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121.
Rapid injection of particles and gas into non-fluidized granular material, and some volcanological implications 总被引:3,自引:3,他引:0
Pierre-Simon Ross James D. L. White Bernd Zimanowski Ralf Büttner 《Bulletin of Volcanology》2008,70(10):1151-1168
In diatremes and other volcanic vents, steep bodies of volcaniclastic material having differing properties (particle size
distribution, proportion of lithic fragments, etc.) from those of the surrounding vent-filling volcaniclastic material are
often found. It has been proposed that cylindrical or cone-shaped bodies result from the passage of “debris jets” generated
after phreatomagmatic explosions or other discrete subterranean bursts. To learn more about such phenomena, we model experimentally
the injection of gas-particulate dispersions through other particles. Analogue materials (glass beads or sand) and a finite
amount of compressed air are used in the laboratory. The gas is made available by rapidly opening a valve—therefore the injection
of gas and coloured particles into a granular host is a brief (<1 s), discrete event, comparable to what occurs in nature
following subterranean explosions. The injection assumes a bubble shape while expanding and propagating upwards. In reaction,
the upper part of the clastic host moves upward and outward above the ‘bubble’, forming a ‘dome’. The doming effect is much
more pronounced for shallow injection depths (thin hosts), with dome angles reaching more than 45°. Significant surface doming
is also observed for some full-scale subterranean blasts (e.g. buried nuclear explosions), so it is not an artefact of our
setup. What happens next in the experiments depends on the depth of injection and the nature of the host material. With shallow
injection into a permeable host (glass beads), the compressed air in the “bubble’ is able to diffuse rapidly through the roof.
Meanwhile the coloured beads sediment into the transient cavity, which is also closing laterally because of inward-directed
granular flow of the host. Depending on the initial gas pressure in the reservoir, the two-phase flow can “erupt” or not;
non-erupting injections produce cylindrical bodies of coloured beads whereas erupting runs produce flaring upward or conical
deposits. Changing the particle size of the host glass beads does not have a large effect under the size range investigated
(100–200 to 300–400 μm). Doubling the host thickness (injection depth) requires a doubling of the initial gas pressure to
produce similar phenomena. Such injections—whether erupting or wholly subterranean—provide a compelling explanation for the
origin and characteristics of multiple cross-cutting bodies that have been documented for diatreme and other vent deposits. 相似文献
122.
Numerical simulation of the thermal maturation, oil generation and migration in the Songliao Basin, Northeastern China 总被引:5,自引:0,他引:5
The discovery of the giant Daqing oil field in the Songliao Basin led to the realisation of the significant petroleum potential of non-marine basins. In order to reconstruct the basin evolution and oil formation, an integrated organic geochemical-basin modelling study along a regional transect across the Songliao Basin was conducted. It provided a regional heat flow evolution model, and revealed post-orogenic or late syn-orogenic maturation in the Central Depression and pre-orogenic maturation in the Southeast Uplift Zone. Kinetic parameters of petroleum generation for the lacustrine source formations are the basis for the simulation of oil generation and migration in the Songliao Basin. Using the principle activation energy peaking at 54 kcal/mol and a pre-exponential factor of about 4.2·1027 Ma−1, the simulation obtained a relatively good match with the measured transformation ratios. The Qingshankou Formation in the West and East Central Depressions constituted the major source in the basin. Major oil generation, migration and accumulation occurred during the Early Tertiary. In the West Central Depression, the generated oils migrated upwards into the Yaojia Formation followed by the updip migration into the Daqing Anticline and towards the local structural high along the West Slope. In contrast, the oil migration in the East Central Depression was dominated by the downward movement from the lower member of the Qingshankou Formation followed by the updip migration towards the Caoyang Anticline. The simulated oil accumulations are in good agreement with discovered oil fields, implying a potential application of the model for prediction and evaluation of new exploration targets in the basin. 相似文献
123.
