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191.
On the relative roles of unipolar and mixed-polarity fields 总被引:1,自引:0,他引:1
Ronald G. Giovanelli 《Solar physics》1982,77(1-2):27-42
Away from plages, solar magnetic fields may be classified as unipolar or as of mixed polarity, though the distinction is strictly arbitrary. The dividing line used here is 0.4 ¦B
minor/B
major¦ 1, where average fields of major and minor polarities are measured over large areas. Some of their statistical properties and cyclical variations are detailed. In unipolar regions, 3 B
major 50 G, B
minor 0.1 B
major, and ¦B¦ 1.1 B
major. In regions of mixed polarity, 3.5 ¦B¦ 10 G.Below latitudes of ± 60°, mixed polarities predominate for about 5 yr around sunspot minimum. For several years around sunspot maximum, unipolar fields fill the 20°–40° zone completely, and occupy about 75% of the 0°–20° and 40°–60° zones.The polar unipolar fields are weak on the whole (Bmajor 4 G for 6 typical days in 1976–79), with small regions having stronger fields at times, probably not exceeding B
major = 10 G. Again B
minor 0.1 B
major. There is no direct way at present of measuring properties of polar mixed fields, such as may occur around sunspot maximum, but by inference ¦B¦ 2 to 5 G.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation. 相似文献
192.
R. G. Giovanelli 《Solar physics》1979,62(2):253-268
A first-order theory is developed for the radiative dissipation of compressive waves in the chromosphere above T
min, where line radiation becomes dominant. The radiative relaxation time, which is the key to dissipation, is shown to depend on wave amplitude, falling greatly for amplitudes 2 km s–1 or more. For a given amplitude, dissipation is greatest for high frequencies, 0.1 s–1, periods 1 min. The observed short-period r.m.s. velocities ~2.4 km s–1 at the D1, level are adequate to provide dissipation balancing chromospheric emission losses.Predictions for the temperature-velocity phase difference and the phase velocity are compatible with observations. 相似文献
193.
Giorgio Bavestrello Riccardo Cattaneo-Vietti Roberto Danovaro Mauro Fabiano 《Marine Ecology》1991,12(4):281-292
Abstract. The detritus rolling down a vertical cliff was studied at Portofino Promontory (Ligurian Sea, Italy) at 16 m depth (January 1988- January 1989). The large amount of collected sediment is mainly due to the position of the traps; they collected not only the sedimenting material, but also the detritus rolling down along the cliff. The amount of sediment matter is 7 times greater in winter than in summer, showing a good correlation with rough seas and rain that cause a "mechanical cleaning" of animal and plant debris (Sérpulid tubes, shells, exuvias. leaves) along the cliff.
The Total Suspended Matter (TSM) in the water column shows maximum values in March and September. The organic fraction has an average concentration of 0.81 mg 1-l . The phytoplanktonic biomass, measured as Chi a , shows an annual cycle with a peak in spring (1–2.7μg·l-1 ). while in other periods of the year the value is about 0.3-0.5 μg·1-1 . A significant relationship was found between organic detritus in the collected sédiments and the Chi a in the water column. The great influence of the rocky wall detritus on the normal trend of the TSM in the coastal water column is pointed out. 相似文献
The Total Suspended Matter (TSM) in the water column shows maximum values in March and September. The organic fraction has an average concentration of 0.81 mg 1
194.
