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排序方式: 共有157条查询结果,搜索用时 15 毫秒
101.
Muthuvel A. Jothibas M. Manoharan C. Jayakumar S. Johnson 《Research on Chemical Intermediates》2020,46(5):2705-2729
Research on Chemical Intermediates - In the present study, biosynthesized CeO2-NPs using Solanum nigrum leaf extract were compared with chemically synthesized one. The synthesized CeO2-NPs were... 相似文献
102.
L. Padmaja C. Ravikumar D. Sajan I. Hubert Joe V. S. Jayakumar G. R. Pettit O. Faurskov Nielsen 《Journal of Raman spectroscopy : JRS》2009,40(4):419-428
Combretastatin‐A2 (CA2), a potential anticancer drug in advanced preclinical development, is extracted from the medicinal plant C ombretum caffrum. The NIR‐FT Raman and FT‐IR spectral studies of the molecule were carried out and a b initio calculations performed at the B3LYP/6‐31G(d) level to derive the equilibrium geometry as well as the vibrational wavenumbers and intensities of the spectral bands. The vibrational analysis showed that the molecule has a similar geometry as that of c is‐stilbene, and has undergone steric repulsion resulting in twisting of the phenyl ring with respect to the ethylenic plane. Vibrational analysis was used to investigate the lowering of the stretching modes, and enhancement of infrared band intensities of the C–H stretching modes of Me2 may be attributed to the electronic effects caused by back‐donation and induction from the oxygen atom. Analysis of phenyl ring modes shows that the CA2 stretching mode 8 and the aromatic C–H in‐plane bending mode are equally active as strong bands in both IR and Raman spectra, which can be interpreted as the evidence of intramolecular charge transfer (ICT) between the OH and OCH3groups via conjugated ring path and is responsible for bioactivity of the molecule. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
103.
M. Snehalatha I. Hubert Joe C. Ravikumar V. S. Jayakumar 《Journal of Raman spectroscopy : JRS》2009,40(2):176-182
Fourier transform Raman and IR as well as UV–visible spectra of the phenothiazine dye Azure A chloride, 3‐amino‐7‐(dimethylamino) phenothiazin‐5‐ium chloride were recorded and analyzed. The spectral interpretation was done following full structure optimization and vibrational wavenumber calculations based on the density functional theory (DFT) using the standard B3LYP/6‐31G(d) basis set. The N H stretching wavenumber is found to be lowered owing to intermolecular N H···S hydrogen bonding. The downshift of C H stretching wavenumber is discussed. The first hyperpolarizability of the dye is calculated. Time‐dependent density functional theory (TD‐DFT) calculations of electronic spectra were performed on the optimized structure and compared with the experimental UV–visible spectrum. The atomic net charges of the molecule reveal the M effect of the nitrogen atoms in the molecule. Stability of the molecule arising from hyperconjugative interactions leading to its nonlinearity and bioactivity, charge delocalization and mesomeric effects have been analyzed using natural bond orbital (NBO) analysis. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
104.
S.K. Sharma P.K. Pujari K. Sudarshan D. Dutta M. Mahapatra S.V. Godbole O.D. Jayakumar A.K. Tyagi 《Solid State Communications》2009,149(13-14):550-554
We report results on positron annihilation spectroscopic (PAS) studies using lifetime and coincidence Doppler broadening techniques in zinc oxide (ZnO) nanoparticles (4 to 40 nm) synthesized by solid state pyrolytic reaction followed by annealing in the temperature range of 200 °C to 800 °C. Positron lifetime in the nanoparticles are observed to be higher than bulk lifetime in all the cases. Theoretical calculation of lifetime indicates the presence of either Zn or (Zn, O) vacancy clusters which migrate and anneal out at high temperature. Comparison of ratio spectra from coincidence Doppler broadening measurement and calculated electron momentum distribution indicates the presence of either Zn or (Zn, O) vacancies. In addition, photoluminescence (PL) measurements have been carried out to examine the role of defects on the intensity of emission in the visible region. 相似文献
105.
