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21.
22.
Ahrens LA Aronson SH Connolly PL Gibbard BG Murtagh MJ Murtagh S Terada S White DH Callas JL Cutts D Hoftun JS Lanou RE Shinkawa T Amako K Kabe S Nagashima Y Suzuki Y Tatsumi S Abe K Beier EW Doughty DC Durkin LS Heagy SM Hurley M Mann AK Newcomer FM Williams HH York T Hedin D Marx MD Stern E 《Physical review letters》1985,54(1):18-21
23.
Laser-induced desorption of proteins 总被引:1,自引:0,他引:1
M Salehpour I Perera J Kjellberg A Hedin M A Islamian P H?kansson B U Sundqvist 《Rapid communications in mass spectrometry : RCM》1989,3(8):259-263
Laser-induced desorption mass spectrometry has been applied to a number of proteins in the mass range 5000-150,000 u. The beam from an excimer-laser-pumped dye-laser at 266 nm has been focused to a spot of about 50 microns in diameter with irradiances in the 10(7) W/cm2 region. A linear time-of-flight mass spectrometer has been used for mass spectrometric measurements, where positive and negative secondary ions of large proteins have been studied. The effect of different experimental parameters on the protein ion-signal intensities are discussed. 相似文献
24.
Masoud Farhadi‐Khouzani Daniel M. Chevrier Prof. Dr. Peng Zhang Prof. Dr. Niklas Hedin Dr. Denis Gebauer 《Angewandte Chemie (International ed. in English)》2016,55(28):8117-8120
Temperature and pH value can affect the short‐range order of proto‐structured and additive‐free amorphous calcium carbonates (ACCs). Whereas a distinct change occurs in proto‐vaterite (pv) ACC above 45 °C at pH 9.80, proto‐calcite (pc) ACC (pH 8.75) is unaffected within the investigated range of temperatures (7–65 °C). IR and NMR spectroscopic studies together with EXAFS analysis showed that the temperature‐induced change is related to the formation of proto‐aragonite (pa) ACC. The data strongly suggest that the binding of water molecules induces dipole moments across the carbonate ions in pa‐ACC as in aragonite, where the dipole moments are due to the symmetry of the crystal structure. Altogether, a (pseudo‐)phase diagram of the CaCO3 polyamorphism in which water plays a key role can be formulated based on variables of state, such as the temperature, and solution parameters, such as the pH value. 相似文献
25.
We investigate quantum mechanical electron transport along the long axis of the DNA molecule using an effective tight-binding model. The overall contour plot of transmission, the current-voltage characteristics, and the differential conductance are examined for the variation of backbone onsite energy, the energy-dependent hopping strength, and the contact coupling between the leads and the DNA molecule. It is shown that as backbone asymmetry increases, the merging and collapse of the two mini-bands take place and an extra resonance peak in the transmission appears. In addition, we present the modulation of voltage threshold in the current-voltage curves and a double-peak structure in the differential conductance due to the disappearance of the merged mini-band. Finally, in the Coulomb blockade regime of asymmetric contact coupling, a distinct and under-unity resonance in the transmission appears due to the interference effects between the DNA molecular bands and the electronic structure of the leads at the DNA-lead interface. 相似文献
26.
We present novel resonant phenomena through parallel non-coupled double quantum dots (QDs) embedded in each arm of an Aharonov-Bohm (AB) ring with magnetic flux passing through its center. The electron transmission through this AB ring with each QD formed by two short-range potential barriers is calculated using a scattering matrix at each junction and a transfer matrix in each arm. We show that as the magnetic flux modulates, a distortion of the grid-like square transmission occurs and an anti-crossing of the resonances appears. Hence, the modulation of magnetic flux in this system can have an equivalent effect to the control of inter-dot coupling between the two QDs. 相似文献
27.
This paper is concerned with new results on data related false lock of Costas loops caused by arm filter distortion of the data. The false lock phenomena is demonstrated to occur for random as well as periodic data and the relative levels of lock are predicted. It is shown that, for the case of random data with Manchester symbols, strong lock points exist when the incoming carrier frequency and the loop VCO frequency differ bynR_{s}/2 (n = 1, 2, 3, ...) Hz where Rs is the data symbol rate. In addition to the loop error signal the lock detection signal(I^{2}Q^{2}) is also analyzed for false lock effects. The theory also applies to the case of NRZ data symbols with the main result being strong false lock points also occur at VCO frequency offsets ofnR_{s}/2 (n = l, 2, 3, ldot) but at different levels than the Manchester data. The results of these analyses lead to schemes capable of detecting false lock. 相似文献
28.
