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41.
Complex coastal change in response to autogenic basin infilling: An example from a sub‐tropical Holocene strandplain 下载免费PDF全文
Christopher J. Hein Duncan M. FitzGerald Luis H. P. de Souza Ioannis Y. Georgiou Ilya V. Buynevich Antonio H. da F. Klein João Thadeu de Menezes William J. Cleary Thelma L. Scolaro 《Sedimentology》2016,63(6):1362-1395
Thick bay‐fill sequences that often culminate in strandplain development serve as important sedimentary archives of land–ocean interaction, although distinguishing between internal and external forcings is an ongoing challenge. This study employs sediment cores, ground‐penetrating radar surveys, radiocarbon dates, palaeogeographic reconstructions and hydrodynamic modelling to explore the role of autogenic processes – notably a reduction in wave energy in response to coastal embayment infilling – in coastal evolution and shoreline morphodynamics. Following a regional 2 to 4 m highstand at ca 5·8 ka, the 75 km2 Tijucas Strandplain in southern Brazil built from fluvial sediments deposited into a semi‐enclosed bay. Holocene regressive deposits are underlain by fluvial sands and a Pleistocene transgressive–regressive sequence, and backed by a highstand barrier‐island. The strandplain is immediately underlain by 5 to 16 m of seaward‐thickening, fluvially derived, Holocene‐age, basin‐fill mud. Several trends are observed from the landward (oldest) to the seaward (youngest) sections of the strandplain: (i) the upper shoreface and foreshore become finer and thinner and shift from sand‐dominated to mud‐dominated; (ii) beachface slopes decrease from >11° to ca 7°; and (iii) progradation rates increase from 0·4 to 1·8 m yr?1. Hydrodynamic modelling demonstrates a correlation between progressive shoaling of Tijucas Bay driven by sea‐level fall and sediment infilling and a decrease in onshore wave‐energy transport from 18 to 4 kW m?1. The combination of allogenic (sediment supply, falling relative sea‐level and geology) and autogenic (decrease in wave energy due to bay shoaling) processes drove the development of a regressive system with characteristics that are rare, if not unique, in the Holocene and rock records. These findings demonstrate the complexities in architecture styles of highstand and regressive systems tracts. Furthermore, this article highlights the diverse internal and external processes and feedbacks responsible for the development of these intricate marginal marine sedimentary systems. 相似文献
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43.
Ioannis Kontogiannis Costis Gontikakis Georgia Tsiropoula Kostas Tziotziou 《Solar physics》2018,293(4):56
We investigate the morphology and temporal variability of a quiet-Sun network region in different solar layers. The emission in several extreme ultraviolet (EUV) spectral lines through both raster and slot time-series, recorded by the EUV Imaging Spectrometer (EIS) on board the Hinode spacecraft is studied along with \(\mbox{H}\upalpha\) observations and high-resolution spectropolarimetric observations of the photospheric magnetic field. The photospheric magnetic field is extrapolated up to the corona, showing a multitude of large- and small-scale structures. We show for the first time that the smallest magnetic structures at both the network and internetwork contribute significantly to the emission in EUV lines, with temperatures ranging from \(8\times 10^{4}~\mbox{K}\) to \(6\times 10^{5}~\mbox{K}\). Two components of transition region emission are present, one associated with small-scale loops that do not reach coronal temperatures, and another component that acts as an interface between coronal and chromospheric plasma. Both components are associated with persistent chromospheric structures. The temporal variability of the EUV intensity at the network region is also associated with chromospheric motions, pointing to a connection between transition region and chromospheric features. Intensity enhancements in the EUV transition region lines are preferentially produced by \(\mbox{H}\upalpha\) upflows. Examination of two individual chromospheric jets shows that their evolution is associated with intensity variations in transition region and coronal temperatures. 相似文献
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The resource-based view (RBV) of the firm has been established as one of the main approaches to strategy formulation for the development of sustainable competitive advantage. Moreover, human resource management can be conceptualised as a source of competitiveness. This paper proposes that RBV could contribute to the confrontation of the hindrances that shipping companies face in the management of their human resources, and to the formation of sustainable competitive advantage. The paper analyses the findings of a field study, regarding the different human resource and crew management practices that are applied by Greek-owned shipping companies. Finally, based on the RBV of the firm, it proposes an integrated framework for managing human resources in the shipping industry in a way that could lead to the formation of sustainable competitive advantage. 相似文献
46.
