全文获取类型
收费全文 | 3563篇 |
免费 | 140篇 |
国内免费 | 50篇 |
专业分类
测绘学 | 87篇 |
大气科学 | 301篇 |
地球物理 | 745篇 |
地质学 | 1394篇 |
海洋学 | 259篇 |
天文学 | 608篇 |
综合类 | 12篇 |
自然地理 | 347篇 |
出版年
2023年 | 15篇 |
2021年 | 46篇 |
2020年 | 64篇 |
2019年 | 88篇 |
2018年 | 94篇 |
2017年 | 108篇 |
2016年 | 124篇 |
2015年 | 109篇 |
2014年 | 131篇 |
2013年 | 191篇 |
2012年 | 122篇 |
2011年 | 181篇 |
2010年 | 164篇 |
2009年 | 206篇 |
2008年 | 188篇 |
2007年 | 171篇 |
2006年 | 160篇 |
2005年 | 142篇 |
2004年 | 140篇 |
2003年 | 100篇 |
2002年 | 96篇 |
2001年 | 71篇 |
2000年 | 70篇 |
1999年 | 59篇 |
1998年 | 54篇 |
1997年 | 56篇 |
1996年 | 54篇 |
1995年 | 43篇 |
1994年 | 29篇 |
1993年 | 31篇 |
1992年 | 27篇 |
1991年 | 40篇 |
1990年 | 23篇 |
1989年 | 26篇 |
1988年 | 32篇 |
1987年 | 38篇 |
1986年 | 24篇 |
1985年 | 30篇 |
1984年 | 31篇 |
1983年 | 18篇 |
1982年 | 30篇 |
1981年 | 31篇 |
1980年 | 28篇 |
1979年 | 17篇 |
1978年 | 17篇 |
1977年 | 20篇 |
1976年 | 17篇 |
1974年 | 26篇 |
1973年 | 21篇 |
1971年 | 14篇 |
排序方式: 共有3753条查询结果,搜索用时 15 毫秒
101.
Martin Schmieder Barry J. Shaulis Thomas J. Lapen Elmar Buchner David A. Kring 《Meteoritics & planetary science》2019,54(8):1808-1827
Laser ablation inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) U–Pb geochronology of shocked zircon grains in a vesicular‐fluidal impact melt rock from the ≥54 km Charlevoix impact structure, Québec, Canada, suggests an Ordovician to Silurian age of 450 ± 20 Ma for the impact. This age is anchored by concordant U–Pb results of ~450 Ma for a U‐rich, cryptocrystalline zircon grain in the melt rock, interpreted as a recrystallized metamict zircon crystal; the U–Th–Pb system of the metamict grain was seemingly chronometrically reset by the Charlevoix impact, but withstood later tectonometamorphic events. The new zircon age for Charlevoix is in agreement with a stratigraphically constrained Late Ordovician maximum age of ~453 Ma and corroborates earlier suggestions that the impact occurred most likely in the Ordovician, and not ~100 Myr later, as indicated by previous K/Ar and 40Ar/39Ar geochronologic results. The latter may reflect postimpact thermal overprint of impactites during the Salinian (Late Silurian to Early Devonian) and/or Acadian (Late Devonian) orogenies. U–Pb geochronology of zircon crystals in anorthosite exposed in the central uplift of the impact structure yielded a Grenvillian crystallization age of 1062 ± 11 Ma. The preferred Ordovician age for the Charlevoix impact structure, which is partially overthrusted by the Appalachian front, suggests the impact occurred during a phase of Taconian tectonism and an episode of enhanced asteroid bombardment of the Earth. Our results, moreover, demonstrate that (recrystallized) metamict zircon grains may be of particular interest in impact geochronology. 相似文献
102.
