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   262338篇
  免费   4422篇
  国内免费   3537篇
测绘学   6983篇
大气科学   19407篇
地球物理   54673篇
地质学   91486篇
海洋学   21952篇
天文学   56802篇
综合类   1025篇
自然地理   17969篇
  2021年   2282篇
  2020年   2641篇
  2019年   2871篇
  2018年   3958篇
  2017年   3725篇
  2016年   5961篇
  2015年   4261篇
  2014年   6946篇
  2013年   14250篇
  2012年   6701篇
  2011年   8251篇
  2010年   7345篇
  2009年   9963篇
  2008年   8642篇
  2007年   8222篇
  2006年   9647篇
  2005年   7794篇
  2004年   7684篇
  2003年   7190篇
  2002年   6749篇
  2001年   6000篇
  2000年   5954篇
  1999年   5212篇
  1998年   5228篇
  1997年   5033篇
  1996年   4689篇
  1995年   4425篇
  1994年   4113篇
  1993年   3867篇
  1992年   3644篇
  1991年   3590篇
  1990年   3772篇
  1989年   3518篇
  1988年   3302篇
  1987年   3850篇
  1986年   3416篇
  1985年   4228篇
  1984年   4739篇
  1983年   4410篇
  1982年   4315篇
  1981年   3933篇
  1980年   3642篇
  1979年   3508篇
  1978年   3485篇
  1977年   3281篇
  1976年   3043篇
  1975年   2958篇
  1974年   2914篇
  1973年   3084篇
  1972年   2022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