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131.
132.
Observational data, high-resolution numerical modelling results and a simple analytical theory are combined in this paper to demonstrate the dependence of the volume transports through tidal inlets on topographical or morphological parameters of a Wadden Sea system. The area of interest covers the East Frisian Wadden Sea and consists of seven weakly connected tidal basins. The observations include time series of tidal gauge data and surface currents measured at a pile station in the backbarrier basin of the island Langeoog, as well as several ADCP transects in the Accumer Ee tidal inlet. The numerical simulations are based on the 3-D primitive equation General Estuarine Transport Model (GETM) with a horizontal resolution of 200 m and terrain following vertical coordinates. The model is forced at its open boundaries with sea-level data from an operational model for the German Bight (German Hydrographic Office). The simple theoretical concepts presented illustrate the effect of topography (hypsometry) in the tidal basins on the temporal variability of the exchange of water. This topographic control is effectuated through the bottom slope in the areas prone to drying and flooding. For our study area it takes about twice as long from slack water to maximum flood current than from slack water to maximum ebb current. The underlying physics of this signal modulation from a more or less harmonic forcing at the open-sea boundary and the quantification of the contributing physical processes are the major results of this paper. Estimates based simply on volume conservation are consistent with observations and results from numerical modelling, but they do not completely capture the actual non-linear tidal response. Our analysis shows that at least during part of the tidal cycle characteristic topographic parameters of the inlet/bay system have a major impact on the rate of exchange of waters between the Wadden Sea and the open ocean. This impact is especially strong during the transition between flood and ebb conditions. The possible morphodynamic responses are also addressed focusing on some common (universal) topographic features in seven tidal basins.Responsible Editor: Hans Burchard 相似文献
133.
双向卫星时频传递系统与应用 总被引:2,自引:0,他引:2
系统地阐述了双向卫星时频传递(TWSTFT)系统的原理、误差因素和结构实现,对系统的模块、流程操作进行了说明,并介绍了TWSTFT在国家授时中心的应用,最后提出了TWSTFT在我国的发展设想。 相似文献
134.
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136.
Derivation of design soil coefficients (S) and response spectral shapes for Eurocode 8 using the European Strong-Motion Database 总被引:1,自引:0,他引:1
A revision is presently under way to upgrade the status of the `Designrecommendations for earthquake resistance of structures', commonlyreferred to as Eurocode 8 (or EC8). In order to improve the definition ofthe design elastic response spectra (ERS) as defined in the Eurocode 8 –Part 1 (Draft May 2001), the values of the soil amplification factors havebeen calculated for sites on sedimentary soils, both stiff (category B) andsoft (category C), with respect to rock sites (category A), such ascontemplated in EC8. The work was performed by a systematic study ofresponse spectra as a function of magnitude and site conditions, usingrecords from the European Strong-Motion Database.The results confirm the occurrence of systematic spectral amplification onsedimentary soils with respect to reference rock in a large set of Europeanstrong motion data. Such amplification has been quantified through ameasure derived from the Housner Spectrum Intensity definition.The values of the soil coefficients recommended in the current version ofEC 8 are shown to be realistic for category C, in the case of a moderateseismicity context. However the values for subsoil class B need to besignificantly increased both for the moderate and high seismicity context. 相似文献
137.
《Chinese Astronomy and Astrophysics》1982,6(1):63-67
We compare the Earth's rotation parameters claculated from various input sets and conclude 1) A reference system comparable to the BIH sustem can be set up using just a few high-precision, evenly-distributed instruments. 2) Chinese instruments for time and latitude determination play an important role in the setting up and maintenance of a global reference system. 3) There seem to be no systematic differences, of an annual or a semi-annual character between the observations by the classical methods and the newer techniques. The difference BIH (1979) – BIH (1968) is probably what has remained of the station errors when the BIH (1968) system was set up. 4) It is possible that some unknown common source of error may exist over a large geographical region, hence, to set up a good reference system, the observing insrtuments should be distributed as evenly as possible over the globe. 相似文献
138.
Kohiyama Masayuki Yamashita Norihiko Sato Tadanobu Hengjian Lu Maki Norio Tanaka Satoshi Hayashi Haruo 《Natural Hazards》2003,29(3):501-522
The Nishinomiya Built Environment Database, which can be used to analyze the disaster process of the 1995 Hanshin-Awaji Earthquake Disaster in Nishinomiya City, has been expanded with new data entries. The database contains the following very detailed datasets: (1) the urbanization area base map, (2) casualty data, (3) three sets of building damage data surveyed by the Nishinomiya City, the Architectural Institute of Japan and the City Planning Institute of Japan, and the Kobe University, (4) building property data based on the real estate tax roll, (5) photographs of the damaged buildings with the information on the place and orientation of the picture, and (6) the estimated distribution of the seismic ground motion. The seismic ground motion was simulated for the southern part of Nishinomiya City and two verification sites in Kobe City and Amagasaki City. In the simulation, the borehole data of public facilities were used to model the surface soils as one-dimensional layers, taking into consideration the fact that the spatial distribution of the sediment/basement interface forms a slope. The model of the fault rupture process simulated the characteristics of the seismic motion at basement level, and amplification effects of the surface layers were evaluated based on multiple reflection theory. The distribution of peak ground acceleration and peak ground velocity was estimated from acceleration response spectra at each borehole point. In addition, the relationship between simulated seismic ground motion and building damage was studied based on newly proposed band-passed spectrum intensity using the expanded database. This confirmed that detailed categorization is necessary in order to evaluate the fragility functions, especially for reinforced concrete structures. The database should provide fundamental information for identifying the relationship between the ground motions and the extent and pattern of building damage, or the pattern of the occurrence of casualties.Presently 相似文献
139.
V. Zervakis K. Nittis L. Perivoliotis C. Tziavos 《Journal of Atmospheric & Ocean Science》2002,8(2):151-172
Expendable Bathythermograph (XBT) observations collected along a transect across the Eastern Mediterranean are compared with the respective predictions of thermocline structure and variability produced by the POSEIDON system's ocean circulation model. The observations, obtained in the framework of the Mediterranean Forecasting System project, cover a complete annual cycle, at a repetition rate of 1-2 transects per month, thus providing an excellent data set for estimating the model's skill to forecast seasonal variability and mesoscale circulation in the upper 450 m of the ocean. The comparison has revealed that the model adequately predicts the seasonal cycle of the evolution of the thermocline but tends to generate less steep thermoclines than observed. Furthermore, the mesoscale circulation is not accurately predicted. For the latter, data assimilation is considered a necessary step towards the improvement of the system. 相似文献
140.
Luciano Telesca Vincenzo LapennaFilippos Vallianatos 《Physics of the Earth and Planetary Interiors》2002,131(1):63-79
Much recent work has been focused on understanding the statistical properties of time-occurrence series of earthquakes. Investigating into the patterns of seismic sequences reveals evidence of scaling features in temporal behavior. This is shown in the clustering properties of seismicity of the western Corinth graben, Greece from 1983 to 2000. Power-law behavior has been found by means of Allan factor analysis and Fourier spectra for the earthquake sequence, with consistent values for the scaling exponents, that decrease with the threshold magnitude. The analysis of the temporal variation of the scaling exponent, performed with different threshold magnitudes, reveals an enhancing of the clusterization in correspondence to larger events. The multifractal analysis of the temporal distribution of the events has shown a decrease of the intermittent character with the threshold magnitude. 相似文献