全文获取类型
收费全文 | 356篇 |
免费 | 26篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 16篇 |
大气科学 | 15篇 |
地球物理 | 139篇 |
地质学 | 106篇 |
海洋学 | 33篇 |
天文学 | 55篇 |
综合类 | 2篇 |
自然地理 | 20篇 |
出版年
2024年 | 1篇 |
2021年 | 12篇 |
2020年 | 11篇 |
2019年 | 8篇 |
2018年 | 14篇 |
2017年 | 18篇 |
2016年 | 31篇 |
2015年 | 15篇 |
2014年 | 19篇 |
2013年 | 23篇 |
2012年 | 25篇 |
2011年 | 24篇 |
2010年 | 24篇 |
2009年 | 31篇 |
2008年 | 18篇 |
2007年 | 16篇 |
2006年 | 11篇 |
2005年 | 19篇 |
2004年 | 11篇 |
2003年 | 10篇 |
2002年 | 7篇 |
2001年 | 6篇 |
2000年 | 7篇 |
1999年 | 4篇 |
1998年 | 3篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1973年 | 1篇 |
1968年 | 1篇 |
1963年 | 1篇 |
排序方式: 共有386条查询结果,搜索用时 15 毫秒
71.
Garrelt Mellema Léon V. E. Koopmans Filipe A. Abdalla Gianni Bernardi Benedetta Ciardi Soobash Daiboo A. G. de Bruyn Kanan K. Datta Heino Falcke Andrea Ferrara Ilian T. Iliev Fabio Iocco Vibor Jelić Hannes Jensen Ronniy Joseph Panos Labroupoulos Avery Meiksin Andrei Mesinger André R. Offringa V. N. Pandey Jonathan R. Pritchard Mario G. Santos Dominik J. Schwarz Benoit Semelin Harish Vedantham Sarod Yatawatta Saleem Zaroubi 《Experimental Astronomy》2013,36(1-2):235-318
The Square Kilometre Array (SKA) will have a low frequency component (SKA-low) which has as one of its main science goals the study of the redshifted 21 cm line from the earliest phases of star and galaxy formation in the Universe. This 21 cm signal provides a new and unique window both on the time of the formation of the first stars and accreting black holes and the subsequent period of substantial ionization of the intergalactic medium. The signal will teach us fundamental new things about the earliest phases of structure formation, cosmology and even has the potential to lead to the discovery of new physical phenomena. Here we present a white paper with an overview of the science questions that SKA-low can address, how we plan to tackle these questions and what this implies for the basic design of the telescope. 相似文献
72.
Mads Faurschou Knudsen Peter Riisager Fabio Donadini Ian Snowball Raimund Muscheler Kimmo Korhonen Lauri J. Pesonen 《Earth and Planetary Science Letters》2008,272(1-2):319-329
All absolute paleointensity data published in peer-reviewed journals were recently compiled in the GEOMAGIA50 database. Based on the information in GEOMAGIA50, we reconstruct variations in the geomagnetic dipole moment over the past 50 kyr, with a focus on the Holocene period. A running-window approach is used to determine the axial dipole moment that provides the optimal least-squares fit to the paleointensity data, whereas associated error estimates are constrained using a bootstrap procedure. We subsequently compare the reconstruction from this study with previous reconstructions of the geomagnetic dipole moment, including those based on cosmogenic radionuclides (10Be and 14C). This comparison generally lends support to the axial dipole moments obtained in this study. Our reconstruction shows that the evolution of the dipole moment was highly dynamic, and the recently observed rates of change (5% per century) do not appear unique. We observe no apparent link between the occurrence of archeomagnetic jerks and changes in the geomagnetic dipole moment, suggesting that archeomagnetic jerks most likely represent drastic changes in the orientation of the geomagnetic dipole axis or periods characterized by large secular variation of the non-dipole field. This study also shows that the Holocene geomagnetic dipole moment was high compared to that of the preceding 40 kyr, and that 4 · 1022 Am2 appears to represent a critical threshold below which geomagnetic excursions and reversals occur. 相似文献
73.