Martin Schiller James N. Connelly Martin Bizzarro 《Meteoritics & planetary science》2017,52(6):1233-1243
The large collection of howardite‐eucrite‐diogenite (HED) meteorites allows us to study the initial magmatic differentiation of a planetesimal. We report Pb‐Pb ages of the unequilibrated North West Africa (NWA) 4215 and Dhofar 700 diogenite meteorites and their mass‐independent 26Mg isotope compositions (26Mg*) to better understand the timing of differentiation and crystallization of their source reservoir(s). NWA 4215 defines a Pb‐Pb age of 4484.5 ± 7.9 Myr and has a 26Mg* excess of +2.3 ± 1.6 ppm whereas Dhofar 700 has a Pb‐Pb age of 4546.4 ± 4.7 Myr and a 26Mg* excess of +25.5 ± 1.9 ppm. We interpret the young age of NWA 4215 as a thermal overprint, but the age of Dhofar 700 is interpreted to represent a primary crystallization age. Combining our new data with published Mg isotope and trace element data suggests that approximately half of the diogenites for which such data are available crystallized within the first 1–2 Myr of our solar system, consistent with a short‐lived, early‐formed magma ocean undergoing convective cooling. The other half of the diogenites, including both NWA 4215 and Dhofar 700, are best explained by their crystallization in slowly cooled isolated magma chambers lasting over at least ~20 Myr. 相似文献
103.
Modelling and extracting 3D geographical data presents numerous challenges that require continual research to attempt to evolve an efficient, reliable and accurate solution. LiDAR data capture and analysis has become a preferred acquisition choice for elevation data because the resulting quality and level of detail far exceeds traditional methods for large survey areas. As with any data collection system, LiDAR is prone to errors. Analysing these errors, ascertaining causes and producing error correction strategies is vital if accurate and confident results are to be obtained. Eight years of LiDAR datasets (from 1998 to 2005) have been closely analysed for a large coastal area of South Wales. This article provides a detailed and accurate summary of the identified LiDAR data issues and subsequent errors which affect the accuracy of end products such as Digital Surface Models (DSMs). 相似文献
104.
M. C. Santos P. Vaníček W. E. Featherstone R. Kingdon A. Ellmann B. -A. Martin M. Kuhn R. Tenzer 《Journal of Geodesy》2006,80(12):691-704
Following our earlier definition of the rigorous orthometric height [J Geod 79(1-3):82–92 (2005)] we present the derivation and calculation of the differences between this and the Helmert orthometric height, which is embedded in the vertical datums used in numerous countries. By way of comparison, we also consider Mader and Niethammer’s refinements to the Helmert orthometric height. For a profile across the Canadian Rocky Mountains (maximum height of ~2,800 m), the rigorous correction to Helmert’s height reaches ~13 cm, whereas the Mader and Niethammer corrections only reach ~3 cm. The discrepancy is due mostly to the rigorous correction’s consideration of the geoid-generated gravity disturbance. We also point out that several of the terms derived here are the same as those used in regional gravimetric geoid models, thus simplifying their implementation. This will enable those who currently use Helmert orthometric heights to upgrade them to a more rigorous height system based on the Earth’s gravity field and one that is more compatible with a regional geoid model. 相似文献
105.
106.
107.
Floodplains are ecotones that form a transition between aquatic and terrestrial environments. These important ecosystems can be described as dynamic spatial mosaics in which water plays an important role in connecting various patches on the floodplain surface. Hydrological connections facilitate the exchange of carbon and nutrients between the river channel and the floodplain and therefore influence the productivity of the entire river system. This paper examines the influence of hydrological connections on the potential exchange of dissolved organic carbon between a large Australian floodplain to a river channel, and the effects of land and water developments on these exchanges. The paper proposes that an understanding of floodplain ecosystems requires an interdisciplinary approach—a recognition of the importance of the three disciplines hydrology, geomorphology and ecology. Large-scale water-resources and floodplain development has significantly altered the spatial and temporal patterns of hydrological characteristics in the Lower Balonne floodplain, Australia. The magnitude, frequency and duration of flooding events have all been reduced. The construction of levees and water storages has also reduced the reactive floodplain surface area. The presented data show the impacts of these changes on the potential supply of dissolved organic carbon from the floodplain surface during periods of inundation. Annual reductions of up to 1293 tonnes of dissolved organic carbon supply were noted and reductions were especially significant for floods with an average recurrence interval of 2 years or less. Some small flood events no longer facilitate the potential supply of dissolved organic carbon from the floodplain to the river channel because of water-resources and floodplain developments. 相似文献
108.
