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221.
K. Praveena K. SadhanaS. Ramana Murthy 《Journal of magnetism and magnetic materials》2011,323(16):2122-2128
Ni0.53Cu0.12Zn0.35Fe2O4/SiO2 nanocomposites with different weight percentages of NiCuZn ferrite dispersed in silica matrix were prepared by microwave-hydrothermal method using tetraethylorthosilicate as a precursor of silica, and metal nitrates as precursors of NiCuZn ferrite. The structure and morphology of the composites were studied using X-ray diffraction and scanning electron microscopy. The structural changes in these samples were characterized using Fourier Transform Infrared Spectrometer in the range of 400-1500 cm−1. The bands in the range of 580-880 cm−1 show a slight increase in intensity, which could be ascribed to the enhanced interactions between the NiCuZnFe2O4 clusters and silica matrix. The effects of silica content and sintering temperature on the magnetic properties of Ni0.53Cu0.12Zn0.35Fe2O4/SiO2 nanocomposites have been studied using electron spin resonance and vibrating sample magnetometer. 相似文献
222.
P. Praveen Kumar Y. Dathu ReddyCh. Venkata Ramana Reddy B. Rama DeviP.K. Dubey 《Tetrahedron letters》2014
Green and efficient one pot, three-component synthesis of novel 2-amino-6-(1,4-dioxo-3,4-dihydrophthalazin)-2(1H)-yl-4-phenyl-4H-pyran-3,5-dicarbonitriles 6 has been developed by condensing 3-(1,4-dioxo-3,4-dihydrophthalazin-(1H)-yl)-3-oxopropanenitrile 3, benzaldehydes 4 and active methylene compounds 5 using l-proline as catalyst in EtOH at RT. 相似文献
223.
B.V. Subba Reddy S. Gopal Reddy M. Ramana Reddy B. Sridhar Manika Pal Bhadra 《Tetrahedron letters》2014
Various aldehydes undergo smooth coupling with a branched homoallylic alcohol appended N-tosyl amine (1 & 3) in the presence of 10 mol % BF3·OEt2 at room temperature to afford a novel class of 1,8-disubstituted octahydropyrano[3,4-c]pyridine and 1,6-disubstituted hexahydrofuro[3,4-c]pyrrole derivatives in good yields, respectively. 相似文献
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226.
Ramana Reddy V. Dodla Abhijit Sen George L. Johnston 《Communications in Nonlinear Science & Numerical Simulation》2003,8(3-4):493
We study the periodic forced response of a system of two limit cycle oscillators that interact with each other via a time delayed coupling. Detailed bifurcation diagrams in the parameter space of the forcing amplitude and forcing frequency are obtained for various interesting limits using numerical and analytical means. In particular, the effects of the coupling strength, the natural frequency spread of the two oscillators and the time delay parameter on the size and nature of the entrainment domain are delineated. For an appropriate choice of time delay, synchronization can occur with infinitesimal forcing amplitudes even at off-resonant driving. The system is also found to display a nonlinear response on certain critical contours in the space of the coupling strength and time delay. Numerical simulations with a large number of coupled driven oscillators display similar behavior. Time delay offers a novel tuning knob for controlling the system response over a wide range of frequencies and this may have important practical applications. 相似文献
227.
Sanjiv Kumar J. V. Ramana S. Vikram Kumar V. S. Raju 《Journal of Radioanalytical and Nuclear Chemistry》2005,265(3):441-446
Summary The determination of atomic composition and thickness of zirconium oxide layers on zirconium based alloys is of practical interest in nuclear industry. This paper describes the application of backscattering spectrometry for the non-destructive determination of composition and thickness of zirconium oxide layers on autoclaved zircaloy coupons. The spectrometry used here is the Rutherford backscattering spectrometry (RBS) with 2.5 MeV α-particles, 3.05 MeV 16O(α,α)16O resonance scattering and 16O(p,p)16O elastic scattering with 2.5 MeV proton beam. Proton backscattering is found to be the most suitable technique for the overall compositional analysis of the layers whereas 3.05 MeV 16O(α,α)16O resonance scattering, for depth profiling of oxygen. The former technique is simple and provides rapid measurements. The lower stopping cross sections of protons and enhanced scattering cross section for oxygen over a wide range of proton energy enable the analysis of oxide layers of larger thicknesses. The thicknesses of these layers determined by backscattering are in good agreement with cross-sectional micrographs taken by scanning electron microscope (SEM). 相似文献
228.
