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排序方式: 共有97条查询结果,搜索用时 31 毫秒
1.
We present measurements of Eulerian longitudinal velocity autocorrelations in homogeneous, isotropic, high-intensity (~9%) free-stream turbulence behind an active grid. Spatial correlations are measured using particle image velocimetry as well as with two-point hot-wire anemometry (HWA), while temporal correlations are measured using HWA. The temporal correlations are transformed into spatial correlations by using Taylor's ‘frozen’ hypothesis with both the mean as well as instantaneous velocities. A model relating Eulerian spatial and temporal autocorrelations is also used for this purpose. The differences from the measured spatial correlation resulting from the use of Taylor's hypothesis on the temporal correlation is quantified; even at this moderately high level of turbulent intensity, the result from the use of the instantaneous velocity as convection velocity is practically indistinguishable from that obtained using the mean velocity. Use of the model produces a good agreement between the estimates of the spatial correlation function. A relation between Eulerian spatial and temporal integral scales is also derived. 相似文献
2.
3.
The synthesis of the Rhodococcus erythropolis siderophores heterobactins A and B, and the structurally related Nocardia heterobactin, is described. Two approaches for the assembly of these asymmetric ligand donor chelators are explored. In the first approach, a scheme predicated on the biosynthesis of the Paracoccus denitrificans siderophore, parabactin, is employed. In this approach, the central donor synthon is added last. In the second scheme, the central donor and the terminal 2,3-dihydroxybenzoyl fragment are first fixed to the ligand’s d-ornithine backbone. This is followed by condensation with the cyclic ornithine hydroxamate glycine segment. The schemes offer a flexible approach to other heterobactins. Job’s plots suggest that heterobactin A and Nocardia heterobactin form 1:1 ligand/metal complexes, while heterobactin B forms a 3:2 ligand/metal complex. 相似文献
4.
Anita Topkar S. Praveenkumar Bharti Aggarwal S. K. Kataria M. D. Ghodgaonkar 《Pramana》2007,69(6):1085-1088
A specific research and development program has been carried out by BARC in India to develop the technology for large area
silicon strip detectors for application in nuclear and high energy physics experiments. These strip detectors will be used
as pre-shower detector in the CMS experiment at LHC, CERN for π
0/λ rejection. The fabrication technology to produce silicon strip detectors with very good uniformity over a large area of ∼40
cm2, low leakage currents of the order of 10 nA/cm2 per strip and high breakdown voltage of >500 V has been developed by BARC. The production of detectors is already under way
to deliver 1000 detector modules for the CMS and 90% production is completed. In this paper, research and development work
carried out to develop the detector fabrication technology is briefly described. The performance of the silicon strip detectors
produced in India is presented. The present status of the detector technology is discussed.
相似文献
5.
Q.M. Zhang Z.-Y. Cheng V. Bharti 《Applied Physics A: Materials Science & Processing》2000,70(3):307-312
This paper presents experimental results showing that in a certain composition range and under a proper electron-irradiation treatment, a normal ferroelectric poly(vinylidene fluoride-trifluoroethylene) copolymer can be converted into a material exhibiting many typical features of relaxor ferroelectrics, suggesting that this is a new class of relaxor ferroelectric material. Furthermore, the irradiated copolymer can generate giant electrostriction (ƽ%) with a high elastic energy density. The X-ray diffraction results obtained from the irradiated copolymer under electric field, indicate that the observed polarization and strain responses are mainly due to the local phase transformation from a non-polar phase to a polar phase. 相似文献
6.
S. B. Beri K. B. Bhalla R. Bhanja A. Bharti V. S. Bhatia G. Claesson S. Garpman S. K. Gupta V. K. Gupta N. Y. Herrstrom B. Jakobsson R. Joseph G. L. Kaul G. Kaur M. Kaur S. Kitroo V. Kumar S. Lokanathan I. Lund L. K. Mangotra I. S. Mitra S. Mookerjee B. Norén A. Oskarsson I. Otterlund Y. Prakash S. Persson N. K. Rao S. Sankhyadhar S. Satti M. M. Sherif K. Söderström S. K. Tuli 《Zeitschrift für Physik A Hadrons and Nuclei》1987,327(4):431-441
40Ar-emulsion interactions are studied, to investigate the question of anomalons, in twoG- 5 emulsion stacks. In about 4600 primary interactions, projectile fragments of Z≧2 for all generations have been followed until they interact or leave the stack. After careful estimation of charges of these fragments, variation of their mean free paths is studied as a function of distance from the preceding interaction. Generation effect,N h dependence and production angle effect are investigated. In addition multi-chain events are analysed separately. Our results do not show anomalons at the 6% level and are consistent with non-occurrence of anomalons. However, this experiment is not sensitive enough to rule out anomalons (with a mfp of the order of 2 to 3 cm) produced at about 1% (or less) level. 相似文献
7.
