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551.
Despite the recent upsurge in rock coast research, many aspects of abrasion and their relationships to other processes remain poorly understood. In this paper, mechanisms subsumed under the general term abrasion were investigated at the beaches of Oia and Sartaña along the Galician coast of NW Spain, in particular at the micro- to meso-scale (mm–cm). Relationships between abrasion and mechanical rock strength served to explore feedbacks between weathering and abrasion on rock coasts, based on measurements of rock surface strength by means of the Equotip (Proceq) method, and stereomicroscope analyses of rock surfaces undergoing varying degrees of abrasion. The results suggest that (1) abrasion along near-vertical rock surfaces leads to a decrease in rock strength with elevation above the top of the basal sediment layer, (2) abrasion processes encompass two different modes, namely, the wave-induced sweeping and dragging of sand and gravel, and the projection of clasts against rock surfaces, each mode depending predominantly on the grain size of the abrasive agent, and (3) the two abrasion modes produce different rock surfaces whose roughness is strongly influenced by the properties of diverse minerals, in particular fracture and cleavage. 相似文献
552.
Implementation and integrated numerical modeling of a landslide early warning system: a pilot study in Colombia 总被引:3,自引:2,他引:1
Christian Huggel Nikolay Khabarov Michael Obersteiner Juan Manuel Ramírez 《Natural Hazards》2010,52(2):501-518
Landslide early warning systems (EWS) are an important tool to reduce landslide risks, especially where the potential for
structural protection measures is limited. However, design, implementation, and successful operation of a landslide EWS is
complex and has not been achieved in many cases. Critical problems are uncertainties related to landslide triggering conditions,
successful implementation of emergency protocols, and the response of the local population. We describe here the recent implementation
of a landslide EWS for the Combeima valley in Colombia, a region particularly affected by landslide hazards. As in many other
cases, an insufficient basis of data (rainfall, soil measurements, landslide event record) and related uncertainties represent
a difficult complication. To be able to better assess the influence of the different EWS components, we developed a numerical
model that simulates the EWS in a simplified yet integrated way. The results show that the expected landslide-induced losses
depend nearly exponentially on the errors in precipitation measurements. Stochastic optimization furthermore suggests an increasing
adjustment of the rainfall landslide-triggering threshold for an increasing observation error. These modeling studies are
a first step toward a more generic and integrated approach that bears important potential for substantial improvements in
design and operation of a landslide EWS. 相似文献
553.
Stream temperature (Ts) is a key water quality parameter that controls several biological, ecological, and chemical processes in aquatic systems. In forested headwaters, exchanges of energy across air-water-streambed interfaces may influence Ts regimes, especially during storm events as the sources of runoff change over space and time. Analysis of the hysteretic behaviour of Ts during storm events may provide insights into rainfall-runoff responses, but such relationships have not been thoroughly investigated. As such, our objectives were to (a) quantify the variability of stream temperature hysteresis across seasons in different sub-regions and (b) investigate the relationship between the hysteretic response and catchment characteristics. Ts hysteresis during storm events was assessed based on the hysteresis index (HI), which describes the directionality of hysteresis loops, and the temperature response index (TRI), which indicates whether Ts increased or decreased during a storm event. We analysed Ts data from 10 forested headwater reaches in two sub-regions (McGarvey and West Fork Tectah) in Northern California. We also performed a clustering analysis to examine the relationship amongst HI, TRI, topographic metrics, and meteorological characteristics of the study areas. Overall, the hysteretic behaviour of Ts varied across seasons—the greatest HI occurred during spring and summer. Interestingly, in the McGarvey streams the variability in Ts hysteresis co-varied strongly with topographic metrics (i.e., upslope accumulative area, average channel slope, topographic wetness index). Comparatively, in West Fork Tectah the variability of Ts hysteresis co-varied most strongly with meteorological metrics (i.e., antecedent rainfall events, solar radiation, and air temperature). Variables such as the gradient between stream and air temperatures, slope, and wetted width were significant for both sub-regional hysteretic patterns. We posit that the drivers of Ts response during storms are likely dependent on catchment physiographic characteristics. Our study also illustrated the potential utility of stream temperature as a tracer for improving the understanding of hydrologic connectivity and shifts in the dominant runoff contributions to streamflow during storm events. 相似文献