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801.
Irene Ylla Isis Sanpera-Calbet Isabel Muñoz Anna M. Romaní Sergi Sabater 《Aquatic Sciences - Research Across Boundaries》2011,73(4):523-535
Amino acid composition (quality) and abundance (quantity) of organic matter (OM) in an intermittent Mediterranean stream were
followed during transitions from wet to dry and dry to wet conditions. Amino acids were analyzed in benthic material (epilithic
biofilms, sand sediments, leaf material) as well as in the flowing water (dissolved organic matter, DOM). A principal component
analysis and the estimation of the amino acid degradation index (DI) elucidated differences in amino acid composition and
quality among the wet–drought–wet cycle. Amino acid content and composition were dependent on the source of OM as well as
on its diagenetic state. The highest-quality OM (high DI and high N content) occurred on epilithic biofilms and the most degraded
and lowest-quality OM occurred in sandy sediments. Differences between the pre- and post-drought periods were evident in DOM
quality; autochthonous-derived material was predominant during the pre-drought (wet period preceding drying), while allochthonous
inputs dominated during the post-drought period (wet period following drying). In contrast, benthic OM compartments were more
stable, but benthic OM quality decreased continuously throughout the drought period. This study revealed that wet–drought–wet
cycles resulted in subtle changes in benthic OM quality, and degradation of DOM was related to flow intermittency. 相似文献
802.
Simulation and detection of tsunami signatures in ocean surface currents measured by HF radar 总被引:3,自引:1,他引:2
Klaus-Werner Gurgel Anna Dzvonkovskaya Thomas Pohlmann Thomas Schlick Eric Gill 《Ocean Dynamics》2011,61(10):1495-1507
High-frequency (HF) surface wave radars provide the unique capability to continuously monitor the coastal environment far
beyond the range of conventional microwave radars. Bragg-resonant backscattering by ocean waves with half the electromagnetic
radar wavelength allows ocean surface currents to be measured at distances up to 200 km. When a tsunami propagates from the
deep ocean to shallow water, a specific ocean current signature is generated throughout the water column. Due to the long
range of an HF radar, it is possible to detect this current signature at the shelf edge. When the shelf edge is about 100 km
in front of the coastline, the radar can detect the tsunami about 45 min before it hits the coast, leaving enough time to
issue an early warning. As up to now no HF radar measurements of an approaching tsunami exist, a simulation study has been
done to fix parameters like the required spatial resolution or the maximum coherent integration time allowed. The simulation
involves several steps, starting with the Hamburg Shelf Ocean Model (HAMSOM) which is used to estimate the tsunami-induced
current velocity at 1 km spatial resolution and 1 s time step. This ocean current signal is then superimposed to modelled
and measured HF radar backscatter signals using a new modulation technique. After applying conventional HF radar signal processing
techniques, the surface current maps contain the rapidly changing tsunami-induced current features, which can be compared
to the HAMSOM data. The specific radial tsunami current signatures can clearly be observed in these maps, if appropriate spatial
and temporal resolution is used. Based on the entropy of the ocean current maps, a tsunami detection algorithm is described
which can be used to issue an automated tsunami warning message. 相似文献
803.
Reconstruction of the eruptive activity on the NE sector of Stromboli volcano: timing of flank eruptions since 15 ka 总被引:1,自引:0,他引:1
Sonia Calvari Stefano Branca Rosa Anna Corsaro Emanuela De Beni Lucia Miraglia Gianluca Norini Jan Wijbrans Enzo Boschi 《Bulletin of Volcanology》2011,73(1):101-112
A multidisciplinary geological and compositional investigation allowed us to reconstruct the occurrence of flank eruptions
on the lower NE flank of Stromboli volcano since 15 ka. The oldest flank eruption recognised is Roisa, which occurred at ~15 ka
during the Vancori period, and has transitional compositional characteristics between the Vancori and Neostromboli phases.
Roisa was followed by the San Vincenzo eruption that took place at ~12 ka during the early stage of Neostromboli period. The
eruptive fissure of San Vincenzo gave rise to a large scoria cone located below the village of Stromboli, and generated a
lava flow, most of which lies below sea level. Most of the flank eruptions outside the barren Sciara del Fuoco occurred in
a short time, between ~9 and 7 ka during the Neostromboli period, when six eruptive events produced scoria cones, spatter
ramparts and lava flows. The Neostromboli products belong to a potassic series (KS), and cluster in two differently evolved
groups. After an eruptive pause of ~5,000 years, the most recent flank eruption involving the NE sector of the island occurred
during the Recent Stromboli period with the formation of the large, highly K calc-alkaline lava flow field, named San Bartolo.
