全文获取类型
收费全文 | 139658篇 |
免费 | 1798篇 |
国内免费 | 1889篇 |
专业分类
测绘学 | 4079篇 |
大气科学 | 9815篇 |
地球物理 | 26964篇 |
地质学 | 52050篇 |
海洋学 | 11687篇 |
天文学 | 28676篇 |
综合类 | 2458篇 |
自然地理 | 7616篇 |
出版年
2022年 | 770篇 |
2021年 | 1317篇 |
2020年 | 1402篇 |
2019年 | 1570篇 |
2018年 | 7542篇 |
2017年 | 6631篇 |
2016年 | 6042篇 |
2015年 | 2169篇 |
2014年 | 3684篇 |
2013年 | 6219篇 |
2012年 | 4665篇 |
2011年 | 7319篇 |
2010年 | 6281篇 |
2009年 | 7759篇 |
2008年 | 6721篇 |
2007年 | 7183篇 |
2006年 | 4800篇 |
2005年 | 3670篇 |
2004年 | 3845篇 |
2003年 | 3660篇 |
2002年 | 3430篇 |
2001年 | 2831篇 |
2000年 | 2737篇 |
1999年 | 2187篇 |
1998年 | 2276篇 |
1997年 | 2061篇 |
1996年 | 1823篇 |
1995年 | 1785篇 |
1994年 | 1533篇 |
1993年 | 1423篇 |
1992年 | 1369篇 |
1991年 | 1395篇 |
1990年 | 1388篇 |
1989年 | 1173篇 |
1988年 | 1124篇 |
1987年 | 1273篇 |
1986年 | 1152篇 |
1985年 | 1411篇 |
1984年 | 1584篇 |
1983年 | 1470篇 |
1982年 | 1377篇 |
1981年 | 1288篇 |
1980年 | 1181篇 |
1979年 | 1133篇 |
1978年 | 1079篇 |
1977年 | 915篇 |
1976年 | 898篇 |
1975年 | 882篇 |
1974年 | 844篇 |
1973年 | 913篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
Natural environmental changes and human impact reflected in sediments of a high alpine lake in Switzerland 总被引:1,自引:0,他引:1
From the high alpine Sägistalsee (1935 m a.s.l.), 13.50 m of continuously laminated sediments comprising the last 9050 years, were analyzed. Even though Sägistalsee is a high elevation site, human-induced environmental changes start as early as 4300 cal. BP and leave a clearly detectable signal in the mineralogy of the sediments, which is much stronger than the signal from natural environmental changes that occurred before this time. Variations in the physical and mineralogical sediment properties of this clastic sequence reflect erosional changes in the catchment, where almost pure limestone contrasts with carbonaceous, quartz-bearing marl, and shist. The calcite/quartz (Cc/Qz) ratio was found to be most indicative of these changes, which occurred around AD 1850 and at 650, 2000, 3700, and 6400 cal. BP. The first four are interpreted as erosion events, which are related to human-induced changes in the vegetation cover and land use. We associate them to the recent development of tourism and grazing, the medieval intensification of pasturing, Roman forest clearance, and Bronze Age forest clearance, respectively. The Cc/Qz-ratio increases significantly within less than 100 years during these events, reflecting the erosion of unweathered or poorly weathered soils. The time intervals in between are characterized by a gradually decreasing Cc/Qz-ratio and reflect the stabilization or formation of new soils. Only the change at 6400 cal. BP, which represents the initial gradual stabilization of the catchment, is related to the immigration of Picea abies. 相似文献
993.
994.
995.
A comparison of subgrid-scale models for large-eddy simulations of convection in the Earth's core 总被引:2,自引:1,他引:2
Bruce A. Buffett 《Geophysical Journal International》2003,153(3):753-765
996.
Shear wave statics using receiver functions 总被引:1,自引:0,他引:1
997.
998.
999.
R. A. SHAKESBY C. J. CHAFER S. H. DOERR W. H. BLAKE P. WALLBRINK G. S. HUMPHREYS 《The Australian geographer》2003,34(2):147-175
Soil water repellency can enhance overland flow and erosion and may be altered by fire. The Christmas 2001 bushfires near Sydney allowed investigation of the relationship between fire severity, water repellency and hydrogeomorphological changes. For two sub-catchments with differences in fire severities in Nattai National Park, south-west of Sydney, this paper considers: (1) the links between fire severity based on SPOT image analysis and ground observation of fire severity and repellency; (2) the textural and organic/minerogenic characteristics of eroded sediment; and (3) erodibility, erosion and deposition of soils in both catchments. Ground surveys show that image analysis reflects well the degree of vegetation consumption by fire, but cannot adequately predict the degree of ground litter consumption, associated soil heating and repellency effects. Fire had varying effects on repellency, leaving it unchanged, destroying it or enhancing it, depending on the soil temperature reached. The main post-fire hydrogeomorphological changes have been widespread erosion and colluvial and alluvial deposition of topsoil in foot-slope locations and river systems, but only localised redistribution of the highly erodible, repellent sandy subsurface layer. The fire did not trigger major geomorphological change in the study area, but fires probably cause important topsoil and nutrient depletion and may also affect water quality. 相似文献
1000.
Environmental and sanitary estimation of small-river water quality is made in the zone of influence of gold-mining facilities in Krasnoyarsk Region. The estimates are based on data on the hydrochemical regime and the characteristics of phytoplankton, microphyto-periphyton, macrozoobenthos, and ichthyofauna collected during the vegetation period of 2000. 相似文献