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71.
Spectral properties and emission efficiencies of GdVO4 phosphors 总被引:2,自引:0,他引:2
M. Anitha P. Ramakrishnan A. Chatterjee G. Alexander H. Singh 《Applied Physics A: Materials Science & Processing》2002,74(2):153-162
GdVO4 with activators Eu, Dy, Sm and Bi has been synthesised by a solid-state reaction. GdVO4:Eu3+ (3%) yielded the highest quantum efficiency of 95%. Interesting energy-transfer properties have been revealed in the mixed-activator
phosphor (GdVO4:Eu3+, Sm3+) when excited in the 4f shell of Sm3+ at 408 nm. Bismuth-activated GdVO4 gives rise to a broad-band emission peaking at 525 nm in comparison to YVO4:Bi3+, which gives an emission peak at 570 nm under UV excitation. The quantum efficiency of GdVO4:Bi3+ increases gradually with bismuth concentration and reaches a maximum of 80% for a bismuth concentration of ≈0.5%. There is
a shift in the excitation band of GdVO4:Bi3+ towards longer wavelengths with increasing concentration of bismuth, which can lead to energy transfer from bismuth to europium
in a phosphor with both these activators. Heat treatment of GdVO4:Bi3+ at 1500 °C for 3–3.5 h resulted in a large percentage of bismuth being lost from the lattice as evaluated by X-ray fluorescence.
However, if a large percentage of bismuth (of the order of 3% or more) is initially added, a sufficient quantity of bismuth
can still be retained after heat treatment, which can lead to the development of ceramic scintillators for X-ray tomographic
applications. Addition of 3–5% boron gives a white GdVO4 phosphor without any chemical treatment.
Received: 27 Feruary 2001 / Accepted: 1 August 2001 / Published online: 30 October 2001 相似文献
72.
73.
Ali Jinnah MM Sasirekha V Ramakrishnan V 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,62(4-5):840-844
Infrared and Raman spectra of L-citrullinium perchlorate crystals have been recorded at room temperature. The vibrational assignments of the observed wavenumbers are proposed on the basis of group theoretical analysis. The presence of carbonyl group indicates that the molecule exists in the ionic form. The shifting of stretching and bending wavenumbers indicates the presence of extensive hydrogen bonding in the crystal. The anion fundamentals however continue to be degenerated. This suggests that its symmetry is not affected in the crystal. 相似文献
74.
75.
Ramakrishnan V Ranbhor R Kumar A Durani S 《The journal of physical chemistry. B》2006,110(18):9314-9323
In search of the link between sequence and conformation in protein structures, we perform molecular dynamics analysis of the effect of stereochemical mutation in end-protected octa-alanine Ac-Ala8-NHMe from poly-L to an alternating-L,D structure. The mutation has a dramatic effect, transforming the peptide from a condition of extreme sensitivity to one of extreme insensitivity to solvent. Examining the molecular folds of poly-L and alternating-L,D structure in atomistic detail, we find them to differ in the relationship between peptide dipolar interactions at the local and nonlocal levels, either conflicting or harmonious depending upon the chain stereochemistry. The stereochemical transformation of interpeptide electrostatics from a condition of conflict to one of harmony explains the long-standing puzzle of why poly-L and alternating-L,D peptides strongly differ in properties such as "stiffness" and solvent sensitivity. Furthermore, it is possible that poly-L stereochemistry is also the fulcrum of protein sensitivity to the effects of amino acid side-chain structures via dielectric arbitrations in interpeptide electrostatics. Indeed the evidence is accumulating that the amino acid side chains differing in alpha-helix and beta-sheet propensities also differ in their desolvating effects in the adjacent and nearest-neighbor peptides and thus possibly in the solvent screening of peptide dipolar interactions. 相似文献
76.
High aspect ratio (>500), neat poly(ethyl 2-cyanoacrylate) nanofibers were synthesized catalytically by vapour phase polymerization under high relative humidity and ambient conditions. 相似文献
77.
V. Ramakrishnan A. Sarua M. Kuball A. Fathima Abdullah 《Journal of Raman spectroscopy : JRS》2010,41(3):320-324
The molecular interaction in the binary mixture of 3‐phenoxybenzaldhyde (3Phbz) and 4‐ethoxybenzaldehyde (4Etob) was analysed in four different solvents. The concentration dependence of vibrational relaxation of the CO stretching band of 3Phbz in different solvents was investigated by varying the concentration of the solute molecule in the solvents by performing Raman spectroscopic measurements. The self‐associated nature and the formation of hydrogen‐bonded complexes in the solute molecule, 4Etob, were considered to analyse the wavenumber separation between the peaks of hydrogen‐bonded and free carbonyl groups. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
78.
Janak Ramakrishnan 《Mathematical Logic Quarterly》2010,56(4):406-408
We prove that a function definable with parameters in an o‐minimal structure is bounded away from ∞ as its argument goes to ∞ by a function definable without parameters, and that this new function can be chosen independently of the parameters in the original function. This generalizes a result in [1]. Moreover, this remains true if the argument is taken to approach any element of the structure (or ±∞), and the function has limit any element of the structure (or ±∞) (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
79.
Seebauer EG Dev K Jung MY Vaidyanathan R Kwok CT Ager JW Haller EE Braatz RD 《Physical review letters》2006,97(5):055503
The technologically useful properties of a crystalline solid depend upon the concentration of defects it contains. Here we show that defect concentrations as deep as 0.5 microm within a semiconductor can be profoundly influenced by gas adsorption. Self-diffusion rates within silicon show that nitrogen atoms adsorbed at less than 1% of a monolayer lead to defect concentrations that vary controllably over several orders of magnitude. The results show that previous measurements of diffusion and defect thermodynamics in semiconductors may have suffered from neglect of adsorption effects. 相似文献
80.
M. Giffhorn B. Becker A. A. Menovsky J. A. Mydosh G. J. Nieuwenhuys S. Ramakrishnan 《高压研究》2013,33(1-6):159-163
Abstract An uniaxial pressure cell for low temperature use is described in detail. Then we present data of the electrical resistance of single crystals of Lu5Ir4Si10, which is known to show a charge-density-wave transition around 83 K and to become superconducting near 3.8 K, both phenomena being anticorrelated under pressure. Since the CDW in Lu5Ir4Si10 is a quasi one-dimensional phenomenon because of a chain-like structure, it responds to uniaxial pressure in a specific way. 相似文献