Martin Muravchik Gijs A. Henstra Gauti T. Eliassen Rob L. Gawthorpe Mike Leeder Haralambos Kranis Emmanuel Skourtsos Julian Andrews 《Basin Research》2020,32(5):1184-1212
Our current understanding on sedimentary deep-water environments is mainly built of information obtained from tectonic settings such as passive margins and foreland basins. More observations from extensional settings are particularly needed in order to better constrain the role of active tectonics in controlling sediment pathways, depositional style and stratigraphic stacking patterns. This study focuses on the evolution of a Plio-Pleistocene deep-water sedimentary system (Rethi-Dendro Formation) and its relation to structural activity in the Amphithea fault block in the Corinth Rift, Greece. The Corinth Rift is an active extensional basin in the early stages of rift evolution, providing perfect opportunities for the study of early deep-water syn-rift deposits that are usually eroded from the rift shoulders due to erosion in mature basins like the Red Sea, North Sea and the Atlantic rifted margin. The depocentre is located at the exit of a structurally controlled sediment fairway, approximately 15 km from its main sediment source and 12 km basinwards from the basin margin coastline. Fieldwork, augmented by digital outcrop techniques (LiDAR and photogrammetry) and clast-count compositional analysis allowed identification of 16 stratigraphic units that are grouped into six types of depositional elements: A—mudstone-dominated sheets, B—conglomerate-dominated lobes, C—conglomerate channel belts and sandstone sheets, D—sandstone channel belts, E—sandstone-dominated broad shallow lobes, F—sandstone-dominated sheets with broad shallow channels. The formation represents an axial system sourced by a hinterland-fed Mavro delta, with minor contributions from a transverse system of conglomerate-dominated lobes sourced from intrabasinal highs. The results of clast compositional analysis enable precise attribution for the different sediment sources to the deep-water system and their link to other stratigraphic units in the area. Structures in the Amphithea fault block played a major role in controlling the location and orientation of sedimentary systems by modifying basin-floor gradients due to a combination of hangingwall tilt, displacement of faults internal to the depocentre and folding on top of blind growing faults. Fault activity also promoted large-scale subaqueous landslides and eventual uplift of the whole fault block. 相似文献
109.
Philip Martin 《Norsk geografisk tidsskrift. Norwegian journal of geography》2013,67(4):210-218
Young Vietnamese men who witnessed their mother's changing economic and labour market situations through the early years of Ð?i m?i (the policy of economic liberalization in Vietnam after 1986) have developed conceptions of masculinity that are ambivalent to notions of male power and authority within what is often termed the ‘traditional’ neo-Confucian family. On the basis of the life narratives of a small group of men in their early twenties, the author suggests that the value young men place on their mother's work and familial influence during Ð?i m?i contrasts with the findings of much gender scholarship on women's social and economic (im) mobility in the 1990s in Vietnam and on young men's own masculinist narratives. Most gender-sensitive research in this area has suggested that Vietnamese women remained curtailed in the early 1990s by a resurgence of male-oriented kinship systems and patriarchal structures at household level. However, the author discusses the young men as being equivocal. While invoking broad Confucian tropes, these men remember their mothers as economically dynamic relative to their fathers. This led to the informants citing their mother's histories of economic risk-taking as exemplifying free-market capability. Further, the finding suggests that Vietnamese women's social and economic mobility in the 1990s strongly affected young men's contemporary ideas and practices related to masculinity. 相似文献
110.