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91.
Past analyses of flare hard X-ray (HXR) spectra have largely ignored the effect of nonuniform ionization along the electron
paths in the thick-target model, though it is very significant for well-resolved spectra. The inverse problem (photon spectrum
to electron injection spectrum F
0(E
0)) is disturbingly non-unique. However, we show that it is relatively simple to allow for the effect in forward fitting of
parametric models of F
0(E
0)) and provide an expression to evaluate it for the usual single power-law form of F
0(E
0)).The expression involves the column depth N
* of the transition region in the flare loop as one of the parameters so data fitting can enable derivation of N
* (and its evaporative evolution) as part of the fitting procedure. The fit to RHESSI data on four flares for a single power
law F
0(E
0)) is much improved when ionization structure is included compared to when the usual fully ionized approximation is used.
This removes the need, in these events at least, to invoke broken power laws, or other forms, of the acceleration spectrum
F
0(E
0)) to explain the observed photon spectrum 相似文献
92.
Aleš Kapička Radka Kodešová Eduard Petrovský Zdeněk Hůlka Hana Grison Martin Kaška 《Studia Geophysica et Geodaetica》2011,55(4):683-696
Several studies have shown that magnetic measurements can be used in assessing soil contamination due to atmospheric deposition
of pollutants. Reliable spatial mapping of magnetic susceptibility of soils assumes high temporal stability of deposited particles,
accumulated in top-soil horizons. One of the main methodological concerns is whether the migration of deposited anthropogenic
ferrimagnetic particles may bias the measured values. Measurements carried out on high-porosity (sandy) soils, or on soils
with a very variable water regime may yield inconsistent values of top-soil magnetic susceptibility as the indicator of contamination.
This study focuses on the laboratory examination of migration of fly ashes from a coal-burning power plant in sands of different
porosity and under a simulated rain regime. Columns of sand of different grain sizes, placed in plastic cylinders, were contaminated
on the surface by the fly ash. The vertical migration of magnetic particles was monitored using measurements of magnetic susceptibility
with an SM400 Kappameter. Calibration measurements in the water environment showed an erroneous performance and resulted in
the technical improvement of the used susceptibility meter (Model 2009). Our results show that the vertical distribution of
flyash particles deposited on fine sand is very stable even after repeated rain simulation. The peak value of magnetic susceptibility
is located in a stable position a few millimeters under the surface. Hence, standard top-soil magnetic mapping is in such
a case reliable and fully representative. Contrary to that, in case of coarse sand, the peak value of magnetic susceptibility
migrates by more than 10 cm. The results will be further used for numerical modeling of contaminant transport in porous media. 相似文献
93.
Impacts of climate change on water resources in the Mediterranean Basin: a case study in Catalonia,Spain 总被引:1,自引:0,他引:1
Diana Pascual Eduard Pla Joan A. Lopez-Bustins Javier Retana Jaume Terradas 《水文科学杂志》2013,58(12):2132-2147
AbstractMost climate change projections show important decreases in water availability in the Mediterranean region by the end of this century. We assess those main climate change impacts on water resources in three medium-sized catchments with varying climatic conditions in northeastern Spain. A combination of hydrological modelling and climate projections with B1 and A2 IPCC emission scenarios is performed to infer future streamflows. The largest reduction (34%) in mean streamflows (for 2076–2100) is expected in the headwaters of the two wettest catchments, while lower decreases (25% of mean value for 2076–2100) are expected in the drier one. In all three catchments, autumn and summer are the seasons with the most notable projected decreases in streamflow, of 50% and 30%, respectively. Thus, ecological flows in the study area might be noticeably influenced by climate change, especially in the headwaters of the wet catchments. 相似文献
94.
Cyclostratigraphic analysis of the Pliocene Zújar section (Guadix-Baza Basin, southeastern Spain) has enabled the recognition of a number of climatically forced cycles reflecting alternating dry and wet periods. Peaks of aridity are recorded at ca. 3.95, 3.55, 3.2, 2.8, and 1.8 myr B.P. The first dry period at about 4.0 myr B.P. corresponds to the early Ruscinian Mammal age, while the second arid interval at about 3.6 myr B.P. corresponds to the establishment of the Mediterranean double seasonality. The significant mammal turnover between the late Ruscinian and early Villanyian stages is placed between chron 2An.2n and the very base of chron 2An.1n, coincident with the dry phase recognized at about 3.2 myr B.P. The fourth aridity maximum at 2.8 myr B.P. roughly coincides with the Equus event in western Europe and is probably related to the beginning of the glacial–interglacial dynamics in the Northern Hemisphere. Finally, the last dry peak at about 1.8 myr B.P. is probably related to the set of mammalian events characterizing the transition from the late Pliocene faunas to those of the early Pleistocene. 相似文献
95.
