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141.
142.
Dwivedi P Puzon G Tam M Langlais D Jackson S Kaplan K Siems WF Schultz AJ Xun L Woods A Hill HH 《Journal of mass spectrometry : JMS》2010,45(12):1383-1393
Comprehensive metabolome analysis using mass spectrometry (MS) often results in a complex mass spectrum and difficult data analysis resulting from the signals of numerous small molecules in the metabolome. In addition, MS alone has difficulty measuring isobars and chiral, conformational and structural isomers. When a matrix-assisted laser desorption ionization (MALDI) source is added, the difficulty and complexity are further increased. Signal interference between analyte signals and matrix ion signals produced by MALDI in the low mass region (<1500 Da) cause detection and/or identification of metabolites difficult by MS alone. However, ion mobility spectrometry (IMS) coupled with MS (IM-MS) provides a rapid analytical tool for measuring subtle structural differences in chemicals. IMS separates gas-phase ions based on their size-to-charge ratio. This study, for the first time, reports the application of MALDI to the measurement of small molecules in a biological matrix by ion mobility-time of flight mass spectrometry (IM-TOFMS) and demonstrates the advantage of ion-signal dispersion in the second dimension. Qualitative comparisons between metabolic profiling of the Escherichia coli metabolome by MALDI-TOFMS, MALDI-IM-TOFMS and electrospray ionization (ESI)-IM-TOFMS are reported. Results demonstrate that mobility separation prior to mass analysis increases peak-capacity through added dimensionality in measurement. Mobility separation also allows detection of metabolites in the matrix-ion dominated low-mass range (m/z < 1500 Da) by separating matrix signals from non-matrix signals in mobility space. 相似文献
143.
Electron paramagnetic resonance (EPR) spectra of Cu2+ ion in ammonium dihydrogen phosphate are studied at liquid nitrogen temperature (77 K). Four magnetically inequivalent Cu2+ sites in the lattice are identified. The angular variation spectra of the crystal in the three orthogonal planes indicate that the paramagnetic impurity, Cu2+ enters the lattice substitutionally in place of NH4+ ions. The spin Hamiltonian parameters are determined with the fitting of spectra to rhombic symmetry crystalline field. The ground state wave function of Cu2+ ion is constructed and found to be predominantly |x2-y2〉. The cubic field parameter (Dq) and tetragonal parameters (Ds and Dt) are determined from optical spectra at room temperature. By correlating EPR and optical absorption spectra, the bonding coefficients are calculated and nature of bonding of metal ion with different ligands in the crystal is discussed. 相似文献
144.
145.
G.D. Dwivedi Amish G. Joshi H. Kevin P. Shahi A. Kumar A.K. Ghosh H.D. Yang Sandip Chatterjee 《Solid State Communications》2012,152(5):360-363
The appearance of ferroelectricity has been observed in magnetically ordered Co(Fe1?xTix)2O4 at room temperature. Magnetization and dielectric constant is found to increase with Ti doping. It is observed from an X-ray Photoemission Spectroscopy study that Ti goes to the octahedral site with (+4) ionic state. An M–H hysteresis curve at room temperature shows the ferrimagnetic ordering and a P–E loop at room temperature clearly indicates the existence of ferroelectricity. 相似文献
146.
The (GdxY1?x)2O3: Er3+, Yb3+ [x=0.0, 0.1, 0.5, 0.9, 1.0] phosphor samples with 0.5 mol% concentration of Er3+ and 3.0 mol% of Yb3+, have been prepared using combustion route. The effect of variation of composition on the morphology, crystallinity and photoluminescence characteristics of the material has been investigated. The samples were post-heated at a temperature 1200 °C, for 5 h. We find systematic color tunability from red to green with an increase of Gd2O3 content in Y2O3 lattice. Further, the post-heated samples show an enhancement of fluorescence intensity for more than fifteen times. The samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), photoluminescence measurement and Fourier transform infrared (FTIR) techniques in order to find out the structural changes in host lattice. An increase in crystallite size has been marked with increasing Gd content while FTIR analysis explains the reason of variation in the fluorescence of rare earth ions in different host matrices. 相似文献
147.
