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51.
Ceria supported copper catalysts were synthesized by laser vaporization and controlled condensation method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDAX) and temperature programmed reduction (TPR). The catalytic activity of the nanopowders for CO oxidation reaction was tested in a fixed bed flow tube reactor in Ar–20%O2–4%CO mixture. Irrespective of the copper content, the catalytic activity of the nanopowders is similar in the initial CO test, and the catalytic activity improves (i.e. the light-off temperature decreases) during a subsequent run. The lowest light-off temperature during the second run is recorded in the material with 20% copper. TEM studies on 20%Cu–CeO2 sample in the as-prepared condition and after CO test exhibit two types of ceria particles namely, polygonal particles 3–5 nm in size and spherical particles of 15–20 nm in size. Rapid cooling of the nanoparticles formed during the laser ablation results in incorporation of a large amount of copper within the ceria as solid solution. Presence of solid solution of copper is confirmed by EDAX and electron diffraction analyses. In addition, copper-rich surface layer of Cu2O is found over the spherical particles. The cerium oxide components are essentially identical before and after CO test, except that the polygonal CeO2 particles contain newly formed fine crystals of CuO. TPR results reveal two reduction peaks, which further supports, the presence of two different copper species in the material. The shift in light-off temperature during the second run is attributed to the synergistic interaction between newly formed CuO crystals with the CeO2 matrix. 相似文献
52.
The set of problems we consider here are generalizations of square-free sequences [A. Thue, Über unendliche Zeichenreichen, Norske Vid Selsk. Skr. I. Mat. Nat. Kl. Christiana 7 (1906) 1-22]. A finite sequence a1a2…an of symbols from a set S is called square-free if it does not contain a sequence of the form ww=x1x2…xmx1x2…xm,xi∈S, as a subsequence of consecutive terms. Extending the above concept to graphs, a coloring of the edge set E in a graph G(V,E) is called square-free if the sequence of colors on any path in G is square-free. This was introduced by Alon et al. [N. Alon, J. Grytczuk, M. Ha?uszczak, O. Riordan, Nonrepetitive colorings of graphs, Random Struct. Algor. 21 (2002) 336-346] who proved bounds on the minimum number of colors needed for a square-free edge-coloring of G on the class of graphs with bounded maximum degree and trees. We discuss several variations of this problem and give a few new bounds. 相似文献
53.
LiCo0.2Fe0.8PO4 cathode material was prepared by succinic assisted soft combustion technique. This method of synthesis ensures homogeneity
of the precursor material, improved activity and crystal grain size. Calcinations at high temperature confirm the purity of
the cathode material. The aim of this work is to investigate the effects of cobalt substitution in LiFePO4. The structural characterization of the products was analysed by the X-ray powder diffraction. Conductivity measurements
were made to characterize the transport property of the cathode material. Fourier transform infrared spectroscopy and differential
scanning calorimeter and thermogravimetry analysis have been studied to investigate the functional group present and the phase
transition involved in the sample, respectively. 相似文献
54.
Optical absorption spectrum of VO2+ ion in sodium zinc sulphate tetrahydrate single crystal has been reported at room and liquid nitrogen temperatures. From the nature and position of the observed bands, they have been attributed to VO2+ ion in C4v symmetry. The crystal field and molecular orbital coefficients have been evaluated. 相似文献
55.
AC conductivity and dielectric properties of sulphate glasses have been studied as a function of temperature, frequency and
variation in interalkali concentration. AC conductivity at frequencies well beyond the dielectric loss peaks seems to arise
from local motion of alkali ions within the neighbouring potential wells. Activation energies for AC conductivity were found
to be very much lower than those for DC conductivity. Further, AC conductivity seems to be independent of interalkali variation,
whereas ε′ and tan δ show a mild degree of mixed alkali effect. The observations made here have been explained on the basis
of a structural model earlier proposed by us for these glasses.
Communication No. 167 from Solid State and Structural Chemistry Unit. 相似文献
56.
Birch reductio and reductive methylations of some substituted naphtholic acids have been examined. The factors influencing the mechanism of reduction process have been discussed. Some of the reduced naphthoic acids are useful synthons for synthesis. 相似文献
57.
Constant potential coulometry at ?0.1 V of decamethylferrocene in a 1.5/l aluminum chloride/1-butylpyridinium chloride melt gave a deep brown solution containing the decamethylferricinium dication. 相似文献
58.
Francois Baccelli Junyi Li Thomas Richardson Sanjay Shakkottai Sundar Subramanian Xinzhou Wu 《Queueing Systems》2012,72(1-2):31-68
The recent deployment of data-rich smart phones has led to a fresh impetus for understanding the performance of wide area ad hoc networks. The most popular medium access mechanism for such ad hoc networks is CSMA/CA with RTS/CTS. In CSMA-like mechanisms, spatial reuse is achieved by implementing energy-based guard zones. We consider the problem of simultaneously scheduling the maximum number of links that can achieve a given signal to interference ratio (SIR). In this paper, using tools from stochastic geometry, we study and maximize the medium access probability of a typical link. Our contributions are two-fold: (i) We show that a simple modification to the RTS/CTS mechanism, viz., changing the receiver yield decision from an energy-level guard zone to an SIR guard zone, leads to performance gains; and (ii) We show that this combined with a simple modification to the transmit power level—setting it inversely proportional to the square root of the link gain—leads to significant improvements in network throughput. Further, this simple power-level choice is no worse than a factor of two away from optimal over the class of all “local” power level selection strategies for fading channels, and further is optimal in the non-fading case. The analysis relies on an extension of the Matérn hard core point process which allows us to quantify both these SIR guard zones and this power control mechanism. 相似文献
59.
60.
S. Sundar Pethaiah G. Paruthimal Kalaignan G. Sasikumar M. Ulaganathan V. Swaminathan 《Journal of Solid State Electrochemistry》2013,17(11):2917-2925
Nano-catalyzed membrane with different platinum (Pt) catalyst loadings (0.25 to 1 mg cm?2) was investigated for proton exchange membrane fuel cell applications, and the Pt loading on the Nafion membrane was prepared by non-equilibrium impregnation reduction method. The prepared catalyzed membranes were subjected to various characterisations, namely, X-ray diffraction, high-resolution scanning electron microscopy (HRSEM) with energy-dispersive X-ray, cyclic voltammetry, polarisation and electrochemical impedance spectroscopy. The polycrystalline fcc cubic structure and the particle size of Pt catalyst were estimated by X-ray diffraction analysis. The membrane with 0.4 mg cm?2 of Pt loading exhibits a favourable surface morphology which is confirmed by HRSEM image. Electrochemical investigations were clearly evident that the uniform distributions of Pt particles with fine pores on Nafion membrane facilitated the three-phase boundary which leads to a better cell performance. Electrochemical impedance spectroscopy demonstrated that the cell constructed using 0.4 mg cm?2 of platinum-loaded membrane has lower resistance than the other Pt loading. 相似文献