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71.
Emö Márton Balázs Bradák Marta Rauch-Włodarska Antek K. Tokarski 《Studia Geophysica et Geodaetica》2010,54(1):121-134
AMS studies earlier carried out on the flysch sediments from the Outer Western Carpathians focused on the sandstone members
deposited from turbidity currents. The main conclusion of these studies was that the dominant features of the AMS fabric developed
during sedimentation and the tectonic overprint was weak. In recent years a large number of claystone (deposited also from
turbidity currents, but in calm water) localities were sampled from the Krosno beds of the Silesian nappe, primarily for paleomagnetic
study. Nevertheless, the AMS of the samples was also measured. The magnetic fabrics of the claystones were dominated by foliation,
but lineations were also expressed and attributed to deformation. The question arose how different are the reactions of the
claystone and the siltstone beds to deformation. 相似文献
72.
73.
Victor?H.?Rivera-MonroyEmail author Robert?R.?Twilley Ernesto?Medina E.?Barry?Moser Leonor?Botero Ana?Marta?Francisco Evelyn?Bullard 《Estuaries and Coasts》2004,27(1):44-57
Geostatistical analysis of selected soil properties were performed in two mangrove sites (B7 and B9) dominated by the mangrove
speciesRhizophora mangle along the San Juan River, Venezuela, to evaluate the effect of forest disturbance on nutrient spatial distributions. Plots
within area B7 were clear-cut in 1972–1973 and in area B9 in 1982–1983. Four plots within each area were systematically selected
and represented natural (2) and regenerated (2) forests. Individual plots were 1.5 ha in B7 and 1.25 ha in B9 and sampled
at a resolution of 25 m. Soil samples were obtained at the intersection of an aligned grid with 90 points in B7 and 78 points
in B9. Measured soil properties included salinity, total nitrogen, total carbon, total phosphorus, osmolality, and pore water
cation concentrations (potassium, calcium, magnesium, and sodium). Sites were sampled in May 1996 and 1997, although spatial
analysis was performed only for the data obtained in May 1997. Geostatistical analysis showed that most of the variables tested
were spatially auto-correlated within each area and that there were no differences between regenerated and natural plots.
Structural variance as a proportion of sample variance ranged from 55–99% for most of the properties. The significant spatial
dependence observed for most of the variables in natural and regenerated plots, despite management schedules, indicates that
clear-cutting did not have an effect on modifying the distribution of nutrient concentrations. These results suggest that
after 15 and 25 yr following forest disturbance nutrient distributions were reestablished either there was not a net effect
on patterns of element loss or tidal input was stronger than plant modifications of soils. 相似文献
74.
Michael Tsimplis Marta Marcos Samuel Somot Bernard Barnier 《Global and Planetary Change》2008,63(4):325-332
Sea level trends and inter-annual variability in the Mediterranean Sea for the period 1960–2000 is explored by comparing observations from tide gauges with sea level hindcasts from a barotropic 2D circulation model, and two full primitive equation 3D ocean circulation models, a regional one and the Mediterranean component of a global one,. In the 2D model, 50% of the sea level variance was found to result from the wind and atmospheric pressure forcing. In the 3D models, 20% of the sea level variance was explained by the steric effects. The sea level residuals at the tide gauges locations, calculated by subtraction of the 2D model output from the sea level observations are significantly correlated (r = 0.4) with the steric signals from the 3D models. After the removal of the atmospheric and the steric contributions the tide-gauge sea level records indicate a period where sea level was stable (1960–1975) and a period where sea level was rising (1975–2000) with rates in the range 1.1–1.8 mm/yr. A part of the residual trend can be explained by the contribution of local land movements (0.3 mm/yr) while its major part indicates a global signal, probably mass addition, appearing after 1975. 相似文献
75.
The November 13, 1985 eruption of Nevado del Ruiz produced a series of pyroclastic flows and surges that eroded channels on the surface of the summit glacier and generated lahars which descended down most of the rivers that drain the volcano. The stratigraphy of the proximal pyroclastic deposits indicates that there were at least four episodes to the eruption. Episode I, deposited an unusual surge consisting of small pieces of ice mixed with ash and exhibiting planar stratification. Ballistically emplaced fragments are also intercalated with this unit. During Episode II, at least two pyroclastic flows were erupted. Their deposits contain the most evolved pumice of the entire eruption; SiO2 content of matrix glass ranges between 74.5 and 74.9%. Episode III is marked by the emplacement of a welded tuff with an average SiO2 content of about 66% in the matrix glass. The final Episode IV was characterized by the development of a high-altitude eruption column and the emplacement of several nonwelded pyroclastic flows. Banded pumice are common in the pyroclastic flow as well as in the pumice fall deposits. Co-existing dark and light pumice bands differ in SiO2 content by 3.5% and in general are similar to the composition of the welded pumice from Episode III.The compositional zonation of the pyroclastic deposits from Episode I to IV suggests that a nearsurface compositionally-stratified portion of the magma body was tapped during Episode II. During Episodes III and IV the main body of magma was involved although the coexistence of the compositionally distinct pumice clasts at similar stratigraphic levels argues for mixing of magma from different levels in the chamber during the eruptive process. 相似文献
76.