Fabio Bertasi Francesco Colosio Gianni Gregorio Marco Abbiati Victor Ugo Ceccherelli 《Marine pollution bulletin》2009,58(5):686-694
Sandy shores on the West coast of the North Adriatic Sea are extensively protected by different types of defence structures to prevent coastal erosion. Coastal defence schemes modify the hydrodynamic regime, the sediment structure and composition thus affecting the benthic assemblages. This study examines the effectiveness in detecting changes in soft bottom assemblages caused by coastal defence structures by using different levels of taxonomic resolution, polychaetes and/or bivalves as surrogates and different data transformations. A synoptic analyses of three datasets of subtidal benthic macrofauna used in studies aimed at assessing the impact of breakwaters along the North Adriatic coast has been done. Analyses of similarities and correlations between distance matrices were done using matrices with different levels of taxonomic resolution, and with polychaetes or bivalves data alone. Lentidium mediterraneum was the most abundant species in all datasets. Its abundance was not consistently related to the presence of defence structures. Moreover, distribution patterns of L. mediterraneum were masking the structure of the whole macrofaunal assemblages. Removal of L. mediterraneum from the datasets allowed the detection of changes in benthic assemblages due to coastal defences. Analyses on different levels of taxonomic resolution showed that the level of family maintained sufficient information to detect the impacts of coastal defence structures on benthic assemblages. Moreover, the outcomes depended on the transformation used. Patterns of distribution of bivalves, used as surrogates, showed low correlations with the patterns of the total macrofaunal species assemblages. Patterns of polychaetes, if identified to the species or genus level showed higher correlations with the whole dataset. However, the identification of polychaetes to species and genus level is as costly as the identification of all macrobenthic taxa at family level.This study provided additional evidences that taxonomic sufficiency is a useful tool in environmental monitoring, also in investigations on the impacts of coastal defence structures on subtidal macrofauna. The use of coarser taxonomic level, being time-efficient, would allow improving sampling designs of monitoring programs by increasing replication in space and time and by allowing long term monitoring studies. 相似文献
74.
Reinaldo L. Bozelli Adriano Caliman Rafael D. Guariento Luciana S. Carneiro Jayme M. Santangelo Marcos P. Figueiredo-Barros Joo J.F. Leal Adriana M. Rocha Letícia B. Quesado Paloma M. Lopes Vinicius F. Farjalla Claudio C. Marinho Fabio Roland Francisco A. Esteves 《Limnologica》2009,39(4):306-313
Human activities are exposing freshwater ecosystems to a wide range of stressors, whose direct and indirect effects can be alleviated or exacerbated through interactive effects with dynamic environmental drivers. This study used long-term data from two Neotropical lacustrine freshwater systems (Batata Lake, an Amazonian floodplain lake and Imboassica lagoon, an Atlantic coastal lagoon) subjected to different kinds of environmental fluctuations (i.e., flood pulse and sandbar opening) and anthropogenic impacts (i.e., siltation and eutrophication). Our objective was to determine whether the effects of human perturbations are contingent on modifications of important biotic and abiotic characteristics through environmental variability. For both ecosystems, environmental variability consistently interacted with anthropogenic perturbations to alter most of the variables analyzed, such as nutrient dynamics, chlorophyll-a concentration, zooplankton and benthic invertebrate species richness, and temporal community stability, which indicates that interactive effects between environmental variability and anthropogenic perturbations may impact a myriad of ecosystem properties. Furthermore, the nature of these interactive effects was highly dependent on the variable considered and on the ecosystem analyzed. For example, at Imboassica lagoon, sandbar openings interacted synergistically with trophic state to increase the phosphorus concentration in the water column. At Batata Lake, flooding generally alleviated the negative effects of siltation on species richness by both diluting inorganic suspended material concentration and by promoting local recruitment from the regional species pool. Such results indicate that our ability to understand and predict the outcome of anthropogenic impacts on inland aquatic systems can be hampered if we consider human stressors as “static” phenomena disconnected from dynamic interactions with major local environmental drivers. 相似文献
75.