96.
Cumulative seismic strain release, during the period from 1964 through 1972, along the East Pacific and Chile rise edges of the Nazca plate is related to cumulative strain release of shallow earthquakes along the South American sinking edge: periods of high strain release along the rises alternated systematically with periods of high strain release along the sink.Volcanic activity (number of volcanoes in eruption per year between 1900 and 1968) migrates from Central to South America at some 900 km/year. High volcanic activity in Central America usually precedes large-magnitude earthquakes in Chile by several years, and would appear to be dynamically interrelated with the alternating strain release along the Nazca plate edges. 相似文献
97.
Tectonic map and overall architecture of the Alpine orogen 总被引:9,自引:0,他引:9
98.
Time lag of syntectonic sedimentation across an alluvial basin: theory and example from the Ebro Basin, Spain 总被引:5,自引:0,他引:5
Merren A. Jones Paul L. Heller† Eduard Roca‡ Miguel Garcés Lluís Cabrera 《Basin Research》2004,16(4):489-506
We propose and test a conceptual framework for evaluating the relative timing of different types of sedimentary indicators of tectonism in alluvial foreland basin settings. We take the first occurrence of a detrital grain from a newly exposed source‐area lithology to provide the best indicator of the onset of tectonic uplift in the source area. Source‐area unroofing may lag behind initial uplift because of the type, thickness and structure of rocks in the uplifted mountain block, drainage patterns and climate. However, once exposed, advective transport disperses grains quickly throughout fluvial systems. Because of increased subsidence rate from thrust belt loading, an increase in sedimentation rate begins coincident with tectonic load emplacement within the flexural half‐width of the basin. However, farther out into the basin increased sedimentation rates lag behind the composition signal because of time lags associated with propagation of the thrust load and attendant sediment loads into the basin. The progradation of syntectonic gravel lags behind all of these signals as a direct function of the relative proportion of gravel fraction within transported sediment and rates and geometry of subsidence, which selectively traps the coarsest grain‐size fractions in the most proximal parts of the basin. We demonstrate this signal attenuation in the syntectonic Horta–Gandesa alluvial system (late Eocene–Oligocene), exposed along the southeast margin of the Ebro Basin, Spain. The results demonstrate that: (1) the time spans between the compositional signal and the progradation of the gravel front can be geologically significant, on the order of more than a million years within as little as 20 km of the thrust front; and (2) time lags between the signals increase with distance away from the deformation front. No lag time was observed between the first appearance of a new clast composition and the arrival of gravel front when the thrust front was within a few tens of metres from the depositional site. In contrast, the time lag was 0.5–1 Myr when the thrust front was about 5–6 km away and it increased to >1 Myr when the deformation front was about 8 km away. At the most extreme position, when the thrust front was 15–20 km away, the gravel front never reached the study area. 相似文献
99.
Edward Venzke 《Bulletin of Volcanology》2005,67(7):689-690
Information included in this summary is based on more detailed reports published in the Bulletin of the Global Volcanism Network, v. 29, no. 11, November 2004 (on the Internet at ). Edited by scientists at the Smithsonian, this Bulletin includes reports provided by a worldwide network of correspondents. The reports contain the names and contact information for all sources. Please note that these reports are preliminary and subject to change as events are studied in more detail. The Global Volcanism Program welcomes further reports of current volcanism, seismic unrest, monitoring data, and field observations. 相似文献
100.
E. Venzke 《Bulletin of Volcanology》2005,68(1):91-92
Information included in this summary is based on more detailed reports published in the Bulletin of the Global Volcanism Network, v. 30, no. 1, January 2005 (on the Internet at ). Edited by scientists at the Smithsonian, this Bulletin includes reports provided by a worldwide network of correspondents. The reports contain the names and contact information for all sources. Please note that these reports are preliminary and subject to change as events are studied in more detail. The Global Volcanism Program welcomes further reports of current volcanism, seismic unrest, monitoring data, and field observations. 相似文献