Coupled limit cycle oscillators with instantaneous mutual coupling offer a useful but idealized mathematical paradigm for
the study of collective behavior in a wide variety of biological, physical and chemical systems. In most real-life systems
however the interaction is not instantaneous but is delayed due to finite propagation times of signals, reaction times of
chemicals, individual neuron firing periods in neural networks etc. We present a brief overview of the effect of time-delayed
coupling on the collective dynamics of such coupled systems. Simple model equations describing two oscillators with a discrete
time-delayed coupling as well as those describing linear arrays of a large number of oscillators with time-delayed global
or local couplings are studied. Analytic and numerical results pertaining to time delay induced changes in the onset and stability
of amplitude death and phase-locked states are discussed. A number of recent experimental and theoretical studies reveal interesting
new directions of research in this field and suggest exciting future areas of exploration and applications. 相似文献
229.
An Orbital‐Free Quantum Hypernetted Chain Model Based Perturbation Theory for Equation of State of Hydrogen and Helium in Warm Dense Regime
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A. Sai Venkata Ramana 《等离子体物理论文集》2015,55(8):606-618
We present in this work, a thermodynamic perturbation theory for equation of state of hydrogen and helium in the warm dense regime. The system is modeled as a mixture of classical point ions and quantum electrons. A perturbation series for Helmholtz free energy and correlation functions of the ions and electrons as a function of density and temperature is proposed. Combining the classical thermodynamic perturbation theory and the orbitial‐free quantum hyper‐netted chain theory, a systematic procedure to obtain the terms of the perturbation series is developed. The ion‐ion correlations are treated within the hyper‐netted chain approximation and the ion‐electron correlations are treated within the Thomas‐Fermi‐Dirac‐Weizsäcker approximation. The method has been applied to obtain isotherms of hydrogen and helium in the warm dense regime. The isotherms are compared with available ab‐initio data and the results are analyzed. A good agreement with ab‐initio data has been observed for pressures greater than one Mbar. Advantages and limitations of the present method are discussed along with possible future improvements. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
230.
Kamal Dua Kavita Pabreja M. V. Ramana 《Journal of Dispersion Science and Technology》2013,34(10):1477-1484
The objective of the present investigation was to study the effect of presence of choline dichloride (CDC) in β-cyclodextrin (β-CD) on in vitro dissolution of aceclofenac (AF) from molecular inclusion complexes. The molecular inclusion complexes of AF with β-CD coprecipitated with CDC in 1:1 and 1:2 M ratio were prepared using kneading method. In vitro dissolution of pure drug, physical mixtures, and cyclodextrin inclusion complexes (AF-β-CD-CDC) were carried out. Molecular inclusion complexes of aceclofenac with coprecipitated β-CD showed considerable increase in the dissolution rate in comparison with physical mixture and pure drug in 0.1 N HCl, pH 1.2 and phosphate buffer, pH, 7.4. Inclusion complexes with 1:2 M ratio showed maximum dissolution rate in comparison to other ratios. FTIR spectroscopy and differential scanning calorimetry studies indicated no interaction between AF and β-CD-CDC in complexes in solid state. Dissolution enhancement was attributed to the formation of water soluble inclusion complexes with the precipitated form of β-CD. The in vitro release from all the formulations was best described by first order kinetics (R 2 = 0.9354 and 0.9268 in 0.1 N HCl and phosphate buffer, respectively) followed by Higuchi release model (R 2 = 0.9029 and 0.9578 in 0.1 N HCl and phosphate buffer, respectively). In conclusion, dissolution of aceclofenac can be enhanced by using the β-CD-CDC coprecipitate as a host molecule. 相似文献