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71.
McDonough JE Weir JJ Carlson MJ Hoff CD Kryatova OP Rybak-Akimova EV Clough CR Cummins CC 《Inorganic chemistry》2005,44(9):3127-3136
The kinetics of the oxidative addition of PhSeSePh and PhTeTePh to the stable 17-electron complex *Cr(CO)3C5Me5 have been studied utilizing stopped-flow techniques. The rates of reaction are first-order in each reactant, and the enthalpy of activation decreases in going from Se (deltaH(double dagger) = 7.0 +/- 0.5 kcal/mol, deltaS(double dagger) = -22 +/- 3 eu) to Te (deltaH(double dagger) = 4.0 +/- 0.5 kcal/mol, deltaS(double dagger) = -26 +/- 3 eu). The kinetics of the oxidative addition of PhSeH and *Cr(CO)3C5Me5 show a change in mechanism in going from low (overall third-order) to high (overall second-order) temperatures. The enthalpies of the oxidative addition of PhE-EPh to *Cr(CO)3C5Me5 in toluene solution have been measured and found to be -29.6, -30.8, and -28.9 kcal/mol for S, Se, and Te, respectively. These data are combined with enthalpies of activation from kinetic studies to yield estimates for the solution-phase PhE-EPh bond strengths of 46, 41, and 33 kcal/mol for E = S, Se, and Te, respectively. The corresponding Cr-EPh bond strengths are 38, 36, and 31 kcal/mol. Two methods have been used to determine the enthalpy of hydrogenation of PhSeSePh in toluene on the basis of reactions of HSPh and HSePh with either *Cr(CO)3C5Me5 or 2-pyridine thione. These data lead to a thermochemical estimate of 72 kcal/mol for the PhSe-H bond strength in toluene solution, which is in good agreement with kinetic studies of H atom transfer from HSePh at higher temperatures. The reaction of H-Cr(CO)3C5Me5 with PhSe-SePh is accelerated by the addition of a Cr radical and occurs via a rapid radical chain reaction. In contrast, the reaction of PhTe-TePh and H-Cr(CO)3C5Me5 does not occur at any appreciable rate at room temperature, even in the presence of added Cr radicals. This is in keeping with a low PhTe-H bond strength blocking the chain and implies that H-TePh < or = 63 kcal/mol. Structural data are reported for PhSe-Cr(CO)3C5Me5 and PhS-Cr(CO)3C5Me5. The two isostructural complexes do not show signs of an increase in steric strain in terms of metal-ligand bonds or angles as the Cr-EPh bond is shortened in going from Se to S. Bond strength estimates of the PhE-H and PhE-EPh derived from density functional theory calculations are in reasonable agreement with experimental data for E = Se but not for E = Te. The nature of the singly occupied molecular orbital of the *EPh radicals is calculated to show increasing localization on the chalcogenide atom in going from S to Se to Te. 相似文献
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A novel thermal desorption technique using a direct-probe device (Chromatoprobe) attached to a gas chromatograph–mass spectrometer
is presented for the thermal pretreatment, characterisation and analysis of molecularly imprinted polymers. The technique
is demonstrated as effective for the removal of volatile materials, including template and unreacted monomers, from methacrylic
acid–ethylene glycol dimethacrylate copolymers imprinted with 2-aminopyridine. Mass spectrometry is a powerful technique for
polymer bleed characterisation. Thermal desorption studies on reloaded template and related compounds are reported as a means
of assessing polymer morphology, specific binding by imprinted polymers compared with reference non-imprinted polymers and
selective binding by an imprinted polymer for its template. Calibration studies on the thermal desorption technique using
an internal standard are presented with R
2 > 0.999. The technique provides a novel method for assessment of polymer thermal stability, composition and morphology. 相似文献
74.
Tonzetich ZJ Schrock RR Wampler KM Bailey BC Cummins CC Müller P 《Inorganic chemistry》2008,47(5):1560-1567
The tungsten nitrido species, [W(mu-N)(CH2-t-Bu)(OAr)2]2 (Ar = 2,6-diisopropylphenyl), has been prepared in a reaction between the alkylidyne species, W(C-t-Bu)(CH2-t-Bu)(OAr)2, and organonitriles. The dimeric nature of the nitride was established in the solid state through an X-ray study and in solution through a combination of 15N NMR spectroscopy and vibrational spectroscopy. Reaction of the nitride with trimethylsilyl trifluoromethanesulfonate afforded the monomeric trimethylsilyl imido species, W(NSiMe3)(CH2-t-Bu)(OAr)2(OSO2CF3), which was also characterized crystallographically. The W2N2 core can be reduced by one electron electrochemically or in bulk with metallocenes to afford the radical anion, {n-Bu4N}{[W(mu-N)(CH2-t-Bu)(OAr)2]2}. Density functional theory calculations suggest that the lowest-energy allowable transition in [W(mu-N)(CH2-t-Bu)(OAr)2]2 is from a highest occupied molecular orbital consisting largely of ligand-based lone pairs into what is largely a metal-based lowest unoccupied molecular orbital. 相似文献
75.
Magnetic-Bottle and Velocity-Map Imaging Photoelectron Spectroscopy of APS- (A=C14H10 or Anthracene): Electron Structure,Spin-Orbit Coupling of APS·, and Dipole-Bound State of APS- 下载免费PDF全文
Qin-qin Yuan Zheng Yang Ren-zhong Li Wesley J. Transue Zhi-peng Li Ling Jiang Niranjan Govind Christopher C. Cummins Xue-Bin Wang 《化学物理学报(中文版)》2018,31(4):463-470
Gaseous dibenzo-7-phosphanorbornadiene P-sulfide anions APS-(A=C14H10 or anthracene) were generated via electrospray ionization, and characterized by magnetic-bottle photoelectron spectroscopy, velocity-map imaging (VMI) photoelectron spectroscopy, and quantum chemical calculations. The electron affinity (EA) and spin-orbit (SO) splitting of the APS· radical are determined from the photoelectron spectra and Franck-Condon factor simulations to be EA=(2.62±0.05) eV and SO splitting=(43±7) meV. VMI photoelectron images show strong and sharp peaks near the detachment threshold with an identical electron kinetic energy (eKE) of 17.9 meV at three different detachment wavelengths, which are therefore assigned to autodetachment from dipole-bound anion states. The B3LYP/6-31++G(d, p) calculations indicate APS· has a dipole moment of 3.31 Debye, large enough to support a dipole-bound electron. 相似文献
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A Frobenius formula is found for the (m, k)-standard characters φσ ρ, of the Hecke algebras Hn(q) of type An-1, where q is a primitive pth root of unity, with p=m+k. 相似文献
80.