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排序方式: 共有166条查询结果,搜索用时 15 毫秒
71.
72.
Eugenia Elzer Dr. Philipp Strobel Volker Weiler Muhammad R. Amin Dr. Peter J. Schmidt Prof. Dr. Alexander Moewes Prof. Dr. Wolfgang Schnick 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(12):e202104121
The nitridoberylloaluminate Ba2[BeAl3N5]:Eu2+ and solid solutions Sr2−xBax[BeAl3N5]:Eu2+ (x=0.5, 1.0, 1.5) were synthesized in a hot isostatic press (HIP) under 50 MPa N2 atmosphere at 1200 °C. Ba2[BeAl3N5]:Eu2+ crystallizes in triclinic space group (no. 2) (Z=2, a=6.1869(10), b=7.1736(13), c=8.0391(14) Å, α=102.754(8), β=112.032(6), γ=104.765(7)°), which was determined from single-crystal X-ray diffraction data. The lattice parameters of the solid solution series have been obtained from Rietveld refinements and show a nearly linear dependence on the atomic ratio Sr : Ba. The electronic properties and the band gaps of M2[BeAl3N5] (M=Sr, Ba) have been investigated by a combination of soft X-ray spectroscopy and density functional theory (DFT) calculations. Upon irradiation with blue light (440–450 nm), the nitridoberylloaluminates exhibit intense orange to red luminescence, which can be tuned between 610 and 656 nm (fwhm=1922–2025 cm−1 (72–87 nm)). In contrast to the usual trend, the substitution of the smaller Sr2+ by larger Ba2+ leads to an inverse-tunable luminescence to higher wavelengths. Low-temperature luminescence measurements have been performed to exclude anomalous emission. 相似文献
73.
本研究了铍(Ⅱ)与对碘偶氮氯膦的显色反应。在0.1mol/LNaAc 溶液中,铍(Ⅱ)与显色剂生成蓝色配合物。最大吸收波长为620nm,其摩尔吸光系数ε620=3.36×10^4L·mol^-1·cm^-1。铍(Ⅱ)含量在0~5.0μg/25mL范围内经尔定律。配合物中Be(Ⅱ)与显色剂的摩尔比为1∶2。该方法可应用于铍青铜、铝合金及水样中微量铍的测定。方法灵敏、快速、简便。 相似文献
74.
Hung I Macdonald CL Schurko RW 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(23):5923-5935
The correlation between anisotropic 9Be NMR (quadrupolar and chemical shielding) interactions and the structure and dynamics in [Cp2Be], [Cp2*Be], and [(C5Me4H)2Be] is examined by solid-state 9Be NMR spectroscopy, as well as by ab initio and hybrid density functional theory calculations. The 9Be quadrupole coupling constants in the three compounds correspond well to the relative degrees of spherical ground-state electronic symmetry of the environment about beryllium. Theoretical computations of NMR interaction tensors are in excellent agreement with experimental values and aid in understanding the origins of NMR interaction tensors and their correlation to molecular symmetry. Variable-temperature (VT) 9Be and 13C NMR experiments reveal a highly fluxional structure in the condensed phase of [Cp2Be]. In particular, the pathway by which the Cp rings of [Cp2Be] 'invert' coordination modes is examined in detail using hybrid density functional theory in order to inspect variations of the 9Be NMR interaction tensors. The activation energy for the 'inversion' process is found to be 36.9 kJ mol(-1) from chemical exchange analysis of 13C VT CP/MAS NMR spectra. The low-temperature (ca. -100 degrees C) X-ray crystal structures of all three compounds have been collected and refined, and are in agreement with previously reported structures. In addition, the structure of the same Cp2Be crystal was determined at 20 degrees C and displays features consistent with increased intramolecular motion, supporting observations by 9Be VT NMR spectroscopy. 相似文献
75.
76.
Peter N. Ascik René Rugango Dr. Andrew C. Simmonett Katherine R. Compaan Prof. Henry F. Schaefer III 《Chemphyschem》2012,13(5):1255-1260
Recent high‐resolution spectroscopic studies by Merritt, Bondybey, and Heaven (Science 2009 , 324, 1548) have heightened the anticipation that small beryllium clusters will soon be observed in the laboratory. Beryllium clusters are important discrete models for the theoretical study of metals. The trigonal bipyramidal Be5 molecule is studied using high‐level coupled cluster methods. We obtain the optimized geometry, atomization and dissociation energies, and vibrational frequencies. The c~CCSDT(Q) method is employed to compute the atomization and dissociation energies. In this approach, complete basis set (CBS) extrapolations at the CCSD(T) level of theory are combined with an additive correction for the effect of iterative triple and perturbative quadruple excitations. Harmonic vibrational frequencies are obtained using analytic gradients computed at the CCSD(T) level of theory. We report an atomization energy of 129.6 kcal mol?1 at the trigonal bipyramid global minimum geometry. The Be5→Be4+Be dissociation energy is predicted to be 39.5 kcal mol?1. The analogous dissociation energies for the smaller beryllium clusters are 64.0 kcal mol?1 (Be4→Be3+Be), 24.2 kcal mol?1 (Be3→Be2+Be), and 2.7 kcal mol?1 (Be2→Be+Be). The trigonal bipyramidal Be5 structure has an equatorial–equatorial bond length of 2.000 Å and an axial–equatorial distance of 2.060 Å. Harmonic frequencies of 730, 611, 456, 583, 488, and 338 cm?1 are obtained at the CCSD(T)/cc‐pCVQZ level of theory. Quadruple excitations are found to make noticeable contributions to the energetics of the pentamer, which exhibits a significant level of static correlation. 相似文献
77.
External uniaxial stress effects on the radiation damage dynamics in a a-Fe b.c.c. structure are studied by means of the computer simulation method. Focused collision chains, defocused ones, and atom-atom collision cascades were simulated. The external uniaxial stresses affect the intervals between a vacancy and an interstitial atom produced due to a collision chain, i.e. changes a dynamical crowdion path. The external stresses change the number of stable point defects and their arrangement in the cascade development region if an atom-atom collision cascade develops in a stressed crystal. The studies of focused collision chains of energies close to the atom displacement threshold energies show that the latter can either increase or decrease due to the external stresses depending on the direction of the effect. 相似文献
78.
79.
80.
Phonon frequencies in beryllium along the principal symmetry directions have been determined by means of the slow neutron
inelastic scattering technique. The data are analysed in terms of a six-neighbour force constant model and the force constants
are evaluated. It is concluded that strong tensor forces are present in beryllium and the importance of this finding to basic
theories of lattice dynamics is pointed out. 相似文献