全文获取类型
收费全文 | 37254篇 |
免费 | 809篇 |
国内免费 | 317篇 |
专业分类
测绘学 | 928篇 |
大气科学 | 2804篇 |
地球物理 | 7527篇 |
地质学 | 13649篇 |
海洋学 | 3283篇 |
天文学 | 7411篇 |
综合类 | 84篇 |
自然地理 | 2694篇 |
出版年
2021年 | 348篇 |
2020年 | 398篇 |
2019年 | 409篇 |
2018年 | 881篇 |
2017年 | 878篇 |
2016年 | 1050篇 |
2015年 | 646篇 |
2014年 | 987篇 |
2013年 | 1991篇 |
2012年 | 1152篇 |
2011年 | 1507篇 |
2010年 | 1319篇 |
2009年 | 1680篇 |
2008年 | 1476篇 |
2007年 | 1436篇 |
2006年 | 1453篇 |
2005年 | 1066篇 |
2004年 | 1120篇 |
2003年 | 1012篇 |
2002年 | 1025篇 |
2001年 | 879篇 |
2000年 | 853篇 |
1999年 | 681篇 |
1998年 | 651篇 |
1997年 | 699篇 |
1996年 | 579篇 |
1995年 | 582篇 |
1994年 | 596篇 |
1993年 | 486篇 |
1992年 | 489篇 |
1991年 | 462篇 |
1990年 | 468篇 |
1989年 | 423篇 |
1988年 | 427篇 |
1987年 | 485篇 |
1986年 | 422篇 |
1985年 | 576篇 |
1984年 | 592篇 |
1983年 | 581篇 |
1982年 | 537篇 |
1981年 | 490篇 |
1980年 | 505篇 |
1979年 | 443篇 |
1978年 | 413篇 |
1977年 | 391篇 |
1976年 | 359篇 |
1975年 | 347篇 |
1974年 | 334篇 |
1973年 | 332篇 |
1971年 | 209篇 |
排序方式: 共有10000条查询结果,搜索用时 859 毫秒
911.
912.
913.
914.
915.
916.
917.
Pensacola Bay, Florida, was in the strong northeast quadrant of Hurricane Ivan when it made landfall on September 16, 2004
as a category 3 hurricane on the Saffir-Simpson scale. We present data describing the timeline and maximum height of the storm
surge, the extent of flooding of coastal land, and the magnitude of the freshwater inflow pulse that followed the storm. We
computed the magnitude of tidal flushing associated with the surge using a tidal prism model. We also evaluated hurricane
effects on water quality using water quality surveys conducted 20 and 50 d after the storm, which we compared with a survey
14 d before landfall. We evaluated the scale of hurricane effects relative to normal variability using a 5-yr monthly record.
Ivan's 3.5 m storm surge inundated 165 km2 of land, increasing the surface area of Pensacola Bay by 50% and its volume by 230%. The model suggests that 60% of the Bay's
volume was flushed, initially increasing the average salinity of Bay waters from 23 to 30 and lowering nutrient and chlorophylla concentrations. Additional computations suggest that wind forcing was sufficient to completely mix the water column during
the storm. Freshwater discharge from the largest river increased twentyfold during the subsequent 4 d, stimulating a modest
phytoplankton bloom (chlorophyll up to 18 μg l−1) and maintaining hypoxia for several months. Although the immediate physical perturbation was extreme, the water quality
effects that persisted beyond the first several days were within the normal range of variability for this system. In terms
of water quality and phytoplankton productivity effects, this ecosystem appears to be quite resilient in the face of a severe
hurricane effect. 相似文献
918.
The release of methane from crater sites following meteorite impact is a possible consequence of the thermal alteration of organic matter, or tapping of reservoired gas of biogenic or abiogenic origin. At least the latter is feasible on Mars. Methane and higher hydrocarbons are susceptible to polymerization and precipitation by radioactive minerals. Where such minerals are present in impact target rocks, the craters can be a preferred site for carbon concentration, and the formation of complex organic molecules. On icy bodies, such as Titan and Europa, methane released by impact could be a fuel for prebiotic chemistry involving other forms of irradiation. 相似文献
919.
Darren F. Mark John Parnell Simon P. Kelley Sarah C. Sherlock 《Journal of Geochemical Exploration》2006,89(1-3):259
Integration of fluid inclusion analysis with high spatial resolution Ar–Ar dating of K-feldspar cements has been used to resolve and reconstruct palaeo-fluid flow. Fluid inclusion analysis allows discrimination of distinct cement phases, thereby identifying discrete episodes of fluid flow. Ar–Ar dating of the same cements via high spatial resolution laserprobe establishes absolute age constraints on the framework previously constructed. Integration of these two datasets yields temperature–composition–time data. 相似文献
920.