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101.
Neville I. Marzwell 《Journal of magnetism and magnetic materials》1977,5(1):67-77
Magnetic susceptibility and electrical resistivity measurements were performed (Pd100?xCox)80P20 alloys where 15 < x < 50. The magnetic properties show that these alloys undergo a ferromagnetic transition between 272 and 399 K as the cobalt concentration increases from 15 to 50 atomic %. Below 20 atomic % Co the short-range exchange interactions which produce the ferromagnetism are unable to establish a long-range magnetic order and a peak in the magnetization shows up at the lowest temperature range under an applied field of 6.0 kOe. The electrical resistivity of these alloys has been measured from 4.2 K up to the vinicity of the melting point (900 K). The electrical resistivity data could be interpreted by the coexistence fo a Kondo-like minimum and ferromagnetism. The minimum becomes less important as the transition metal concentration increases. The coefficients of In T and T2 become smaller and concentration dependent. The spin ordering in such alloys can be simulated as either the ordering due to an applied “external field” or as an increase in “internal fields”. These are due to an increase in transition metal concentration. The negative magnetoresistivity is a strong indication of the existence of localized moment. 相似文献
102.
Jones AR Winter R Greaves GN Smith IH 《The journal of physical chemistry. B》2005,109(49):23154-23161
The glass-forming reactions between sodium carbonate (Na2CO3) and silica (SiO2) have been investigated by 23Na, 29Si, and 13C magic-angle spinning (MAS) NMR spectroscopy. The multinuclear MAS NMR approach identifies and quantifies reaction products and intermediates, both glassy and crystalline. A series of powdered batches of initial composition Na2CO3.xSiO2 (x = 1, 2) corresponding to a sodium metasilicate (Na2SiO3) and sodium disilicate (Na2Si2O5) stoichiometry were investigated after periods of isothermal and nonisothermal heat treatments at different temperatures. Analysis of the 23Na quadrupolar coupling parameters has identified the early reaction product in all cases as crystalline Na2SiO3. In the nonisothermal experiment, this reaction is preceded by an early silica-rich melt phase formed around 850 degrees C. The early reactions are controlled by solid-state Na+ diffusion across the reaction zone in the grain interface layer. Crystalline Na2SiO3 precipitates in the interface layer, increasing its thickness between the Na2CO3 and the SiO2 grains and slowing down the rate of Na+ migration. This creates a secondary phase, which is temperature dependent. At low temperatures, where Na+ migration is impaired, the production of Na2SiO3 ceases and silica-richer phases are precipitated. In the case of the sodium disilicate batch, where excess SiO2 is present, a secondary reaction of Na2SiO3 with SiO2 forming a glassy phase is observed. A transient carbon-bearing phase has been identified by 13C NMR as a NaCO3- complex loosely bound to bridging oxygens in the silicate network at the SiO2 grain surface. 相似文献
103.
Flesch R Kosugi N Bradeanu IL Neville JJ Rühl E 《The Journal of chemical physics》2004,121(17):8343-8350
Cluster size effects in core excitons below the N 1s ionization energy of nitrogen clusters are reported in the energy regime 405-410 eV. These results are compared to the molecular Rydberg states as well as the corresponding bulk excitons of condensed nitrogen. The experimental results are assigned using ab initio calculations. It is found that the lowest excitons (N 1s-->3ssigma and N 1s-->3ppi) are blueshifted relative to the molecular Rydberg transitions, whereas others (N 1s-->3dpi and N 1s-->4ppi) show a redshift. Results from ab initio calculations on (N(2))(13) clearly indicate that the molecular orientation within a cluster is critical to the spectral shift, where bulk sites as well as inner- and outer-surface sites are characterized by different inner-shell absorption energies. These results are compared to the experimental spectra as well as previous work on site-selectively excited atomic van der Waals clusters, providing an improved spectral assignment of core exciton states in weakly bound molecular clusters and the corresponding condensed phase. 相似文献
104.
