全文获取类型
收费全文 | 1004篇 |
免费 | 62篇 |
国内免费 | 14篇 |
专业分类
测绘学 | 33篇 |
大气科学 | 65篇 |
地球物理 | 325篇 |
地质学 | 359篇 |
海洋学 | 64篇 |
天文学 | 164篇 |
综合类 | 5篇 |
自然地理 | 65篇 |
出版年
2023年 | 5篇 |
2022年 | 23篇 |
2021年 | 15篇 |
2020年 | 27篇 |
2019年 | 23篇 |
2018年 | 48篇 |
2017年 | 50篇 |
2016年 | 51篇 |
2015年 | 54篇 |
2014年 | 66篇 |
2013年 | 68篇 |
2012年 | 64篇 |
2011年 | 65篇 |
2010年 | 63篇 |
2009年 | 82篇 |
2008年 | 58篇 |
2007年 | 45篇 |
2006年 | 30篇 |
2005年 | 41篇 |
2004年 | 27篇 |
2003年 | 32篇 |
2002年 | 27篇 |
2001年 | 15篇 |
2000年 | 12篇 |
1999年 | 13篇 |
1998年 | 12篇 |
1997年 | 7篇 |
1996年 | 6篇 |
1995年 | 2篇 |
1994年 | 5篇 |
1992年 | 1篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1971年 | 1篇 |
1969年 | 3篇 |
排序方式: 共有1080条查询结果,搜索用时 250 毫秒
961.
Clive Finlayson José Carrión Kimberly Brown Geraldine Finlayson Antonio Sánchez-Marco Darren Fa Joaquín Rodríguez-Vidal Santiago Fernández Elena Fierro Marco Bernal-Gómez Francisco Giles-Pacheco 《Quaternary Science Reviews》2011,30(11-12):1525-1532
Although hardly applied to human palaeoecology, bird fossils offer a unique opportunity for quantitative studies of the hominin habitat. Here we reconstruct the Homo habitat niche across a large area of the Palaearctic, based on a database of avian fauna for Pleistocene sites. Our results reveal a striking association between Homo and habitat mosaics. A mix of open savannah-type woodland, wetlands and rocky habitats emerges as the predominant combination occupied by Homo across a wide geographical area, from the earliest populations of the Lower Palaeolithic to the latest hunter-gatherer communities of the Upper Palaeolithic. This observation is in keeping with the view that such landscapes have had long standing selective value for hominins. 相似文献
962.
Marco Bonini Federico Sani Giovanna Moratti Marco G. Benvenuti 《Journal of Geodynamics》2011,51(2-3):125-140
We examine the structural characteristics and the tectonic evolution of some key areas along the thrust front of the Lucania sector of the Southern Apennines, which also represents the southwestern boundary of the Adria Plate. The results of our study have allowed the identification of a complex tectonic history manifested by the presence of structural elements compatible with different stress fields. Particularly, during the Pleistocene the area experienced a transition from a compressional setting, characterised by NE-ENE shortening, to a post-Middle Pleistocene strike-slip/extensional phase controlled by NE-ENE-directed lateral extension associated with a horizontal NW-NNW-trending σ1 axis. Roughly coaxial transitional stress fields apparently accompanied the progression between these two main regimes. This major change in tectonic setting can be framed into the fragmentation processes of the Adriatic Plate. We propose that the Mid-Adriatic Ridge, a WNW-ESE-trending belt of inverted Mesozoic grabens underwater the Adriatic Sea, has increasingly accommodated the NNW-directed Africa-Adria convergence giving the way to the Africa shortening to propagate into the Lucania Apennines. Furthermore, the comparison with GPS data suggests the existence of an important deep-seated tectonic boundary beneath the Apennines. This element is expected to focus seismicity and may represent an important discontinuity fragmenting Adria. 相似文献
963.
Marco Conedera Willy Tinner Christophe Neff Manfred Meurer Angela F. Dickens Patrik Krebs 《Quaternary Science Reviews》2009,28(5-6):555-576
Biomass burning and resulting fire regimes are major drivers of vegetation changes and of ecosystem dynamics. Understanding past fire dynamics and their relationship to these factors is thus a key factor in preserving and managing present biodiversity and ecosystem functions. Unfortunately, our understanding of the disturbance dynamics of past fires is incomplete, and many open questions exist relevant to these concepts and the related methods. In this paper we describe the present status of the fire-regime concept, discuss the notion of the fire continuum and related proxies, and review the most important existing approaches for reconstructing fire history at centennial to millennial scales. We conclude with a short discussion of selected directions for future research that may lead to a better understanding of past fire-regime dynamics. In particular, we suggest that emphasis should be laid on (1) discriminating natural from anthropogenic fire-regime types, (2) improving combined analysis of fire and vegetation reconstructions to study long-term fire ecology, and (3) overcoming problems in defining temporal and spatial scales of reference, which would allow better use of past records to gain important insights for landscape, fire and forest management. 相似文献
964.
