which the electrochemical reactions are coupled to chemical reactions or adsorption of the oxidized species. Potential cycling of the platinum electrode in solutions containing 0.026 M EDOT+0.05 M HP-β-CD+0.1 M LiClO4 between −0.5 and 1.2 V yields an adherent and smooth polymer film of poly(ethylenedioxythiophene), as shown in the SEM examination. In situ resistance measurements carried out with the polymer films in the electroactive region show a minimum resistance in the potential range of 0.3–0.4 V. Even the electrochemically-reduced films are found to possess some residual electrical conductivity. 相似文献
53.
The first total synthesis of (±)-lagopodin A and a formal total synthesis of enokipodins A and B is described. The requisite precursors containing two vicinal quaternary carbon atoms were assembled employing Claisen rearrangement and an RCM reaction as key steps starting from 2,5-dimethoxy-4-methylacetophenone. 相似文献
54.
S. Viveka G. Vasantha Dinesha S. Naveen N. K. Lokanath 《Molecular Crystals and Liquid Crystals》2016,629(1):135-145
The present study describes the synthesis, spectroscopic, and single crystal X-ray structural analysis of ethyl 5-methyl-1-phenyl-1H-pyrazole-4-carboxylate. The pyrazole ester of formula [C13H14N2O2] was prepared from the three-component one-pot condensation reaction of ethyl acetoacetate, N,N-dimethyldimethoxymethanamine, and phenyl hydrazine. The product was crystallized by using ethanol as solvent. The structure of the compound was confirmed by elemental analysis, Fourier transforms infrared (IR), thermogravimetric analysis, UV-visible (UV-Vis), 1H NMR, and single-crystal X-ray diffraction studies. The gas-phase molecular geometry and the electronic structure-property of the molecule were calculated at the density functional theory. The frontier molecular orbitals, theoretical UV-Vis, and IR stretching vibrations were also reported. The compound crystallizes in the monoclinic system with the space group P21/c and Z = 4. The unit cell parameters are a = 12.141(3) Å, b = 13.934(4) Å, c = 7.2777(18) Å, and β = 97.816(14)0. The structure is stabilized by an intermolecular interaction of type C-H···O and the structure also involves C-H···π interactions. 相似文献
55.
B. Shekhar P. Vasantha B. Sathish Kumar P.V. Anantha Lakshmi V. Ravi Kumar S. Satyanarayana 《应用有机金属化学》2019,33(9)
Three chromium ternary complexes with metformin (met) as a primary ligand and bipyridine (bipy) or ortho‐phenylenediamine (opda) or ortho‐phenanthroline (phen) as secondary ligand were synthesized. These complexes [Cr (Cl)2(Hmet)(bipy)]‐( 1 ), [Cr (Cl)2(Hmet)(opda)]‐( 2 ) and [Cr (Cl)2(Hmet)(phen)]‐( 3 ) were characterized by LC–MS, elemental analysis, molar conductance, thermal analysis, infrared spectroscopy, electronic spectroscopy. The geometrical structures have been found to be octahedral. Degradation pattern of the compounds is shown by thermal studies. The Kinetic parameters‐ energy of activation (Ea), enthalpy (ΔH), entropy (ΔS) and free energy changes (ΔG) have been determined by thermogravimetric data. Coats‐Redfern integration method with thirteen kinetic models was used to calculate the kinetic and thermodynamic parameters for the degradation of all the complexes. The stabilities of the complexes were obtained from their molecular orbital structures from which the quantum chemical parameters were calculated using the HOMO‐LUMO energies. UV–Visible absorption, fluorescence, and viscosity measurements have been conducted to assess the interaction of the complexes with CT DNA. The complexes showed absorption hyperchromism in its UV–Vis spectrum with DNA. The binding constants Kb from UV–Vis absorption studies were 3.1x104, 4.4x104, 5x104 M?1 for 1, 2, 3 respectively and Stern–Volmer quenching constants (Ksq) from fluorescence studies were 0.137, 0.532, 0.631 for 1, 2, 3 respectively. Finally, viscosity measurements revealed that the binding of the complexes with CT‐DNA could be surface binding, mainly due to groove binding. The activity of complexes towards DNA cleavage decrease in the order of 3 > 2 > 1.The light switching properties of the complexes were also evaluated. The complexes were docked in to B‐DNA sequence, 5′(D*AP*CP*CP*GP*AP*CP*GP*TP*CP*GP*GP*T)‐3′ retrieved from protein data bank (PDB ID: 423D), using Discovery Studio 2.1 software. 相似文献
56.