Y. S. Joe V. Vargiamidis A. M. Satanin E. R. Hedin Y. D. Kim 《Journal of Experimental and Theoretical Physics》2018,126(6):705-711
new scenario for the occurrence of a Fano resonance in the transmission probability of electron waveguides is investigated using a coupled-channel theory. Both a quantum dot and an antidot with either short- or finite-range interaction are embedded in the electron waveguide. Particularly, when the Fano resonance occurs close to the mobility edge (channel threshold), it is shown that Γ~U 12 4/3 , where Γ is the resonance width and U12 is the coupling strength between bound state and continuum. This is in contrast to the usual result Γ ~U 12 2 , which is valid when the resonance occurs far from the mobility edge. Furthermore, it is shown that increasing the size of both dot and antidot leads to larger resonance width. 相似文献
29.
A mechanistic study of the formation of mesoporous structures from in situ AC conductivity measurements 总被引:1,自引:0,他引:1
Garcia-Bennett AE Brohede U Hodgkins RP Hedin N Strømme M 《Langmuir : the ACS journal of surfaces and colloids》2007,23(19):9875-9881
The purpose of this work is to study the kinetics of self-assembly in the formation mechanism of anionic templated mesoporous solids (AMS-n) during the first few seconds of the synthesis as well as to demonstrate the use of alternating ion current (AIC) conductivity measurements to follow the self-assembly in complex hybrid systems. The formation of different AMS-n caged-type mesostructures through the delayed addition of the silica source is demonstrated and explained in terms of the interaction between the co-structure-directing agent (CSDA) and the oppositely charged surfactant headgroup regions. Our findings, supported by transmission electron microscopy, 29Si magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, dynamic light scattering (DLS) measurements, and powder X-ray diffraction suggest that the interaction of the CSDA with the surfactant headgroup occurs within seconds after its addition to the synthesis gel leading to interaction between the polymerizing CSDAs and the oppositely charged micelle and to an increase in the micelle-CSDA aggregate size. Both DLS and AIC measurements agree that this process occurs within the first 1000 s after addition of the CSDA to the synthesis gel at room temperature. In addition to the mechanistic study it was found that the intermediate materials are comprised of a three-layer entity. Time-dependent 29Si MAS NMR studies reveal that an organo-silica layer forms around the micelles prior to a condensed outer inorganic shell of silica. 相似文献
30.
Mesoporous silica particles (Davisil) were functionalized with aminopropyltriethoxysilane (APTES) in a fractional factorial design with 19 different synthesis and uptake experiments. The number of amino groups and the uptake of CO(2) were optimized in a 2(V)(5-1) design. Most important to functionalization was the amount of water present during synthesis, the reaction time, and pretreating the silica with a mineral acid; certain two-way interactions were shown to be statistically significant as well. Modifications performed at 110 or 80 °C showed no significant differences concerning amine content or uptake of CO(2). Properly choosing center points for the discrete variables is problematic and is somewhat related to the lack of fit with respect to CO(2) uptake; the regression was good. Solid-state (29)Si NMR showed that the APTES was mainly fully condensed. Specific surface areas did not correlate with the number of n-propylamine groups on the silica, which is indicative of differential levels of heterogeneity in the coverage of propylamines. The uptake of CO(2) and N(2) was measured from -20 to 70 °C and from 0 to 1 bar and parametrized by the Freundlich isotherm. Amine-modified silica adsorbed significant amounts of CO(2), especially at the low partial pressure, which is important for CO(2) capture from flue gas. At such pressures, samples with a high density of amine (4 amines/nm(2)) showed a much higher uptake of CO(2) than did those with densities of ~2-3 amines/nm(2), reflecting differential tendencies to form propylammonium-propylcarbamate ion pairs; these require close proximity among amine groups to form. Water affected the uptake of carbon dioxide in different ways. Certain samples took up more moist CO(2) gas than dry CO(2), and others took up less moist CO(2) than dry CO(2), which is indicative of differential tendencies toward water adsorption. We conclude that experimental design is a time-efficient approach to the functionalization of silica with propylamine groups. 相似文献