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181.
Daniele Carbone Gennaro Budetta Filippo Greco Hazel Rymer 《Journal of Volcanology and Geothermal Research》2003,123(1-2):123
Systematic investigation of discrete gravity measurements has continued at Mount Etna since 1986. The network now covers an area of 400 km2 with about 70 stations 0.5–3 km apart. Mass redistributions occurring at depths ranging between about 8 km below sea level and a few hundred metres below the surface (magma level changes within the shallower parts of the feeding conduits) have been identified from these data. Conventional (discrete) microgravity monitoring on a network of stations furnishes only instantaneous states of the mass distribution at continuously active systems. In order to obtain information on the rate at which the volcanic processes (and thus mass transfers) occur, three stations for continuously recording gravity where installed on Mount Etna in 1998. A 16-month long sequence from one of the continuously running stations (PDN, located 2 km from the active northeast crater at the summit of Etna volcano) is presented. After removing the effects of Earth Tide and tilt, the correlation of the residual gravity sequence with simultaneous recordings of meteorological parameters acquired at the same station was analysed. Once the meteorological effects have also been removed, continuous gravity changes are within 10 μGal of gravity changes measured using conventional microgravity observations at sites very close to the continuous station. This example shows how discrete and continuous gravity observations can be used together at active volcanoes to get a fuller and more accurate picture of the spatial and temporal characteristics of volcanic processes. 相似文献
182.
The occurrence of the freshwater genus Tanousia Servain 1881 (Hydrobiidae) in the Middle Pleistocene lacustrine succession of the Piànico-Sèllere Basin (Bergamo, Northern Italy) represents a significant biostratigraphical discovery. The Tanousia were recovered from the basal part of the carbonate varved bed (BVC), in siltysandy slump sediments, and from the lower and middle parts of the La Palazzina Member (MLP) of the Piànico formation. The BVC unit, in which a dated tephra layer occurs, accumulated during an interglacial phase, as shown by pollen analyses. The MLP Tanousia-bearing layers have been laid down during cool–temperate climate oscillation. The Piànico population of Tanousia displays great morphological variability but is similar to T. runtoniana (Sandberger, 1880), T. stenostoma (Nordmann, 1901) and T. cf. T. stenostoma (Nordmann, 1901), from the Bavelian and Cromerian interglacial deposits of late Early and early Middle Pleistocene age in Northern Europe. As for these species, the Tanousia population from Piànico appears to indicate fluvial conditions under a fully temperate climate. 相似文献
183.
Rita Colognola Pietro Masturzo Giovanni Fulvio Russo Mlchele Scardi Daniele Vlnci Eugenio Fresi 《Marine Ecology》1986,7(3):265-285
Abstract. Two forms of Rissoa auriscalpium were found in Posidonia oceanica beds around the Island of Ischia (Gulf of Naples). In order to investigate their taxonomical value and to quantify the discriminating features found, the radular, conchometric, genetic, and ecological features of the two forms were analyzed. Ecological observations showed that the distribution of the two forms is strongly correlated with hydrodynamic factors. 相似文献
184.
185.
186.
Mingda Lv Xi Liu Sean R. Shieh Tianqi Xie Fei Wang Clemens Prescher Vitali B. Prakapenka 《Physics and Chemistry of Minerals》2016,43(4):301-306
Using a diamond-anvil cell and synchrotron X-ray diffraction, the compressional behavior of a synthetic qandilite Mg2.00(1)Ti1.00(1)O4 has been investigated up to about 14.9 GPa at 300 K. The pressure–volume data fitted to the third-order Birch–Murnaghan equation of state yield an isothermal bulk modulus (K T0) of 175(5) GPa, with its first derivative \(K_{T0}^{{\prime }}\) attaining 3.5(7). If \(K_{T0}^{{\prime }}\) is fixed as 4, the K T0 value is 172(1) GPa. This value is substantially larger than the value of the adiabatic bulk modulus (K S0) previously determined by an ultrasonic pulse echo method (152(7) GPa; Liebermann et al. in Geophys J Int 50:553–586, 1977), but in general agreement with the K T0 empirically estimated on the basis of crystal chemical systematics (169 GPa; Hazen and Yang in Am Miner 84:1956–1960, 1999). Compared to the K T0 values of the ulvöspinel (Fe2TiO4; ~148(4) GPa with \(K_{T0}^{{\prime }} = 4\)) and the ringwoodite solid solutions along the Mg2SiO4–Fe2SiO4 join, our finding suggests that the substitution of Mg2+ for Fe2+ on the T sites of the 4–2 spinels can have more significant effect on the K T0 than that on the M sites. 相似文献
187.
