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801.
802.
Experimental and numerical modelling of sedimentation in a rectangular shallow basin 总被引:9,自引:6,他引:3
Sameh A. KANTOUSH Erik BOLLAERT and Anton J. SCHLEISS Dr. Ecole Polytechnique Fédérale de Lausanne 《国际泥沙研究》2008,23(3):212-232
Numerical simulation of flows in shallow reservoirs has to be checked for its consistency in predicting real flow conditions and sedimentation patterns. Typical flow patterns may exhibit flow separation at the inlet, accompanied by several recirculation and stagnation areas all over the reservoir surface. The aim of the present research project is to study the influence of the geometry of a reservoir on sediment transport and deposition numerically and experimentally, focusing on a prototype reservoir depth between 5 and 15 m as well as suspended sediment transport.
A series of numerical simulations is presented and compared with scaled laboratory experiments, with the objective of testing the sensitivity to different flow and sediment parameters and different turbulence closure schemes. Different scenarios are analyzed and a detailed comparison of preliminary laboratory tests and some selected simulations are presented.
The laboratory experiments show that suspended sediment transport and deposition are determined by the initial flow pattern and by the upstream and downstream boundary conditions. In the experiments, deposition in the rectangular basin systematically developed along the left bank, although inflow and outflow were positioned symmetrically along the centre of the basin. Three major horizontal eddies developed influencing the sediment deposition pattern. Although asymmetric flow patterns are privileged, a symmetric pattern can appear from time to time. This particular behaviour could also be reproduced by a two-dimensional depth-averaged flow and sediment transport model (CCHE2D). The paper presents numerical simulations using different turbulence closure schemes (k-ε and eddy viscosity models). In spite of the symmetric setup, these generally produced an asymmetric flow pattern that can easily switch sides depending on the assumptions made for the initial and boundary conditions. When using the laboratory experiment as a reference, the most reliable numerical results have been obtai 相似文献
A series of numerical simulations is presented and compared with scaled laboratory experiments, with the objective of testing the sensitivity to different flow and sediment parameters and different turbulence closure schemes. Different scenarios are analyzed and a detailed comparison of preliminary laboratory tests and some selected simulations are presented.
The laboratory experiments show that suspended sediment transport and deposition are determined by the initial flow pattern and by the upstream and downstream boundary conditions. In the experiments, deposition in the rectangular basin systematically developed along the left bank, although inflow and outflow were positioned symmetrically along the centre of the basin. Three major horizontal eddies developed influencing the sediment deposition pattern. Although asymmetric flow patterns are privileged, a symmetric pattern can appear from time to time. This particular behaviour could also be reproduced by a two-dimensional depth-averaged flow and sediment transport model (CCHE2D). The paper presents numerical simulations using different turbulence closure schemes (k-ε and eddy viscosity models). In spite of the symmetric setup, these generally produced an asymmetric flow pattern that can easily switch sides depending on the assumptions made for the initial and boundary conditions. When using the laboratory experiment as a reference, the most reliable numerical results have been obtai 相似文献
803.
G. P. Bernardini D. Borrini A. Caneschi F. Di Benedetto D. Gatteschi S. Ristori M. Romanelli 《Physics and Chemistry of Minerals》2000,27(7):453-461
An EPR and SQUID magnetometry study of Cu2FeSnS4 (stannite) and Cu2ZnSnS4 (kesterite) has been performed in order to gain a deeper insight into the crystal chemistry of these minerals, in which the
mixed character of bonds lends uncertainty to the determination of the metal valence states. EPR investigations were performed
down to almost liquid nitrogen temperature on both natural and synthetic samples of stannite and kesterite. The interpretation
of their parameters (g- and T-tensors) was refined by computer simulation. The main feature of all the spectra is the unstructured signal centered at about
0.310 T due to the presence of Cu(II). The absence of structure in the signal is due to spin-spin exchange interaction between
Cu(II) and Fe(II), pointing to a diluted distribution of Cu(II). The temperature dependence of the Cu(II) signal can be related
to a topological variation of the first-neighbors coordination. The SQUID measurements, while allowing a more precise interpretation
of the EPR data, led to a full characterization of magnetic behavior of stannite and kesterite down to liquid helium temperature,
evidencing antiferromagnetic interactions between the Fe(II) ions in all samples but in synthetic kesterite. From the EPR
and SQUID experimental data no evidence was provided for the existence of two different structures for stannite and kesterite.
Received: 2 August 1999 / Accepted: 7 January 2000 相似文献
804.
805.
Experimentelle Arbeiten, die von der Universitäts-Sternwarte Jena in Zusammenarbeit mit chemischen Institutionen durchgeführt wurden, haben gezeigt, daß Pyroxengläser vielversprechende Kandidaten zur Identifizierung von Silikatstaubteilchen in der Umgebung sehr junger Objekte in Molekülwolken, z. B. BN-Objekten und T-Tauri-Sternen, sind. Die Wichtigkeit dieser Experimente besteht darin, daß sie die zur Modellierung der Quellen benötigren optischen Daten liefern und daß sie es ermöglichen, die mineralogische Beschaffenheit des Teilchenmaterials zu verstehen. In dieser Arbeit werden die Schritle, die in der jüngsten Zeit von der Jenaer Staubarbeitsgruppe in beide Richtungen unternommen wurden, beschrieben. 相似文献