全文获取类型
收费全文 | 1598篇 |
免费 | 198篇 |
国内免费 | 411篇 |
专业分类
测绘学 | 27篇 |
大气科学 | 92篇 |
地球物理 | 254篇 |
地质学 | 1342篇 |
海洋学 | 160篇 |
天文学 | 29篇 |
综合类 | 17篇 |
自然地理 | 286篇 |
出版年
2024年 | 23篇 |
2023年 | 33篇 |
2022年 | 60篇 |
2021年 | 64篇 |
2020年 | 101篇 |
2019年 | 90篇 |
2018年 | 68篇 |
2017年 | 98篇 |
2016年 | 81篇 |
2015年 | 102篇 |
2014年 | 114篇 |
2013年 | 127篇 |
2012年 | 90篇 |
2011年 | 85篇 |
2010年 | 64篇 |
2009年 | 99篇 |
2008年 | 110篇 |
2007年 | 118篇 |
2006年 | 102篇 |
2005年 | 94篇 |
2004年 | 64篇 |
2003年 | 61篇 |
2002年 | 42篇 |
2001年 | 27篇 |
2000年 | 46篇 |
1999年 | 39篇 |
1998年 | 33篇 |
1997年 | 24篇 |
1996年 | 27篇 |
1995年 | 17篇 |
1994年 | 19篇 |
1993年 | 15篇 |
1992年 | 14篇 |
1991年 | 8篇 |
1990年 | 13篇 |
1989年 | 7篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 5篇 |
1980年 | 2篇 |
1978年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有2207条查询结果,搜索用时 15 毫秒
11.
In this provenance study of late Palaeozoic metasediments of the Eastern Andean Metamorphic Complex (EAMC) along the south
Patagonian proto-Pacific margin of Gondwana, the palaeogeological setting of the continental margin in Devonian–Carboniferous
and Permian times is reconstructed. The study is based on detrital heavy mineral contents, chemical compositions of tourmaline
grains, and whole rock element and Nd-Sr isotopic compositions. Element and isotopic compositions reveal that Devonian–Carboniferous
metaturbidites deposited before the development of a Late Carboniferous–Permian magmatic arc along the margin were mainly
fed from felsic, recycled, old continental rocks. The last recycling phase involved erosion of metasediments that were exposed
in Patagonia. Feeder systems to the basin cut either through epidote-rich or garnet-rich metasediments. In Permian time, EAMC
metaturbidites were deposited next to the evolving magmatic arc and were derived from felsic, crustal rocks. Two provenance
domains are recognised. The metasediments of the northern one are chemically similar to those of the Devonian–Carboniferous
metasediments. This domain was fed from the metasedimentary host rocks of the magmatic arc. The southern domain probably was
fed from the arc proper, as indicated mainly by the dominance of metaplutonic lithic fragments, abundant detrital biotite,
and the major element composition of the metasediments. 相似文献
12.
Stéphanie Brichau Jean-Patrick Respaut Patrick Monié 《International Journal of Earth Sciences》2008,97(4):725-738
During the development of the Variscan orogeny, large amounts of granitic melt were produced, giving rise to the intrusion
of granitoids at different structural levels. Despite numerous studies, ages available from previous work on the Cévennes
granites remain largely imprecise. In order to better constrain the age and emplacement mode of these granites, we have combined
U–Pb dating on monazites and zircons and 40Ar/39Ar dating on biotites with petrological observations, major element chemical analysis and SEM zircon imaging on five samples
from the Aigoual–St Guiral–Liron and Mont Lozère granitic massifs. The results revealed that granitic intrusions and cooling
in Southern Cévennes occurred in a short time span at ∼306 Ma after the main episode of regional metamorphism. Petrological
and chemical data suggest that they result from a mixing between mantle-derived basic magmas (lamprophyres) and lower crust
acid magmas. At a regional scale the production of these melts occurred at the end of crustal thickening induced by nappe
stacking, at the same time as the late anatectic events recorded further north in the Velay dome and the granulite facies
metamorphism recorded in metasedimentary granulite enclaves brought up by Tertiary volcanoes of the Velay area (Bournac). 相似文献
13.