Electron Paramagnetic Resonance and Optical Absorption of VO2+ Doped Bis (glycinato) Mg (II) Monohydrate Single Crystals
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We investigate the electron paramagnetic resonance (EPR) of VO2+ ions in bis (glycinato) Mg (II) monohydrate single crystals at room temperature. Detailed EPR analysis indicates the presence of only one VO2+ site. The vanadyl complexes are found to take up the substitutional position. The angular variation of the EPR spectra in three planes a*b, bc and ca* are used to determine principal g and A tensors. The values of spin Hamiltonian parameters are gx= 2.1447× 10-4, gy= 1.9974×10-4, gz= 1.9131×10-4, Ax= 49×10-4, Ay= 60×10-4, Az= 82×10-4 cm-1. The optical absorption study is also carried out at room temperature and absorption bands are assigned to various transitions. The theoretical band positions are obtained using energy expressions and a good agreement is found with the experimental data. By correlating EPR and optical data, different molecular orbital coefficients are evaluated and the nature of bonding in the crystal is discussed. 相似文献
148.
A prototype pulsed electron beam irradiation facility for radiation processing of food and medical products is being commissioned
at our centre in Indore, India. Analysis of surface dose and uniformity for a pulsed beam facility is of crucial importance
because it is influenced by various operating parameters such as beam current, pulse repetition rate (PRR), scanning current
profile and frequency, scanning width and product conveying speed. A large number of experiments are required to determine
the harmonized setting of these operating parameters for achieving uniform dose. Since there is no readily available tool
to set these parameters, use of Monte Carlo methods and computational tools can prove to be the most viable and time saving
technique to support the assessment of the dose distribution. In the present study, Monte Carlo code, MCNP, is used to simulate
the transport of 10 MeV electron beam through various mediums coming into the beam path and generate an equivalent dose profile
in a polystyrene phantom for stationary state. These results have been verified with experimentally measured dose profile,
showing that results are in good agreement within 4%. The Monte Carlo simulation further has been used to optimize the overlapping
between the successive pulses of a scan to achieve ±5% dose uniformity along the scanning direction. A mathematical model,
which uses the stationary state data, is developed to include the effect of conveyor speed. The algorithm of the model is
discussed and the results are compared with the experimentally measured values, which show that the agreement is better than
15%. Finally, harmonized setting for operating parameters of the accelerator are derived to deliver uniform surface dose in
the range of 1–13 kGy/pass. 相似文献
149.
150.
R. Brandt M. Ochs J. -S. Wan Th. Schmidt E. -J. Langrock P. Vater J. Adam V. P. Bamblevskij V. Bradnova L. K. Gelovani V. K. Kalinnikov M. I. Krivopustov B. A. Kulakov A. N. Sosnin V. P. Perelygin V. S. Pronskikh V. I. Stegailov V. M. Tsoupko-Sitnikov G. Modolo R. Odoj P. -W. Phiippen J. -C. Adloff F. Pape M. Debeauvais M. Zamani-Valassiadou S. R. Hashemi-Nezhad K. K. Dwivedi S. -L. Guo L. Li Y. -L. Wang B. Wilson 《Radiation measurements》1999,31(1-6):497-506
Experiments using 1.5 GeV, 3.7 GeV and 7.4 GeV protons from the Synchrophasotron, LHE, JINR, Dubna, Russia, on extended Pb- and U-targets were carried out using SSNTD and radiochemical sensors for the study of secondary neutron fluences. We also carried out first transmulation studies on the long-lived radwaste nuclei 129I and 237Np.
In addition, we carried out computer code simulation studies on these systems using LAHET and DCM/CEM codes. We have difficulties to understand rather large transmutation rates observed experimentally when they are compared with computer simulations. There seems to be a rather fundamental problem understanding the large transmutation rates as observed experimentally in Dubna and CERN, as compared to those theoretical computer simulations mentioned above. 相似文献