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41.
Salvador E. Lluch-Cota Eugenio A. Aragón-Noriega David Aurioles-Gamboa Richard C. Brusca Roberto Cortés-Altamirano Alfonso Esquivel-Herrera Michel E. Hendrickx Hugo Herrera-Cervantes Miguel Lavín Daniel B. Lluch-Cota Silvio G. Marinone Sofia Ortega-García Alejandro Parés-Sierra Mauricio Ramírez-Rodríguez Richard A. Schwartzlose Arturo P. Sierra-Beltrán 《Progress in Oceanography》2007,73(1):1-26
The Gulf of California is unique because of its geographical location and conformation. It hosts diverse ecosystems and important fisheries that support industry and provide livelihood to coastal settlements. It is also the site of interests and problems, and an intense interaction among managers, producers, and conservationists. In this report, we scrutinize the abiotic (hydrography, climate, ocean circulation, and chemistry) and biotic (phyto- and zooplankton, fish, invertebrates, marine mammals, birds, and turtles) components of the marine ecosystem, and some particular aspects of climate variability, endemisms, harmful algal blooms, oxygen minimum layer, and pollution. We also review the current conditions and conflicts around the main fisheries (shrimp, small and large pelagic fishes, squid, artisanal and sportfishing), the most important human activity in the Gulf of California. We cover some aspects of management and conservation of fisheries, especially the claimed overexploitation of fish resources and the ecosystems, and review proposals for creating networks of marine protected areas. We conclude by identifying main needs for information and research, particularly the integration of data bases, the implementation of models and paleoreconstructions, establishment of monitoring programs, and the evaluation of fishing impacts and management actions. 相似文献
42.
Abstract. Posidonia oceanica prairies have been studied and mapped around the Island of Ischia and in adjacent waters. Prairies were found to cover an area of 15.7 km2 and to be distributed between 0.5 and 39 m depth. The observed distribution is comparable to those reported by previous authors indicating that prairies have not undergone remarkable regressions in the last 50 years. Patterns recorded within the beds and at their lower limits, as indicated also by their sediments characteristics, are correlated to hydrodynamic energy. Two main types of water motion are responsible for the different types of erosive features: a) steady currents flowing parallel to the coast; b) rip-, wave induced currents flowing normal to the coast. 相似文献
43.
44.
Eugenio Molina-Navarro Antonio Sastre-Merlín Rosa Vicente Silvia Martínez-Pérez 《Hydrogeology Journal》2014,22(5):1115-1129
A small calcareous basin in central Spain was studied to establish the role of groundwater in the Pareja Limno-reservoir. Limno-reservoirs aim to preserve a constant water level in the riverine zone of large reservoirs to mitigate the impacts arising from their construction. Groundwater flow contribution (mean 60 %) was derived by recharge estimation. In situ measurements (spring discharge, electrical conductivity and sulfate) were undertaken and spring discharge was compared with a drought index. Twenty-eight springs were monitored and three hydrogeological units (HGUs) were defined: a carbonate plateau (HGU1), the underlying aquitard (HGU2), and the gypsum-enriched HGU3. HGU1 is the main aquifer and may play a role in the preservation of the limno-reservoir water level. Hydrogeochemical sampling was conducted and the code PHREEQC used to describe the main geochemical processes. Weathering and dissolution of calcite and gypsum seem to control the hydrogeochemical processes in the basin. Water progresses from Ca2+–HCO3 – in the upper basin to Ca2+–SO4 2– in the lower basin, where HGU3 outcrops. A clear temporal pattern was observed in the limno-reservoir, with salinity decreasing in winter and increasing in summer. This variation was wider at the river outlet, but the mixing of the river discharge with limno-reservoir water buffered it. 相似文献
45.
46.
Carmelo Ferlito Marco Viccaro Eugenio Nicotra Renato Cristofolini 《Bulletin of Volcanology》2010,72(10):1179-1190
Over the last 2 years, the south east crater (SEC) at Mt. Etna (Italy) has been characterised by the intermittent emission
of lava flows, often accompanied by paroxysmal episodes with violent strombolian activity and/or lava fountains. One of the
most intense and intriguing episodes occurred on November 16, 2006 during strombolian and effusive activity from the very
top of the SEC. At the eastern base of the crater, a violent and short-lasting outburst generated a 300-m-high eruptive curtain
of finely fragmented magma and steam, which collapsed in a few seconds giving rise to a small but significant pyroclastic
flow. The paroxysm was preceded by progressive sliding of the eastern flank of the SEC edifice, which led to the formation
of a large niche. Previously published models explain the outburst as due to rapid vaporisation of water contained in sediments
on contact with hot lava flowing along the flank of the SEC or, alternatively, to gravitational collapse of a destabilised
portion of the eastern flank of the crater. However, several lines of evidence suggest that these models do not adequately
explain the paroxysm, which we propose was associated with the explosive emission of magma during the rapid opening of an
ESE-WNW-oriented fracture at the eastern base of the SEC. Moreover, geochemical data of the products associated with this
episode show that they are the most primitive and gas-rich among those erupted during the entire 2006 period. We suggest that
the paroxysm of November 16, 2006, which occurred at base of the SEC, was a magma outburst due to rapid ground fracturing
related to a drop in confining pressure upon the underlying dyke consequent to the sliding of the eastern flank of the SEC
cone. Specifically, the unloaded shallow portion of the feeding dyke did not restrain the arrival of a new batch of gas-rich
magma, which worked its way out by fracturing the base of the niche at its weakest point. This paroxysm appears significant
because it reveals the potential development of syn-eruptive dynamics acting directly on the uppermost portion of the plumbing
system which is able to generate pyroclastic flows even on basaltic volcanoes such as Mount Etna. 相似文献
47.
