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51.
ABSTRACTWe thank Allen and Berghuijs for continuing the discussion on field hydrology and data sharing and discuss two incentives to promote data collection and sharing in hydrological sciences: a collaborative attitude and additional funding to make data publicly available. 相似文献
52.
ABSTRACT Groundwater level fluctuations are caused by spatial and temporal superposition of processes within and outside the aquifer system. Most of the subsurface processes are usually observed on a small scale. Upscaling to the regional scale, as required for future climate change scenarios, is difficult due to data scarcity and increasing complexity. In contrast to the limited availability of system characteristics, high-resolution data records of groundwater hydrographs are more generally available. Exploiting the information contained in these records should thus be a priority for analysis of the chronical lack of data describing groundwater system characteristics. This study analyses the applicability of 63 indices derived from daily hydrographs to quantify different dynamics of groundwater levels in unconfined gravel aquifers from three groundwater regions (Bavaria, Germany). Based on the results of two different skill tests, the study aids index selection for different dynamic components of groundwater hydrographs. 相似文献
53.
Fossil beetles and pollen were examined from an intermorainal bog at Puerto Edén, Isla Wellington, Chile (latitude 49°08'S, longitude 74°25'W). Wood from near the base of the section has an age of 12 960 ± 150 yr BP. Occurrence of flightless beetle species in the basal peat sample is evidence that some members of the biota survived the last glacial maximum in refugia. The assumption that the Chilean Channels were entirely ice-covered is incorrect. Plants and insects that invaded the deglaciated terrain were those of an Empetrum heathland in which patches of Nothofagus forest were restricted to sheltered locations. The climate supporting the heathland is inferred to have been windier and probably drier than that of the present day. From 13 000 yr BP to 9500 yr BP Nothofagus forest expanded, possibly in response to less windiness and more available moisture. Neither the fossil beetle nor pollen data support a return to significantly colder conditions between 11 000 and 10 000 yr BP at the time of the Younger Dryas Stade. From 9500 to 5500 yr BP the climate was as wet as that of the present day, based on an increased representation of the pollen of moorland plants and of aquatic beetle species. From 5500 to 3000 yr BP the climate was drier, as indicated by the expansion of Empetrum heath and the reduction in mesic habitats. From 3000 yr BP to the present-day mesic habitats dominated as the climate returned to a wetter mode. The alternatively wetter and drier episodes are attributed to latitudinal shifts in the position of storm tracks in the belt of Southern Westerlies. 相似文献
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56.
Amaelle Landais Valérie Masson-Delmotte Jean Jouzel Dominique Raynaud Sigfus Johnsen Christof Huber Markus Leuenberger Jakob Schwander Bénédicte Minster 《Climate Dynamics》2006,26(2-3):273-284
The mechanisms involved in the glacial inception are still poorly constrained due to a lack of high resolution and cross-dated
climate records at various locations. Using air isotopic measurements in the recently drilled NorthGRIP ice core, we show
that no evidence exists for stratigraphic disturbance of the climate record of the last glacial inception (∼123–100 kyears
BP) encompassing Dansgaard–Oeschger events (DO) 25, 24 and 23, even if we lack sufficient resolution to completely rule out
disturbance over DO 25. We quantify the rapid surface temperature variability over DO 23 and 24 with associated warmings of
10±2.5 and 16±2.5°C, amplitudes which mimic those observed in full glacial conditions. We use records of δ18O of O2 to propose a common timescale for the NorthGRIP and the Antarctic Vostok ice cores, with a maximum uncertainty of 2,500 years,
and to examine the interhemispheric sequence of events over this period. After a synchronous North–South temperature decrease,
the onset of rapid events is triggered in the North through DO 25. As for later events, DO 24 and 23 have a clear Antarctic
counterpart which does not seem to be the case for the very first abrupt warming (DO 25). This information, when added to
intermediate levels of CO2 and to the absence of clear ice rafting associated with DO 25, highlights the uniqueness of this first event, while DO 24
and 23 appear similar to typical full glacial DO events. 相似文献
57.
Nikolaus Gussone Gerald Langer Markus Geisen Blair A. Steel Ulf Riebesell 《Earth and Planetary Science Letters》2007,260(3-4):505-515
Four species of marine calcifying algae, the coccolithophores Calcidiscus leptoporus, Helicosphaera carteri, Syracosphaera pulchra and Umbilicosphaera foliosa were grown in laboratory cultures under temperatures varying between 14 and 23 °C, and one species, C. leptoporus, under varying [CO32−], ranging from 105 to 219 μmol/kg. Calcium isotope compositions of the coccoliths resemble in both absolute fractionation and temperature sensitivity previous calibrations of marine calcifying species e.g. Emiliania huxleyi (coccolithophores) and Orbulina universa (planktonic foraminifera) as well as inorganically precipitated CaCO3, but also reveal small species specific differences. In contrast to inorganically precipitated calcite, but similar to E. huxleyi and O. universa, the carbonate ion concentration of the medium has no statistically significant influence on the Ca isotope fractionation of C. leptoporus coccoliths; however, combined data of E. huxleyi and C. leptoporus indicate that the observed trends might be related to changes of the calcite saturation state of the medium. Since coccoliths constitute a significant portion of the global oceanic CaCO3 export production, the Ca isotope fractionation in these biogenic structures is important for defining the isotopic composition of the Ca sink of the ocean, one of the key parameters for modelling changes to the marine Ca budget over time. For the present ocean our results are in general agreement with the previously postulated and applied mean value of the oceanic Ca sink (Δsed) of about − 1.3‰, but the observed inter- and intra-species differences point to possible changes in Δsed through earth history, due to changing physico-chemical conditions of the ocean and shifts in floral and faunal assemblages. 相似文献
58.
Sediments attributed to flooding events of River Danube concerning the bleaching of the optical stimulated luminescence (OSL) signal were investigated. It is demonstrated that the OSL signal in both quartz and feldspar is not completely but differentially bleached in the sediment grains. Partial bleaching of the samples is clearly indicated by the scatter of equivalent dose determined for several individual single aliquots. It is also shown that residual ages in feldspars are significantly higher than those calculated for quartz. It is furthermore demonstrated that analysing measurement-time dependent equivalent dose estimates is not a suitable method to identify partial bleaching in the investigated sediment grains. However, the transport and deposition process of the investigated samples was probably disturbed by an artificial input of sediment, and this case study may thus not be representative of undisturbed high flood events in the past. 相似文献
59.
60.
Markus Bth 《Tectonophysics》1978,50(1):T9-T17
Energy-time release curves are calculated for Swedish and for Fennoscandian earthquakes, both curves exhibiting a sharp break around the year 1910. The similarity of this behaviour with world-wide energy release curves suggests that Fennoscandian earthquakes are related to the global tectonics, probably via plate motions on the border between the North Atlantic and the Eurasian continent. 相似文献