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111.
Aquatic flow over a submerged vegetation canopy is a ubiquitous example of flow adjacent to a permeable medium. Aquatic canopy
flows, however, have two important distinguishing features. Firstly, submerged vegetation typically grows in shallow regions.
Consequently, the roughness sublayer, the region where the drag length scale of the canopy is dynamically important, can often
encompass the entire flow depth. In such shallow flows, vortices generated by the inflectional velocity profile are the dominant
mixing mechanism. Vertical transport across the canopy–water interface occurs over a narrow frequency range centered around
f
v
(the frequency of vortex passage), with the vortices responsible for more than three-quarters of the interfacial flux. Secondly,
submerged canopies are typically flexible, coupling the motion of the fluid and canopy. Importantly, flexible canopies can
exhibit a coherent waving (the monami) in response to vortex passage. This waving reduces canopy drag, allowing greater in-canopy velocities and turbulent stresses.
As a result, the waving of an experimental canopy reduces the canopy residence time by a factor of four. Finally, the length
required for the set-up and full development of mixing-layer-type canopy flow is investigated. This distance, which scales
upon the drag length scale, can be of the same order as the length of the canopy. In several flows adjacent to permeable media
(such as urban canopies and reef systems), patchiness of the medium is common such that the fully developed condition may
not be representative of the flow as a whole. 相似文献
112.
A rut is a depression or groove formed into the ground by the travel of wheels and tracks. Ruts can cause severe influences on soil and vegetation, and reduce vehicle mobility. In this paper, rut depth and rut width were used as the main indicators to quantify a rut. A new indicator, rut index, was proposed, combining rut depth and rut width. A Light Armored Vehicle (LAV) and a High Mobility Multi-purpose Wheeled Vehicle (HMMWV) were used for testing the influence of turning radius on rut depth, rut width and rut index. The LAV and the HMMWV were operated in spiral patterns at different speeds. Differential GPS data for the vehicles were collected every second during the spiral. Rut measurements were manually taken every 4-7 m along each of the spiral tracks. The results of field tests indicate that rut depth, rut width and rut index increase with the decrease of turning radius, especially when turning radius is less than 20 m. Velocity influences rut formation for the LAV but not HMMWV. 相似文献
113.
Cuello-Nuñez Susana Benning Jocelyn Liu Chuan Branton Peter Hu Jin McAdam Kevin G. Coburn Steven Braybrook Julian Goenaga-Infante Heidi 《Analytical and bioanalytical chemistry》2018,410(26):6795-6806
Analytical and Bioanalytical Chemistry - Fractionation data for cadmium in tobacco products, as obtained by sequential leaching of cadmium species with ICP-MS/MS analysis, and separately by X-ray... 相似文献
114.
In this paper the effect of bias and geometric symmetry breaking on the electronic spectrum of a model molecular system is studied. Geometric symmetry breaking can either enhance the dissipative effect of the bias, where spectral peaks are disabled, or enable new excitations that are absent under zero bias conditions. The spectral analysis is performed on a simple model system by solving for the electronic response to an instantaneously impulsive perturbation in the dipole approximation. The dynamical response is extracted from the electronic equations of motion as expressed by the Keldysh formalism. This expression provides for the accurate treatment of the electronic structure of a bulk-coupled system at the chosen model Hamiltonian electronic structure level. 相似文献
115.
Wiesenmayer E Luetkens H Pascua G Khasanov R Amato A Potts H Banusch B Klauss HH Johrendt D 《Physical review letters》2011,107(23):237001
It is widely believed that, in contrast to its electron-doped counterparts, the hole-doped compound Ba(1-x)K(x)Fe(2)As(2) exhibits a mesoscopic phase separation of magnetism and superconductivity in the underdoped region of the phase diagram. Here, we report a combined high-resolution x-ray powder diffraction and volume-sensitive muon spin rotation study of Ba(1-x)K(x)Fe(2)As(2) showing that this paradigm does not hold true in the underdoped region of the phase diagram (0≤x≤0.25). Instead we find a microscopic coexistence of the two forms of order. A competition of magnetism and superconductivity is evident from a significant reduction of the magnetic moment and a concomitant decrease of the magnetoelastically coupled orthorhombic lattice distortion below the superconducting phase transition. 相似文献
116.