188.
Salvatore Alparone Daniele Andronico Tiziana Sgroi Ferruccio Ferrari Luigi Lodato Danilo Reitano 《Natural Hazards》2007,43(3):333-350
Volcanic eruptions may create a wide range of risks in inhabited areas and, as a consequence, major economic damage to the
surrounding territory. An example of volcanic hazard was given between 1998 and 2001 by Mt. Etna volcano, in Italy, with its
frequent paroxysmal explosive activity that caused more than a hundred fire-fountain episodes. In the period January–June
2000, in particular, 64 lava fountains took place at the Southeast Crater. During the most intense explosive phase of each
episode, a sustained column often formed, reaching up to 6 km above the eruptive vent. Then, the column started to expand
laterally causing more or less copious tephra fallout on the slopes of Etna; ash and lapilli, therefore, constituted a serious
danger for vehicular and air traffic. A software and hardware warning system was developed to mitigate the volcanic hazard
indicating the areas affected by potential ash and lapilli fallout. The alert system was mainly based on the good correspondence
between the pattern of volcanic tremor amplitude and the evolution of explosive activity. When a fixed tremor threshold was
exceeded, a semiautomatic process started to send faxes to Civil Defence and Municipalities directly affected by tephra fallout,
together with information on wind directions from the Meteorological Office. The application of this methodology, during the
last 14 eruptive episodes in 2000 and the 14 events occurred in 2001, demonstrated the good correspondence between the forecasts
on the areas affected by tephra fallout and the effective tephra distribution on land. Despite the integrity of the performance
provided by the alert system, small discrepancies occurred in the technical procedure of alerting, for which possible solutions
have been discussed. The improvement of this type of system, could become basic for the Etnean region and be proposed for
similar volcanic areas throughout the world. 相似文献
189.
Microgravity observations at Mt. Etna have been routinely performed as both discrete (since 1986) and continuous (since 1998)
measurements. In addition to describing the methodology for acquiring and reducing gravity data from Mt. Etna, this paper
provides a collection of case studies aimed at demonstrating the potential of microgravity to investigate the plumbing system
of an active volcano and detect forerunners to paroxysmal volcanic events. For discrete gravity measurements, results from
1994–1996 and 2001 are reported. During the first period, the observed gravity changes are interpreted within the framework
of the Strombolian activity which occurred from the summit craters. Gravity changes observed during the first nine months
of 2001 are directly related to subsurface mass redistributions which preceded, accompanied and followed the July-August 2001
flank eruption of Mt. Etna. Two continuous gravity records are discussed: a 16-month (October 1998 to February 2000) sequence
and a 48-hour (26–28 October, 2002) sequence, both from a station within a few kilometers of the volcano's summit. The 16-month
record may be the longest continuous gravity sequence ever acquired at a station very close to the summit zone of an active
volcano. By cross analyzing it with contemporaneous discrete observations along a summit profile of stations, both the geometry
of a buried source and its time evolution can be investigated. The shorter continuous sequence encompasses the onset of an
eruption from a location only 1.5 km from the gravity station. This gravity record is useful for establishing constraints
on the characteristics of the intrusive mechanism leading to the eruption. In particular, the observed gravity anomaly indicates
that the magma intrusion occurred “passively” within a fracture system opened by external forces. 相似文献
190.
The statistical distribution of the daily Snow Water Equivalent (SWE) is investigated for a network of gauging stations in the Alpine part of Lombardia region, in the central Italian Alps. An event based data analysis is carried out using a 14 year long data set dating back to 1989. SWE is estimated when the new snow depth is greater than 6 cm. The SWE sample average in time is shown to be related to physiographic attributes of the gauging area, thus not being homogeneous in space. The values of SWE scaled by their average, or index value, instead show well approximated homogeneity of the second order moment, or coefficient of variation, in space. This suggests the use of a regional approach for frequency estimation of SWE. The frequency of occurrence of the normalized values of SWE is evaluated and tentatively accommodated by four probability distributions, often adopted in statistical modeling of hydrological variables. The Lognormal distribution shows the best performance. Single site distribution fitting is then carried out using the regional distribution, providing satisfactory results. 相似文献