Geoarchaeological research on the sedimentary fill of rockshelters and caves in the Gebel Qara (Dhofar, Southern Oman) has revealed the onset of heavy rains at 8700 yr B.P. These rains, produced by strengthening of the Southwest monsoon, abruptly altered the dry environment dominant in the area since the Pleistocene‐Holocene transition. Comparison of cave fills from the southern and northern fringes of the Gebel Qara indicates that the monsoon effects were limited to the southern and central part of the mountain range, directly facing the sea, and did not penetrate into the Nejd Desert. © 2005 Wiley Periodicals, Inc. 相似文献
76.
Fabio Scarciglia Rosanna De Rosa Giuseppe Vecchio Carmine Apollaro Gaetano Robustelli Filippo Terrasi 《Journal of Volcanology and Geothermal Research》2008
This paper focuses on the main morphological, physical, chemical and mineralogical features of an andic-like soil, widely outcropping in the Sila upland plateau of Calabria (southern Italy), and its potential role in tephrostratigraphy. A multidisciplinary and multiscale approach allowed identification of this soil as a “masked” distal archive of volcanic products, developed on granite rocks and sediments with a coeval pyroclastic input during pedogenesis. The study demonstrates that the contribution of volcanic parent materials can be successfully hypothesized and assessed even in the absence, limited extent or poor preservation of primary eruptive products. The soil has an Andisol-like appearance, despite laboratory data that do not match the entire suite of diagnostic criteria for the Andisol taxonomic order. Geomorphological, stratigraphic and pedologic results, coupled with tephrostratigraphic and radiometric data, concur to suggest a Late Pleistocene(?) to Holocene age of the Andisol-like soil. In particular, the rhyolitic chemical composition of small-sized glass fragments (identified by SEM–EDS analyses) indicates soil genesis contributed by volcanic ash, probably sourced from Aeolian Arc explosive activity spanning the last 30 ka. Accordingly, the evidence of limited relict clay illuviation and the specific type of pedogenesis allowing the development of andic properties (in turn related to the neoformation of clay minerals from the weathering of volcanic glass) are consistent with a climatic shift from a seasonally-contrasted to a constantly humid pedoenvironment. This change can be ascribed to the Lateglacial(?) or Early–Middle Holocene to Late Holocene transition. Calibrated AMS 14C dates performed on charcoal fragments sampled from three representative soil profiles, provide Late Holocene ages (3136 ± 19, 343 ± 16 and 92 ± 24 yr BP), in accord with archaeological finds. On the basis of the consistent stratigraphic position, lateral continuity and wide extent, the soil can be considered a good pedostratigraphic marker in the Sila highlands and is informally defined as the “Cecita Lake geosol”. It supplies valuable time constraints for the underlying (occasionally overlying) deposits and/or soils. Moreover, it allows regional-scale morphostratigraphic correlations and detailed reconstruction of Late Pleistocene–Holocene geomorphic events in Calabria, a very suitable region for distal tephra deposition in the central Mediterranean peri-volcanic area. The effects of high-energy volcanic eruptions are interfingered with or superimposed by other geomorphic processes and climatic or anthropogenic signals. 相似文献
77.
The explosive behavior and the rheology of lavas in basaltic volcanoes, usually driven by differentiation, can also be significantly
affected by the kinetics of magma degassing in the upper portion of the feeding system. The complex eruption of 2001 at Mt.
Etna, Italy, was marked by two crucial phenomena that occurred at the Laghetto vent on the southern flank of the volcano:
1) intense explosive activity and 2) at the end of the eruption, emission of a lava flow with higher viscosity than flows
previously emitted from the same vent. Here, we investigate the hypothesis that these events were driven by the injection
of volatile-rich magma into the feeding system. The input and mixing of this magma into a reservoir containing more evolved
magma had the twofold effect of increasing 1) the overall concentration of volatiles and 2) their exsolution with consequent
efficient vesiculation and degassing. This led to an explosive stage of the eruption, which produced a ~75-m-high cinder cone.
