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161.
Indium silicate activated by terbium was found to be an efficient phosphor with CR excitation, the luminosity of which was comparable to the most luminous of other terbium-activated silicates. For the preparation of this phosphor, alkaline earth metal flourides proved to act as a good mineralizer. The best result was obtained when a mixture of 1 mol In2O3, 2.2 mol SiO2, 0.015 mol Tb4O7 and 0.05 mol BaF2 was fired at 1 400°C in air for 4 h. Other rare earth luminescent centers such as Ce, Pr, Eu, Dy, Er and Tm were examined but none showed noticeable emission. Some UV excitation properties are also described. 相似文献
162.
163.
Steroid family has various bioactivities and characteristic polycyclic structure. Although several synthetic methods have been reported, more efficient way is desired for medicinal chemistry. In this Letter, we synthesized pseudoenantiomers of tricyclic enones toward both enantiomers for ABC-ring moiety of steroids utilizing d-mannitol as a chiral source. The key steps are radical domino cyclization of polyalkenyl-β-keto ester into tricyclic keto ester and subsequent dealkoxycarbonylation. 相似文献
164.
We show that suitably designed magnetic semiconductor heterostructures consisting of Mn delta (delta)-doped GaAs and p-type AlGaAs layers, in which the locally high concentration of magnetic moments of Mn atoms are controllably overlapped with the two-dimensional hole gas wave function, realized remarkably high ferromagnetic transition temperatures (T(C)). A significant reduction of compensative Mn interstitials by varying the growth sequence of the structures followed by low-temperature annealing led to high T(C) up to 250 K. The heterostructure with high T(C) exhibited peculiar anomalous Hall effect behavior, whose sign depends on temperature. 相似文献
165.
We propose an efficient methodology for predicting approximate shapes and size distribution of micelles. The methodology is a judicious combination of a conventional thermodynamic approach, the reference interaction site model (RISM) theory, and the Monte Carlo (MC) simulated annealing technique. Solvent effects are fully incorporated using the RISM theory with our robust and very efficient algorithm for solving the RISM equations, and the MC technique is applied only to surfactant molecules. The methodology is potentially applicable to realistic models of surfactant and solvent molecules with all-atom potentials. As the first step, however, it is illustrated for simplified models having only essential characteristics of the amphiphiles. We estimate the critical micelle concentration, approximate shapes, and size distributions at some surfactant concentrations. Roles of the solvent and effects due to the type of the surfactant molecule are discussed in detail. 相似文献
166.
The soft TO-phonon modes were investigated below the cubic-rhombohedral transition temperature in Pb1?xGexTe (x=0.05) and SnTe. We observed resolved Raman spectra from ordinary and extraordinary modes. The temperature dependence of the spectra was analyzed in terms of phonon-phonon interactions. We also discussed origins of extra Raman spectra which appear even in the high temperature phase. The energy gain of valence bonding electrons due to lattice distortions was estimated to be ≈109erg/cm3 by analyzing anomalous temperature behavior of the optical dielectric constant. This is about two order of magnitude larger than the depth of the well of free energy. 相似文献
167.
Strong electron-phonon interaction effects in modulated transient reflectance spectra of Ga.50In.50P
Time-resolved modulated reflection spectrum below the fundamental edge of MBE-grown direct-gap GaxIn1-xP (x = 0.5) has been studied by using sensitive picosecond excite-probe methods. The spectrum at 77K shows considerable structure in comparison with previous steady-state photoluminescence data. In particular, a strong optical phonon coupling effect has been observed in the excitation spectrum, suggestive of an acceptor bound polaron. 相似文献
168.
S. Sugai 《Solid State Communications》1982,44(8):1141-1143
Lattice vibrations in 2H-TaSe2 have been reinvestigated by Raman scattering in view of the recent orthorhombic structure of the commensurate charge density wave (CCDW) phase. The renormalization of six charge density waves on two layers gives four Ag modes and two B1g modes in the orthorhombic CCDW phase, in place of two A1g modes and two E2g modes in the hexagonal CCDW phase which had been believed. The splitting of the E2g modes to the Ag and B1g modes in the orthorhombic symmetry depends on the interlayer interaction. The observed small splitting less than 3 cm-1 shows the weak interlayer interaction. The energies of the four Ag modes and the two B1g modes are presented as a function of temperature. 相似文献
169.
A novel radical method for the stereoselective introduction of an ethynyl group has been developed. When a solution of ethynyldimethylsilyl (EDMS) or [2-(trimethylsilyl)ethynyl]dimethylsilyl (TEDMS) ethers of trans-2-iodoindanol was treated with Et(3)B followed by tetrabutylammonium fluoride in toluene, atom transfer 5-exo-cyclization and subsequent elimination occurred to give cis-2-ethynylindanol in high yield. The method was shown to be useful in the introduction of an ethynyl group in various five- and six-membered-ring iodohydrins. Furthermore, 2'-deoxy-2'-C-ethynyluridine (6) and -cytidine (7), which were designed as novel antimetabolites, were readily synthesized by using this method as the key step. This would be the first example in which a radical reaction was used for introducing an ethynyl group. 相似文献
170.
The high-energy tail of the ion energy distribution is heated by an instability with broad-band frequency spectrum having a peak a little above the ion-cyclotron frequency. The tail heating of the ions is enhanced under a mirror configuration of the magnetic field. 相似文献