Charmaine Arderne Kyle Fraser Batchelor Bhawna Uprety Rahul Chandran Heidi Abrahamse 《Acta Crystallographica. Section C, Structural Chemistry》2020,76(7):663-672
The reactivity of the cobalt(III) complexes dichlorido[tris(2‐aminoethyl)amine]cobalt(III) chloride, [CoCl2(tren)]Cl, and dichlorido(triethylenetetramine)cobalt(III) chloride, [CoCl2(trien)]Cl, towards different amino acids (l ‐proline, l ‐asparagine, l ‐histidine and l ‐aspartic acid) was explored in detail. This study presents the crystal structures of three amino acidate cobalt(III) complexes, namely, (l ‐prolinato‐κ2N,O)[tris(2‐aminoethyl)amine‐κ4N,N′,N′′,N′′′]cobalt(III) diiodide monohydrate, [Co(C5H8NO2)(C6H18N4)]I2·H2O, I , (l ‐asparaginato‐κ2N,O)[tris(2‐aminoethyl)amine‐κ4N,N′,N′′,N′′′]cobalt(III) chloride perchlorate, [Co(C4H7N2O3)(C6H18N4)](Cl)(ClO4), II , and (l ‐prolinato‐κ2N,O)(triethylenetetramine‐κ4N,N′,N′′,N′′′)cobalt(III) chloride perchlorate, [Co(C4H7N2O3)(C6H18N4)](Cl)(ClO4), V . The syntheses of the complexes were followed by characterization using UV–Vis spectroscopy of the reaction mixtures and the initial rates of reaction were obtained by calculating the slopes of absorbance versus time plots. The initial rates suggest a stronger reactivity and hence greater affinity of the cobalt(III) complexes towards basic amino acids. The biocompatibility of the complexes was also assessed by evaluating the cytotoxicity of the complexes on cultured normal human fibroblast cells (WS1) in vitro. The compounds were found to be nontoxic after 24 h of incubation at concentrations up to 25 mM. 相似文献
117.
118.
The ground‐state equilibrium geometries, electronic structures and vertical excitation energies of methyl‐ and methoxyl‐substituted phenol radical cations and phenoxyl radicals have been investigated using time‐dependent density‐functional theory (namely TD‐B3LYP) and complete‐active‐space second‐order perturbation theory (CASPT2). The “anomalous” large redshifts of the absorption maxima of the phenol radical species observed in the ultraviolet–visible spectral region upon di‐meta‐methoxyl substitution are reproduced by the calculations. Furthermore, these “anomalous” shifts which were unexplained to date can be rationalized on the basis of a qualitative molecular orbital perturbation analysis. 相似文献
119.
Erin Hart Damini Grover Heidi Zettl Victoria Koshevarova Michael H. Abraham 《Physics and Chemistry of Liquids》2016,54(2):141-154
Experimental data have been compiled from the published chemical and engineering literature on the enthalpies of solvation for 92 different inorganic gases and organic vapours in acetic acid. The compiled data are used to derive mathematical correlations based on the Abraham solvation parameter model. The derived expressions describe the experimental solvation enthalpies in acetic acid to within a standard deviation (SD) of 2.2 kJ mol?1. Principal Component Analysis (PCA) on the five equation coefficients from a derived Abraham model correlation shows that acetic acid does not resemble hydroxylic solvents in terms of enthalpic interactions, but is more akin to moderately polar solvents such as ethyl acetate or acetone. 相似文献
120.
Linjalahti H Feng G Mareque-Rivas JC Mikkola S Williams NH 《Journal of the American Chemical Society》2008,130(13):4232-4233
The catalysis of phosphoryl transfer by metal ions has been intensively studied in both biological and artificial systems, but the status of the transient pentacoordinate phosphoryl species (as transition state or intermediate) is the subject of considerable debate. We report that dinuclear metal ion complexes that incorporate second sphere hydrogen bond donors not only promote the cleavage of RNA fragments just as efficiently as the activated analogue HPNPP but also provide the first examples of metal ion catalyzed phosphate diester isomerization close to neutral pH. This observation implies that the reaction catalyzed by these complexes involves the formation of a phosphorane intermediate that is sufficiently long-lived to pseudorotate. 相似文献