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71.
Wind-Direction Effects on Urban-Type Flows 总被引:2,自引:2,他引:0
Jean Claus O. Coceal T. Glyn Thomas S. Branford S. E. Belcher Ian P. Castro 《Boundary-Layer Meteorology》2012,142(2):265-287
Practically all extant work on flows over obstacle arrays, whether laboratory experiments or numerical modelling, is for cases
where the oncoming wind is normal to salient faces of the obstacles. In the field, however, this is rarely the case. Here,
simulations of flows at various directions over arrays of cubes representing typical urban canopy regions are presented and
discussed. The computations are of both direct numerical simulation and large-eddy simulation type. Attention is concentrated
on the differences in the mean flow within the canopy region arising from the different wind directions and the consequent
effects on global properties such as the total surface drag, which can change very significantly—by up to a factor of three
in some circumstances. It is shown that for a given Reynolds number the typical viscous forces are generally a rather larger
fraction of the pressure forces (principally the drag) for non-normal than for normal wind directions and that, dependent
on the surface morphology, the average flow direction deep within the canopy can be largely independent of the oncoming wind
direction. Even for regular arrays of regular obstacles, a wind direction not normal to the obstacle faces can in general
generate a lateral lift force (in the direction normal to the oncoming flow). The results demonstrate this and it is shown
how computations in a finite domain with the oncoming flow generated by an appropriate forcing term (e.g. a pressure gradient)
then lead inevitably to an oncoming wind direction aloft that is not aligned with the forcing term vector. 相似文献
72.
73.
Werner Conrad Karel Diviš Claus Elstner Rezensent Z. Šimon 《Studia Geophysica et Geodaetica》1979,23(2):114-121
Summary Results of gravity measurements performed in 1977 along a WE-profile situated in the GDR area are discussed. Systematic influences caused by the variations of the hydrologic conditions in the local regions of the observation points reach 100 nm s–2. From the results of the yearly repeated gravity measurements (1970/77) a mean yearly gravity variation of about 20 nm s–2 a–1 was calculated for the sedimentary eastern part of the profile. 相似文献
74.
This paper presents a spatial decision support tool that implements the Ordered Weighted Averaging (OWA) method. OWA is a
family of multicriteria evaluation operators characterised by two sets of weights: criterion importance weights and order
weights. We propose a highly interactive way of choosing, modifying, and fine-tuning the decision strategy defined by the
order weights. This exploratory approach to OWA is supported by a graphical representation of the operator's behaviour in
terms of decision risk and tradeoff/dispersion between criteria. Our prototype implementation is based on the CommonGIS software,
and thus, Web-enabled and working with vector data. We successfully demonstrate online, exploratory support of spatial decision
strategies using a data set of skiing resorts in Wallis, Switzerland.
Received: 24 September 2002 / Accepted: 10 January 2003 相似文献
75.
Assessment of the stability of H/V spectral ratios from ambient noise and comparison with earthquake data in the Cologne area (Germany) 总被引:3,自引:0,他引:3
Stefano Parolai Sandra M. Richwalski Claus Milkereit Peter Bormann 《Tectonophysics》2004,390(1-4):57-73
Situated in an active tectonic region the highly industrialised Cologne area (Germany) suffers from moderate-sized earthquakes. Our contribution to the mitigation of earthquake risk includes a microzonation study using ambient seismic noise and earthquake recordings from two field campaigns. An analysis of these data using the horizontal-to-vertical (H/V) as well as the classical spectral ratio (CSR) technique led to the following observations and conclusions: (1) The spatial variation in the thickness of the sedimentary cover is reliably retrieved using the fundamental resonance frequency estimated from the peak in the (H/V) ratio of ambient noise. (2) This fundamental resonance frequency is stable in time, but the amplitude of the peak (the amplification factor) is not. (3) The relative amplification variation of the H/V ratio in the area should therefore be checked systematically with repeated measurements before drawing conclusions about its significance. (4) The analysis of the H/V ratio of ambient noise provides the lower frequency bound, above which amplification may occur. (5) The shapes of the spectral ratios obtained by the different methods are generally in good agreement. However, the analysis of earthquake data shows that significant amplification of ground motion may also occur at frequencies higher than the fundamental one even when thick sediments are present. 相似文献
76.
H. J. Spero D. J. Andreasen P. Sorgeloos 《International Journal of Salt Lake Research》1993,2(2):133-139
Stable carbon and nitrogen isotope ratios have been determined on 41 strains ofArtemia sp. from different geographic regions around the world. The δ13C and δ15N values ranged between −13.7 to−25.0 per mil and −0.7 to 21.2 per mil respectively.Artemia δ13C values from coastal environments are consistent with a marine origin for the food sourceArtemia from inland salt lakes have a range of carbon isotope values suggesting C3, C4 and CAM based organic matter could form the base of theArtemia food chain. These data indicate thatArtemia having a wide range of carbon and nitrogen isotope values are available for tropho-dynamic research studies that quantify
the effect of respired CO2 on tissue and CaCO3 shell13C/12C ratios. Such stable isotope variation also suggests that stable isotope fingerprinting remains a viable technique for identifying
specificArtemia collection sites. 相似文献
77.
Pyrheliometric measurements at Davos, Switzerland from 1909 to 1979 are used to reconstruct the time history of atmospheric transmission. Measurements were numerous enough to allow yearly and seasonal values of atmospheric transmission to be determined. Other than the eruptions of Katmai in 1912 and Agung in 1963, there are no significant long-term changes in atmospheric transmission observed at this central European site. The implications of this result upon those theories of climatic change which depend upon changes in atmospheric transmission are briefly considered. 相似文献
78.
通过对亚美尼亚Kajaran的一口自流井流量数据和电导率数据的多年分析,我们发现这口井对远场大震的响应非常敏感。一般同震流量增加,震后大约滞后一小时传导率减小。传导率在震后大约三周时趋于最小,然后需要数月时间来恢复震前水平。例如,1999年8月17土耳其Izm itMW7.6级地震,相距1 400 km,引起流量增加25%,传导率减小6%。流量也可以显示潮汐的波动,这种波动的幅度(顶点到顶点)约为水井产生的平均波动的5%,但传导率数据的潮汐信号并不明显,且不稳定。监测期11次地震引起最大同震静态应变异常的估算均低于10-9,只有一次正常状态小于潮汐应变。所以,远震相关的井水异常是地震地面振动引起的,而非同震变形。我们提出混有地下水的模型来解释观察到的现象,此模型考虑了这个特殊的地下水系统的特殊状态:封闭的含水层含两类在水化组分上具有很大差异的地下水,地下水和微破裂的混合区域与自流井的液压相互关联。认为与地震相关的异常,是由自流井附近的局部水头增加产生的,而局部水头的增加是由于地震波的通过引起的。本文讨论了可能的机制,对异常的时间变化曲线进行了模拟。 相似文献
79.
Hinzen Klaus-G. Krummel Heinrich Weber Bernd Fleischer Claus 《Journal of Seismology》2022,26(5):863-873
Journal of Seismology - A steadily increasing number of citizen seismological stations, often located in populated areas, record a plethora of man-made events. These events are especially of... 相似文献
80.