14.
During the Late Carboniferous to Early Permian, a rift was formed by post-collisional extension after ocean closure or an island arc-related basin formed by Paleo-Asian Ocean (PAO) subduction in the Xi Ujimqin area. Nevertheless, the closure time of the PAO is still under debate. Thus, to identify the origin of the PAO, the geochemistry and U-Pb age of zircons were analyzed for the extra-large deep marine, polymict clastic boulders and sandstones in the Shoushangou Formation within the basin. The analyses revealed magmatic activity and tectonic evolution. The conglomerates include megaclasts of granite (298.8 ± 9.1?Ma) and granodiorite porphyry (297.1 ± 3.1?Ma), which were deposited by muddy debris flow. Results of this study demonstrated that the boulders of granitoids have the geochemistry of typical I-type granite, characterized by low Zr + Nb + Ce + Y and low Ga/Al values. The granitoid boulders were formed in island arc setting, indicating the presence of arc magmatism in the area that is composed of the Late Carboniferous to Early Permian subduction-related granitoid in southern Xi Ujimqin. Multiple diagrams for determining sedimentary provenance using major and trace elements indicate that Shoushangou sediments originated from continental island arc-related felsic rocks. Detrital zircon U-Pb age cluster of 330–280?Ma was obtained, indicating input from granite, ophiolite, Xilin Gol complex, and Carboniferous sources to the south. The basin was geographically developed behind the arc during the Early Permian period because the outcropped intrusive rocks in the Late Carboniferous to Early Permian form a volcanic arc. The comprehensive analyses of source areas suggest that Shoushangou sediments developed in a backarc basin in response to the northward subduction of the PAO. The backarc basin and intrusive rocks, in addition to previously published Late Carboniferous to Early Permian magmatic rocks of arc unit in Xilin Gol, confirm the presence of an Early Permian trench-arc-basin system in the region, represented by the Baolidao arc and Xi Ujimqin backarc basin. This study highlights the importance and potential of combined geochemical and geochronological studies of conglomerates and sandstone for reconstructing the geodynamic setting of a basin. 相似文献
15.
Seismic activity associated with the subducting motion of the Philippine Sea plate beneath the Kanto district, Japan 总被引:1,自引:1,他引:1
Sadaki Hori 《Tectonophysics》2006,417(1-2):85
The Pacific plate and the Philippine Sea plate overlap and subduct underneath the Kanto region, central Japan, causing complex seismic activities in the upper mantle. In this research, we used a map selection tool with a graphic display to create a data set for earthquakes caused by the subducting motion of the Philippine Sea plate that are easily determined. As a result, we determined that there are at least four earthquake groups present in the upper mantle above the Pacific plate. Major seismic activity (Group 1) has been observed throughout the Kanto region and is considered to originate in the uppermost part of mantle in the subducted Philippine Sea plate, judging from the formation of the focal region and comparison with the 3D structure of seismic velocity. The focal mechanism of these earthquakes is characterized by the down-dip compression. A second earthquake layer characterized by down-dip extension (Group 2), below the earthquakes in this group, is also noted. The focal region for those earthquakes is considered to be located at the lower part of the slab mantle, and the Pacific plate located directly below is considered to influence the activity. Earthquakes located at the shallowest part (Group 3) form a few clusters distributed directly above the Group 1 focal region. Judging from the characteristics of later phases in these earthquakes and comparing against the 3D structure of seismic velocity, the focal regions for the earthquakes are considered to be located near the upper surface of the slab. Another earthquake group (Group 4) originates further below Group 2; it is difficult to consider these earthquakes within a single slab. The seismic activities representing the upper area of the Philippine Sea plate are Group 3. This paper proposes a slab geometry model that is substantially different from conventional models by strictly differentiating the groups. 相似文献
16.
