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121.
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123.
The local density of states and the charge distribution in a cluster model of hydrogenated amorphous silicon is calculated using the recursion method. The results indicate an average charge transfer of 0.3 electrons from silicon to hydrogen. In addition Si-H dipoles carry small negative charges, which are neutralized by a positively charged bulk of silicon atoms. There are also static spatial charge fluctuations, which are due to the topological disorder. 相似文献
124.
The cross section for the 42Ca(p, γ)43Sc reaction has been measured over the lab energy range from 0.7 to 5.5 MeV using a positron spectrometer to measure the annihilation radiation from the decay of 3.9 h 43Sc. Stellar reaction rates NA〈σv〉 have been calculated from the experimental cross section curve for a series of three temperatures of interest for explosive oxygen and silicon burning in stars. The calculated rates are compared with the theoretical predictions of Woosley et al. and found to be in agreement within the experimental errors and the quoted validity of the theoretical calculation 相似文献
125.
K.A. Mohamed G.C. King F.H. Read 《Journal of Electron Spectroscopy and Related Phenomena》1977,12(3):229-237
The lifetime of the (B3Σ+υ= 0, 1 state of the CN radical has been measured by the photon-photon delayed coincidence technique, the CN radical being produced by electron impact dissociation of acetonitrile. This is the first lifetime measurement in a free radical by this method. The optical cascade in the band spectrum of CN used for the present measurement is H2Πr - B2Σ+ - X2Σ+. The lifetime of the (B2Σ+)υ=0, 1 state in CN has been found to be 61.1 ± 7.6 ns. 相似文献
126.
Reflection-adsorption infrared spectroscopy has been combined with thermal desorption and surface stoichiometry measurements to study the structure of CO chemisorbed on a {111}- oriented platinum ribbon under uhv conditions. Desorption spectra show a single peak at coverages > 1014 molecules cm?2, with the desorption energy decreasing with increasing coverage up to 0.4 of a monolayer, and then remaining constant at ≈135 kJ mol?1 until saturation. The “saturation” coverage at 300 K is 7 × 1014 molecules cm?2, and no new low temperatures state is formed after adsorption at 120 K. Infrared spectra show a single very intense, sharp band over the spectral range investigated (1500 to 2100 cm?1), which first appears at low coverages at 2065 cm?1 and shifts continuously with increasing coverage to 2101 cm?1 at 7 × 1014 molecules cm?2. The halfwidth of the band at 2101 cm?1 is 9.0 cm?1, independent of temperature and only slightly dependent on coverage. The band intensity does not increase uniformly with increasing coverage, and hysteresis is observed between adsorption and desorption sequences in the variation of both the band intensity and frequency as a function of coverage. The frequency shift and the virtual invariance of the absorption band halfwidt with increasing coverage (Jespite recent LEED evidence for overlayer compression in this system) are attributed to strong dipole-dipole coupling in the overlayer. 相似文献
127.
The alcoholic extract of Gymnosporia trilocularis Hay. (Celastraceae) was found to exhibit antitumor activities against P388 lymphocytic leukemia and KB cell culture systems. From this extract β-amyrin ( 1 ), β-sitosterol ( 2 ) and its monoglucoside ( 6 ), stigmasterol ( 3 ) and its monoglucoside ( 7 ), campesterol ( 4 ) and its monoglucoside ( 8 ), maniladiol ( 5 ), dulcitol ( 9 ) and six yet unidentified principles ( 10–15 ) were isolated. The stereochemistry of C-16-OH of maniladiol ( 5 ) was confirmed spectroscopically by 1H nmr to be equatorial. Of all the isolated compounds, the mixture of three steroid monoglucosides ( 6:7:8 =28:1.1:1) exhibited cytotoxicity (ED50=2.6×100 mcg/ml) and 5 showed only marginal effect (ED50=2.1×101 mcg/ml) in KB test system. 相似文献
128.
The vapor phase absorption spectrum of thiophosgene (Cl2CS) in the 2500–2900 Å region consists of a broad intense band (. On the red side of this a vibrationally discrete structure is found which becomes increasingly diffuse and merges into the broad band as the wavelength is decreased. It is shown that this vibrational structure can be explained as due to a , electronic transition between a planar ground state and a pyramidal excited state of the molecule. In the latter state, the CS stretching mode ν1′(a1) = 681 cm?1 and the CCl bending mode ν3′(a1) = 147 cm?1. From the inversion doublet splitting of the out-of-plane mode ν4′(b1), the barrier to inversion is calculated to be ~126 cm?1, with an equilibrium out-of-plane angle of ~20°. 相似文献
129.
The results of a vibrational and rotational analysis of the banded transition in are presented. Only three of the six vibrational modes are active in the spectrum with , , and . The spin forbidden transition gains intensity primarily by a mixing of the and states. This is confirmed by a rotational analysis of the 000 band of both isotopes. The rotational analysis shows that the coupling in the state is near Hund's case b and that the spin constants are nearly 10 times greater than those observed for CH2O. A calculation shows that this difference is due to the greater spin orbit coupling of S in CH2S and to the smaller energy differences between the , , , and the states. The r0 structure calculated from the rotational constants is , , βHCH = 119.6°, and α (out of plane) = 16.0°. A simultaneous fit of the vibrational levels in ν′4 of CH2S and CD2S to a double minimum potential function yielded a barrier to molecular inversion of 13 cm?1 and an equilibrium out-of-plane angle of 15°. 相似文献
130.