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排序方式: 共有325条查询结果,搜索用时 187 毫秒
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Marek Pękala Jan Dirk Kramers Hans Niklaus Waber Thomas Gimmi Peter Alt-Epping 《Applied Geochemistry》2009
The Opalinus Clay formation in North Switzerland is a potential host rock for a deep underground radioactive waste repository. The distribution of 238U, 234U and 230Th was studied in rock samples of the Opalinus Clay from an exploratory borehole at Benken (Canton of Zurich) using MC-ICP-MS. The aim was to assess the in situ, long-term migration behaviour of 234U in this rock. Very low hydraulic conductivities of the Opalinus Clay, reducing potential of the pore water and its chemical equilibrium with the host rock are expected to render both 238U and 230Th immobile. If U is heterogeneously distributed in the Opalinus Clay, gradients in the supply of 234U from the rock matrix to the pore water by the decay of 238U will be established. Diffusive redistribution separates 234U from its immobile parent 238U resulting in bulk rock 234U/238U activity disequilibria. These may provide a means of estimating the mobility of 234U in the rock if the diffusion rate of 234U is significant compared to its decay rate. Sampling was carried out on two scales. Drilling of cm-spaced samples from the drill-core was done to study mobility over short distances and elucidate possible small-scale lithological control. Homogenized 25-cm-long portions of a 2-m-long drill-core section were prepared to provide information on transport over a longer distance. Variations in U and/or Th content on the cm-scale between clays and carbonate-sandy layers are revealed by β-scanning, which shows that the (dominant) clay is richer in both elements. 相似文献
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Alexander Bartholomä Adam Kubicki Thomas H. Badewien Burghard W. Flemming 《Ocean Dynamics》2009,59(2):213-225
The German Wadden Sea (southern North Sea) sediments are composed of both cohesive and non-cohesive deposits. The spatial
distribution patterns are mainly driven by wind-induced waves and tidal currents. Transport intensity and duration depend
on the hydrodynamic conditions, which vary over time. In this paper, the transport of suspended sediment was investigated
on seasonal, tidal and hourly time scales in the back-barrier system of Spiekeroog Island. Long- and short-term data of fair
weather periods and two storm events were investigated based on stationary and mobile measurements of currents and waves by
Acoustic Doppler Current Profiler (ADCP), in situ particle size and suspended sediment concentration (SSC) measurements by
laser in situ scattering and transmissometry (LISST) as well as wind records. The ADCP backscatter intensities were calibrated
by means of LISST volume concentration data in order to quantify longer term SSCs and fluxes in the back-barrier system. Values
up to 120 mg l−1 were recorded, but concentrations more commonly were below 60 mg l−1. The long-term results confirm former observations of a balanced budget during low-energy (fair weather) conditions in the
study area. In general, SSCs were higher during spring tides than during neap tides. The data also clearly show the remobilisation
of sediment by tidal current entrainment. The records include two severe storm events, “Britta” (1st November 2006) and “Kyrill”
(18th January 2007). The data reveal very complex temporal flow and transport patterns. During both storm events, the export
of material was mainly controlled by the interaction of wind, waves and tidal phase. The typical ebb-dominance occurring during
fair-weather conditions was temporarily neutralised and even reversed to a flood-dominated situation. During “Kyrill”, the
wind and high-waves setup in conjunction with the tidal phase was even able to compress the duration of two successive ebb
cycles by over 70%. Although SSCs increased during both storms and higher turbulence lifted particle clouds upwards, an export
of suspended matter towards the North Sea was only observed under the conditions taking place during “Britta”. Such fluxes,
however, are currently still difficult to quantify because the backscatter intensity during high energy events includes a
substantial amount of noise produced by the high turbulence, especially near the water surface. 相似文献
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David H. Hughes Marek J. Kukula † James S. Dunlop Todd Boroson 《Monthly notices of the Royal Astronomical Society》2000,316(1):204-224
We present optical (∼3200 to ∼9000 Å) off-nuclear spectra of 26 powerful active galaxies in the redshift range 0.1≤ z ≤0.3, obtained with the Mayall and William Herschel 4-m class telescopes. The sample consists of radio-quiet quasars, radio-loud quasars (all with −23≥ M V ≥−26) and radio galaxies of Fanaroff–Riley Type II (with extended radio luminosities and spectral indices comparable to those of the radio-loud quasars). The spectra were all taken approximately 5 arcsec off-nucleus, with offsets carefully selected so as to maximize the amount of galaxy light falling into the slit, whilst simultaneously minimizing the amount of scattered nuclear light. The majority of the resulting spectra appear to be dominated by the integrated stellar continuum of the underlying galaxies rather than by light from the non-stellar processes occurring in the active nuclei, and in many cases a 4000-Å break feature can be identified. The individual spectra are described in detail, and the importance of the various spectral components is discussed. Stellar population synthesis modelling of the spectra will follow in a subsequent paper. 相似文献
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Timo Tiira Tomasz Janik Elena Kozlovskaya Marek Grad Annakaisa Korja Kari Komminaho Endre HegedŰs Csaba Attila Kovács Hanna Silvennoinen Ewald BrŰckl 《Pure and Applied Geophysics》2014,171(7):1129-1152
We have studied the lateral velocity variations along a partly buried inverted paleo–rift in Central Lapland, Northern Europe with a 2D wide-angle reflection and refraction experiment, HUKKA 2007. The experiment was designed to use seven chemical explosions from commercial and military sites as sources of seismic energy. The shots were recorded by 102 stations with an average spacing of 3.45 km. Two-dimensional crustal models of variations in P-wave velocity and Vp/Vs-ratio were calculated using the ray tracing forward modeling technique. The HUKKA 2007 experiment comprises a 455 km long profile that runs NNW–SSE parallel to the Kittilä Shear Zone, a major deformation zone hosting gold deposits in the area. The profile crosses Paleoproterozoic and reactivated Archean terranes of Central Lapland. The velocity model shows a significant difference in crustal velocity structure between the northern (distances 0–120 km) and southern parts of the profile. The difference in P-wave velocities and Vp/Vs ratio can be followed through the whole crust down to the Moho boundary indicating major tectonic boundaries. Upper crustal velocities seem to vary with the terranes/compositional differences mapped at the surface. The lower layer of the upper crust displays velocities of 6.0–6.1 km/s. Both Paleoproterozoic and Archean terranes are associated with high velocity bodies (6.30–6.35 km/s) at 100 and 200–350 km distances. The Central Lapland greenstone belt and Central Lapland Granitoid complex are associated with a 4 km-thick zone of unusually low velocities (<6.0 km/s) at distances between 120 and 220 km. We interpret the HUKKA 2007 profile to image an old, partly buried, inverted continental rift zone that has been closed and modified by younger tectonic events. It has structural features typical of rifts: inward dipping rift shoulders, undulating thickness of the middle crust, high velocity lower crust and a rather uniform crustal thickness of 48 km. 相似文献