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101.
Ultrafine particles of barium ferrite from a citrate precursor 总被引:2,自引:0,他引:2
V. K. Sankaranarayanan Q. A. Pankhurst D. P. E. Dickson C. E. Johnson 《Journal of magnetism and magnetic materials》1993,120(1-3):73-75
Ultrafine particles of barium ferrite produced by the precursor method have sizes between 5 and 100 nm. These particles have relatively low magnetisations and high coercivities. Mössbauer spectra exhibit different relative areas for the 4fiv and 2b sites compared to the bulk which partly explains the low magnetisations. 相似文献
102.
Evaluating the Free Energies of Solvation and Electronic Structures of Lithium‐Ion Battery Electrolytes
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Mehdi Shakourian‐Fard Ganesh Kamath Subramanian K. R. S. Sankaranarayanan 《Chemphyschem》2016,17(18):2916-2930
Adaptive biasing force molecular dynamics simulations and density functional theory calculations were performed to understand the interaction of Li+ with pure carbonates and ethylene carbonate (EC)‐based binary mixtures. The most favorable Li carbonate cluster configurations obtained from molecular dynamics simulations were subjected to detailed structural and thermochemistry calculations on the basis of the M06‐2X/6‐311++G(d,p) level of theory. We report the ranking of these electrolytes on the basis of the free energies of Li‐ion solvation in carbonates and EC‐based mixtures. A strong local tetrahedral order involving four carbonates around the Li+ was seen in the first solvation shell. Thermochemistry calculations revealed that the enthalpy of solvation and the Gibbs free energy of solvation of the Li+ ion with carbonates are negative and suggested the ion–carbonate complexation process to be exothermic and spontaneous. Natural bond orbital analysis indicated that Li+ interacts with the lone pairs of electrons on the carbonyl oxygen atom in the primary solvation sphere. These interactions lead to an increase in the carbonyl (C=O) bond lengths, as evidenced by a redshift in the vibrational frequencies [ν(C=O)] and a decrease in the electron density values at the C=O bond critical points in the primary solvation sphere. Quantum theory of atoms in molecules, localized molecular orbital energy decomposition analysis (LMO‐EDA), and noncovalent interaction plots revealed the electrostatic nature of the Li+ ion interactions with the carbonyl oxygen atoms in these complexes. On the basis of LMO‐EDA, the strongest attractive interaction in these complexes was found to be the electrostatic interaction followed by polarization, dispersion, and exchange interactions. Overall, our calculations predicted EC and a binary mixture of EC/dimethyl carbonate to be appropriate electrolytes for Li‐ion batteries, which complies with experiments and other theoretical results. 相似文献
103.
R. Sankaranarayanan Jane H. Sheeba M. Lakshmanan 《Chaos, solitons, and fractals》2007,33(5):1618-1624
Evolution of quantum fidelity for two-level systems is studied in the context of periodic echo. For time independent case, we obtain a formal condition on the governing Hamiltonians under which the systems display periodic quantum echo. In addition, a revisit of single spin-1/2 system exposed to uniform rotating magnetic field elucidates that the well known Rabi oscillation is a simple mechanism to generate such echoes. 相似文献
104.
Spectral characteristics of 2-amino-3-benzyloxy pyridine: Effects of solvents,pH, and β-cyclodextrin
A. Antony Muthu Prabhu R. K. Sankaranarayanan S. Siva V. K. Subramanian N. Rajendiran 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2010,84(13):2270-2283
Spectral characteristics of 2-amino-3-benzyloxypyridine (2ABP) has been studied in solvents of different polarity, pH, and
β-cyclodextrin (β-CD) and compared with 2-amino pyridine (2AP). The inclusion complex of both amino pyridine (AP) molecules
with β-CD are analysed by UV-visible, fluorimetry, FTIR, 1H NMR, SEM and AM1 methods. The solvent studies shows no significant shift observed in absorption maxima between both AP molecules,
but in the excited state a slight red shift is noticed in 2ABP than in 2AP which indicates that the addition of benzyloxy
group in 2AP does not effectively increase the resonance interaction in 2ABP. The regular red shift observed in acidic pH
solutions suggests intramolecular proton transfer (IPT) interaction in both molecules. β-CD studies shows that in pH ∼7, 2ABP
forms 1: 2 inclusion complex from 1: 1 inclusion complex and 1: 1 inclusion complex is formed in pH ∼ 1. In pH ∼ 7, a red
shift observed in 2ABP with lower β-CD concentration suggests aromatic ring encapsulated in the β-CD cavity and blue shift
noticed at higher β-CD concentrations indicates pyridine ring encapsulated in the β-CD cavity. 相似文献
105.
