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151.
Indoor Radon concentrations have been carried out simultaneously at the villages of S. Venerina and Acireale, which are located on the south-eastern flank of Mt. Etna volcano. Both investigation sites are partially affected by the same fault system, which plays an important role in the dynamics of the volcano, especially before and during eruptive periods. Measurements were performed in the period from January 2006 until April 2006, just prior to an eruption which took place on 14th July 2006. Indoor Radon monitoring at S. Venerina, was carried out at two buildings located nearby, characterized by a different type of construction. These buildings were chosen because they can be considered as representative of both the historical centre and the new neighbourhoods of the village. At the same time, a Radon active monitor was operating in-soil near the two aforesaid edifices. Cross-correlation analysis between the in-soil one with both the indoor S. Venerina Radon series indicated different temporal correlation, probably due to the different types of building foundations and constructive materials of their walls, both causing the different indoor accumulation. S. Venerina’s indoor Radon values taken at the new building showed similar trends and the same anomalies as the ones recorded at Acireale. The simultaneous increase in indoor Radon concentration was observed at both sites from the last ten days of March, when a significant increase in the CO2 efflux was recorded. Increases in volcanogenic gases occurred very probably throughout an inflating state of the volcano during the pre-eruptive period, which caused the wide opening of the fractures. Lastly, variations in indoor Radon concentrations observed before an eruption, indicate the suitability of the investigated sites for in-soil Radon monitoring at a low altitude of the south-eastern flank of Mt. Etna. Moreover, in this place repeated and long period Radon indoor measurements should be carried out due to high potential indoor accumulation which depends from the volcanic activity, as this could constitute a serious danger to public health. 相似文献
152.
Marta Tárraga Servando De La Cruz-Reyna Ana T. Mendoza-Rosas Roberto Carniel Alicia Martínez-Bringas Alicia García Ramon Ortiz 《Acta Geophysica》2012,60(3):664-681
The continuous background seismic activity contains information on the internal state of a volcanic system. Here, we report
the influence of major regional tectonic earthquakes (M > 5 in most cases) on such state, reflected as changes in the spectral and dynamical parameters of the volcano continuous
seismic data. Although changes do not always occur, analysis of five cases of earthquake-induced variations in the signals
recorded at Popocatépetl volcano in central México reveal significant fluctuations following the tectonic earthquakes. External
visible volcanic activity, such as small to moderate explosions and ash emissions, were related to those fluctuations. We
briefly discuss possible causes of the variations. We conclude that recognition of fluctuations in the dynamical parameters
in volcano monitoring seismic signals after tectonic earthquakes, even those located in the far field, hundreds of kilometers
away, may provide an additional criterion for eruption forecasting, and for decision making in the definition of volcanic
alert levels. 相似文献
153.
Mariano Bonomo Alejandro Fabián Zucol Beatriz Gutiérrez Téllez Andrea Coradeghini María Susana Vigna 《Journal of Paleolimnology》2009,41(2):273-296
This paper presents results of interdisciplinary palaeoenvironmental research carried out on a sediment sequence from the
Nutria Mansa 1 archaeological site. This late Holocene site is located in the Pampean plains, Argentina. Siliceous microfossils
were recorded (i.e. phytoliths, diatoms, chrysophytes, sponges) and micro-charcoal was analyzed. In addition, fauna identified
at the site were correlated with regional palaeoclimatic evidence. Based on the microfossil associations, we concluded that
the human occupations occurred beside a fluvial and brackish-freshwater lacustrine setting. Grass communities were located
on its margins that developed under a warm temperate climate with evidence for dryness and marked seasonality in part of the
record. Although some stratigraphic and faunal evidence indicates a possible temperature increase, these fluctuations were
not sufficient to extirpate mammals of arid and cold environments. 相似文献
154.