Ostreopsis ovata is an epiphytic potentially toxic dinoflagellate. It has a world-wide distribution, normally associated with other epiphytic or benthic dinoflagellates. In tropical seas O. ovata is often associated with the genera Gambierdiscus, Coolia and Prorocentrum, causing cinguatera fish poisoning. Recently, Ostreopsis spp. blooms in the Tyrrhenian and southern Adriatic Sea have been related to human health problems, such as breathing and skin irritation. Here we report the first record of Ostreopsis cfr. ovata in the Northern Adriatic Sea. O. cfr. ovata was isolated from macroalgae in two areas, the Gulf of Trieste (Italy) and close to Rovinj (Croatia). The microalga was identified by scanning electron microscopy and by fluorescence light microscopy. Size range and thecal pore structure were similar to those described for O. cfr. ovata in previous studies. Ostreopsis cfr. ovata was present on all the macroalgae collected, particularly browns and reds. The microalgal association on macroalgae was mostly composed of Ostreopsis sp., Coolia monotis and Coscinodiscus sp. 相似文献
965.
Michael A. Dopita Daniela Calzetti Jesús Maíz Apellániz William P. Blair Knox S. Long Max Mutchler Bradley C. Whitmore Howard E. Bond John MacKenty Bruce Balick Marcella Carollo Michael Disney Jay A. Frogel Robert O’Connell Donald Hall Jon A. Holtzman Randy A. Kimble Patrick McCarthy Francesco Paresce Abhijit Saha Alistair R. Walker Joe Silk Marco Sirianni John Trauger Rogier Windhorst Erick Young 《Astrophysics and Space Science》2010,330(1):123-131
We present narrow band, continuum subtracted Hα, [S ii], Hβ, [O iii] and [O ii] data taken with the Wide Field Camera 3 on the Hubble Space Telescope in the nearby dwarf starburst galaxy NGC 4214. From these images, we identify seventeen new planetary nebula candidates, and seven supernova remnant candidates. We use the observed emission line luminosity function of the planetary nebulae to establish a new velocity-independent distance to NGC 4214. We conclude that the PNLF technique gives a reddening independent distance to NGC 4214 of 3.19±0.36 Mpc, and that our current best-estimate of the distance to this galaxy ids 2.98±0.13 Mpc. 相似文献
966.
B. Viticchié M. Vantaggiato F. Berrilli D. del Moro V. Penza E. Pietropaolo M. Rast 《Astrophysics and Space Science》2010,328(1-2):39-42
Various small scale photospheric processes are responsible for spatial and temporal variations of solar emergent intensity. The contribution to total irradiance fluctuations of such small scale features is the solar irradiance background. Here we examine the statistical properties of irradiance background computed via a n-body numerical scheme mimicking photospheric space-time correlations and calibrated by means of IBIS/DST spectro-polarimetric data. Such computed properties are compared with experimental results derived from the analysis of a VIRGO/SPM data. A future application of the model here presented could be the interpretation of stellar irradiance power spectra observed by new missions such as Kepler. 相似文献
967.
Emő Márton Dario Zampieri Paolo Grandesso Vlasta Ćosović Alan Moro 《Tectonophysics》2010,480(1-4):57-72
The central-western and the eastern Southern Alps are separated by the triangular shaped Adige embayment, which belongs to stable Adria and was the site of pelagic sedimentation from the Tithonian through Maastrichtian. The first part of this study presents paleomagnetic results from the Tithonian–Cenomanian Biancone and Turonian–Maastrichtian Scaglia Rossa formations sampled at 33 geographically distributed and biostratigraphically dated localities.The new and high quality paleomagnetic results from the Adige embayment are then combined with coeval paleomagnetic directions from autochthonous Istria (Márton et al., 2008), which also belongs to stable Adria. The combined data set (which for the Late Albian–Maastrichtian time period is constructed similarly to the synthetic African curve by Besse and Courtillot, 2002, 2003) reveals an important tectonic event (Late Aptian–Early Albian) characterized by 20° CCW rotation and sedimentary hiatus.Comparison between paleomagnetic declinations/inclinations expected in an African framework (i.e. with the assumption that Adria is still an African promontory) leads to the following conclusions. The time-distributed Tithonian and Berriasian (150–135 Ma) paleomagnetic directions exhibit the “African hairpin” with an inclination minimum and a sudden change from CW to CCW rotation at 145 Ma. Concerning the younger ages, the declinations for Adria continue to follow the African trend of CCW rotation till the end of Cretaceous. However, the Tithonian–Maastrichtian declination curve for stable Adria is displaced by 10° from the “African” curve as a result of two rotations. The first, an about 20° CW rotation of Adria with respect to Africa took place between the Maastrichtian and the mid-Eocene. During this time the orientation of Adria remained the same, while Africa continued its CCW rotation. The younger rotation (30°CCW) changed the orientation of Adria relative to Africa as well as to the present North. 相似文献
968.