The trend of eruptive fissures since 15 ka ranges from N30°E to N55°E, and corresponds to the magma intrusions radiating from
the main feeding system of the volcano. 相似文献
804.
Chromite ores formation is still a debated topic and, in this study, detailed analyses of major, minor elements by EMPA and Rare Earth Elements (REE) by SIMS, were performed on silicate inclusions detected in chromite grains of chromitite pods, enveloping dunites and on clinopyroxene of lherzolitic host rock of well known Trodoos chromite ores. Results show the complexity of relationships among lithologies that reflects the subtlety of genetic events and of chromite ore occurrence.Analyses of textural and chemical features have led to a better understanding of the chromite ore genetic process, that is related to a supra-subduction geodynamic setting where partial melting processes were overlapped by metasomatic events.Metasomatism, that marks the general genetic context, is characterized by the presence of a hydrated boninitic melt that favors the precipitation of chromite ores. Chromite ores, typical of ophiolite complexes and usually enveloped by dunite are, in this case, characterized by the presence of two different types of dunites whose geochemical differences are reflected by olivine mineral chemistry and by different REE patterns of analyzed clinopyroxenes. Such geochemical marks, related to different magmatic and metasomatic events, could be a main key for location of fertile or barren dunites in terms of chromite ore occurrence in the field. 相似文献
805.
Carlo Bertok Luca Martire Elena Perotti Anna d’Atri Fabrizio Piana 《Swiss Journal of Geoscience》2011,104(2):237-255
The Middle–Upper Jurassic succession of the Marguareis–Mongioie area (Ligurian Briançonnais Domain), developed in a protected shelf environment evolving into a pelagic plateau, bears clear evidence of synsedimentary tectonics such as: growth fault-related structures; neptunian dykes; marked lateral variations in stratigraphic thicknesses testifying to the juxtaposition of sectors characterized by different sedimentation and subsidence rates; discordant, anomalous stratigraphic contacts corresponding to paleoescarpments; nodular beds showing evidence of fluidification interpreted as seismites; and the occurrence of sand-sized quartz grains pointing to denudation of Permo-Triassic quartz-rich rocks. Such evidence documents an important Middle-Late Jurassic post-breakup tectonic activity, which was more effective in controlling the basin topography than the Early Jurassic syn-rift tectonic phase. Two main tectono-sedimentary stages, one occurring during the Bathonian, the other falling within the Callovian–Kimmeridgian interval, were reconstructed. The first stage can be referred to a fault-related activity occurring shortly after the initial stages of oceanic spreading of the Ligurian Tethys; the second can be genetically related to the far effects of the first rifting stage of the Bay of Biscay and the Valais basin. 相似文献
806.
Bianchi TS Cook RL Perdue EM Kolic PE Green N Zhang Y Smith RW Kolker AS Ameen A King G Ojwang LM Schneider CL Normand AE Hetland R 《Marine environmental research》2011,72(5):248-257
Here we present results of an initial assessment of the impacts of a water diversion event on the concentrations and chemical composition of dissolved organic matter (DOM) and bacterioplankton community composition in Barataria Bay, Louisiana U.S.A, an important estuary within the Mississippi River Delta complex. Concentrations and spectral properties of DOM, as reflected by UV/visible absorbance and fluorescence, were strikingly similar at 26 sites sampled along transects near two western and two eastern areas of Barataria Bay in July and September 2010. In September 2010, dissolved organic carbon (DOC) was significantly higher (568.1-1043 μM C, x=755.6+/-117.7 μM C, n=14) than in July 2010 (249.1-577.1 μM C, x=383.7+/-98.31 μM C, n=14); conversely, Abs254 was consistently higher at every site in July (0.105-0.314) than in September (0.080-0.221), averaging 0.24±0.06 in July and 0.15±0.04 in September. Fluorescence data via the fluorescence index (FI450/500) revealed that only 30% (8 of 26) of the July samples had an FI450/500 above 1.36, compared to 96% (25 of 26) for the September samples. This indicates a more terrestrial origin for the July DOM. Bacterioplankton from eastern sites differed in composition from bacterioplankon in western sites in July. These differences appeared to result from reduced salinities caused by the freshwater diversion. Bacterioplankton communities in September differed from those in July, but no spatial structure was observed. Thus, the trends in bacterioplankton and DOM were likely due to changes in water masses (e.g., input of Mississippi River water in July and a return to estuarine waters in September). Discharge of water from the Davis Pond Freshwater Diversion (DPFD) through Barataria Bay may have partially mitigated some adverse effects of the oil spill, inasmuch as DOM is concerned. 相似文献
807.