57.
A simple, highly repeatable and reproducible method for the estimation of Paclitaxel (TAX) in micro volume amounts of rat plasma is successfully developed and validated. The extraction procedure using 800 μL of ice-cold acetonitrile is very simple and economical with high sensitivity. The rectangular ratiograms and purity curve demonstrate the selectivity of the method. The validation and stability results show that propylparaben (PP) is a suitable internal standard (resolution 7.70 ± 0.15 min) for the estimation of TAX in micro volume rat plasma. TAX and PP are separated by isocratic reversed-phase high-performance liquid chromatography with diode array UV method with a retention time of 8.0 ± 0.25 and 5.3 ± 0.15 min, respectively, with a total run time of 10 min. The system suitability results show that the method has good reproducibility. The stability of TAX is well studied in rat plasma, and the % RSD of all stability studies of TAX are well within the acceptable range of ± 20 % at the lower limit of quantitation (LLOQ) and ± 15% at all quality control levels. The limit of detection (LOD) and LLOQ of the method are 5 and 10 ng/mL, respectively. This rapid method is successfully used to study the i.v pharmacokinetic of TAX at 10 mg/kg in wistar rats, and drug concentration is detected up to 24 h. 相似文献
58.
Andiappan Murugan Vasantha Krishna KadambarSreekanth Bachu M. Rajashekher ReddyVenkatarao Torlikonda Sulur G. ManjunathaSridharan Ramasubramanian Sudhir NambiarGareth P. Howell Jane Withnall 《Tetrahedron letters》2012,53(43):5739-5741
A simple and efficient procedure for the regio-selective synthesis of 1,2-aminoalcohols from terminal epoxides and chlorohydrins by using NaHMDS as the source of amine is reported. The wider scope and utility of this method is demonstrated. 相似文献
59.
We numerically investigate the dynamics of soliton propagation at 850 nm in chloroform filled liquid core photonic crystal fiber (LCPCF) by using both finite element method (FEM) and split step Fourier method (SSFM). We propose a novel chloroform filled PCF structure that operates as a single mode at 850 nm featuring an enhanced dispersion and nonlinearity for efficient soliton propagation with low input pulse energy and low loss over small distances. We adopt the projection operator method (POM) to derive the pulse parameter equations which clearly describes the impact of fourth order dispersion on the pulse propagation in the proposed PCF. To analyse the quality of the pulse, we perform the stability analysis of pulse propagation numerically and compare our results of the newly designed chloroform filled PCF with that of standard silica PCF. From the stability analysis, we infer that the soliton pulse propagation in modified chloroform filled PCF is highly stable against the perturbation. 相似文献
60.
A Highly Sensitive and Selective Multiwall Carbon Nanotubes/Nafion/Au Microarrays Electrode for Dopamine Determination 下载免费PDF全文
This work presents the fabrication of Nafion (Nf) or Nafion/Multiwalled Carbon Nanotubes (Nf/MWCNTs) modified gold microarray (Au‐µA) and macro‐(Au‐M)electrode biosensors. The surface morphologies of the above electrodes were examined using SEM. The catalytic properties of the above electrodes towards dopamine were tested using square wave voltammetric technique. The Nf/MWCNT/Au‐µA electrode exhibited a wide range (0.1–1000 nM) of linearity among the other electrodes. The LOD of Nf/MWCNT/Au‐µA electrode was 50 pM for dopamine in the presence of 5000 µM ascorbic acid. Therefore, the Nf/MWCNT/Au‐µA biosensor was applied for the determination of dopamine in human serum. 相似文献