Pierre-Marie Poulain Riccardo Barbanti Sergey Motyzhev Andrei Zatsepin 《Deep Sea Research Part I: Oceanographic Research Papers》2005,52(12):2250-2274
The near-surface circulation in the Black Sea is studied with the data of 54 satellite-tracked drifters in the period 1999–2003. The drifter trajectories confirm the prevalence of the Rim Current trapped on the continental slope (between water depths of 400 and 1800 m) along the periphery of the basin where sub-inertial speeds can reach 1 m/s. Some drifters were found to complete an entire basin loop with the Rim Current in 90–180 days. Meanders and loops in the tracks prove the existence of mostly anticyclonic circulation features inshore of the Rim Current, including strong signatures of the Batumi and Sevastopol eddies. They also reveal the presence of cyclonic and anticyclonic currents in most areas of the Black Sea. Pseudo-Eulerian statistics (averaged in 50-km bins), that is, mean currents and the corresponding velocity variances, show a strong and highly fluctuating signature of the Rim Current and the enhanced variability associated with the Batumi and Sevastopol eddies. The latter is also collocated with the branching of the Rim Current southwest of the Crimean Peninsula. It is shown that the kinetic energy is mainly in the mean for the Rim Current and in the velocity fluctuations elsewhere. Seasonal variability is also explored. The Rim Current tends to form a stronger single loop trapped on the continental slope in winter/spring, whereas in summer/fall the mean circulation is more meandering, recirculation cells appear in the central areas and the bifurcation southwest of Crimea is enhanced. There is some evidence of the reversal of sense of rotation of the currents in the Batumi Eddy region, changing from mainly anticyclonic in summer/fall to cyclonic in winter/spring. Mean residence times were calculated in the 50-km bins, with values ranging from a few days in the central basin to 8 days in the northwestern coastal area. Globally, the kinetic energy levels were found higher in winter–spring and lower in summer–fall, with a significant maximum in March. Single-particle Lagrangian statistics were computed for the entire basin, for the two extended seasons, and in selected local areas. Velocity variance, diffusivity and Lagrangian integral time scales are generally larger in the zonal direction. Globally, the velocity variance is 174 and 127 cm2/s2 in the zonal and meridional directions, respectively, after the removal of the pseudo-Eulerian mean circulation. For the zonal direction, a diffusivity value of 4.5×107 cm2/s and Lagrangian integral time and space scales of 3 days and 34 km were found. For the meridional direction, these statistics amount to 4.5×107 cm2/s, 1.2 days and 12.2 km. Seasonal and geographical variations of these Lagrangian statistics were also assessed, showing variations between 1.9 (0.9) 107 and 8.3 (2.0) 107 cm2/s for the diffusivity in the zonal (meridional) direction. Integral time and space scales vary between 1 and 4.7 days, and 8.8 and 58 km, respectively. Seasonal differences are significant only in the zonal direction, where the diffusivity increases from 3.1×107 to 5.9×107 cm2/s and the integral scales vary from 2.1 days (24 km) to 3.8 days (44 km) from summer/fall to winter/spring. 相似文献
195.
Imaging and modelling the subsurface structure of volcanic calderas with high-resolution aeromagnetic data at Vulcano (Aeolian Islands,Italy) 总被引:2,自引:0,他引:2
Isabel Blanco-Montenegro Riccardo De Ritis Massimo Chiappini 《Bulletin of Volcanology》2007,69(6):643-659
In this paper, we present a magnetic model of the subsurface structure of Vulcano island based on high-resolution aeromagnetic
data. Three profiles across the most intense magnetic anomalies over the Piano and Fossa calderas were selected for the magnetic
modelling, which was constrained by structural and volcanological data, previous geophysical models, paleomagnetic data, and
borehole stratigraphy obtained from two deep wells. The interpretation of the magnetic sources represents a significant contribution
to the understanding of the Piano and Fossa calderas’ underlying structure, providing us with evidence of the lateral discontinuity
between them at depth. We propose that the positive magnetic anomalies in the Piano caldera area are caused by: (a) the remnants
of an early submarine volcano; (b) an outcropping dyke swarm related to the feeding system of the Primordial Vulcano phase
(beneath Mt. Saraceno); and (c) the presence of a non-outcropping dyke system intruded along a NE–SW-oriented intra-caldera
fault (beneath the eastern part of the Piano caldera). Offshore, to the west, the magnetic anomaly map suggests the presence
of a submarine volcanic structure, not revealed by bathymetric data, which could represent the eruptive centre, the presence
of which has been indirectly deduced from the outcrop of eastern-dipping lavas on the western seashore. Magnetic modelling
of the Fossa caldera points to the presence of a highly magnetized cone-like body inside the Fossa cone, centred beneath the
oldest crater rims. We interpret this body as a pile of tephritic lavas emplaced in an early phase of activity of the Fossa
cone, suggesting that the volume of mafic lavas that erupted at the beginning of the construction of the Fossa edifice was
more significant than has previously been deduced. Furthermore, the presence of a magnetized body inside the Fossa cone implies
that high temperatures are contained in very limited spaces, do not affect its bulk inner structure, and are restricted to
fumarolic conduits and vents. In addition, structures beneath the western and northern part of the Fossa caldera are revealed
to have null or low magnetization, which can be ascribed to the presence of pyroclasts and hyaloclastites in this area as
well as to a large volume of hydrothermally altered materials. This suggests that the hydrothermal system, with a very limited
extension at present, affected a larger area in the past, especially beneath the western part of the caldera. 相似文献
196.
197.
