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91.
92.
In order to study the Kohn-Sham frontier molecular orbital energies in the complete basis limit, a comparative study between localized functions and plane waves, obtained with the local density approximation exchange-correlation functional is made. The analyzed systems are ethylene and butadiene, since they are theoretical and experimentally well characterized. The localized basis sets used are those developed by Dunning. For the plane-waves method, the pseudopotential approximation is employed. The results obtained by the localized basis sets suggest that it is possible to get an estimation of the orbital energies in the limit of the complete basis set, when the basis set size is large. It is shown that the frontier molecular orbital energies and the energy gaps obtained with plane waves are similar to those obtained with a large localized basis set, when the size of the supercell and the plane-wave expansion have been appropriately calibrated. 相似文献
93.
Lumetta GJ Rapko BM Garza PA Hay BP Gilbertson RD Weakley TJ Hutchison JE 《Journal of the American Chemical Society》2002,124(20):5644-5645
Evaluation of the malonamide substructure with respect to binding site preorganization and complementarity for lanthanide metal ions suggests a new ligand architecture specifically designed to enhance lanthanide ion affinity. Consideration of conformational reorganization, restricted bond rotation, and donor group orientation suggests that typical malonamide structures, for example, N,N,N'N'-tetrahexylpropane-1,3-diamide (1), N,N'-dibutyl-N,N'-dimethyl-2-tetradecylpropane-1,3-diamide (2), or N,N,N'N'-tetramethylpropane-1,3-diamide (6), are poorly organized for metal ion complexation. Molecular mechanics analyses show that the unfavorable enthalpic and entropic terms are eliminated by the use of the novel bicyclic architecture found in 3,9-diaza-3,9-dimethylbicyclo[4.4.0]decane-2,10-dione (7). Diamide 7 was prepared, and the X-ray crystal structure of the complex [Eu(7)(2)(NO(3))(3)] exhibits the same chelate conformation predicted by the molecular mechanics model. A hydrophobic derivative, 3,9-diaza-3,9-dioctylbicyclo[4.4.0]decane-2,10-dione (8), was prepared, and solvent extraction studies reveal that the preorganized architecture of 8 gives a dramatic enhancement in binding affinity, exhibiting Eu(3+) distribution coefficients that are 7 orders of magnitude larger than a typical malonamide ligand, 1. 相似文献
94.
Narayan G. BhatAmanda Garza 《Tetrahedron letters》2003,44(36):6833-6835
(Z)-1-Trimethylsilyl-1-alkenes easily prepared by the hydroboration of the corresponding 1-trimethylsilyl-1-alkynes followed by protonolysis with acetic acid, readily react with dibromoborane-methyl sulfide complex in dichloromethane for 6 h. The resulting solution is then treated with 1,3-propane diol in a 1:1 mixture of dichloromethane and n-pentane at 0°C for half an hour to provide the corresponding gem-dimetalloalkanes containing boron and silicon. These alpha-trimethylsilylalkylboronate esters are purified by vacuum distillation in high yields (72-84%) and the structures of these novel intermediates are further confirmed by selective oxidation with alkaline hydrogen peroxide to provide the corresponding alcohols containing trimethylsilyl group. 相似文献
95.
96.
97.
Since Newton first considered the motion of a spherical pendulum over 200 years ago, many researchers have studied its dynamic
response under a variety of conditions. The characteristic of the problem that has invited so much investigation was that
a spherical pendulum paradigms much more complex phenomena. Understanding the response of a paradigm gives an almost multiplicative
effect in the understanding of other phenomena that can be modeled as a variant of the paradigm. The spherical pendulum has
been used to damp irregular motion in helicopters and on space stations as well as for many other applications. In this study
an inverted impacting spherical pendulum with large deflection was investigated. The model was designed to approximate an
ideal pendulum, with the pendulum bob contributing the vast majority of the mass moment of inertia of the system. Two types
of bearing mechanisms and tracking devices were designed for the system, one of which had low damping coefficient and the
other with a relatively high damping coefficient. An experimental investigation was performed to determine the dynamics of
an inverted, impacting spherical pendulum with large deflection and vertical parametric forcing. The pendulum system was studied
with nine different bobs and two different base configurations. During the experiments, the frequency of the excitation remained
between 24.6 and 24.9 Hz. It was found that sustained conical motions did not naturally occur. The spherical pendulum system
was analyzed to determine under what conditions the onset of Type I response (a repetitive motion in which the pendulum bob
does not traverse through the apex. The bob strikes the same general area of the restraint without striking the opposite side
of the restraint.), sustainable Type II response (this is the repetitive motion in which the pendulum bob traverses through
the apex. The bob strikes opposite sides of the restraint.), and mixed mode response (motion in which the pendulum bob randomly
strikes either the same area of the restrain or the opposite side of the restraint) occurred. 相似文献
98.
K.?F.?Soto A.?Carrasco T.?G.?Powell K.?M.?Garza L.?E.?MurrEmail author 《Journal of nanoparticle research》2005,7(2-3):145-169
A range of manufactured nanoparticulate materials, including Ag, TiO2, Fe2O3, Al2O3, ZrO2, Si3N4, and a range of carbonaceous nanoparticulate materials: single-wall and multi-wall carbon nanotube aggregates and aggregated nanoparticles of black carbon, as well as commercial (mineral grade) chrysotile asbestos nanotube aggregates, have been rigorously characterized by transmission electron microscopy. These nanoparticulate materials ranged in primary particle sizes from roughly 3 to 150 nm (except for the nanotube materials with lengths in excess of 15 μm). Aggregate sizes ranged from 25 nm to 20 μm. Comparative cytotoxicological assessment of these nanomaterials was performed utilizing a murine (lung) macrophage cell line. Considering the chrysotile asbestos to be a positive control, and assigning it a relative cytotoxicity index of unity (1.0), relative cytotoxicity indexes were observed as follows at concentrations of 5 μg/ml: 1.6 and ∼ 0.4 for Ag and TiO2, respectively; 0.7–0.9 for the Fe2O3, Al2O3 and ZrO2, 0.4 for the Si3N4, 0.8 for the black carbon, and 0.9 to 1.1 for the carbon nanotube aggregate samples. Observations of a cytotoxic response, nearly identical to that for chrysotile asbestos, for multi-wall carbon nanotube aggregates which very closely resemble anthropogenic multi-wall carbon nanotubes in the environment, raise some concern for potential health effects, especially for long-term exposure.This revised version was published online in August 2005 with a corrected issue number. 相似文献
99.
A new ultrasonic method — thermoacoustic analysis — is reported for the detection of the added chemical preservatives in branded
milk. The nature of variation and shift in the thermal response of the acoustic parameters specific acoustic impedance, adiabatic
compressibility and Rao’s specific sound velocity for different samples of branded milk as compared to the chemical added
pure milk are explained as due to the presence of chemicals in these branded samples. 相似文献
100.
W G Deskins D C Winter H P Sheng C Garza 《The Journal of the Acoustical Society of America》1985,77(2):756-758
A technique to estimate the body volume of newborns has been developed using the principle of the Helmholtz resonator. The change in the resonance frequency of a small cavity after an infant is placed inside can be used to determine the body volume of the infant. A prototype system, termed an acoustic plethysmograph, was built and used to measure the volume of newborn miniature pigs. Results of the animal body volume measurements compare favorably (within an average of 1.1%) with body volumes measured by hydrostatic weighing. 相似文献