A study of the reaction initiated by the thermal decomposition of di-t-butyl peroxide (DTBP) in the presence of (CH3)2C?CH2 (B) at 391–444 K has yielded kinetic data on a number of reactions involving CH3 (M·), (CH3)2CCH2CH3 (MB·) and (CH3)2?CH2C(CH3)2CH2CH3 (MBB·) radicals. The cross-combination ratio for M· and MB· radicals, rate constants for the addition to B of M· and MB· radicals relative to those for their recombination reactions, and rate constants for the decomposition of DTBP, have been determined. The values are, respectively, where θ = RT ln 10 and the units are dm3/2 mol?1/2 s?1/2 for k2/k and k9/k, s?1 for k0, and kJ mol?1 for E. Various disproportionation-combination ratios involving M·, MB·, and MBB· radicals have been evaluated. The values obtained are: Δ1(M·, MB·) = 0.79 ± 0.35, Δ1(MB·, MB·) = 3.0 ± 1.0, Δ1(MBB·, MB·) = 0.7 ± 0.4, Δ1(M·, MBB·) = 4.1 ± 1.0, Δ1(MB·, MBB·) = 6.2 ± 1.4, and Δ1(MBB·, MBB·) = 3.9 ± 2.3, where Δ1 refers to H-abstraction from the CH3 group adjacent to the center of the second radical, yielding a 1-olefin. © 1994 John Wiley & Sons, Inc. 相似文献
105.
A procedure was developed for different modes of calibration transfer in near-infrared (NIR) spectroscopy, which included a method for the selection of a subset of samples appropriate for transfer. As a worked example, these guidelines were applied to the transfer of a multivariate calibration model, representing a validated NIR single tablet assay for the active within an intact pharmaceutical product, between three equivalent dispersive NIR transmission instruments. Transfer was first evaluated between two instruments, representing the situation where both were available during calibration development. A spectral correction method alone, applied to the transfer instrument, was not sufficient to facilitate transfer, with further optimisation of the calibration model using a novel wavelength selection algorithm necessary to remove regions of the spectral range that resulted in skewed predictions on the second instrument. Through this approach, a single calibration model was found to be equally accurate and precise on the two instruments. A procedure, using the Kennard-Stone algorithm, is described for determining a reduced number of samples as a transfer set using only the spectral information from the original instrument. The purpose of the subset was to permit transfer to a new instrument where that instrument was not available until after calibration development or where it was undesirable to re-measure the full sample set (i.e. due to excessive reference chemistry). Utilising the transfer set, transfer to a third instrument was evaluated. The calibration model, optimised between the first two instruments, was not directly applicable for the third instrument, with further wavelength selection required to remove a small region of spectral data. On completion, using a full statistical evaluation, a single calibration model was found to be equally accurate and precise on all three instruments. 相似文献
106.
Interest in thermal and chemical stability of surface-supported organic networks has stimulated recent attempts to covalently interlink adsorbed molecular species into extended nanostructures. We show, using low-temperature scanning tunneling microscopy, that imidization of anhydrides and amines adsorbed on Au(111) can be thermally initiated under controlled ultrahigh vacuum conditions. Using two types of amine-functionalized polyphenyl molecules together with the organic semiconductor PTCDA, monolayer thick linear polymeric strands and a porous polymeric network with nanoscale dimensions are obtained. 相似文献
107.
This communication compares the accuracy of a micro open parallel plate system (microOPPS) with a conventional packed column for predicting isotherm data by using the H-root method (HRM). HRM is restricted to compounds obeying the Langmuir isotherm model. The performance of the two chromatographic systems was simulated by using comprehensive mathematical models. Operating conditions were varied and their effects on the accuracy of predictions was evaluated. Better accuracy in the isotherm predictions was obtained with the packed column due to its higher efficiency. However, good predictions can be obtained with the microOPPS with the advantage of significantly lower sample consumption. 相似文献
108.
Neville V. Smith 《固体与材料科学评论》1971,2(1):45-83
Photoemission has emerged over the last decade as a powerful method for studying electronic band structures. The applicabhty of the method to metals was established by Berglund and Spicer1 in their landmark experiments on Cu and Ag. It had been believed, largely on the basis of optical absorption data, that the upper edge of the d bands in Cu and Ag lay at 2 and 4 eV below the Fermi level, respectively. Berglund and Spicer's measurements of the photoelectron energy spectra revealed these edges in a spectacular way and also uncovered some of the substructure of the d bands. Since then the technique has undergone some refinement and has been applied to a large number of materials. Photoemission measurements share the advantage of optical absorption measurements in that they are able to probe electronic states well removed from the Ferrni level. They have the added advantage that they give the initial and final energies as well as the frequencies of prominent optical transitions. 相似文献
109.
110.