Jayakumar Beena Divya Kontham Kulangara Varsha Kesavan Madhavan Nampoothiri 《Applied biochemistry and biotechnology》2012,167(5):1314-1324
Five newly isolated lactic acid bacteria were identified as Weissella cibaria, Enterococcus faecium, and three different strains of Lactobacillus plantarum by 16S rRNA sequencing. Essential probiotic requirements of these isolates such as tolerance to phenol, low pH, high sodium chloride, and bile salt concentration were checked. Efficiency in adherence to mucin and hydrophobicity of the bacterial cell were also evaluated by in vitro studies. Antimicrobial activities against some pathogens were tried, and the sensitivity of these strains against 25 different antibiotics was also checked. Further studies revealed Weissella and Enterococcus as substantial producers of folic acid. Folate is involved as a cofactor in many metabolic reactions, and it has to be an essential component in the human diet. The folate level in the fermented samples was determined by microbiological assay using Lactobacillus casei NCIM 2364 as indicator strain. The three strains of L. plantarum showed significant inhibitory activity against various fungi that commonly contaminate food stuffs indicating their potential as a biopreservative of food material. 相似文献
106.
B.B. Lahiri S. Bagavathiappan P.R. Reshmi John Philip T. Jayakumar B. Raj 《Infrared Physics & Technology》2012,55(2-3):191-199
Active (lock-in and pulsed) thermography technique is used to quantify defect features in specimens of glass fiber reinforced polymer, high density rubber, low density rubber and aluminum bonded low density rubber with artificially produced defects. The relationship between phase contrast and thermal contrast with defect features are examined. Using lock-in approach, the optimal frequencies for different specimens are determined experimentally. It is observed that with increasing defect depth, the phase contrast increases while the thermal contrast decreases. Defects with radius to depth ratio greater than 1.0 are found to be discernible. The phase difference between sound and defective region as a function of square root of excitation frequency for glass fiber reinforced polymer specimen is found to be in good agreement with the predictions of Bennet and Patty model [1]. Further, using pulsed thermography, the defects depth could be measured accurately for glass fiber reinforced polymer specimen from the thermal contrast using the analytical approach of Balageas et al. [2]. 相似文献
107.
M. Jayakumar K. A. Venkatesan T. G. Srinivasan P. R. Vasudeva Rao 《Journal of Radioanalytical and Nuclear Chemistry》2010,284(1):79-85
The electrochemical behavior of ruthenium(III) and rhodium(III) in nitric acid medium has been studied at platinum and stainless
steel electrodes by cyclic voltammetry. The cyclic voltammograms consisted of surge in cathodic current occurring at potentials
of −0.13 V (Vs. Pd) and −0.15 V (Vs. Pd), which culminates into peaks at −0.47 V and −0.5 V due to the reductions of Ru(III)
and Rh(III) to their metallic forms, respectively. Electrodeposition was carried out at stainless steel electrode and unlike
palladium, the recovery of ruthenium and rhodium was limited to ~4% and ~14%, respectively. However, a different scenario
was observed in case of electrodeposition from a ternary solution containing all these platinum metals. Ruthenium and rhodium
deposited underpotentially in the presence of palladium and the recovery of ~20% and ~5% was observed for ruthenium and rhodium,
respectively. Evolution of RuO4 at the anode and deposition of RuO2 in the anodic side was observed in all cases during electrolysis of ruthenium(III) containing solutions. 相似文献
108.
Hamed Ashraf M. Shabana Ahmed A. Jayakumar Paramsothy Letherwood Michael D. 《Nonlinear dynamics》2011,66(4):809-824
Existing multibody system (MBS) algorithms treat articulated system components that are not rigidly connected as separate
bodies connected by joints that are governed by nonlinear algebraic equations. As a consequence, these MBS algorithms lead
to a highly nonlinear system of coupled differential and algebraic equations. Existing finite element (FE) algorithms, on
the other hand, do not lead to a constant mesh inertia matrix in the case of arbitrarily large relative rigid body rotations.