We study the effects of a non-singular gravitational potential on satellite orbits by deriving the corresponding time rates
of change of its orbital elements. This is achieved by expanding the non-singular potential into power series up to second
order. This series contains three terms, the first been the Newtonian potential and the other two, here R
1 (first order term) and R
2 (second order term), express deviations of the singular potential from the Newtonian. These deviations from the Newtonian
potential are taken as disturbing potential terms in the Lagrange planetary equations that provide the time rates of change
of the orbital elements of a satellite in a non-singular gravitational field. We split these effects into secular, low and
high frequency components and we evaluate them numerically using the low Earth orbiting mission Gravity Recovery and Climate
Experiment (GRACE). We show that the secular effect of the second-order disturbing term R
2 on the perigee and the mean anomaly are 4″.307×10−9/a, and −2″.533×10−15/a, respectively. These effects are far too small and most likely cannot easily be observed with today’s technology. Numerical
evaluation of the low and high frequency effects of the disturbing term R
2 on low Earth orbiters like GRACE are very small and undetectable by current observational means. 相似文献
47.
Ioannis Panagiotopoulos Vasilios Kapsimalis Ioannis Hatzianestis Theodore D. Kanellopoulos Chara Kyriakidou 《Environmental Earth Sciences》2010,61(5):983-993
Surficial and sub-surficial sediments obtained from the lower course of the Kifissos River, which drains the Athens Basin,
have been analyzed for heavy metals and aliphatic and polycyclic hydrocarbons. Oddly, the calculated enrichment factors for
the identified heavy metals, with the baseline taken from a pristine area in the adjacent Saronikos Gulf, are very low excluding
only those related to Cu and Zn. In contrast, the enrichment factors for the measured hydrocarbons are particularly high.
However, physicochemical water conditions and annual flushing episodes of the Kifissos River may have reduced significantly
the sediment chemical fingerprint found out by the present study. Moreover, an evaluation of the fluvial sediment quality
based on the enriched Cu and Zn amounts and concentration of PAH fraction with a consideration of the biological thresholds
proposed by the National Oceanic and Atmospheric Administration (USA) reveals little probability for serious biological impairments.
Additionally, sediment toxicity due to the sediment PAH load may be considered as minimum. 相似文献
48.