Efficient volatile loss and the consequent increase of the liquidus temperature brought about the nucleation of Fe-oxides
and other anhydrous crystalline phases, which significantly increased the magma viscosity in the upper part of the conduit,
leading to the emission of a high viscosity lava flow that ended the eruption. The 2001 eruption has offered the opportunity
to investigate the important role that input of volatile-rich magma may exert in controlling not only the geochemical features
of erupted lavas but also the eruption dynamics. These results present a new idea for interpreting similar eruptions in other
basaltic volcanoes and explaining eruptions with uncommonly high explosivity when only basic magmas are involved. 相似文献
78.
Stefano Catalano Giorgio De Guidi Gianni Lanzafame Carmelo Monaco Luigi Tortorici 《Journal of Geodynamics》2009,48(2):75-82
Structural observations carried out on the volcanic Island of Pantelleria show that the tectonic setting is dominated by NNE trending normal faults and by NW-striking right-lateral strike-slip faults with normal component of motion controlled by a ≈N 100°E oriented extension. This mode of deformation also controls the development of the eruptive fissures, dykes and eruptive centres along NNE–SSW belts that may thus represent the surface response to crustal cracking with associated magma intrusions. Magmatic intrusions are also responsible for the impressive vertical deformations that affect during the Late Quaternary the south-eastern segment of the island and producing a large dome within the Pantelleria caldera complex. The results of the structural analysis carried out on the Island of Pantelleria also improves the general knowledge on the Late Quaternary tectonics of the entire Sicily Channel. ESE–WNW directed extension, responsible for both the tectonic and volcano-tectonic features of the Pantelleria Island, also characterizes, at a greater scale, the entire channel as shown by available geodetic and seismological data. This mode of extension reactivates the older NW–SE trending fault segments bounding the tectonic troughs of the Channel as right-lateral strike-slip faults and produces new NNE trending pure extensional features (normal faulting and cracking) that preferentially develop at the tip of the major strike-slip fault zones. We thus relate the Late Quaternary volcanism of the Pelagian Block magmatism to dilatational strain on the NNE-striking extensional features that develop on the pre-existing stretched area and propagate throughout the entire continental crust linking the already up-welled mantle with the surface. 相似文献
79.
Engineering vibration monitoring by GPS: long duration records 总被引:1,自引:0,他引:1
Monitoring the performance of any structure requires real-time measurements of the change of position of critical points.Different techniques can be used for this purpose,each one offering advantages and disadvantages.The technique based on satellite positioning systems(GPS,GLONASS and the future GALILEO)seems to be very promising at least for long period structures.The GPS in particular provides sampling rates that are able to track dynamic displacements with high accuracy.Its service ability is indepen... 相似文献
80.
A methodology for the correction of systematic errors in a simplified atmospheric general‐circulation model is proposed. First, a method for estimating initial tendency model errors is developed, based on a 4‐dimensional variational assimilation of a long‐analysed dataset of observations in a simple quasi‐geostrophic baroclinic model. Then, a time variable potential vorticity source term is added as a forcing to the same model, in order to parameterize subgrid‐scale processes and unrepresented physical phenomena. This forcing term consists in a (large‐scale) flow dependent parametrization of the initial tendency model error computed by the variational assimilation. The flow dependency is given by an analogues technique which relies on the analysis dataset. Such empirical driving causes a substantial improvement of the model climatology, reducing its systematic error and improving its high frequency variability. Low‐frequency variability is also more realistic and the model shows a better reproduction of Euro‐Atlantic weather regimes. A link between the large‐scale flow and the model error is found only in the Euro‐Atlantic sector, other mechanisms being probably the origin of model error in other areas of the globe. 相似文献