In this paper, new FE/MBS meshes that employ linear connectivity conditions and allow for arbitrarily large rigid body displacements
between the finite elements are introduced. The large displacement FE absolute nodal coordinate formulation (ANCF) is used to obtain linear element connectivity conditions in the case of large relative rotations between the finite
elements of a mesh. It is shown in this paper that a linear formulation of pin (revolute) joints that allow for finite relative
rotations between two elements connected by the joint can be systematically obtained using ANCF finite elements. The algebraic
joint constraint equations, which can be introduced at a preprocessing stage to efficiently eliminate redundant position coordinates,
allow for deformation modes at the pin joint definition point, and therefore, this new joint formulation can be considered
as a generalization of the pin joint formulation used in rigid MBS analysis. The new pin joint deformation modes that are
the result of C
0 continuity conditions, allow for the calculations of the pin joint strains which can be discontinuous as the result of the
finite relative rotation between the elements. This type of discontinuity is referred to in this paper as nonstructural discontinuity in order to distinguish it from the case of structural discontinuity in which the elements are rigidly connected. Because ANCF finite elements lead to a constant mass matrix, an identity generalized
mass matrix can be obtained for the FE mesh despite the fact that the finite elements of the mesh are not rigidly connected.
The relationship between the nonrational ANCF finite elements and the B-spline representation is used to shed light on the
potential of using ANCF as the basis for the integration of computer aided design and analysis (I-CAD-A). When cubic interpolation
is used in the FE/ANCF representation, C
0 continuity is equivalent to a knot multiplicity of three when computational geometry methods such as B-splines are used.
C
2 ANCF models which ensure the continuity of the curvature and correspond to B-spline knot multiplicity of one can also be
obtained. Nonetheless, B-spline and NURBS representations cannot be used to effectively model T-junctions that can be systematically
modeled using ANCF finite elements which employ gradient coordinates that can be conveniently used to define element orientations
in the reference configuration. Numerical results are presented in order to demonstrate the use of the new formulation in
developing new chain models. 相似文献
109.
Manickam Bakthadoss Anthonisamy Devaraj Jayakumar Srinivasan 《Journal of heterocyclic chemistry》2015,52(2):418-424
In this article, a simple method for the synthesis of bis(di(indolyl)aryl)methanes is described. The iodine‐catalyzed (5 mol %) reaction of indoles with various bis(salicylaldehyde) derivatives affords the bis(di(indolyl)aryl)methanes in excellent yields. The reaction works well under mild reaction condition with shorter reaction time. 相似文献
110.
Sayed FN Mandal BP Jayakumar OD Arya A Kadam RM Dixit A Naik R Tyagi AK 《Inorganic chemistry》2011,50(22):11765-11772
A series of Mn-substituted BaMgF(4) samples have been synthesized by a hydrothermal route. X-ray diffraction study reveals that the products are monophasic in nature. Scanning electron microscopy (SEM) and energy-dispersive spectrometry (EDS) studies were carried out to investigate the morphology and stoichiometry for these compounds. X-ray photoelectron spectroscoy (XPS) and electron spin resonance (ESR) studies were done to confirm the oxidation state of dopant ion. Room temperature ferromagnetism was observed on Mn substitution at the Mg site in BaMgF(4) samples. The saturation magnetization increases initially, shows a peaking effect, and then decreases with further increase in Mn concentration in BaMg(1-x)Mn(x)F(4) (0.0 ≤ x ≤ 0.15). However, ferroelectricity was found to decrease with an increase in Mn concentration in the series of investigated BaMg(1-x)Mn(x)F(4) (0.0 ≤ x ≤ 0.15) samples. First-principle calculations, using the projector augmented wave potentials on Mn-substituted BaMgF(4), confirmed the decrease in magnetic moment with an increase in Mn content beyond certain concentration. These samples exhibit very weak magnetocapacitive coupling, which can be attributed to the very small magnetic signal observed in these samples. 相似文献