Stephanos P. Kilias Jon Naden Ioannis Cheliotis Thomas J. Shepherd Heleni Constandinidou John Crossing Ioannis Simos 《Mineralium Deposita》2001,36(1):32-44
The Profitis Ilias gold deposit, located on the western part of Milos Island, Greece, is the first epithermal gold deposit
discovered in the Pliocene–Pleistocene Aegean volcanic arc. Estimated ore reserves are 5 million tonnes grading 4.4 g/tonne
Au and 43 g/tonne Ag. The deposit is closely associated with a horst and graben structure, and occurs in a series of steep
interconnected crustiform-banded quartz veins up to 3 m wide, extending to depths of at least 300 m. The mineralisation occurs
in three stages and is hosted by 3.5–2.5 Ma old silicified and sericitised rhyolitic lapilli-tuffs and ignimbrites. It consists
of pyrite, galena, chalcopyrite, electrum and native gold. Additionally, adularia occurs with quartz mainly in veins. Homogenisation
temperatures of primary liquid-rich inclusions vary from 145 to 399 °C for the ore stage, and 112 to 263 °C for the post-ore
stage. Salinities range between 0.1 and 11.4 wt% NaCl equiv. and 0.93 to 8.5 wt% NaCl equiv. for the ore stage and the post-ore
stage, respectively. Rare vapour-rich inclusions in ore stage quartz homogenise between 368 and 399 °C and estimates of eutectic
melting (−25 to −38 °C) indicate the presence of Ca and Mg in the ore fluids. Sample elevation versus fluid inclusion Th–salinity relationships show (1) a high-salinity trend, where moderate-temperature (300–250 °C) and moderate-salinity brines
(∼3 wt% NaCl equiv.) trend to high-salinity (up to 15 wt% NaCl equiv.) fluids with lower (∼25–50 °C) homogenisation temperatures,
and (2) a high-Th trend where moderate-salinity and moderate-temperature brines (200–250 °C; 3 wt% NaCl equiv.) develop into low-salinity (<1 wt%
NaCl equiv.), high-temperature (>350 °C) fluids. These trends are best explained by extreme boiling and vapourisation phenomena
between 200 and 250 °C. The 430–450 m asl (metres above sea level) level marks the transition between a lower liquid-dominated
segment of the system where only the steep high-salinity trend is seen, and an upper vapour-dominated segment where the high-Th trend or a combination of both are seen. There is a close spatial association between mineable gold grades and the upper
segment of the system. Depth-to-boiling curves suggest that the paleo-surface was ∼200 m above the present summit of Profitis
Ilias. Comparison of the mineralisation and fluid geochemistry at Profitis Ilias with that of the nearby modern geothermal
system indicates that the processes of metal mineralisation have probably been continuous since the Late Pliocene.
Received: 24 February 2000 / Accepted: 15 July 2000 相似文献
49.
Ioannis Gatsis reas Pavlopoulos & Isaak Parcharidis 《Geografiska Annaler: Series A, Physical Geography》2001,83(4):217-228
Natural hazards are mostly related to the activation of combined geomorphological and geological processes that control landform development. The study area is located in the NE part of Peloponnese (Corinthos prefecture). It is a typical agricultural area with intense relief, the result of active tectonics and important human intervention. This study demonstrates the benefits from the synergism of SAR data (ERS-2) and optical data (SPOT2-XS) in order to highlight the possible natural-hazardprone areas. These data give different and complementary information since the radar signal depends mostly on topography, surface roughness and soil moisture, whereas the visible/infrared channels provide spectral information mostly on vegetation and land use/cover. The application presented here was focused on the enhancement of the high erosion risk areas, the improvement of the terrain interpretation, the mapping and highlighting of the landform morphology, and a more accurate determination of the main factors that control the flooding risk of Corinthos town. 相似文献
50.
Ioannis K. Koukouvelas Georgia Pe-Piper David J. W. Piper 《International Journal of Earth Sciences》2006,95(6):963-976
The lengths and widths have been measured for 69 component bodies of composite plutons along the Cobequid Shear Zone. Plutons on major fault strands, those with mylonite zones >0.1 km wide, exhibit evidence of multiple intrusion of magma batches. Small plutons along short faults in stepover zones appear related to rapid emplacement of magma in bodies 1.5–4 km long by 0.1–2 km wide. Such small plutons show low enrichment in incompatible elements in older component bodies, but increasing amounts in younger bodies as a result of progressive magma expulsion from crystal mush during crystallization and shear-enhanced compaction in fault zones. Wider plutons generally occur along longer fault strands accommodating more strain and penetrating deeper into the crust and show enrichment in incompatible elements. The width of the mylonitic fault zone is about 15% of the width of these plutons. The length-to-width ratio of component bodies and composite plutons varies between 2 and 11. The best-fit line describing these data has a slope of 1.056, which implies scaling behavior between plutonism and tectonic processes. Scalar properties of plutonic bodies are similar to those of faults, but scalar relationships observed in component bodies do not apply to composite plutons. 相似文献