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41.
Anastasios A. Tsonis 《Climate Dynamics》2009,33(7-8):1069-1074
A thorough analysis of a proxy El Nino/Southern Oscillation (ENSO) record indicates that a bifurcation occurred in the ENSO system sometime around 5,000 years b.p. As a result of this bifurcation the attractor became higher dimensional and a new mechanism of instability was introduced. As a consequence of these changes the system switched from a dynamics where the normal condition (La Nina) was dominant to a dynamics characterized by more frequent and stronger El Nino events. 相似文献
42.
Paraskevi N. Polymenakou Antonio Pusceddu Anastasios Tselepides Thalia Polychronaki Antonia Giannakourou Carla Fiordelmondo Eleni Hatziyanni Roberto Danovaro 《Continental Shelf Research》2005,25(19-20):2570
Abundance of benthic bacteria, heterotrophic nanoflagellates and ciliates, extracellular enzymatic activities, bacterial C production, C mineralisation and sediment community oxygen consumption rates were measured in the Thermaikos Gulf (Northeastern Mediterranean), before (September 2001), and during intense trawling activities (October 2001 and February 2002). The biochemical composition of sedimentary organic matter has revealed that bottom trawling had an effect on the trophic state of Thermaikos Gulf. Changes on the benthic microbial food web were also recorded, during the three sampling seasons. Even though trawling-induced sediment resuspension did not alter significantly the abundance of the microbial components, with the exception of the most impacted station, it determined changes regarding their relative importance. Thus, the ratios of bacterium to nanoflagellates and ciliate to nanoflagellates abundance increased in the trawled stations, causing a sudden increase in bacterial C production, in comparison to the non-trawled station. Four months later, the effects of trawling on the microbial food web were less evident, masked possibly by the drastic decrease in the water temperature. The results of the present work suggest that bottom trawling induces alteration of the sedimentological variables and can be considered as a factor affecting the function of the microbial food web in marine coastal ecosystems. These alterations cause faster mobilisation of organic C buried in the sediment and increase nutrient concentrations and availability in the system, thus inducing an effect that could lead to coastal eutrophication. 相似文献
43.
Seismic performance and dynamic response of bridge–embankments during strong or moderate ground excitations are investigated through finite element (FE) modelling and detailed dynamic analysis. Previous research studies have established that bridge–embankments exhibit increasingly flexible performance under high‐shear deformation levels and that soil displacements at bridge abutment supports may be significant particularly in the transverse direction. The 2D equation of motion is solved for the embankment, in order to evaluate the dynamic characteristics and to describe explicitly the seismic performance and dynamic response under transverse excitations accounting for soil nonlinearities, soil–structure interaction and imposed boundary conditions (BCs). Using the proposed model, equivalent elastic analysis was performed so as to evaluate the dynamic response of approach embankments while accounting for soil–structure interaction. The analytical procedures were applied in the case of a well‐documented bridge with monolithic supports (Painter Street Overcrossing, PSO) which had been instrumented and embankment participation was identified from its response records after the 1971 San Fernando earthquake. The dynamic characteristics and dynamic response of the PSO embankments were evaluated for alternative BCs accounting for soil–structure interaction. Explicit expressions for the evaluation of the critical embankment length Lc are provided in order to quantify soil contribution to the overall bridge system under strong intensity ground excitations. The dynamic response of the entire bridge system (deck–abutments–embankments) was also evaluated through simplified models that considered soil–structure interaction. Results obtained from this analysis are correlated with those of detailed 3D FE models and field data with good agreement. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
44.
Abstract. Sediment characteristics determining macrofauna communities were investigated on the continental shelf of Crete. The sedimentary environment of the outer continental shelf of Crete is characterized by a silty substrate with significant decrease in chlorophyll a and organic carbon concentration with depth. Redox potential values indicated an ample supply of oxygen at all depths. Values of most production-related parameters TOC, chlorophyll a , ATP were found at the low end of the range reported from the literature even though the sampling stations were very close to the coastline. Organic carbon to chlorophyll ratios in the sediments indicated that most of the organic material is of phytoplankton origin; the quality of the organic material in the outer shelf, however, seems to be of lower bioavailability. 相似文献
45.
Steven J. Schwartz Timothy Horbury Christopher Owen Wolfgang Baumjohann Rumi Nakamura Patrick Canu Alain Roux Fouad Sahraoui Philippe Louarn Jean-André Sauvaud Jean-Louis Pinçon Andris Vaivads Maria Federica Marcucci Anastasios Anastasiadis Masaki Fujimoto Philippe Escoubet Matt Taylor Steven Eckersley Elie Allouis Marie-Claire Perkinson 《Experimental Astronomy》2009,23(3):1001-1015
Most of the visible universe is in the highly ionised plasma state, and most of that plasma is collision-free. Three physical
phenomena are responsible for nearly all of the processes that accelerate particles, transport material and energy, and mediate
flows in systems as diverse as radio galaxy jets and supernovae explosions through to solar flares and planetary magnetospheres.
