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Icy surfaces like the polar caps of Mars, comets, Edgeworth-Kuiper belt objects or the surface areas of many moons in the outer Solar System behave different than rock and soil surfaces when irradiated by solar light. The latter ones absorb and reflect incoming solar radiation immediately at the surface. In contrast, ices are partially transparent in the visible spectral range and opaque in the infrared. Due to this fact it is possible for the solar radiation to reach a certain depth and increase the temperature of the sub-surface layers directly. This internal temperature rise is called “solid-state greenhouse effect,” in analogy to the classical greenhouse effect in an atmosphere. It may play an important role in the energy balance of various icy bodies in the Solar System. Within the scope of a project conducted at the Space Research Institute of the Austrian Academy of Sciences in Graz the solid-state greenhouse effect was investigated experimentally and theoretically. A number of experiments with diverse materials, focussing mainly on layered samples with a surface cover consisting of transparent H2O-ice, were performed. The samples were irradiated under cryo-vacuum conditions by a solar simulator. The temperature distributions inside the samples were measured and compared with the results of numerical model calculations. We found that the predicted sub-surface temperature maximum is very clearly measurable in glass beads samples with various particle size distributions, but can also be detected in transparent compact surface ice layers. However, in the latter case it is less distinct than originally expected. Measuring the effect by laboratory methods turned out to be a difficult task due to the shallow depth where the temperature maximum occurs. 相似文献
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Independent calendar year chronologies are a basic requirement for the establishment of high resolution land-ice teleconnections.
The annually laminated Meerfelder Maar record provides both an independent chronology, established by varve counting, and
high resolution lithological proxy data for the period of the last Glacial/Interglacial transition. These data reveal a series
of four periods of climatic deterioration coinciding with negative isotopic deviations in the GRIP record signal, thus demonstrating
the synchronicity of environment changes in Western Germany and temperature shifts in Greenland. The terrestrial data supports
a further sub-division of the event stratigraphy based on the GRIP core, by introducing the cold event GI-1c2 between 13 500
and 13 400 calendar years BP. Multiproxy analyses reveal that the environmental response at Meerfelder Maar was not linear
throughout the Lateglacial but was modified by local processes. A change in the response of the lake environment to climate
deterioration was observed during sub-stage GI-1b (Gerzensee oscillation), the only event with gradual rather than abrupt
transitions. The two-fold character of the Younger Dryas as seen in the GRIP record is more pronounced in the Meerfelder Maar
record. This lithological signal occurred with a delay of 60 years to the GRIP signal, and has been linked to a shift in the
catchment. It is proposed that the trigger for this shift was a trend towards a more humid second half of the Younger Dryas.
Received: 21 May 1999 / Accepted: 18 August 1999 相似文献
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Robert Stein Dali Georgobiani Regner Trampedach Hans-Günter Ludwig Åke Nordlund 《Solar physics》2004,220(2):229-242
P-mode oscillations in the Sun and stars are excited stochastically by Reynolds stress and entropy fluctuations produced by
convection in their outer envelopes. The excitation rate of radial oscillations of stars near the main sequence from K to
F and a subgiant K IV star have been calculated from numerical simulations of their surface convection zones. P-mode excitation
increases with increasing effective temperature (until envelope convection ceases in the F stars) and also increases with
decreasing gravity. The frequency of the maximum excitation decreases with decreasing surface gravity. 相似文献
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Erika?Kaufmann Günter?Kargl Norbert?I.?K?mleEmail author Manfred?Steller Johann?Hasiba Florian?Tatschl Stefan?Ulamec Jens?Biele Marc?Engelhardt Jens?Romstedt 《Earth, Moon, and Planets》2009,105(1):11-29
One possibility to explore the subsurface layers of icy bodies is to use a probe with a “hot tip", which is able to penetrate
ice layers by melting. Such probes have been built and used in the past for the exploration of terrestrial polar ice sheets
and may also become useful tools to explore other icy layers in the Solar System. Examples for such layers are the polar areas
of Mars or the icy crust of Jupiter’s moon Europa. However, while on Earth a heated probe launched into an ice sheet always
causes melting with subsequent refreezing, the behaviour of such a probe in a low pressure environment is quite different.
We report on the results of some experiments with a simple “melting probe" prototype with two different kinds of hot tips
in a vacuum environment. For one of the tips the probe moved into two types of ice samples: (i) compact water ice and (ii)
porous water ice with a snow (firn) like texture. It was also found that the penetration behaviour was basically different
for the two sample types even when the same kind of tip was used. While in the porous sample the ice was only subliming, the
phase changes occurring during the interaction of the tip with the compact ice are much more complex. Here alternating phases
of melting and sublimation occur. The absence of the liquid phase has severe consequences on the performance of a “melting
probe" under vacuum conditions: In this environment we find a high thermal resistance between the probe surface and the underlying
ice. Therefore, only a low percentage of the heat that is generated in the tip is used to melt or sublime the ice, the bulk
of the power is transferred towards the rear end of the probe. This is particularly a problem in the initial phases of an
ice penetration experiment, when the probe has not yet penetrated the ice over its whole length. In the compact ice sample,
phases could be observed, where a high enough gas pressure had built up locally underneath the probe, so that melting becomes
possible. Only during these melting periods the thermal contact between the probe and the ice is good and in consequence the
melting probe works effectively. 相似文献
27.
Temporal variation of suspended sediment transport in the Koga catchment,North Western Ethiopia and environmental implications 下载免费PDF全文
Event sediment transport and yield were studied for 45 events in the upstream part of the 260 km2 agricultural Koga catchment that drains to an irrigation reservoir. Discharge and turbidity data were collected over a period of more than a year, accompanied by grab sampling. Turbidity was very well correlated with the sediment concentrations from the samples (r = 0.99), which allowed us to estimate the temporal patterns of sediment concentrations within events. The hysteresis patterns between discharge and sediment concentrations were analysed to provide insight into the different sediment sources. Anticlockwise patterns are the dominant hysteresis patterns in the area, suggesting smaller contributions of suspended sediment from the river channels than from the hillslopes and agricultural areas. Complicated types of hysteresis patterns were mostly observed for long events with multiple peaks. For a given discharge, sediment yields in August and September, when the catchment was almost completely covered with vegetation, were much smaller than during the rest of the rainy season. The hysteresis patterns and timing suggest that the sediment availability from the agricultural areas and hillslopes affects sediment yields more strongly than does peak discharge. Two distinct types of sediment rating curves were observed for the season when the agricultural land was covered with vegetation and when it was not, indicating the dominating contribution of land use/cover to sediment yields in the catchment. The rate of suspended sediment transport in the area was estimated as 25.6 t year?1 ha?1. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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Ohne Zusammenfassung 相似文献
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Ohne Zusammenfassung 相似文献
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