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991.
Cold room physical modelling of periglacial solifluction processes on an experimental slope of 12° is described, and data on soil temperatures, surface frost heave, thaw consolidation, downslope soil movement and porewater pressures over seven freeze–thaw cycles are presented. These data are analyzed in the context of laboratory determination of the rheometry of the experimental soils at high moisture contents. It is concluded that the observed thaw-induced solifluction represents pre-failure soil shear strain and results from loss of strength due to the combined effects of raised porewater pressures during thaw consolidation and upward seepage pressures as water flows towards the surface away from the thaw front. An investigation of the rheometry of thawing soils offers the prospect of an analytical model to predict rates and depths of periglacial solifluction. © 1997 by John Wiley & Sons, Ltd. 相似文献
992.
993.
Recent excavations at Nahal Neqarot Rockshelter in the Central Negev, Israel, revealed 60 cm of in situ sediments. The associated lithic industry is mostly attributable to the Middle Epipalaeolithic Ramonian industry, though there is also evidence for sporadic earlier and later Epipalaeolithic use of the site. This is confirmed by three accelerator 14C dates, which contribute to a better understanding of the chronological framework for the Epipalaeolithic in the region. Microscopic examination of charred wood remains uncovered with the lithics, revealed the dominance of juniper, which is presently extinct in the nearby contemporaneous vegetation, otherwise composed of still extant taxa. © 1998 John Wiley & Sons, Inc. 相似文献
994.
The Permian Hutchinson Salt Member of the Wellington Formation of the Sumner Group of Kansas (USA) has multiple scientific and industrial uses. Although this member is highly utilized, there has not been a sedimentological study on these rocks in over 50 years, and no study has investigated the full thickness of this member. Past publications have inferred a marine origin as the depositional environment. Here, this marine interpretation is challenged. The goals of this study are to fully document sedimentological and stratigraphic characteristics of the Permian Hutchinson Salt Member in the Atomic Energy Commission Test Hole 2 core from Rice County, Kansas. This study documents colour, mineralogy, sedimentary textures, sedimentary structures, diagenetic features and stratigraphic contacts in core slab and thin sections. The Hutchinson Salt Member is composed of five lithologies: bedded halite, siliciclastic mudstone, displacive halite, bedded gypsum/anhydrite and displacive gypsum/anhydrite. These lithologies formed in shallow surface brines and mudflats that underwent periods of flooding, evapoconcentration and desiccation. Of note are the paucity of carbonates, lack of marine-diagnostic fossils, absence of characteristic marine minerals and lithofacies, and the stratigraphic context of the Hutchinson with associated continental deposits. The Hutchinson Salt Member was most likely deposited in an arid continental setting. This new interpretation offers a refined view of Pangaea during the middle Permian time. 相似文献
995.
Stratigraphic hierarchy and three-dimensional evolution of an exhumed submarine slope channel system
Daniel Bell David M. Hodgson Anna S. M. Pontén Larissa A. S. Hansen Stephen S. Flint Ian A. Kane 《Sedimentology》2020,67(6):3259-3289
Submarine slope channel systems have complicated three-dimensional geometries and facies distributions, which are challenging to resolve using subsurface data. Outcrop analogues can provide sub-seismic-scale detail, although most exhumed systems only afford two-dimensional constraints on the depositional architecture. A rare example of an accessible fine-grained slope channel complex set situated in a tectonically quiescent basin that offers seismic-scale, down-dip and across-strike exposures is the Klein Hangklip area, Tanqua-Karoo Basin, South Africa. This study investigates the three-dimensional architecture of this channel complex set to characterise the stratigraphic evolution of a submarine channel-fill and the implications this has for both sediment transport to the deep-oceans and reservoir quality distribution. Correlated sedimentary logs and mapping of key surfaces across a 3 km2 area reveal that: (i) the oldest channel elements in channel complexes infill relatively deep channel cuts and have low aspect-ratios. Later channel elements are bound by comparatively flat erosion surfaces and have high aspect-ratios; (ii) facies changes across depositional strike are consistent and predictable; conversely, facies change in successive down depositional dip positions indicating longitudinal variability in depositional processes; (iii) stratigraphic architecture is consistent and predictable at seismic-scale both down-dip and across-strike in three-dimensions; (iv) channel-base-deposits exhibit spatial heterogeneity on one to hundreds of metres length-scales, which can inhibit accurate recognition and interpretations drawn from one-dimensional or limited two-dimensional datasets; and (v) channel-base-deposit character is linked to sediment bypass magnitude and longevity, which suggests that time-partitioning is biased towards conduit excavation and maintenance rather than the fill-phase. The data provide insights into the stratigraphic evolution and architecture of slope channel-fills on fine-grained continental margins and can be utilised to improve predictions derived from lower resolution and one-dimensional well data. 相似文献
996.
Spielman Seth E. Tuccillo Joseph Folch David C. Schweikert Amy Davies Rebecca Wood Nathan Tate Eric 《Natural Hazards》2020,100(1):417-436
Natural Hazards - As a concept, social vulnerability describes combinations of social, cultural, economic, political, and institutional processes that shape socioeconomic differentials in the... 相似文献
997.
