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11.
Moser DF Bosse T Olson J Moser JL Guzei IA West R 《Journal of the American Chemical Society》2002,124(16):4186-4187
A number of disilanes have been synthesized from a stable silylene, 1 (N,N'-di-tert-butyl-1,3-diaza-2-silacyclopent-4-en-2-ylidene), and a variety of halocarbons. It is proposed that disilane formation is a result of an initial halophilic interaction between the silylene and halocarbon. Formation of disilanes from 1 and CCl4, 2a, CHCl3, 2b, CH2Cl2, 2c, benzyl chloride, 2d, and bromobenzene, 5, are described here. An X-ray crystal structure of 2b was determined. 相似文献
12.
13.
The effect of paramagnetic relaxation on perturbed angular distributions is treated for nuclei interacting with their electronic shells via isotropic hyperfine interaction. The conditions are given under which Blume's analytical stochastic-model result for the nuclear perturbation factorsG k (t) can be derived quantum mechanically. Systems with arbitrary nuclear spin, but electronic spinS=1/2 may be calculated without resorting to the assumption necessary forS>1/2. Explicit closed expressions forG k (t) can be found for this particular case. 相似文献
14.
15.
Ooms KJ Feindel KW Willans MJ Wasylishen RE Hanna JV Pike KJ Smith ME 《Solid state nuclear magnetic resonance》2005,28(2-4):125-134
Results from a solid-state 139La NMR spectroscopic investigation of the anhydrous lanthanum(III) halides (LaX3; X=F, Cl, Br, I) at applied magnetic fields of 7.0, 9.4, 11.7, 14.1, and 17.6 T are presented and highlight the advantages of working at high applied magnetic field strengths. The 139La quadrupolar coupling constants are found to range from 15.55 to 24.0 MHz for LaCl3 and LaI3, respectively. The lanthanum isotropic chemical shifts exhibit an inverse halogen dependence with values ranging from −135 ppm for LaF3 to 700 ppm for LaI3, which represents nearly half of the total lanthanum chemical shift range. The spans of the magnetic shielding tensors also vary widely, from 35 to 650 ppm for the solid LaF3 through LaI3. DFT calculations of the 139La electric field gradient and magnetic shielding tensors have been performed and provide a qualitative interpretation of the trends observed experimentally. 相似文献
16.
We classify the complete metrics of nonnegative sectional curvature on M
2 × 2, where M
2 is any compact 2-manifold. 相似文献
17.
J. Bosse 《Il Nuovo Cimento D》1990,12(4-5):481-497
Summary A new derivation of the mode-coupling theory of liquid dynamics is presented which is applicable to both quantum and classical
systems. A clear distinction between the basic underlying hyphotheses and the more technical approximations has been attempted.
Asymptotic corrections to the dynamics of modes due to mode-coupling effects and selfconsistent mode-coupling theories emerge
from the original idea as two markedly different branches of application.
Paper presented at the workshop ?Highlights on Simple Liquids?, held in Turin at ISI on 1–3 May, 1989. 相似文献
18.
Pyrite undergoes a series of exothermic reactions during mine roasting to porous hematite. At low temperatures, the first non-refractive phase to form is ferrous sulphate and could be a cheaper alternative to hematite roasting for the mining industry. In this study, pyrite powder is heated in air at temperatures between 200 and 370 °C for 1 to 256 h in a temperature and time series. The rate of oxidation of pyrite to ferrous sulphate is modelled by combining the Arrhenius equation with the Weibull function to extract reliable thermodynamic data, including the energy of activation, the frequency factor and the overall order of reaction. From the thermodynamic data obtained, two possible oxidation mechanisms are recognized, depending on the bond dissociation energies of the S–S and Fe–S bonds in pyrite. 相似文献
19.
The effect of time step,thermostat, and strain rate on ReaxFF simulations of mechanical failure in diamond,graphene, and carbon nanotube
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Benjamin D. Jensen Kristopher E. Wise Gregory M. Odegard 《Journal of computational chemistry》2015,36(21):1587-1596
As the sophistication of reactive force fields for molecular modeling continues to increase, their use and applicability has also expanded, sometimes beyond the scope of their original development. Reax Force Field (ReaxFF), for example, was originally developed to model chemical reactions, but is a promising candidate for modeling fracture because of its ability to treat covalent bond cleavage. Performing reliable simulations of a complex process like fracture, however, requires an understanding of the effects that various modeling parameters have on the behavior of the system. This work assesses the effects of time step size, thermostat algorithm and coupling coefficient, and strain rate on the fracture behavior of three carbon‐based materials: graphene, diamond, and a carbon nanotube. It is determined that the simulated stress‐strain behavior is relatively independent of the thermostat algorithm, so long as coupling coefficients are kept above a certain threshold. Likewise, the stress‐strain response of the materials was also independent of the strain rate, if it is kept below a maximum strain rate. Finally, the mechanical properties of the materials predicted by the Chenoweth C/H/O parameterization for ReaxFF are compared with literature values. Some deficiencies in the Chenoweth C/H/O parameterization for predicting mechanical properties of carbon materials are observed. © 2015 Wiley Periodicals, Inc. 相似文献
20.
Thomas T. Nakashima Kristopher J. Harris Roderick E. Wasylishen 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2010,202(2):162-172
For quadrupolar nuclei with spin quantum numbers equal to 3/2, 5/2 and 7/2, the intensities of the NMR transitions in a single crystal are examined as a function of the rf excitation flip angle. Single-quantum NMR intensities are calculated using density matrix theory beginning under various non-equilibrium conditions and are compared with those determined experimentally. As a representative spin-3/2 system, the flip-angle dependence of the 23Na NMR intensities of a single crystal of NaNO3 was investigated beginning with the inversion of the populations associated with one of the satellite transitions. Subsequently, the populations of both satellite transitions were inverted using highly frequency-selective hyperbolic secant pulses. Calculated and experimental intensities are in good agreement. As an example of a spin-5/2 system, the flip-angle dependence of the 27Al NMR transition intensities was determined using a single crystal of sapphire, Al2O3, starting under different nuclear spin population conditions. The experimental trends mimicked those predicted by the density matrix calculations but the agreement was not as good as for the spin-3/2 case. Some SIMPSON simulations were also carried out to confirm the results generated by our density matrix calculations. The theoretical flip-angle behavior of the NMR transition intensities obtained from a spin-7/2 spin system is also discussed. 相似文献