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911.
Self-assembly patterns formed upon solvent evaporation of aqueous cetyltrimethylammonium bromide-coated gold nanoparticles of various shapes 总被引:5,自引:0,他引:5
Gold nanocrystals of various shapes, which were produced in high yield in the presence of cetyltrimethylammonium bromide (CTAB), showed a range of two-dimensional self-assembly patterns upon drying from aqueous solution. The interparticle spacings were independent of the size and shape of the gold nanocrystals. Energy-dispersive X-ray analysis (EDAX) and Fourier-transform infrared (FTIR) spectroscopic studies revealed that the CTAB molecules adsorb onto surfaces of the gold nanocrystals in a bilayer or multilayer fashion, consistent with other groups' results. Zeta potential measurements showed that CTAB-coated nanocrystals were positively charged and the zeta potential remained almost the same upon two centrifugations and redispersion of the nanocrystals in deionized water, confirming the high stability of the surfactant-nanoparticle interaction. The nanocrystal shape strongly influenced the nature of the self-assembly patterns, in some cases in accord with theoretical predictions. CTAB is proposed as the medium for self-assembly, via interdigitation of its hydrophobic chains from adjacent nanocrystals for close contact, or via sharing a layer of counterions for larger inter-nanocrystal spacings. 相似文献
912.
Rubin Ye Anthony B. Murphy Takamasa Ishigaki 《Plasma Chemistry and Plasma Processing》2007,27(2):189-204
The species densities and the thermal and chemical nonequilibrium phenomena in an Ar–H2 radio frequency inductively coupled plasma reactor used for hydrogenation of materials have been investigated through numerical
simulation. The mathematical model consists of a two-temperature fluid dynamics model and a chemical kinetics model that takes
into account the effect of local chemical nonequilibrium. Computations are carried out for the rf plasma running at 11.7 kW
and 27 kPa for different Ar–H2 mixtures and for pure argon. Predicted results for the electron and heavy-species temperatures, the species densities, as
well as the degree of thermal and chemical nonequilibrium, are presented in detail. It is found that the electron and hydrogen
atom densities in the reactor and in the near-wall region of the torch are strongly altered by nonequilibrium effects. The
hydrogen atom density remains high in the reactor zone, and peaks in a region that has been found to be attractive for material
processing. Deviations from thermal and chemical equilibrium are greatly reduced by the addition of hydrogen to an argon plasma. 相似文献
913.
Wagner NL Kloss JM Murphy KL Bennett DW Dixon DA 《Journal of chemical information and computer sciences》2001,41(1):50-55
Ab initio electronic structure calculations on a series of ligands, p-RC6H4NC:, indicate, that the energy of the LUMO correlates with the electron-withdrawing/donating capabilities of the substituent group, which determines the relative pi-acidity of the ligand. Depending on the nature of the para substituent group on the aryl isocyanide ligand, bis(aryl isocyanide) complexes of tungsten-containing bulky bidentate arylphosphine ligands adopt either cis or trans conformations. The frontier molecular orbital formalism predicts that strong pi-acids, which contain electron-withdrawing groups, tend to polarize sufficient charge density away from the metal center to effect the formation of the sterically less favorable but electronically stabilized cis conformer. Density functional theory calculations on similar complexes containing phosphines which do not impose severe steric contraints indicate that the balance between steric and electronic stabilization can be effectively predicted by comparing the relative energies of the ligand LUMOs. 相似文献
914.
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917.
Lewis acid promoted anomerisation has potential in O- or S-glycoside synthesis. Herein, the anomerisation kinetics of thirty-one β-d-glucopyranosides was determined to determine how particular acyl protecting groups and their location influence reactivity towards a Lewis acid promoted reaction. The replacement of acetyl groups with benzoyl groups led to reduced reactivity when located at O-3, O-4 and O-6. However a reactivity increase was observed when the acetyl group was replaced by a benzoyl group at O-2. The 2,3,4,6-tetra-O-(4-methoxy)benzoate had an?~2-fold increase in rate when compared to the tetrabenzoate. 相似文献
918.
Vanessa M. Nepomuceno Hiyoung Kim Yuanqing Ding Hongbing Liu Mark Sadek Daneel Ferreira Sesselja Omarsdottir Brian T. Murphy 《Tetrahedron》2018,74(52):7421-7425
A collaborative program to discover new specialized metabolites from aquatic environments of Iceland led to the deconvolution of tetrahydroisoquinoline amide E/Z rotamers [(E/Z)-N-acetyl-MY336-a; 1] and conformers produced by a Streptomyces sp. All structures were elucidated by NMR and MS analysis, and interpretation of electronic circular dichroism (ECD) data. ECD and optical rotation (OR) simulations permitted the unequivocal assignment of the absolute configuration of compound 1 and provided an important example of delineating the spectroscopic contributions of equilibrating rotamers and boat/chair conformers of a common natural product scaffold. 相似文献
919.
We measured the concentrations of Pb and its isotope ratios in coconmittantly obtained tap water and plumbing materials by inductively coupled mass spectrometry (ICP-MS). The Pb concentrations were determined by external calibration with209Bi as an internal standard. Isotope ratios were measured and mass discrimination corrected by normalization to NIST SRM-981 (common lead isotopic standard). Student/s t-test was used to compare the isotopic ratios of206Pb/207Pb,206Pb/208Pb, and207Pb/208Pb in the tap water with those in various plumbing materials. The comparisons revealed that the source of Pb in most of the tap water samples was derived from copper pipe or solder. 相似文献
920.