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   3429篇
  免费   295篇
  国内免费   439篇
测绘学   770篇
大气科学   478篇
地球物理   387篇
地质学   540篇
海洋学   520篇
天文学   29篇
综合类   347篇
自然地理   1092篇
  2024年   19篇
  2023年   35篇
  2022年   127篇
  2021年   182篇
  2020年   154篇
  2019年   178篇
  2018年   108篇
  2017年   166篇
  2016年   178篇
  2015年   202篇
  2014年   230篇
  2013年   191篇
  2012年   248篇
  2011年   247篇
  2010年   200篇
  2009年   200篇
  2008年   166篇
  2007年   184篇
  2006年   213篇
  2005年   177篇
  2004年   120篇
  2003年   119篇
  2002年   86篇
  2001年   76篇
  2000年   82篇
  1999年   54篇
  1998年   34篇
  1997年   38篇
  1996年   24篇
  1995年   25篇
  1994年   23篇
  1993年   22篇
  1992年   16篇
  1991年   11篇
  1990年   6篇
  1989年   2篇
  1988年   4篇
  1987年   4篇
  1986年   2篇
  1985年   3篇
  1984年   3篇
  1983年   2篇
  1979年   1篇
  1978年   1篇
排序方式: 共有4163条查询结果,搜索用时 343 毫秒
21.
22.
Fisheries in boreal ecosystems   总被引:2,自引:1,他引:2  
  相似文献   
23.
This study takes cognizance of the fact that the TIOMIN (TIOMIN Resources Inc. of Canada) project has resulted in controversy over its handling of environmental issues and especially the Environmental Impact Assessment (EIA). The authors address many of the protracted issues that have slowed the development of the mining project in Kwale. The main emphasis is on the impacts of the mining and mineral separation processes on the environment, including the governing legislation, the role of consultation and public participation, and socioeconomic issues. In their public documents TIOMIN has specified neither the type of minerals it wants to extract from the area nor their chemical composition. It is well known, however that the titanium minerals and zircon targeted have impurities of iron, thorium and uranium. In the absence of an Environmental Management Plan, the effects of stockpiling radioactive wastes and other impurities that could possibly lead to environmental degradation in both the terrestrial and marine environments have not been publically addressed. The measures proposed to mitigate ecological damage as a result of the establishment of a minerals processing plant in the area seem inadequate. Pollution resulting from accidental spillage or breakage could have significant impact on marine life and residents living near the mining site. Other issues that have not been addressed satisfactorily pertain to the use of surface and underground water. The area already faces a huge water deficit and the calculations presented on aquifer recharge and stream flow rates do not indicate the large quantities of water that would be required in the mineral processing plant. The project, if approved in its present state, risks violation of international conventions. Furthermore, it could cause a conflict between Kenya and Tanzania in the event of an oil spill at the proposed ship loading facility at Shimoni. The proposed mining area includes the district's most fertile land, is home to many fisherfolk and is a major tourist destination. An analysis of the effects of this project on other available opportunities must be thoroughly understood to ascertain the economic and environmental benefits and costs of the mining venture. The proposed compensation rate of $1,000 per acre, for resettlement for example, appears to be grossly inadequate. Compensation should take into account family size and structure family assets and the cost of relocation.  相似文献   
24.
25.
26.
27.
28.
29.
In recent years, the red tide erupted frequently, and caused a great economic loss. At present, most literatures emphasize the academic research on the growth mechanism of red tide alga. In order to find out the characters of red tide in detail and improve the precision of forecast, this paper gives some new approaches to dealing with the red tide. By the extreme values, we deal with the red tide frequency analysis and get the estimation of T-times red tide level U (T) , which is the level once the consistence of red tide alga exceeds on the average in a period of T times.  相似文献   
30.
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