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   256300篇
  免费   4295篇
  国内免费   3358篇
测绘学   6837篇
大气科学   18972篇
地球物理   53536篇
地质学   88765篇
海洋学   21183篇
天文学   55882篇
综合类   994篇
自然地理   17784篇
  2021年   2223篇
  2020年   2584篇
  2019年   2837篇
  2018年   3289篇
  2017年   3050篇
  2016年   5607篇
  2015年   4186篇
  2014年   6895篇
  2013年   14203篇
  2012年   6404篇
  2011年   7613篇
  2010年   6728篇
  2009年   9354篇
  2008年   8179篇
  2007年   7588篇
  2006年   9587篇
  2005年   7614篇
  2004年   7541篇
  2003年   7021篇
  2002年   6660篇
  2001年   5962篇
  2000年   5923篇
  1999年   5186篇
  1998年   5215篇
  1997年   5008篇
  1996年   4665篇
  1995年   4415篇
  1994年   4100篇
  1993年   3838篇
  1992年   3617篇
  1991年   3586篇
  1990年   3754篇
  1989年   3501篇
  1988年   3293篇
  1987年   3842篇
  1986年   3406篇
  1985年   4213篇
  1984年   4725篇
  1983年   4404篇
  1982年   4313篇
  1981年   3919篇
  1980年   3644篇
  1979年   3506篇
  1978年   3478篇
  1977年   3273篇
  1976年   3039篇
  1975年   2956篇
  1974年   2920篇
  1973年   3071篇
  1972年   2024篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
From July, 1975 to November, 1976 mussels from the Laguna Veneta, north-east Italy, and the adjacent Adriatic Sea were collected bimonthly at ten stations and analysed for 3,4-benzopyrene (BaP) and perylene (Pe) content. Mean concentrations were in the range 12·0–135·1 μg/kg dry weight for BaP and 1·5–16·9 μg/kg for Pe, but values as high as 327 μg/kg for BaP and 71 μg/kg for Pe have been measured. The distribution of BaP and Pe closely matches previous results on petroleum hydrocarbon contamination in mussels from this area and indicates that the major portion of BaP and Pe in these bivalves is due principally to human activities.  相似文献   
993.
994.
995.
996.
The decline of the herring stocks and the gadoid outburst   总被引:2,自引:1,他引:2  
  相似文献   
997.
998.
Existing methods for the determination of the various forms of iodine present in seawater are laborious or unwieldy in use. This paper describes modified forms of the iodate and total iodine methods described by Barkley and Thompson (1960), a spectrophotometric procedure for iodate determination derived from Johannesson's (1958) work, and an automatic method for total iodine determination. Procedures for iodate and total-iodine determination which are suitable for use aboard ship, are recommended. Both procedures for iodate determination returned a standard deviation close to 0.5 μg/l when several replicate samples of a seawater containing approximately 30 μg/l of iodate-iodine were analysed. The automatic method for total iodine determination yielded a standard deviation of 0.8 μg/l by the repeated analysis of a seawater containing a total of approximately 50 μg/l of iodine. Suitable methods for the filtration and storage of seawater are also described.  相似文献   
999.
Abstract. Benthic metabolism and standing stocks were investigated in the deep Red Sea between 21o and 27oN, Activity was assessed by the determination of respiration rates with a shipboard method and by calculating oxygen consumption from the activity in the electron transport system. We attempted to compare results from different latitudes within the warm Red Sea and with data from cold Atlantic environments. Our investigations were part of an environmental risk assessment to evaluate future mining of metalliferous sediments from the Atlantis II Deep.  相似文献   
1000.
OBS’s were deployed for 26 to 29 days in the eastern Bismarck Sea to investigate the back-arc spreading. Hypocenters of 186 shallow earthquakes were determined using P- and S-waves from at least five stations. In the western survey area, a transform fault zone is marked by a linear micro-earthquake activity striking N65°W and less than 5 km wide. The predominant type of their focal mechanisms is strike-slip. In the eastern area, several intermittent zones of micro-earthquakes and their strike-slip type focal mechanisms suggest the location of short-length transform faults separating en-echelon spreading ridges.  相似文献   
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