Neelesh Bharti Shukla 《Polymer Degradation and Stability》2009,94(8):1238-1244
The oxidative degradation of poly(acrylic acid) (PAA), a water soluble polymer, was studied at various temperatures with different concentrations of persulfates, potassium persulfate (KPS), ammonium persulfate (APS) and sodium persulfate (SPS). The photodegradation of PAA was also examined with APS as oxidizer. The degraded samples were analyzed for the time evolution of molecular weight distribution by gel permeation chromatography. A theoretical model based on the continuous distribution kinetics was developed that accounted for the polymer degradation and the dissociation of persulfate. The rate coefficients for the oxidative and photooxidative degradation of PAA were determined from the parametric fit of the model with experimental data. The rate of degradation increased with increasing amount of persulfate in both oxidative and photooxidative degradation. The rate of degradation also increased with increasing temperature in the case of oxidative degradation. 相似文献
8.
Sanjay K. Bharti Saurabh K. Patel Gopal Nath Ragini Tilak Sushil K. Singh 《Transition Metal Chemistry》2010,35(8):917-925
Six Cu(II) complexes of Schiff base ligands of arylidene-2-(4-(4-bromo/methoxy-phenyl)thiazol-2-yl) hydrazines have been synthesized,
characterized and screened for DNA cleavage and antimicrobial activities. The chemical structures of the complexes were deduced
by physicochemical and spectroscopic methods. Elemental analyses indicated that the stoichiometry of the complexes is CuL2 (L = Schiff base ligand). The DNA cleavage activities of the complexes were evaluated by agarose gel electrophoresis in the
presence and absence of oxidant (H2O2) and free radical scavenger (DMSO). All the six complexes showed significant nuclease activity in the presence of H2O2, and two of the complexes showed moderate nuclease activity even in the absence of oxidant. The complexes did not show nuclease
activity in the presence of free radical scavenger. The compounds were tested for activity against selected bacteria and fungi. 相似文献
9.
A polycrystalline rare earth double perovskite oxide, strontium cerium antimonate, Sr2CeSbO6 (SCS), is synthesized by solid-state reaction technique. The X-ray diffraction pattern at room temperature of SCS shows orthorhombic phase with the lattice parameters, a = 8.84 Å, b = 6.22 Å, and c = 5.83 Å. Fourier transform infrared spectrum shows two phonon modes of the sample at around 550 cm?1 and 670 cm?1 due to the antisymmetric SbO6 stretching vibration. The compound shows significant frequency dispersion in its dielectric properties. The complex impedance plane plots show that the relaxation (conduction) mechanism in SCS is purely a bulk effect arising from the semiconductive grains having the grain resistance = 3.8 × 106 Ω and the grain capacitance = 1.03 × 10?10 F at 603 K. The frequency-dependent conductivity spectra follow the universal power law. The conductivity at 100 Hz varies from 2 × 10?7 Sm?1 to 1.97 × 10?5 Sm?1 with the increase of temperature from 303 K to 703 K, respectively. The relaxation mechanism of the sample in the framework of electric modulus formalism is modelled by Davidson–Cole equation. The activation energy of the sample, calculated from both conductivity and modulus spectra is found to be ~0.15 eV. Such a value of activation energy indicates that the conduction mechanism for SCS is due to electron hopping. The scaling behaviour of imaginary electric modulus suggests that the relaxation describes the same mechanism at various temperatures. 相似文献
10.
A single phase rare earth double perovskite oxide Ba2CeNbO6 (BCN) is synthesized by solid-state reaction technique for the first time. The X-ray diffraction pattern of the sample at room temperature shows monoclinic structure, with the lattice parameters, a=5.9763 Å, b=5.975 Å and c=8.48 Å and β=90.04°. Impedance spectroscopy is used to study the ac electrical behavior of this material as a function of frequency (102-106 Hz) at various temperatures (30-450 °C). A relaxation is observed in the entire temperature range. Conduction mechanism is investigated by fitting the complex impedance data to Cole-Cole equation. Complex impedance plane plots show only one semicircular arc, indicating only the grain contribution of dielectric relaxation. The scaling behavior of imaginary part of electric modulus (M″) and imaginary part of electrical impedance (Z″) suggests that the relaxation describes the same mechanism at various temperatures. The frequency dependence of conductivity is interpreted in terms of the jump relaxation model and is fitted to Jonscher's power law. The values of dc conductivities extracted from the Jonscher power law varies from 2.79×10−7 to 3.5×10−5 Sm−1 with the increase in temperature from 100 to 450 °C. The activation energies (0.37 eV) extracted from M″(ω) and Z″(ω) peaks are found to follow the Arrhenius law. 相似文献