V. Piscopo M. Barbieri V. Monetti G. Pagano S. Pistoni E. Ruggi D. Stanzione 《Hydrogeology Journal》2006,14(8):1508-1521
A conceptual hydrogeological model of the Viterbo thermal area (central Italy) has been developed. Though numerous studies have been conducted on its geological, geochemical and geothermal features, there is no generalized picture defining the origin and yield of the hydrothermal system. These latter aspects have therefore become the objectives of this research, which is based on new hydrogeological and geochemical investigations. The geological setting results in the coexistence of overlapped interacting aquifers. The shallow volcanic aquifer, characterized by fresh waters, is fed from the area around the Cimini Mountains and is limited at its base by the semiconfining marly-calcareous-arenaceous complex and low-permeability clays. To the west of Viterbo, vertical upflows of thermal waters of the sulphate-chloride-alkaline-earth type with higher gas contents, are due to the locally uplifted carbonate reservoir, the reduced thickness of the semiconfining layer and the high local geothermal gradient. The hot waters (30–60°C) are the result of deep circulation within the carbonate rocks (0.5–1.8 km) and have the same recharge area as the volcanic aquifer. The upward flow in the Viterbo thermal area is at least 0.1 m3/s. This flow feeds springs and deep wells, also recharging the volcanic aquifer from below. 相似文献
17.
Ground fissuring is a recurrent problem in many countries where water extraction surpasses the natural recharge of aquifers. Due to differential settlement, the soil layer undergoes deformation and cracks with serious consequences for civil infrastructure. Here, we propose an approximate analysis of the fissuring process that can be used to predict the location of cracks, which increasingly affect some middle- and large-sized cities in the world. For that purpose, the ground loss theory is applied to sediments overlying a sinusoidal-shaped graben. This analysis shows the existence of a tensile zone at the border of the graben with maximal values on its shoulder where tension cracks are more likely to appear. It also shows that soil deformation under differential settlement may evolve into ground faulting if water withdrawal continues. Finally, when a crack has completely developed, the tensile zone shifts towards the center of the graben, creating a new area for potential cracking and faulting. 相似文献
18.
19.
滇中震旦系碳酸盐岩破碎地层的钻探护孔新技术 总被引:1,自引:1,他引:1
破碎地层中钻探,采用有效的护孔技术是避免孔内事故发生的重要手段,同时也是保证完成钻探各项技术经济指标的先决条件。本文阐述了在具代表性的磷矿破碎地层中钻进所遇到的护孔难题及其所采用的护孔新技术、新方法。 相似文献
20.
Hazard Zoning for Landslides Connected to Torrential Floods in the Jerte Valley (Spain) by using GIS Techniques 总被引:2,自引:0,他引:2
Carrasco R.M. Pedraza J. Martin-Duque J.F. Mattera M. Sanz M.A. Bodoque J.M. 《Natural Hazards》2003,30(3):361-381
The Jerte Valley is anortheast-southwest tending graben located in the mountainous region of west central Spain (Spanish Central System). Mass movements have been a predominant shaping process on the Valley slopes during the Quaternary. Present day activity is characterized as either `first-time failure' (shallow debris slides and debris flows) or `reactivations' of pre-existing landslides deposits.A delineation of landslide hazard zoningwithin the Valley has been carried out by using the detailed documentation of a particular event (a debris slide and a sequel torrential flood, which occurred on the Jubaguerra stream gorge), and GIS techniques. The procedure has had four stages, which are: (1) the elaboration of a susceptibility map (spatial prediction) of landslides; (2) the elaboration of a map of `restricted susceptibility' in the particular case of slopes that are connected to streams and torrents (gorges); (3) the elaboration of a digital model which relates the altitude to the occurrence probability of those particular precipitation conditions which characterized the Jubaguerra event and (4) the combination of the probability model with the `restricted susceptibility map', to establish `critical zones' or areas which are more prone to the occurrence of phenomena that have same typology as this one. 相似文献