应用主分量分析法对昌黎、青光、宝坻、红山等台站(1975—1977年)三年的每月五个静日地磁绝对磁场的资料及相应时间的太阳黑子相对数的资料进行计算。结果表明,第一主分量与太阳黑子相对数对应很好,相关系数为0.9以上,而第二主分量与太阳黑子相对数的相关系数为0.03左右。对于在某一固定频率而变化的地磁外源场,内外场的比例几乎恒定在一定水平上,而在唐山地震前内外场比值有明显的异常变化,笔者认为,这个恒定水平的偏离可能是由于地壳内应力不断积累导致的地下电导率的变化而引起的。用这种方法不仅可以消除地磁场的非局部变化,而且利用内外场比值的偏离或监视内场的变化可能为使用地磁场预报地震提供一个依据。 相似文献
808.
Maria Anna De Rosa 《地震工程与结构动力学》1989,18(3):377-388
The dynamical properties of a foundation beam on a Winkler soil have been recently discussed by using the power series method14 and the finite element method.15, 17 – 19 The first method can be applied only if the Winkler soil is linearly distributed along the whole span: on the contrary, the second method is more general, but it requires considerable computational efforts. In this paper a recently developed discretization method has been shown to be particularly well suited for dynamic analysis of foundation beams, in the presence of second order destabilizing effects. The procedure is based on the Hamilton principle, and the equation of motion is deduced from the corresponding Lagrange equations. According to the proposed method, the structure is reduced to a set of rigid bars, connected together by elastic cells. The convergence of the method is shown to be quite rapid, so that a small number of Lagrangian coordinates has to be introduced, and the resulting eigenvalue problem can be easily solved. Numerical comparisons are also performed with the available data of the literature, and the agreement is shown to be excellent. Two particularly unusual cases are illustrated, in order to emphasize the method's peculiarities. Finally, the influence of the axial forces on the fundamental vibration frequency is discussed, both for conservative and non-conservative forces. 相似文献
809.
The morphotectonic framework of the Central Apennines is given by faulted blocks bounded by normal faults, mostly trending NW–SE, NNW–SSE and NE–SW, which cut previous compressive structures. Such a structural setting is consistent with the focal mechanisms of the earthquakes which often occur in this area. In this paper, three lithologically different normal fault-generated mountain fronts are analysed in order to assess the relations between their geomorphic features and active tectonics. They border the Norcia depression (Sibillini Mts, Umbria), the Amatrice–Campotosto plateau (Laga Mts, Lazio) and the Fucino basin (Marsica Mts, Abruzzi). The Norcia depression is bounded by a N20°W trending normal fault to the east and by a parallel antithetic fault to the west. The main fault has a 1000 m throw and gives rise to a wide fault escarpment, characterized by: (1) sharp slope breaks due to low angle gravity faults; (2) important paleolandslides; and (3) several fault scarplets on the piedmont belt affecting Quaternary deposits. The Amatrice–Campotosto plateau is delimited by the western slope of Mt Gorzano which runs along a N20°W trending normal fault having a 1500m throw. Minor parallel faults dislocate Quaternary landforms. Large-scale massmovements also occur here. The Fucino basin was struck by the 1915 Avezzano earthquake (I=XI MCS) which produced extensive surface faulting along two parallel NW trending normal fault escarpments on the eastern border of the basin. There is paleoseismic evidence including buried gravity graben in Late Glacial gravels and tectonic dip-slip striations on Holocene calcitic crusts covering bedrock normal fault planes. These data suggest that active extensional tectonics plays a major role in the slope morphogenesis of the Central Apennines and they indicate the importance of geomorphic analysis in seismic zonation of this area. 相似文献
810.
Anna Bohman Erik Glaas Johannes Klein Mia Landauer Tina-Simone Neset Björn-Ola Linnér Sirkku Juhola 《Climatic change》2018,149(2):121-129
This essay discusses the concept of usefulness of research for climate change adaptation. Based on prior research and stakeholder interactions with policymakers and practitioners in the Nordic countries, we contend that critical issues related to the usefulness of adaptation research seem less associated with content (i.e. research outputs), but rather centre around the efforts made to design and communicate research, that is, to put research at the service of society and make the case for adaptation on the political agenda. This, we argue, to some extent mirrors the situation and political context in the Nordic countries, where adaptation in many locations still is an issue in its infancy, not firmly established on the political agendas, and where working procedures are not yet institutionally settled. In this context, science is considered and sometimes used as a discursive tool to make the case for adaptation. Based on the calls for research that inspires, raises hope and helps to raise the issue of adaptation on the political agendas, we elaborate the role of honest issue advocates for researchers in the field of adaptation science. 相似文献