Red or buff‐coloured sandstones and siltstones of fluvial origin comprise approximately 80% of the Ringerike Group, a late Silurian Old Red Sandstone (ORS) sequence that crops out extensively in the Oslo Region of southern Norway. These fluvial sediments are lithostratigraphically ascribed to two laterally equivalent formations—the Stubdal Formation (to the north of Oslo) and the Skien Formation (to the south of Oslo). The fluvial strata of each of the two formations have a distinct style of sandbody geometry, facies, provenance, and palaeocurrent direction. Within the Stubdal Formation, shallow channelized sandbodies, low‐ to upper‐flow regime sedimentary structures, a Caledonide provenance and a palaeoflow toward the southeast are evident. Within the Skien Formation, sandbody geometry is entirely sheet form, with upper‐flow regime sedimentary structures, a provenance from Precambrian rocks to the northern and local parts of the Oslo Region and a palaeoflow toward the east. No stratal contact can be seen between the two fluvial formations, due to a 15 km break in exposure between the southernmost Stubdal Formation and the northernmost Skien Formation. Relationships with adjacent formations indicate that they are diachronous, lateral equivalents. Given the abrupt change in sedimentary style between the two formations, it is proposed that a barrier had developed within the foreland basin, diverting the ORS fluvial systems in southern Norway, from a southward (north of Oslo), to an eastward direction (south of Oslo). This diversion had implications for depositional gradient, fluvial regime and provenance, resulting in the differences visible in the deposits of those rivers. The barrier invoked is arguably a Caledonide blind thrust fault that developed a topographic high, running east–west through the vicinity of Oslo, during the late Silurian. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
998.
Ulrich Kolb Melvyn B. Davies rew King Hans Ritter 《Monthly notices of the Royal Astronomical Society》2000,317(2):438-446
Cygnus X-2 appears to be the descendant of an intermediate-mass X-ray binary (IMXB). Using Mazzitelli's stellar code we compute detailed evolutionary sequences for the system and find that its prehistory is sensitive to stellar input parameters, in particular the amount of core overshooting during the main-sequence phase. With standard assumptions for convective overshooting a case B mass transfer starting with a 3.5-M⊙ donor star is the most likely evolutionary solution for Cygnus X-2. This makes the currently observed state rather short-lived, of order 3 Myr, and requires a formation rate > 10−7 –10−6 yr−1 of such systems in the Galaxy. Our calculations show that neutron star IMXBs with initially more massive donors (≳4 M⊙ ) encounter a delayed dynamical instability; they are unlikely to survive this rapid mass transfer phase. We determine limits for the age and initial parameters of Cygnus X-2 and calculate possible dynamical orbits of the system in a realistic Galactic potential, given its observed radial velocity. We find trajectories which are consistent with a progenitor binary on a circular orbit in the Galactic plane inside the solar circle that received a kick velocity ≤200 km s−1 at the birth of the neutron star. The simulations suggest that about 7 per cent of IMXBs receiving an arbitrary kick velocity from a standard kick velocity spectrum would end up in an orbit similar to Cygnus X-2, while about 10 per cent of them reach yet larger Galactocentric distances. 相似文献
999.
Numerical studies of flow over a sill: sensitivity of the non-hydrostatic effects to the grid size 总被引:1,自引:1,他引:0
A non-hydrostatic terrain-following model in cross sectional form is applied to study the processes in the lee of a sill in
an idealized stratified fjord during super-critical tidal inflow. A sequence of numerical studies with horizontal grid sizes
in the range from 100 to 1.5625 m are performed. All experiments are repeated using both hydrostatic and non-hydrostatic versions
of the model, allowing a systematic study of possible non-hydrostatic pressure effects and also of the sensitivity of these
effects to the horizontal grid size. The length scales and periods of the internal waves in the lee of the sill are gradually
reduced and the amplitudes of these waves are increased as the grid size is reduced from 100 down to 12.5 m. With a further
reduction in grid size, more short time and space scale motions become superimposed on the internal waves. Associated with
the internal wave activity, there is a deeper separation point that is fairly robust to all parameters investigated. Another
separation point nearer to the top of the sill appears in the numerical results from the high-resolution studies with the
non-hydrostatic model. Associated with this shallower separation point, an overturning vortex appears in the same set of numerical
solutions. This vortex grows in strength with reduced grid size in the non-hydrostatic experiments. The effects of the non-hydrostatic
pressure on the velocity and temperature fields grow with reduced grid size. In the experiments with horizontal grid sizes
equal to 100 or 50 m, the non-hydrostatic pressure effects are small. For smaller grid sizes, the time mean velocity and temperature
fields are also clearly affected by the non-hydrostatic pressure adjustments. 相似文献
1000.
Rafał Iwański Anna Odzimek Lasse B.N. Clausen Vijay Kanawade Ingrid Cnossen Niklas J.T. Edberg 《Acta Geophysica》2009,57(3):760-777
The first red sprite events scientifically observed from Poland on 20/21 July 2007, during the two-week SPARTAN Sprite-Watch
2007 campaign, are analysed in the context of the meteorological conditions over Poland and the Czech Republic at that time.
The phenomena were detected and recorded from the IMWM High-Mountain Meteorological Observatory at Mount Śnieżka using a low-light
television CCD camera. Meteorological conditions over the south-west Poland were monitored on the basis of information from
the Polish and Czech meteorological radar and lightning detection systems and also from satellite infra-red difference images,
indicating the development of thunderstorm clouds over central Europe. Four sprite events detected in the night-time of 20/21
July indicate that in this region sprites are produced by massive storm cells built on warm fronts which are supplied by warm
and humid tropical air masses during local summer thunderstorm season. 相似文献