These processes in turn result from the coupling amongst phenomena at macroscopic fluid scales, smaller ion scales, and down
to electron scales. Cross-Scale, in concert with its sister mission SCOPE (to be provided by the Japan Aerospace Exploration
Agency—JAXA), is dedicated to quantifying that nonlinear, time-varying coupling via the simultaneous in-situ observations
of space plasmas performed by a fleet of 12 spacecraft in near-Earth orbit. Cross-Scale has been selected for the Assessment
Phase of Cosmic Vision by the European Space Agency.
相似文献
46.
Seb Oliver Robert G. Mann Ruth Carballo Alberto Franceschini Michael Rowan-Robinson Maria Kontizas Anastasios Dapergolas Evanghelos Kontizas Aprajita Verma David Elbaz Gian Luigi Granato Laura Silva Dimitra Rigopoulou J. Ignacio Gonzalez-Serrano Steve Serjeant reas Efstathiou Paul P. van der Werf 《Monthly notices of the Royal Astronomical Society》2002,332(3):536-548
We present results from a deep mid-infrared survey of the Hubble Deep Field South (HDF-S) region performed at 6.7 and 15 μm with the ISOCAM instrument on board the Infrared Space Observatory ( ISO ). The final map in each band was constructed by the co-addition of four independent rasters, registered using bright sources securely detected in all rasters, with the absolute astrometry being defined by a radio source detected at both 6.7 and 15 μm. We sought detections of bright sources in a circular region of radius 2.5 arcmin at the centre of each map, in a manner that simulations indicated would produce highly reliable and complete source catalogues using simple selection criteria. Merging source lists in the two bands yielded a catalogue of 35 distinct sources, which we calibrated photometrically using photospheric models of late-type stars detected in our data. We present extragalactic source count results in both bands, and discuss the constraints that they impose on models of galaxy evolution, given the volume of space sampled by this galaxy population. 相似文献
47.
48.
Jeremie Vaubaillon Pavel Koten Anastasios Margonis Juraj Toth Regina Rudawska Maria Gritsevich Joe Zender Jonathan McAuliffe Pierre-Dominique Pautet Peter Jenniskens Detlef Koschny Francois Colas Sylvain Bouley Lucie Maquet Arnaud Leroy Jean Lecacheux Jiri Borovicka Junichi Watanabe Jürgen Oberst 《Earth, Moon, and Planets》2015,114(3-4):137-157
49.
Hermine Landt Paolo Padovani †‡ Eric S. Perlman § Paolo Giommi Hayley Bignall Anastasios Tzioumis 《Monthly notices of the Royal Astronomical Society》2001,323(3):757-784
We have searched the archived, pointed ROSAT Position Sensitive Proportional Counter data for blazars by correlating the WGACAT X-ray data base with several publicly available radio catalogues, restricting our candidate list to serendipitous X-ray sources with a flat radio spectrum ( α r ≤0.70, where S ν ∝ ν − α ). This makes up the Deep X-ray Radio Blazar Survey (DXRBS). Here we present new identifications and spectra for 106 sources, including 86 radio-loud quasars, 11 BL Lacertae objects, and nine narrow-line radio galaxies. Together with our previously published objects and already-known sources, our sample now contains 298 identified objects: 234 radio-loud quasars [181 flat-spectrum quasars: FSRQ ( α r ≤0.50) and 53 steep-spectrum quasars: SSRQ], 36 BL Lacs and 28 narrow-line radio galaxies. Redshift information is available for 96 per cent of these. Thus our selection technique is ∼90 per cent efficient at finding radio-loud quasars and BL Lacs. Reaching 5-GHz radio fluxes ∼50 mJy and 0.1–2.0 keV X-ray fluxes a few ×10−14 erg cm−2 s−1 , DXRBS is the faintest and largest flat-spectrum radio sample with nearly complete (∼85 per cent) identification. We review the properties of the DXRBS blazar sample, including redshift distribution and coverage of the X-ray-radio–power plane for quasars and BL Lacs. Additionally, we touch upon the expanded multiwavelength view of blazars provided by DXRBS. By sampling for the first time the faint end of the radio and X-ray luminosity functions, this sample will allow us to investigate the blazar phenomenon and the validity of unified schemes down to relatively low powers. 相似文献
50.
Lucyna Kedziora-Chudczer David L. Jauncey Mark A. Wieringa Anastasios K. Tzioumis Hayley E. Bignall 《Astrophysics and Space Science》2001,278(1-2):113-117
We present results of the ATCA IDV Survey of southern extragalactic radio sources. We discuss briefly the properties of the
22 new intraday variable sources discovered in the Survey. The follow-up observations of a few extreme examples of strong
intraday variability are presented. We find that the characteristics of the total flux density fluctuations at different wavelengths
are consistent with intersteller scintillations (ISS) of the microarcsecondsize soorten components. However, the scintillating
components of a few extreme IDVs are characterized by the brightness temperatures far exceeding the T
B=1012 K limit. The relativistic beaming invoked in such sources would require Doppler factors up to as high as δ∼ 103.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献