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   23554篇
  免费   988篇
  国内免费   8039篇
安全科学   1591篇
废物处理   1401篇
环保管理   1838篇
综合类   12792篇
基础理论   3941篇
环境理论   2篇
污染及防治   8056篇
评价与监测   992篇
社会与环境   950篇
灾害及防治   1018篇
  2024年   20篇
  2023年   352篇
  2022年   1065篇
  2021年   880篇
  2020年   698篇
  2019年   691篇
  2018年   832篇
  2017年   1028篇
  2016年   1041篇
  2015年   1251篇
  2014年   1715篇
  2013年   2428篇
  2012年   1910篇
  2011年   2013篇
  2010年   1528篇
  2009年   1484篇
  2008年   1614篇
  2007年   1404篇
  2006年   1359篇
  2005年   952篇
  2004年   713篇
  2003年   891篇
  2002年   828篇
  2001年   670篇
  2000年   732篇
  1999年   762篇
  1998年   644篇
  1997年   565篇
  1996年   525篇
  1995年   443篇
  1994年   345篇
  1993年   298篇
  1992年   254篇
  1991年   171篇
  1990年   106篇
  1989年   82篇
  1988年   71篇
  1987年   43篇
  1986年   38篇
  1985年   24篇
  1984年   23篇
  1983年   21篇
  1982年   20篇
  1981年   17篇
  1979年   4篇
  1978年   4篇
  1975年   4篇
  1974年   4篇
  1973年   3篇
  1972年   3篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
详细讨论了卫星遥感技术在长江流域水资源管理方面的应用问题,提出了两种实用的方法:①卫星遥感技术在灌溉水资源管理方面的应用;②长江流域地下水、地表水资源估算。进一步分析了两种方法的特点,介绍了卫星遥感技术的优点及用途,建议在长江流域水资源管理中加以利用。  相似文献   
33.
农业生产地域分工与农产品专业化生产是使农业从自然经济阶段向以市场为导向的商品农产品生产转变的一个标志。本文在分析该区农业布局现状及其存在问题的基础上,提出了农业总体布局的设想与不同类型地域农业开发的主攻方向与对策,并对市场经济体制下粮食、棉花、猪、禽、水产品等农产品生产基地的地域选择、建设规模与技术措施等进行了探讨。  相似文献   
34.
35.
INTRODUCTIONIn recent thirty years, due to the decreasing fertility andincreasing life expectancy, China's population is aging ata very rapid pace and the elderly population size is keepingon growing. During the dramatic aging progress, the oldestold group in China is catching our eyes. More and moreold people of China are becoming the oldest old. Theextremely old population (aged 80 and above) is increasingat 5.1% annually, while the old population above 65 isincreasing at 2.9%, and the…  相似文献   
36.
The coastal water of northeast Taiwan island, called 'Yin-Yang Hai' for its distinct yellow colour compared with blue offshore water, was investigated from 1989 to 1990 by the authors. Biological study showed the dominant species of plankton to be Copepoda, Cladocera, planktonic eggs and Diatoma. Dominant species of benthos were young crabs, Amphipoda and Annelida, with Amphipoda usually occurring in heavily polluted areas. Heavy metal data showed that the concentration of copper was high. the copper and iron concentration in algae of the intertidal zone was also high. the concentrations of iron and copper in inshore water were also higher than in offshore water. By comparison of the pH and salinity distribution of this area, we conclude that this coastal water has been polluted by acid waste water from coastal industry. the suspended solids concentration in sea water is high. Flocculation occurring at the boundary of fresh and saline water might be a reason for the distinct yellow colour of the water of this area. Further study is required.  相似文献   
37.
Adults of the sea urchin Arachnoides placenta (L.) were induced to spawn, and eggs were fertilized at 28°C in September 1989. After 5 min, eggs were transferred to 28, 31, 34, or 37°C and reared to metamorphosis. Embryos were observed at 20-min intervals during the first 2 h; larvae were observed daily. The cleavage was higher at higher temperatures. Embryos reared at 28°C were still at the 4th cleavage (16-cell stage) after 100 min, while those at 34°C had reached the 5th cleavage (32-cell stage). All embryos reared at 37°C died on the second day. Incidence of abnormality was 20 to 30% at 28 and 31°C, 48% at 34°C, and 77% at 37°C. The 8-arm stage was reached after 4 d at 28°C, 3 d at 31°C and 2 d at 34°C. Larvae displayed decreasing body length and arm length with increasing temperature. Larvae at 31°C have relatively long arms, as a result of a decrease in body length, not because of increased arm length. Incidence of metamorphosis was 43.9±1.7% (mean/plusmn;SD) at 28°C, 24.5±1.9% at 31°C, and 5.3% at 34°C. The size of metamorphosed juveniles was significantly larger at 28°C than at 31 and 34°C. Temperatures of 31°C negatively affect larvae and juveniles of the sand dollar.  相似文献   
38.
39.
Environment, Development and Sustainability - In order to reveal the distribution and migration law of downwind and upwind coal cutting, total dust (TD) and respirable dust (RD) concentration...  相似文献   
40.
Environment, Development and Sustainability - This study analyzes the evolution of the land use structure, demographic reconstruction, and social reconstruction of Dachangshan Island, Changhai...  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