Distribution of polycyclic musks in water and particulate matter of the Lippe River (Germany) 总被引:3,自引:0,他引:3
The occurrence and distribution of polycyclic musks in the Lippe River system (a tributary of the Rhine River, Germany) was investigated in order to observe the dynamic transport and partitioning of these compounds between aqueous and particulate phases after their discharge into the river by sewage effluents. 1,3,4,6,7,8-Hexahydro-4,6,6,7,8,8-hexamethylcyclopenta[g]-2-benzopyrane (HHCB), 7-acetyl-1,1,3,4,4,6-hexamethyl-1,2,3,4-tetrahydronaphthalene (AHTN), 6-acetyl-1,1,2,3,3,5-hexamethylindane (AHMI) and 4-acetyl-1,1-dimethyl-6-tert.-butylindane (ADBI) concentrations were determined in 19 water and surface sediment samples which were taken from a longitudinal section of the river. HHCB and AHTN were present in each of the water samples at concentrations ranging from <10 to 180 ng l−1 and <10 to 70 ng l−1, respectively. The load of dissolved HHCB and AHTN was calculated on the basis of compound concentrations in water and the corresponding river runoff data and ranged from 3 to 293 g day−1 and from 1 to 108 g day−1, respectively. Increasing loads of HHCB and AHTN along the river reflect a high input of sewage effluents to the densely populated areas along the central part of the river. Decreasing loads at the lower reaches indicate that in the corresponding river sections the rate of removal of musks was higher than the rate of input. Degradation and/or adsorption to particulate matter are processes that might explain this phenomenon. Consequently, high concentrations of HHCB and AHTN were detected in surface sediments from the Lippe River (from 5 to 191 μg kg−1 and from 2 to 1399 μg kg−1, respectively). HHCB/AHTN ratios in sediment samples were lower (average 1.2) than in water samples (average 2.9), suggesting the preferential adsorption of AHTN to particulate matter. 相似文献
124.
Wind gaps in actively growing mountain ranges are unique geomorphological features testifying to the competition between tectonics and fluvial incision. Although it is clear that these landforms reflect the defeat of rivers during sustained rock uplift, the role of climate changes in their formation has never been explored. Here, we use a coupled tectonics–landscape evolution model to show that temporal changes in precipitation rate exert an important control on wind gap formation. In models with a constant precipitation rate, rivers flowing across a growing range are either defeated at an early stage or they abandon their valleys very late, if at all. If precipitation varies, wind gaps form mostly c. 100–200 ka after a transition to drier conditions because of sediment aggradation upstream of the range. Our results suggest that the Pliocene–Quaternary aridification of Central Asia contributed to wind gap formation in active mountain ranges in the foreland of northeastern Tibet. 相似文献
125.
By means of population synthesis models with variable α/Fe ratios we derive average ages, metallicities, and [α/Fe] element
enhancements for a sample of 126 field and cluster early-type galaxies. We find a clear positive relation between [α/Fe] and
velocity dispersion. Zero-point, slope, and scatter of this correlation are the same for cluster and field galaxies. In particular,
the [α/Fe] ratios and mean ages of cluster ellipticals are positively correlated. This strongly reinforces the view that the
[α/Fe] element enhancement in ellipticals is produced by star formation timescales rather than by variations of the initial
mass function. These results indicate that the more massive the galaxy, the shorter is its star formation timescale, and the
higher is the redshift of the bulk of star formation. This finding is not compatible with the predictions from models of hierarchical
galaxy formation. The lenticular and field galaxies of the investigated sample do not follow the correlation between age and
[α/Fe], but contain a non-negligible fraction of galaxies with young average ages and high [α/Fe] ratios.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
126.
Mordecai-Mark Mac Low Michael D. Smith Ralf S. Klessen Andreas Burkert 《Astrophysics and Space Science》1998,261(1-4):195-196
Supersonic and super-Alfvénic turbulent motions generate an intricate pattern of shock waves through which the turbulence
decays. We here illustrate the spatial structure during shock formation and decay.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
127.