Brick-like texture and radial rays in Triassic pisolites of Lombardy,Italy: A clue to distinguish ancient aragonitic pisolites 总被引:1,自引:0,他引:1
Triassic pisolites from the Calcare Rosso, Lombardy, Italy, were formed in a hypersaline vadose environment and now show alternating dolomite and calcite laminae. The calcite consists either of microsparite laminae with a brick-like fabric, or of a mass of mosaic crystals with the external form of square-ended rays.These features suggest that the original laminae and rays were aragonitic, like those of the Holocene supratidal pisolites of the Persian Gulf, which consist of alternating laminae of unoriented nannomicrite with Mg-rich mucilaginous material, and aragonitic fibers with radial orientation separated by mucilaginous films. It is suggested that the transformation to brick-like and ray textures passed through the following diagenetic path: (1) original formation of fibrous aragonite laminae; (2) local aggrading recrystallization of aragonite fibers to large square-ended rays during hypersaline phases; (3) dolomitization of Mg-rich mucilaginous nannomicrite laminae during hyposaline phases; (4) inversion of the aragonite fibers and rays to calcite on a piece-by piece basis that preserved the original textural details, when the pH or Mg/Ca ratio dropped.The brick-like and ray fabrics have not been found in laminae of continental freshwater pisolites because these were deposited as equant and stable crystals of low-Mg calcite. These textures consequently make it possible to establish the chemistry of the depositional and early diagenetic milieu for some ancient pisolitic rocks. 相似文献
198.
AN ION PROBE CONTRIBUTION TO RARE EARTH ELEMENT INVESTIGATION OF GABBRO GOG-1 USING SECONDARY ION MASS SPECTROMETRY 总被引:1,自引:0,他引:1
Luisa OTTOLINI Piero BOTTAZZI Riccardo VANNUCCI Massimo ODDONE 《Geostandards and Geoanalytical Research》1992,16(1):13-19
An updated REE measurement of Gabbro GOG-1 was carried out by means of secondary ion mass spectrometry (SIMS). The availability of high amount of rock powder allowed the sample to be well ground and homogenized before analysis. Fused glass pellets were employed for SIMS investigations. REE data were compared with new ICP-AES and NAA analyses. REE results from all employed analytical techniques show good agreement and are consistent with in-situ SIMS measurements of REE in major mineral phases forming GOG-1. Extensive homogeneity tests seem to confirm the possibility to using this rock as a reference material for earth sciences. 相似文献
199.
The coupled hydro‐mechanical state in soils coming from consolidation/subsidence processes and undergoing plasticity phenomena is here evaluated by means of the subloading surface model. The most important feature of this theory is the abolition of the distinction between the elastic and plastic domains, as it happens in the conventional elastoplastic models. This means that plastic deformations are generated whenever there is a change in stress and a smoother elastoplastic transition is produced. The plasticity algorithm has been implemented in the PLASCON3D FE code, coupling hydro‐thermo‐mechanical fields within a saturated (locally partially saturated) porous medium subjected to external loads and water/gas withdrawals from deep layers (aquifers/reservoirs). The 3D model has been first calibrated and validated against examples taken from the literature, and then subsidence analyses at regional scales due to gas extractions have been developed to predict the evolution of settlements and pore pressure in soils for long‐term scenarios. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
200.
Riccardo Brunino Ignacio Trujillo Frazer R. Pearce Peter A. Thomas 《Monthly notices of the Royal Astronomical Society》2007,375(1):184-190
Using the Millennium N -body Simulation we explore how the shape and angular momentum of galaxy dark matter haloes surrounding the largest cosmological voids are oriented. We find that the major and intermediate axes of the haloes tend to lie parallel to the surface of the voids, whereas the minor axis points preferentially in the radial direction. We have quantified the strength of these alignments at different radial distances from the void centres. The effect of these orientations is still detected at distances as large as 2.2 R void from the void centre. Taking a subsample of haloes expected to contain disc-dominated galaxies at their centres we detect, at the 99.9 per cent confidence level, a signal that the angular momentum of those haloes tends to lie parallel to the surface of the voids. Contrary to the alignments of the inertia axes, this signal is only detected in shells at the void surface (1 < R < 1.07 R void ) and disappears at larger distances. This signal, together with the similar alignment observed using real spiral galaxies, strongly supports the prediction of the Tidal Torque theory that both dark matter haloes and baryonic matter have acquired, conjointly, their angular momentum before the moment of turnaround. 相似文献