全文获取类型
收费全文 | 457篇 |
免费 | 13篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 7篇 |
大气科学 | 43篇 |
地球物理 | 21篇 |
地质学 | 276篇 |
海洋学 | 26篇 |
天文学 | 5篇 |
自然地理 | 95篇 |
出版年
2019年 | 2篇 |
2016年 | 3篇 |
2015年 | 3篇 |
2014年 | 8篇 |
2013年 | 26篇 |
2012年 | 7篇 |
2011年 | 14篇 |
2010年 | 10篇 |
2009年 | 17篇 |
2008年 | 12篇 |
2007年 | 15篇 |
2006年 | 10篇 |
2005年 | 21篇 |
2004年 | 15篇 |
2003年 | 14篇 |
2002年 | 5篇 |
2001年 | 6篇 |
2000年 | 10篇 |
1999年 | 11篇 |
1998年 | 18篇 |
1997年 | 35篇 |
1996年 | 27篇 |
1995年 | 12篇 |
1994年 | 20篇 |
1993年 | 8篇 |
1992年 | 7篇 |
1991年 | 16篇 |
1990年 | 20篇 |
1989年 | 10篇 |
1988年 | 12篇 |
1987年 | 10篇 |
1986年 | 9篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 6篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1972年 | 2篇 |
1971年 | 3篇 |
1970年 | 1篇 |
1968年 | 1篇 |
1967年 | 2篇 |
1966年 | 2篇 |
1963年 | 3篇 |
1962年 | 1篇 |
排序方式: 共有473条查询结果,搜索用时 671 毫秒
421.
DAVID ROBERTSON 《Geographical review》1999,89(4):533-553
ABSTRACT. Storm chasing is widely perceived as a new form of extreme sport or adventure travel. Each spring increasing numbers of tourists descend on the Southern Plains, the center of storm chasing in the United States, but little is known about their activities. According to longtime chasers, popular portrayals of storm pursuits are highly misleading, and growing participation in the sport is affecting storm chasing in the region. This study introduces the storm-chasing enterprise. Using route information and comments supplied by veteran chasers, I describe the spatial patterns of storm-chasing on the Southern Plains. Comparing the behavior and motivations of longtime enthusiasts with popular portrayals of the activity permits me to dispel many myths and to discuss the nature and future of this growing but little-understood recreational pursuit. 相似文献
422.
423.
强震前后广义地震应变释放过程的丛集特征 总被引:1,自引:0,他引:1
利用基于小波变换的多重分形奇异谱估计方法,研究了部分强震前后地震活动广义应变.释放过程的多重分形特征。结果表明,晨中区附近- -定范围内地展活动广义应变释放过程具有多重分形特征,但多重分形维数谱随7变化复杂,在强震发生前多重分形维数谱没有明显的变化。广义地震应变释放过程的多重分形奇异谱形态和Hausdorff奇异指数范围能提供更多关于地屣活动过程的信息,特别当η取较大值时Hausdorff奇异指数范围在强晨前明显变窄。研究还表明深源地展和浅源地晨发生前广义应变释放过程多重分形特征存在明显不同。 相似文献
424.
DAVID STEWART 《Geology Today》1988,4(4):130-137
Discovery of the southern North Sea gas fields and, by 1970, several billion-barrel oil fields in the central North Sea encouraged oil companies to explore in the deeper, less hospitable waters of the northern North Sea. There, seismic surveys revealed a pre-Cretaceous unconfmity with 'highs' forming potential oil traps. One of the largest of these buried 'highs' was drilled by ShelllEsso, and oil was found in quantity in Middle Jurassic deltaic sandstones. This led to the discovery of eight major oil fields with reserves in excess of 7500 million barrels. Detailed studies of the sandstone reservoirs of the Brent Delta are enabling petroleum geologists and engineers to maximize recovery from these northern fields. 相似文献
425.
Microbial processes in the Negev phosphorites (southern Israel) 总被引:3,自引:0,他引:3
ABSTRACT Microscopic and SEM observations indicate that cyanobacterial activity was important during the formation of the Campanian Negev phosphorites. One aspect of such activity is the development of phosphorites through the binding of phosphate particles. These sediments often demonstrate a conspicuous smooth cryptalgal lamination. The algal binder was fossilized as intertwined phosphatic sheaths that coat and seal off the phosphate grains. Different types of sheaths representing the remnants of an algal community were found. Thick apatite overgrowth commonly deforms the microbial fossils converting them into barely recognizable forms. Fabrication of phosphate particles is another aspect of the microbial activity. Phosphate algal coated grains are a common constituent of the Negev phosphorites. The algal coating consists of stacked phosphatic tubes and colonies of coccoid unicells with an apatite infilling. Fragmented phosphatic sheath bundles form another type of phosphate particle produced by algae. Obliteration of algal structures is common, resulting in undifferentiated groundmasses of cryptocrystalline apatite. The extremely close connection between microbial structures and phosphatization processes suggests cyanobacterial participation in phosphorus enrichment. 相似文献
426.
