首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   92篇
  免费   6篇
测绘学   1篇
大气科学   5篇
地球物理   16篇
地质学   34篇
海洋学   4篇
天文学   18篇
自然地理   20篇
  2021年   2篇
  2019年   1篇
  2018年   1篇
  2017年   1篇
  2016年   3篇
  2015年   3篇
  2014年   4篇
  2013年   3篇
  2012年   4篇
  2011年   2篇
  2010年   2篇
  2009年   2篇
  2008年   2篇
  2007年   8篇
  2006年   3篇
  2005年   2篇
  2004年   4篇
  2003年   3篇
  2002年   3篇
  2001年   3篇
  1999年   5篇
  1998年   5篇
  1997年   1篇
  1996年   2篇
  1995年   1篇
  1994年   3篇
  1993年   1篇
  1991年   1篇
  1990年   1篇
  1988年   2篇
  1987年   1篇
  1986年   2篇
  1985年   1篇
  1984年   2篇
  1982年   1篇
  1981年   2篇
  1980年   1篇
  1979年   2篇
  1977年   2篇
  1976年   3篇
  1974年   1篇
  1965年   1篇
  1962年   1篇
排序方式: 共有98条查询结果,搜索用时 93 毫秒
81.
Middleton Run, a severely acid mine drainage (AMD) impacted tributary of Little Raccoon Creek, drains a sub-watershed area of 3.67 km2 (2.28 square miles). Averaging 58.7 kg/day (129.4 lbs/day) at its mouth, demonstrated aluminum loads from Middleton Run are particularly severe. A preliminary study of two previously unmonitored tributaries was conducted to justify future treatment projects. Monthly chemical water quality data were collected for 6 months. Soil leachate samples collected on five strip mining sites within the sub-watershed were analyzed for acidity, alkalinity, pH, aluminum and iron. Soil leachate tests have shown that one of the pits has a much larger pollution production potential and should be targeted for remediation.  相似文献   
82.
83.
84.
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   
85.
86.
The broad 2800 Å absorption feature discovered by Karim, Hoyle, and Wickramasingle is instrumental in origin. The feature is produced by IUE detector saturation effects in overexposed spectra.  相似文献   
87.
Early diagenetic properties of Amazon shelf muds are dominated by nonsulfidic Fe and Mn cycling, resulting in relatively little S deposition compared to previously studied marine margin environments. Despite abundant potential reactants typical of sulfidic deposits, authigenic sulfides represent only ~ 10% of diagenetically reduced Fe, and DOP (degree of pyritization) is only ~0.02. The average C/S (wt wt–1) ratio of buried sediment below the zone of SO4 2- reduction is ~ 7.4, ~ 2.6 times more than the commonly assumed modern shelf average of ~ 2.8. The deltaic burial rate forS is ~ 0.65 × 106 tons yr–1. Relatively lowS deposition is promoted by terrestrial weathering that delivers reactive oxide debris, but apparently depends most strongly on reoxidation and rapid burial by intense physical reworking and fluid-mud formation. Diagenetic models of S distributions demonstrate rapid sediment reworking (~ 10–100 cm yr–1 as apparent advection), substantialS reoxidation (84–98%), and in one case, massive sediment deposition of up to ~ 5 m of sediment in ~ 1 year. Extremely low DOP coupled with dominance by nonsulfidic reduced-Fe minerals and lack of biogenic sedimentary structures may be an indicator in marine organic-rich muds of intense physical reworking under oxygenated waters.  相似文献   
88.
Monoclonal antibody directed against a major β-naphthoflavone (BNF)-induced form of teleost cytochrome P-450, P-450E (equivalent to P-450c in rat) was used to immunolocalize this enzyme in liver, gill and heart of scup and trout. Liver sections from both species showed P-450E in the cytoplasm of hepatocytes. No regional differences were observed which might indicate zonation of cytochrome P-450E within subpopulations of hepatocytes. Scup exocrine pancreatic cells were only weakly positive. In the gill of both fish, cytochrome P-450E was restricted to the endothelium (pillar cells) of secondary lamellae, where fluorescence appeared as a chain in longitudinal sections through lamellae and as star-shaped clusters in en face views. Sections of ventricular wall in both species revealed P-450E was restricted to endothelium at margins of muscle bands limiting heart ventricular lumen. Localization in the specific cells of these and other organs may be fundamentally important in understanding the role of cytochrome P-450E.  相似文献   
89.
The cycle of organic carbon burial and exhumation moderates atmospheric chemistry and global climate over geologic timescales. The burial of organic carbon occurs predominantly at sea in association with clay-sized particles derived from the erosion of uplifted continental rocks. It follows that the history of the fine-grained particles on land may bear on the nature of the organic carbon buried. In this study, the evolution of clay-associated organic matter was followed from bedrock source to the seabed in the Eel River sedimentary system of northern California using natural abundance 13C and 14C tracers. Approximately half of the fine-grained organic carbon delivered to the shelf is derived from ancient sedimentary organic carbon found in the uplifted Mesozoic-Tertiary Franciscan Complex of the watershed. The short residence time of friable soils on steep hill slopes, coupled with rapid sediment accumulation rates on the shelf-slope, act to preserve the ancient organic carbon. A comparable quantity of modern organic carbon is added to particles in the watershed and on the shelf and slope. The bimodal mixture of ancient and modern C in soils and sediments may be characteristic of many short, mountainous rivers. If the Eel River chemistry is typical of such rivers, more than 40 Tg of ancient organic C may be delivered to the world’s oceans each year. A flux of that magnitude would have a significant influence on marine and global C-cycles.  相似文献   
90.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号