Transient simulation of the last glacial inception. Part I: glacial inception as a bifurcation in the climate system 总被引:2,自引:2,他引:0
Reinhard Calov Andrey Ganopolski Martin Claussen Vladimir Petoukhov Ralf Greve 《Climate Dynamics》2005,24(6):545-561
We study the mechanisms of glacial inception by using the Earth system model of intermediate complexity, CLIMBER-2, which
encompasses dynamic modules of the atmosphere, ocean, biosphere and ice sheets. Ice-sheet dynamics are described by the three-dimensional
polythermal ice-sheet model SICOPOLIS. We have performed transient experiments starting at the Eemiam interglacial, at 126 ky
BP (126,000 years before present). The model runs for 26 kyr with time-dependent orbital and CO2 forcings. The model simulates a rapid expansion of the area covered by inland ice in the Northern Hemisphere, predominantly
over Northern America, starting at about 117 kyr BP. During the next 7 kyr, the ice volume grows gradually in the model at
a rate which corresponds to a change in sea level of 10 m per millennium. We have shown that the simulated glacial inception
represents a bifurcation transition in the climate system from an interglacial to a glacial state caused by the strong snow-albedo
feedback. This transition occurs when summer insolation at high latitudes of the Northern Hemisphere drops below a threshold
value, which is only slightly lower than modern summer insolation. By performing long-term equilibrium runs, we find that
for the present-day orbital parameters at least two different equilibrium states of the climate system exist—the glacial and
the interglacial; however, for the low summer insolation corresponding to 115 kyr BP, we find only one, glacial, equilibrium
state, while for the high summer insolation corresponding to 126 kyr BP only an interglacial state exists in the model.
相似文献
Reinhard CalovEmail: |
128.
Harald Karg Andrew Carter Manfred R. Brix Ralf Littke 《International Journal of Earth Sciences》2005,94(2):180-192
Apatite fission-track analyses were carried out on outcrop and core samples from the Rhenish massif and the Carboniferous Ruhr Basin/Germany in order to study the late- and post-Variscan thermal and exhumation history. Apatite fission-track ages range from 291±15 Ma (lower Permian) to 136±7 Ma (lower Cretaceous) and mean track lengths vary between 11.6 m and 13.9 m, mostly displaying unimodal distributions with narrow standard deviations. All apatite fission-track ages are younger than the corresponding sample stratigraphic age, indicating substantial post-depositional annealing of the apatite fission-tracks. This agrees with results from maturity modelling, which indicates 3500–7000 m eroded Devonian and Carboniferous sedimentary cover. Numerical modelling of apatite fission-track data predicts onset of exhumation and cooling not earlier than 320 Ma in the Rhenish massif and 300 Ma in the Ruhr Basin, generally followed by late Carboniferous–Triassic cooling to below 50–60°C. Rapid late Variscan cooling was followed by moderate Mesozoic cooling rates of 0.1–0.2°C/Ma, converting into denudation rates of <1 mm/a (assuming a stable geothermal gradient of 30°C/km). Modelling results also give evidence for some late Triassic and early Jurassic heating and/or burial, which is supported by sedimentary rocks of the same age preserved at the rim of the lower Rhine Basin and in the subsurface of the Central and Northern Ruhr Basin. Cenozoic exhumation and cooling of the Rhenish massif is interpreted as an isostatic response to former erosion and major base-level fall caused by the subsidence in the lower Rhine Basin. 相似文献
129.
Alexander Matul Andrea Abelmann Ralf Tiedemann Andre Kaiser Dirk Nürnberg 《Geo-Marine Letters》2002,22(1):25-32
Five radiolarian datum events have been recorded in the Late Quaternary sediment section from the Sea of Okhotsk, using age assignments based on oxygen-isotope stratigraphy: the last occurrence datum (LOD) of Stylacontarium acquilonium (at about 329 ka), the LOD of Spongodiscus sp. (at about 287 ka), the LOD of Amphimelissa setosa (at about 72 ka), the LOD of Lychnocanoma nipponica sakaii (at about 28 ka), and the L. nipponica sakaii acme event (at about 72 ka). The LODs of S. acquilonium, Spongodiscus sp. and A. setosa appear to be synchronous in comparison with those in the Subarctic North Pacific, but the LOD and the acme event of L. nipponica sakaii show an apparent diachroneity with the corresponding North Pacific events. 相似文献
130.
Many of the sampling methods used in oceanographic sciences today date back decades, if not centuries. Although there has been a marked change in how sampling for chemical oceanography is carried out it still relies on taking samples of seawater from a research vessel in most cases. Assessing processes on small timescales as well as transient events requires higher temporal and spatial resolution of measurements; long time series stations require high duration deployments of instruments. Both requirements can only be adequately satisfied by in situ sensors; for the physical parameters off the shelf instruments are available, in the field of chemical oceanography only a few parameters, such as oxygen, are covered by off the shelf instruments, for most parameters adequate instrumentation only exists in the form of prototypes, if at all. Chemical in situ sensors are needed to gain new insights in how the oceans and the life in it works. 相似文献