427.
DAVID M. MARTILL 《Geology Today》1987,3(2):59-63
The Eocene Green River Formation fishes of southwestern Wyoming are among the best preserved and best known fossil fishes yet discovered. Collecting them is hard work and a very technical and time-consuming process, but is made worthwhile by the fantastic setting in which the fossils occur. This is an account of a collecting trip under the leadership ofDr Lance Grande to expand the already spectacular collection of Green River fishes in the Field Museum of Natural History, Chicago. 相似文献
428.
DAVID A. R. POOLE JOAR SKITEM TORE O. VORREN 《Boreas: An International Journal of Quaternary Research》1994,23(2):122-138
Based on four shallow drillings in the outer part of the Bjørnøya trough, palaeoenvironments of foraminifera in glacigenic sediments are discussed. Different methods were used; detailed foraminiferal analysis, oxygen and carbon stable isotope analysis and transfer functions. Six different foraminiferal assemblage zones were found. One zone, AA, appears to be pre-Pleistocene in age and contains an abundance of reworked early Tertiary foraminifera. Four of the assemblage zones have a dominant arctic foraminiferal content; however, a marked boreal input is evident, particularly in zone B where B. marginata dominates. We suggest that B. marginata has been resedimented from pre-Eemian 'warm' deposits. Its occurrence in these older warm intervals possibly reflects a lower input of the Norwegian Current into the area and possibly an increase in the relative nutrient content of the water masses. The six zones have also differing numbers of foram./gram sediment. An assemblage zone where a boreal component of foraminifera ( E. nipponica, P. bulloides ) dominates was found, zone C. We define this particular assemblage zone to be of Eemian age (isotope substage 5e). The foraminiferal assemblage composition and the oxygen and carbon isotopes from zone C indicate that oceanographic conditions in the Barents Sea during the Eemian were slightly different from those of the present and that, possibly, Atlantic waters were more prevalent. 相似文献
429.
Modelling of turbidity currents on Navy Submarine Fan, California Continental Borderland 总被引:2,自引:1,他引:2
Several Holocene turbidites can be correlated across much of Navy Fan through more than 100 sediment core localities. The uppermost muddy turbidite unit is mapped throughout the northern half of the fan; its volume, grain-size distribution and the maximum height of deposition on the basin slopes are known. These parameters can be related to the precise channel morphology and mesotopography revealed by deep-tow surveys. Thus there is sufficient information to estimate detailed flow characteristics for this turbidity current as it moved from fan valley to distal basin plain. On the upper fan, the gradient and the increasing downstream width of the channel and only limited flow overspill suggest that the flow had a Froude number close to 1.0. The sediment associated with the channel indicates friction velocities of about 0.06 m s?1 and flow velocities of about 0.75 m s?1. Using this flow velocity and channel dimensions, sediment concentration (~2×10?3) and discharge are estimated, and from a knowledge of the total volume of sediment deposited, the flow duration is estimated to be from 2 to 9 days. It is shown that the estimates of Froude number, drag coefficient, and sediment concentration are not likely to vary by more than a factor of 2. On the mid-fan, the flow was much thicker than the height of the surface relief of the fan and it spread rapidly. The cross-flow slope, determined from the horizontal extent of turbidite sediment, is used to estimate flow velocity, which is confirmed by consideration of both sediment grain size and rate of deposition. This again allows sediment concentration and discharge to be estimated. The requirements of flow continuity, entrainment of water during flow expansion, and observed sediment deposition provide checks on all these estimates, and provide an integrated picture of the evolution of the flow. The flow characteristics of this muddy turbidity current are well constrained compared to those for more sand-rich late Pleistocene and early Holocene turbidity currents on the fan. 相似文献
430.
Sedimentation in ice-covered Lake Hoare, Antarctica 总被引:2,自引:0,他引:2
SUSAN S. NEDELL DAVID W. ANDERSEN STEVEN W. SQUYRES† F. GORDON LOVE‡ 《Sedimentology》1987,34(6):1093-1106
The sedimentation mechanisms that occur in ice-covered Lake Hoare, Antarctica are examined, to determine how sediment enters the lake, and how the sedimentation pattern affects blue-green algal growth at the lake bottom. The 3 m-thick ice cover contains pebbly sand as much as 2 m below the surface. Sediment with similar texture and mineralogy is found at the lake bottom. This evidence, together with the lack of sediment in the inflowing stream and the markedly different texture of sediment from the other terrains around the lake suggest that most of the sediment at the lake bottom comes in through the ice cover. Sand grains intermittently migrate through porous ice on the surface, water-filled vertical gas-channels penetrating two-thirds of the ice cover, and possibly through cracks in the ice that act as conduits. The algae at the lake bottom are able to survive in part because sediment that comes through the ice cover does not obliterate them. 相似文献