A new multidisciplinary study, combining geology, petrography, and geochemistry, on the rocks of the isolated hill of Mount
Calanna (Mount Etna, Italy) has provided evidence for the existence of a dyke swarm, formed by more than 200 dykes distributed
over an area of ~0.7 km2, with an intensity of intrusion up to 40%. All bodies are deeply altered, and the geological and mesostructural surveying
of 132 dykes revealed that they intruded in E–W direction, with an average dip of 60°. The faults affecting the outcrop have
in general an E–W strike and dip of ~55°: these have all normal motion and have been interpreted as coeval with the dykes.
This interpretation contrasts with the previous hypothesis that considered Mount Calanna as a thrust resulting from compressive
deformation resulting from the gravitational spreading of the volcanic edifice. Mount Calanna is here interpreted as the uppermost
portion of a vertically extensive magmatic plexus that fed the eruptive activity of one (or more) eruptive center/s sited
in the Valle del Bove area. Measurements of the apparent densities on 23 dykes and host rock samples give an average value
of 2,420 kg/m3 for the entire complex, ~15% lower than the density expected for hawaiitic magma, placing an important constraint on the
geophysical identification of similar structures. Considering that Mount Etna is not an old eroded edifice but an active and
growing volcano, the exposure of this subvolcanic structure can be regarded as exceptional. Its geometry and physical characteristics
can be thus regarded as an interesting example of the present-day shallow plumbing system of Mount Etna as well as of other
basaltic volcanoes. 相似文献
48.
Seven tectonic subsidence curves, based on outcrop data, have been calculated in order to constrain the geodynamic evolution of the Permian–Mesozoic sedimentary succession (up to 10 km thick) of the Central Southern Alps basin (Italy). The analysis of the tectonic subsidence curves, covering a time span of about 200 Ma, allowed us to quantify the subsidence rates, to document the activity of syndepositional fault systems and calculate their slip rates. Different stages, in terms of duration and magnitude of subsidence‐uplift trends, have been identified in the evolution of the basin. The fault activity, reconstructed by comparing subsidence curves from adjacent sectors, resulted as highly variable both temporally and spatially. Strike‐slip tectonics was coeval to Permian sedimentation, as suggested by the strong differences in the subsidence rates in the sections. The evolution and subsidence rates suggest a continental shelf deposition from Early Triassic to Carnian, when subsidence came to a stop. A rapid resumption of subsidence is observed from the Norian, with a subsidence pulse in the Late Norian, followed by the regional uplift, in the Late Rhaetian. The following Early Jurassic subsidence is characterized by tectonic subsidence similar to that of the Norian. The Norian and Early Jurassic pulses were characterized by the highest slip rates along growth faults and are identified as two distinct tectonic events. The Norian–Rhaetian event is tentatively related to transtensional tectonics whereas the Early Jurassic event is related to crustal extension. The Early Jurassic subsidence records a shift in space an time of the beginning of the extensional stage, from Late Hettangian to the east to Late Pliensbachian–Toarcian to the west. From the Toarcian to the Aptian, the curves are compatible with regional thermal subsidence, later followed (Albian–Cenomanian) by uplift pulses in a retrobelt foreland basin (from Cenomanian onward). 相似文献
49.
Operational earthquake forecasting (OEF) relies on real-time monitoring of seismic activity in an area of interest to provide constant (e.g., daily) updates of the expected number of events exceeding a certain magnitude threshold in a given time window (e.g., 1 week). It has been demonstrated that the rates from OEF can be used to estimate expected values of the seismic losses in the same time interval OEF refers to. This is a procedure recently defined as operational earthquake loss forecasting (OELF), which may be the basis for rational short-term seismic risk assessment and management. In Italy, an experimental OELF system, named MANTIS-K, is currently under testing. It is based on weekly rates of earthquakes exceeding magnitude (M) 4, which are updated once a day or right after the occurrence in the country of an M 3.5+ earthquake. It also relies on large-scale structural vulnerability and exposure data, which serve to the system to provide continuously the weekly expected number of: (1) collapsed buildings, (2) displaced residents, and (3) casualties. While the probabilistic basis of MANTIS-K was described in previous work, in this study OELF is critically discussed with respect to three recent Italian seismic sequences. The aim is threefold: (1) illustrating all the features of the OELF system in place; (2) providing insights to evaluate whether if it would have been a useful additional tool for short-term management; (3) recognizing common features, if any, among the losses computed for different sequences. 相似文献
50.