Mechanisms driving polymagmatic activity at a monogenetic volcano, Udo, Jeju Island, South Korea 总被引:3,自引:1,他引:2
Marco Brenna Shane J. Cronin Ian E. M. Smith Young Kwan Sohn Karoly Németh 《Contributions to Mineralogy and Petrology》2010,160(6):931-950
High-resolution, stratigraphically ordered samples of the Udo tuff cone and lava shield offshore of Jeju Island, South Korea,
show complex geochemical variation in the basaltic magmas that fed the eruption sequence. The eruption began explosively,
producing phreatomagmatic deposits with relatively evolved alkali magma. The magma became more primitive over the course of
the eruption, but the last magma to be explosively erupted had shifted back to a relatively evolved composition. A separate
sub-alkali magma batch was subsequently effusively erupted to form a lava shield. Absence of weathering and only minor reworking
between the tuff and overlying lava implies that there was no significant time break between the eruptions of the two magma
batches. Modelling of the alkali magma suggests that it was generated from a parent melt in garnet peridotite at c. 3 to 3.5 GPa
and underwent mainly clinopyroxene + olivine ± spinel fractionation at c. 1.5 to 2 GPa. The sub-alkali magma was, by contrast,
generated from a chemically different peridotite with residual garnet at c. 2.5 GPa and evolved through olivine fractionation
at a shallower level compared to its alkali contemporary. The continuous chemostratigraphic trend in the tuff cone, from relatively
evolved to primitive and back to evolved, is interpreted to have resulted from a magma batch having risen through a single
dyke and erupted the batch’s head, core and margins, respectively. The alkali magma acted as a path-opener for the sub-alkali
magma. The occurrence of the two distinct batches suggests that different magmatic systems in the Jeju Island Volcanic Field
have interacted throughout its history. The polymagmatic nature of this monogenetic eruption has important implications for
hazard forecasting and for our understanding of basaltic field volcanism. 相似文献
969.
Károly Németh Shane J. Cronin Miguel J. Haller Marco Brenna Gabor Csillag 《Central European Journal of Geosciences》2010,2(3):339-361
The Pannonian Basin (Central Europe) hosts numerous alkali basaltic volcanic fields in an area similar to 200 000 km2. These volcanic fields were formed in an approximate time span of 8 million years producing smallvolume volcanoes typically considered to be monogenetic. Polycyclic monogenetic volcanic complexes are also common in each field however. The original morphology of volcanic landforms, especially phreatomagmatic volcanoes, is commonly modified. by erosion, commonly aided by tectonic uplift. The phreatomagmatic volcanoes eroded to the level of their sub-surface architecture expose crater to conduit filling as well as diatreme facies of pyroclastic rock assemblages. Uncertainties due to the strong erosion influenced by tectonic uplifts, fast and broad climatic changes, vegetation cover variations, and rapidly changing fluvio-lacustrine events in the past 8 million years in the Pannonian Basin have created a need to reconstruct and visualise the paleoenvironment into which the monogenetic volcanoes erupted. Here phreatomagmatic volcanic fields of the Miocene to Pleistocene western Hungarian alkali basaltic province have been selected and compared with modern phreatomagmatic fields. It has been concluded that the Auckland Volcanic Field (AVF) in New Zealand could be viewed as a prime modern analogue for the western Hungarian phreatomagmatic fields by sharing similarities in their pyroclastic successions textures such as pyroclast morphology, type, juvenile particle ratio to accidental lithics. Beside the AVF two other, morphologically more modified volcanic fields (Pali Aike, Argentina and Jeju, Korea) show similar features to the western Hungarian examples, highlighting issues such as preservation potential of pyroclastic successions of phreatomagmatic volcanoes. 相似文献
970.