全文获取类型
收费全文 | 620篇 |
免费 | 131篇 |
国内免费 | 74篇 |
专业分类
测绘学 | 30篇 |
大气科学 | 29篇 |
地球物理 | 137篇 |
地质学 | 313篇 |
海洋学 | 70篇 |
天文学 | 3篇 |
综合类 | 20篇 |
自然地理 | 223篇 |
出版年
2024年 | 1篇 |
2023年 | 5篇 |
2022年 | 12篇 |
2021年 | 27篇 |
2020年 | 19篇 |
2019年 | 20篇 |
2018年 | 33篇 |
2017年 | 37篇 |
2016年 | 22篇 |
2015年 | 35篇 |
2014年 | 27篇 |
2013年 | 71篇 |
2012年 | 26篇 |
2011年 | 39篇 |
2010年 | 28篇 |
2009年 | 43篇 |
2008年 | 30篇 |
2007年 | 27篇 |
2006年 | 25篇 |
2005年 | 22篇 |
2004年 | 26篇 |
2003年 | 25篇 |
2002年 | 20篇 |
2001年 | 21篇 |
2000年 | 22篇 |
1999年 | 17篇 |
1998年 | 18篇 |
1997年 | 17篇 |
1996年 | 11篇 |
1995年 | 8篇 |
1994年 | 11篇 |
1993年 | 12篇 |
1992年 | 21篇 |
1991年 | 10篇 |
1990年 | 8篇 |
1989年 | 7篇 |
1988年 | 12篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有825条查询结果,搜索用时 15 毫秒
51.
R. V. Rohli A. J. Vega M. R. Binkley S. D. Britton H. E. Heckman J. M. Jenkins Y. Ono D. E. Sheeler 《Applied geography (Sevenoaks, England)》2001,21(4)
Impacts on water resources caused by human activity, natural climate variation and long-term climate change are unclear in the US Great Lakes region. Improved understanding of the impact of atmospheric circulation on stream discharge variability into the Lakes is thus important. In this analysis, monthly surface and mid-tropospheric circulation patterns suggest that surface pressure variations over Missouri and Illinois are most strongly correlated to discharge. The mid-tropospheric patterns most directly related to discharge place the Great Lakes in a trough-to-ridge flow pattern. The analysis confirms that at this scale, lee shore advection resulting in ‘lake-effect’ precipitation is not very important to regional discharge, and neither are variations in the Pacific–North American teleconnection. 相似文献
52.
Variation in growth, physiology and ionic relations patterns of Allenrolfea occidentalis, a perennial halophyte of dry habitats, was studied under field conditions from May 1996 to November 1997. An A. occidentalis community has a characteristic soil pH of 7·3–8·3. During the two years, the population was exposed to great variations in soil salinity, from 29 to 146 dS m−1, and soil moisture, ranging from drought (9·2%) to wet (19%). The salt concentrations were significantly higher in the surface soil layers than in the subsurface layers. Seasonal changes in dry weight are directly related to soil salinity stress. Allenrolfea occidentalis had greater growth and biomass production under saline conditions. Na+and Cl−ions were accumulated in plant tissues in much greater amounts than K+, Ca2+, and Mg2+. Soil salinities were significantly reduced at the end of the growing season. Water potentials of the shoots decreased significantly with increasing salinity. The plant (Fv/Fmratio) was more affected by salinity and irradiation levels during the summer period. 相似文献
53.
M. Mastalerz C. Souch G. M. Filippelli N. L. Dollar S. M. Perkins 《International Journal of Coal Geology》2001,46(2-4)
Cores from the Great Marsh area of the Indiana Dunes National Lakeshore were examined in order to document variations in concentration, type and size of anthropogenic organic matter (AnOM—coal, coke, etc.) and discuss their relationship to the concentration of such trace elements as Pb, Zn, and Mn in the near-surface sediment section. The results indicate that the first appearance of AnOM corresponds to the onset of industrialization in the area. There is also a general relationship between the occurrence of AnOM and Zn, Pb, and Mn. Trace metals were likely transported from the industrial sites to the area of their deposition as sulfur-bearing coatings on small anthropogenic particles. After deposition, these sulfur-bearing compounds reacted with organic matter within the marsh. As a result of bacterial reduction, the pyrite was produced, as suggested by a close relationship between the pyrite and AnOM. Distance from the industrial complex upwind as well as local hydrologic conditions are among the major factors controlling distribution of AnOM and trace elements. At the same distance from the source, types and sizes of AnOM are influenced by the duration and frequency of flooding. 相似文献
54.
分析了大华北浅源地震与日本海西部及我国东北深震的关系,认为本世纪来日本海西部—我国东北深震经历了5个相对活跃期,大华北各地震区相应经历这5个活跃期的影响期。根据大华北M≧6级浅源地震与深震活动的相关性,建立了太平洋板块楔形俯冲带端部重大深震事件导致大华北浅源M≧6级地震发生的板块俯冲模型,应变波传播速度约94km/年,地表视速度约100km/年。重大深震事件突出、模型稳定性强,预测实验表明模型公式可做大华北地震监测参考。用本模型可以解释浅源地震迁移、各地震区地震与深震活动相关等现象。 相似文献
55.
56.
57.
Jane?M.?HammarstromEmail author Robert?R.?SealII Allen?L.?Meier John?C.?Jackson 《Environmental Geology》2003,45(1):35-57
Metal cycling via physical and chemical weathering of discrete sources (copper mines) and regional (non-point) sources (sulfide-rich shale) is evaluated by examining the mineralogy and chemistry of weathering products in Great Smoky Mountains National Park, Tennessee, and North Carolina, USA. The elements in copper mine waste, secondary minerals, stream sediments, and waters that are most likely to have negative impacts on aquatic ecosystems are aluminum, copper, zinc, and arsenic because these elements locally exceed toxicity guidelines for surface waters or for stream sediments. Acid-mine drainage has not developed in streams draining inactive copper mines. Acid-rock drainage and chemical weathering processes that accompany debris flows or human disturbances of sulfidic rocks are comparable to processes that develop acid-mine drainage elsewhere. Despite the high rainfall in the mountain range, sheltered areas and intermittent dry spells provide local venues for development of secondary weathering products that can impact aquatic ecosystems.Electronic Supplementary Material Supplementary material is available for this article if you access the article at . A link in the frame on the left on that page takes you directly to the supplementary material.
相似文献
Jane M. HammarstromEmail: Phone: +1-703-6486165Fax: +1-703-6486252 |
58.
59.
A late Quaternary ichthyofauna from Homestead Cave, Utah, provides a new source of information on lake history in the Bonneville basin. The fish, represented by 11 freshwater species, were accumulated between 11,200 and 1000 14C yr B.P. by scavenging owls. The 87Sr/86Sr ratio of Lake Bonneville varied with its elevation; 87Sr/86Sr values of fish from the lowest stratum of the cave suggest they grew in a lake near the terminal Pleistocene Gilbert shoreline. In the lowest deposits, a decrease in fish size and an increase in species tolerant of higher salinities or temperatures suggest multiple die-offs associated with declining lake levels. An initial, catastrophic, post-Provo die-off occurred at 11,300–11,200 14C yr B.P. and was followed by at least one rebound or recolonization of fish populations, but fish were gone from Lake Bonneville sometime before 10,400 14C yr B.P. This evidence is inconsistent with previous inferences of a near desiccation of Lake Bonneville between 13,000 and 12,000 14C yr B.P. Peaks in Gila atraria frequencies in the upper strata suggest the Great Salt Lake had highstands at 3400 and 1000 14C yr B.P. 相似文献
60.