R. Sulpizio R. Bonasia P. Dellino D. Mele M. A. Di Vito L. La Volpe 《Bulletin of Volcanology》2010,72(5):559-577
Pyroclastic density currents (PDCs) generated during the Plinian eruption of the Pomici di Avellino (PdA) of Somma–Vesuvius
were investigated through field and laboratory studies, which allowed the detailed reconstruction of their eruptive and transportation
dynamics and the calculation of key physical parameters of the currents. PDCs were generated during all the three phases that
characterised the eruption, with eruptive dynamics driven by both magmatic and phreatomagmatic fragmentation. Flows generated
during phases 1 and 2 (EU1 and EU3pf, magmatic fragmentation) have small dispersal areas and affected only part of the volcano
slopes. Lithofacies analysis demonstrates that the flow-boundary zones were dominated by granular-flow regimes, which sometimes
show transitions to traction regimes. PDCs generated during eruptive phase 3 (EU5, phreatomagmatic fragmentation) were the
most voluminous and widespread in the whole of Somma–Vesuvius’ eruptive history, and affected a wide area around the volcano
with deposit thicknesses of a few centimetres up to more than 25 km from source. Lithofacies analysis shows that the flow-boundary
zones of EU5 PDCs were dominated by granular flows and traction regimes. Deposits of EU5 PDC show strong lithofacies variation
northwards, from proximally thick, massive to stratified beds towards dominantly alternating beds of coarse and fine ash in
distal reaches. The EU5 lithofacies also show strong lateral variability in proximal areas, passing from the western and northern
to the eastern and southern volcano slopes, where the deposits are stacked beds of massive, accretionary lapilli-bearing fine
ash. The sedimentological model developed for the PDCs of the PdA eruption explains these strong lithofacies variations in
the light of the volcano’s morphology at the time of the eruption. In particular, the EU5 PDCs survived to pass over the break
in slope between the volcano sides and the surrounding volcaniclastic apron–alluvial plain, with development of new flows
from the previously suspended load. Pulses were developed within individual currents, leading to stepwise deposition on both
the volcano slopes and the surrounding volcaniclastic apron and alluvial plain. Physical parameters including velocity, density
and concentration profile with height were calculated for a flow of the phreatomagmatic phase of the eruption by applying
a sedimentological method, and the values of the dynamic pressure were derived. Some hazard considerations are summarised
on the assumption that, although not very probable, similar PDCs could develop during future eruptions of Somma–Vesuvius. 相似文献
155.
Characterization of salt-water intrusion in the lower Esino Valley, Italy using a three-dimensional numerical model 总被引:1,自引:0,他引:1
A seawater-intrusion study was conducted at an oil-refinery site located on the coast in the lower Esino Valley, Italy. A steady-state density-dependent flow model was used in order to understand the position of the freshwater/salt-water interface, as influenced by the hydrogeologic structure and the presence of industrial activities and a river. Collected data and model results showed that in a large part of the area, the salt-water interface is steep and can penetrate only a few meters inland. On the other hand, close to the river mouth, seawater represents the main saline source for the aquifer. The river, in connection with the sea, can enhance seawater encroachment into the coastal aquifer; a long-term survey of river level and chloride concentrations in groundwater is recommended to further improve the physical model and to obtain a better calibration. At the refinery site, two “secondary” sources of saline water were identified and were demonstrated to have had a great influence on the presence of brackish waters in the unconfined aquifer: leakage from the fire-extinguishing system (network of pipes containing seawater) and rough sea events. This confirmed that groundwater contamination by chloride can result from means other than seawater intrusion. 相似文献
156.
In coastal Louisiana, the development of large-scale freshwater diversion projects has led to controversy over their effects
on oyster resources. Using controlled laboratory experiments in combination with a field study, we examined the effects of
pulsed freshwater events (freshet) of different magnitude, duration, and rate of change on oyster resources. Laboratory and
field evidence indicate that low salinity events (<5 psu) decreased Perkinsus marinus infection intensities. Furthermore, when salinity was low (<5 psu), parasite infection intensities continued to decrease
even as temperatures exceeded 20°C. At the same time, oyster growth was positively correlated with salinity. To maximize oyster
production, data indicate that both low and high salinity events will be necessary. 相似文献
157.
A one-dimensional composition model of Titan's upper atmosphere is constructed, coupling 36 neutral species and 47 ions. Energy inputs from the Sun and from Saturn's magnetosphere and updated temperature and eddy coefficient parameters are taken into account. A rotating technique at constant latitude and varying local-time is proposed to account for the diurnal variation of solar inputs. The contributions of photodissocation, neutral chemistry, ion-neutral chemistry, and electron recombination to neutral production are presented as a function of altitude and local time. Local time-dependent mixing ratio and density profiles are presented in the context of the TA and T5 Cassini data and are compared in detail to previous models. An independent and simplified ion and neutral scheme (19-species) is also proposed for future 3D-purposes. The model results demonstrate that a complete understanding of the chemistry of Titan's upper atmosphere requires an understanding of the coupled ion and neutral chemistry. In particular, the ionospheric chemistry makes significant contributions to production rates of several important neutral species. 相似文献
158.
西藏高原夏季降水对ENSO的响应 总被引:3,自引:0,他引:3
通过合成分析指出包括雅藏布江中西段在内的西藏高原中西部地区夏季(6-8月)降水在ENSO的不同位相期间存在着显著的差异。利用交叉谱和奇异值分解等方法,分析了高原夏季降水场与太平洋海温场在时间和空间上的联系,结果表明,ENSO的暖(冷)位相期,高原大部分地区夏季降水以偏少(多)为主。 相似文献
159.
160.