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排序方式: 共有122条查询结果,搜索用时 15 毫秒
1.
以十四酸根阴离子柱撑Zn-Al水滑石Zn0.77Al0.22(OH)2.0.22C13H27COO.0.81 H2O(记为ZnAl-14A)为预撑前体,在水溶液中用离子交换法将以2∶17缺位杂多酸根离子(P2Mo16VO61)11-记为(P Mo V)为配体的稀土杂多配阴离子Ce(P2Mo16VO61)219-(记为Ce(PMoV)2)插层组装到水滑石层板间,合成了一种具有大的层间距(3.37 nm)的超分子插层材料Zn0.77Al0.23(OH)2.0.0105[Ce(P1.9Mo15.7V1.1O61)2].0.011C13H27COO.0.83H2O(记为ZnAl-Ce(PMoV)2)。用ICP,IR,XRD和DTA对产物的组成和结构进行了表征。结果表明,该产物中Ce(PMoV)2配阴离子沿其长轴垂直于层板的方向分布于水滑石层间;产物具有规整的层状结构和热稳定性;产物对乙酸与正丁醇的酯化反应,二甘醇的脱水-环化反应和H2O2氧化环己烷的反应有良好的催化性能,且易于回收重复使用。 相似文献
2.
C. Bucci G. Guidi G.M. DeMunari M. Manfredi P. Podini R. Tedeschi P.R. Crippa A. Vecli 《Chemical physics letters》1978,57(1):41-44
The precession frequencies of muonium in a molecular radical state have been observed by μSR technique in diluted solutions of 2,6-dihydroxy-5-methyl-pyrimidine (thymine) in water. The conditions for the observation of the radicals are discussed in terms of the interdependent roles played by the chemical reaction time for muonium and by the external magnetic field. A comparison with the known ESR data on solid thymine confirms that the observed product of the muonium's reaction is an adduct radical with an hyperfine interaction reduced to 7% ± 1% of the muonium value 相似文献
3.
S. P. Kozyrev I. V. Kucherenko M. Cestelli Guidi R. Triboulet 《Physics of the Solid State》2007,49(12):2307-2311
The paper reports on assignment of lattice reflection spectra of the Hg1?x Znx Te alloys (x = 0.10, 0.35, and 0.55) measured in the 40–300-K temperature interval and on a comparative analysis of the lattice vibration parameters for two alloy systems, HgZnTe and HgCdTe, in the low-frequency optical vibration region (the region of the anomalous Hg-Te vibrational mode in HgTe). While the parameters of the fundamental lattice modes are closely similar, the temperature dependences of the low-frequency modes of the two alloy systems are radically different. Their thermal activation energies for the HgZnTe and HgCdTe alloys are 3.3 and 50.0 meV, respectively. The results of the experiment are treated in terms of the double-well potential model for the Hg atom in the alloy lattice. 相似文献
4.
A. Voloshynovskii P. Savchyn I. Karbovnyk S. Myagkota M. Cestelli Guidi M. Piccinini A.I. Popov 《Solid State Communications》2009,149(15-16):593-597
The comparative far-infrared spectroscopy studies of Rb0.8Cs0.2Cl and Rb0.8Cs0.2Cl containing CsPbCl3 nanocrystals between 170 and 320 K are reported. The effect of cesium lead chloride nanocrystals on the phonon modes of the host matrix, particularly manifested in different temperature behavior of LO–TO splitting and the temperature dependence of high frequency dielectric constant, are demonstrated. 相似文献
5.
6.
Combining recent and new inelastic neutron scattering data for the molecular cyclic cluster Cr8 produces a deep understanding of the low lying excitations in bipartite antiferromagnetic Heisenberg rings. The existence of the L band, the lowest rotational band, and the E band, essentially spin wave excitations, is confirmed spectroscopically. The different significance of these excitations and their physical nature is clearly established by high-energy and Q-dependence data. 相似文献
7.
Allodi G Cestelli Guidi M De Renzi R Caneiro A Pinsard L 《Physical review letters》2001,87(12):127206
We report a (139)La NMR investigation of low-doped insulating manganite samples (LaMnO(3+delta) and La(1-y)Ca(y)MnO(3+delta)) as a function of temperature. A volume fraction with fast nuclear relaxations was revealed by the inhomogeneous loss of the NMR signal over a broad temperature interval. Comparison with muon spin rotation data demonstrates that the wipeout of the (139)La signal is mainly due to slowly fluctuating electric field gradients. This provides strong evidence for the slow diffusion of lattice excitations, identified with Jahn-Teller small polarons. 相似文献
8.
D. Puzzovio M.C. Carotta A. Cervi A. El Hachimi J.P. Joly F. Gaillard V. Guidi 《Solid State Ionics》2009,180(36-39):1545-1552
Temperature-programmed desorption (TPD) and a differential form of it, called intermittent temperature-programmed desorption (ITPD), turned out to be powerful characterising techniques for chemoresistive materials applied to gas sensing. We investigated samples of SnO2, TiO2 and solid solutions of them (TixSn1 ? xO2). TPD and ITPD experiments were carried out in vacuum, with samples previously treated in pure O2 (100 Torr, 500 °C, 30 min). Amounts of desorbed O2 corresponded for all Ti-containing samples to less than 10% of a compact monolayer of ions O2?. Corresponding values of the apparent activation energy of desorption (Eapp) were calculated directly from the Arrhenius plots for each partial TPD and ranged from about 100 to 330 kJ mol? 1 (1.16 to 3.82 eV). 相似文献
9.
Leonardo F. Guidi Domingos H. U. Marchetti 《Communications in Mathematical Physics》2001,219(3):671-702
We consider a quasilinear parabolic differential equation associated with the renormalization group transformation of the
two-dimensional hierarchical Coulomb system in the limit as the size of the block L&\darr; 1. We show that the initial value problem is well defined in a suitable function space and the solution converges,
as t→∞, to one of the countably infinite equilibrium solutions. The j
th nontrivial equilibrium solution bifurcates from the trivial one at . These solutions are fully described and we provide a complete analysis of their local and global stability for all values
of inverse temperature β >0. Gallavotti and Nicoló's conjecture on infinite sequence of “phases transitions” is also addressed.
Our results rule out an intermediate phase between the plasma and the Kosterlitz–Thouless phases, at least in the hierarchical
model we consider.
Received: 29 November 1999 / Accepted: 13 January 2001 相似文献
10.
Vanina Guidi 《Tetrahedron letters》2010,51(38):5086-5090
The l-proline organocatalytic homodimerization of 2-cyclohexenone has been studied and it is concluded that the mechanism of the reaction follows competing pathways involving either a two-step imine/enamine addition or a concerted Diels-Alder cycloaddition where the ultimate product distribution is dependent upon the ratio of the organocatalyst to 2-cyclohexenone and a base present. 相似文献