77.
Marta Volonteri 《Astronomy and Astrophysics Review》2010,18(3):279-315
Evidence shows that massive black holes reside in most local galaxies. Studies have also established a number of relations between the MBH mass and properties of the host galaxy such as bulge mass and velocity dispersion. These results suggest that central MBHs, while much less massive than the host (~0.1%), are linked to the evolution of galactic structure. In hierarchical cosmologies, a single big galaxy today can be traced back to the stage when it was split up in hundreds of smaller components. Did MBH seeds form with the same efficiency in small proto-galaxies, or did their formation had to await the buildup of substantial galaxies with deeper potential wells? I briefly review here some of the physical processes that are conducive to the evolution of the massive black hole population. I will discuss black hole formation processes for ‘seed’ black holes that are likely to place at early cosmic epochs, and possible observational tests of these scenarios. 相似文献
78.
Marta S.M. Mantovani Wladimir Shukowsky B.B. de Brito Neves André Rugenski 《Geophysical Prospecting》2008,56(5):751-760
A semi-detailed gravity survey was carried out over an area of 650 km2 localized in the Eo-Neoproterozoic coastal zone of Paraiba State where 548 new gravity stations were added to the existing database. Gravity measurements were made with a LaCoste and Romberg model G meter with a precision of 0.04 mGal. The altitude was determined by barometric levelling with a fixed base achieving a 1.2 m measure of uncertainty, corresponding to an overall accuracy of 0.24 mGal for the Bouguer anomaly. The residual Bouguer map for a 7th degree regional polynomial showed a circumscribed negative anomaly coincident with a localized aero-magnetic anomaly and with hydro-thermally altered outcrops, near the city of Itapororoca. The 3D gravity modelling, constrained by geologic mapping was interpreted as a low density, fractured and/or altered material with a most probable volume of approximately 23 km3 , extending to about 8,500 m depth. This result is in accordance with a volcanic body associated with hydrothermal processes accompanied by surface mineralization evidence, which may be of interest to the mining industry. 相似文献
79.
Disturbances produced by geomagnetic storms in the higher regions of the Earth’s atmosphere, such as in the ionospheric F2
region and in the lower ionosphere, are relatively better known than those produced at lower altitudes, where the effects
of geomagnetic storms have been little studied. During magnetically perturbed conditions, some changes in pressure and temperature
at high latitudes have been observed, from the surface level to heights of around 30 km, but there are no morphological studies
and/or patterns of behavior. Moreover, the physical mechanisms are still unknown and what exists is a matter of controversy.
Thus, the aim of this paper is to contribute to the vertical profile of the effects of geomagnetic storms as observed in the
lower sectors of the atmosphere. For that, we study the variations of two atmospheric parameters (temperature and wind speed)
during an intense geomagnetic storm (minimum Dst = −300 nT), at heights between about 6 km and 20 km. The data used were obtained
from weather balloon flights carried out at low, mid and mid-high latitudes in different longitudinal sectors of the northern
hemisphere, which took place twice per day: 00:00 and 12:00 UT. Small, but statistically significant changes in temperature
and in zonal component of the neutral winds are observed at mid-high latitudes, which can be linked to short-term geomagnetic
forcing. However, the results show different atmospheric response to the geomagnetic storm in the different longitudinal sectors
at tropospheric and stratospheric levels, which suggests a regional character of the geomagnetic storms effects at tropospheric
levels. 相似文献
80.
Maria F. Gazulla Marta Rodrigo Monica Orduña Carmen M. Gómez 《Geostandards and Geoanalytical Research》2012,36(2):201-217
This article describes a series of methods developed for the determination of total carbon (CTotal), organic carbon (Corg), hydrogen, nitrogen and sulfur. The following elemental analysers were used: LECO model RC‐412 for the determination of organic carbon, total carbon and hydrogen; LECO model CS‐200 for the determination of total carbon and sulfur; LECO model TN‐400 for the determination of nitrogen; and LECO model TruSpec CHNS for the determination of organic carbon, total carbon, hydrogen, nitrogen and sulfur. Uncertainty and limits of detection and quantification were calculated for each method, as well as the running costs to define the most effective instrument for each material and each analyte. Accuracy was checked by the application of the Sutarno–Steger test. Finally, a compilation of the results obtained in the determination of CTotal, Corg, H, N and S in forty‐nine reference materials is presented. 相似文献