A. Antony Muthu Prabhu R.K. Sankaranarayanan S. Siva N. Rajendiran 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2009,74(2):484-497
The absorption and fluorescence spectra of fast violet-B (FVB) and benzanilide (BA) have been analysed in different solvents, pH and β-cyclodextrin. The inclusion complex of FVB with β-CD is investigated by UV–visible, fluorimetry, AM 1, FTIR and SEM. The absorption maximum of FVB (anilino substitution) is red shifted than that of BA, but the benzoyl substitution hardly changed the ground state structure of BA. Compared to BA, the emission maxima of FVB largely blue shifted in cyclohexane and aprotic solvents, but red shifted in protic solvents and the longer wavelength maxima in FVB is due to the intramolecular charge transfer (TICT). In BA, the normal emission originates from a locally excited state and the longer wavelength band due to intramolecular proton transfer in non-polar/aprotic solvents and in protic solvents it is due to TICT state. β-CD studies reveal that, FVB forms 1:2 complex from 1:1 complex and BA forms 1:2 complex with β-CD. 相似文献
106.
Chinnakonda S. Gopinath Kandasamy Thirunavukkarasu Sankaranarayanan Nagarajan 《化学:亚洲杂志》2009,4(1):74-80
Transient state kinetics of the catalytic oxidation of CO with O2 on Pd‐surfaces has been measured under isothermal conditions by using a molecular beam approach. Systematic studies were carried out as a function of reaction temperature and CO+O2 composition. With sufficient kinetic evidence, we have demonstrated the positive influence of subsurface oxygen towards CO‐adsorption and oxidation to CO2 at high temperatures (600–900 K) on Pd‐surfaces, and the likely electronic nature of the surface changes with oxygen in the subsurface. These studies also provide a direct proof for CO‐adsorption with a significantly reactive sticking coefficient at high temperatures on Pd‐surfaces exhibiting a significant subsurface O‐coverage. 相似文献
107.
Yildirim H Greeley JP Sankaranarayanan SK 《Physical chemistry chemical physics : PCCP》2012,14(13):4565-4576
Li transport characteristics are studied by means of density functional theory (DFT) and molecular dynamics (MD) simulations in order to investigate concentration effects on Li chemical diffusivity and conductivity in TiO(2) rutile. Our MD simulations predict one-dimensional diffusion of Li ions via jumps between the octahedral sites along the channels parallel to the c-axis. The diffusion barrier and diffusion coefficient (at room temperature) for the isolated Li, determined by means of DFT calculations, correspond to 60 meV and 9.1 × 10(-6) cm(2) s(-1), respectively. Such a small barrier suggests rapid mass transport along the channels. MD simulations are performed to evaluate the concentration dependent diffusivity profiles. The changes in Li energetics and dynamics are studied as a function of Li content, which is varied primarily between 10% and 50%. In addition, we consider a couple of compositions over 50% although this is above the intercalation limit. Our results suggest that Li diffusivity is strongly dependent on the Li?∶?TiO(2) ratio, and it decreases with increasing Li concentration. For instance, at room temperature, we find Li diffusivity for high concentrations (50% Li) to be three orders of magnitude slower than that for lower concentrations (10% Li). Our analyses on the energetics and dynamics suggest that the changes in the diffusivities originate from successive increases in the barriers with increasing concentration. The decrease in diffusivity as a function of increasing Li content is attributed to the fact that additional Li ions successively block the energetically preferred vacant sites along the channels. Our analyses also show that increasing Li concentration enhances the Li-Li repulsion within the channels, and as a result, diffusion is hindered. We also compare concentration-dependent diffusivities for Li diffusion in anatase, rutile and amorphous TiO(2). Interestingly, we find differing concentration dependence of the diffusivity in these chemically identical but structurally non-equivalent TiO(2) polymorphs. Our study suggests that these differences result from intrinsic structural characteristics of TiO(2) polymorphs, which ultimately contribute to intercalation limit, diffusivity, ionic conductivity, and the electrochemical performance in energy storage applications. 相似文献
108.
LetQ(u 1,…,u 1) =Σd ij u i u j (i,j = 1 tol) be a positive definite quadratic form inl(≥3) variables with integer coefficientsd ij (=d ji ). Puts=σ+it and for σ>(l/2) write $$Z_Q (s) = \Sigma '(Q(u_1 ,...,u_l ))^{ - s} ,$$ where the accent indicates that the sum is over alll-tuples of integer (u 1,…,u l ) with the exception of (0,…, 0). It is well-known that this series converges for σ>(l/2) and that (s-(l/2))Z Q (s) can be continued to an entire function ofs. Let σ be any constant with 0<σ<1/100. Then it is proved thatZ Q (s)has ?δTlogT zeros in the rectangle(|σ-1/2|≤δ, T≤t≤2T). 相似文献
109.
In the present paper we have investigated the self-focusing behaviour of radially symmetrical rippled Gaussian laser beam
propagating in a plasma. Considering the nonlinearity to arise from relativistic phenomena and following the approach of Akhmanov
et al, which is based on the WKB and paraxial-ray approximation, the self-focusing behaviour has been investigated in some detail.
The effect of the position and width of the ripple on the self-focusing of laser beam has been studied for arbitrary large
magnitude of nonlinearity. Results indicate that the medium behaves as an oscillatory wave-guide. The self-focusing is found
to depend on the position parameter of ripple as well as on the beam width. Values of critical power has been calculated for
different values of the position parameter of ripple. Effects of axially and radially inhomogeneous plasma on self-focusing
behaviour have been investigated and presented here. 相似文献
110.
RK Choudhury 《Pramana》2001,57(2-3):585-600
Nuclear fission process involves large scale shape changes of the nucleus, while it evolves from a nearly spherical configuration
to two separated fission fragments. The dynamics of these shape changes in the nuclear many body system is governed by a strong
interplay of the collective and single particle degrees of freedom. With the availability of heavy ion accelerators, there
has been an impetus to study the nuclear dynamics through the investigations of nucleus-nucleus collisions involving fusion
and fission process. From the various investigations carried out in the past years, it is now well recognized that there is
large scale damping of collective modes in heavy ion induced fission reactions, which in other words implies that nuclear
motion is highly viscous. In recent years, there have been many experimental observations in heavy ion induced fission reactions
at medium bombarding energies, which suggest possible occurrence of various non-equilibrium modes of fission such as quasi-fission,
fast fission and pre-equilibrium fission, where some of the internal degrees of freedom of the nucleus is not fully equilibrated.
We have carried out extensive investigations on the fission fragment angular distributions at near barrier bombarding energies
using heavy fissile targets. The measured fragment anisotropies when compared with the standard saddle point model (SSPM)
calculations show that for projectile-target systems having zero or low ground state spins, the angular anisotropy exhibits
a peak-like behaviour at the sub barrier energies, which cannot be explained by the SSPM calculations. For projectiles or
targets with large ground state spins, the anomalous peaking gets washed out due to smearing of the K-distribution by the intrinsic entrance channel spins. Recently studies have been carried out on the spin distributions of
fission fragments through the gamma ray multiplicity measurements. The fission fragments acquire spin mainly from two sources:
(i) due to rigid rotation of the nascent fragments at scission and (ii) due to statistical excitation of the spin bearing
collective modes in the fissioning nucleus. One of the collective modes — the tilting mode depends on the K quantum number and is responsible for the emission angle dependence of fragment spin. In our studies, we have shown conclusively
that the collective statistical spin modes get strongly suppressed for high K values corresponding to large rotational frequencies along the fission axis. These results bring out the importance of the
dynamical effects in the heavy ion induced fusion-fission reactions. The present article will review the work carried out
on the above aspects in heavy ion fission reactions as well as on the fission time scales, and some of the recent studies
on the mass-energy correlations of fission fragments at near-barrier bombarding energies. 相似文献