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   29419篇
  免费   4944篇
  国内免费   30417篇
安全科学   2355篇
废物处理   1492篇
环保管理   2375篇
综合类   38188篇
基础理论   5221篇
环境理论   2篇
污染及防治   11101篇
评价与监测   2107篇
社会与环境   832篇
灾害及防治   1107篇
  2024年   21篇
  2023年   334篇
  2022年   988篇
  2021年   818篇
  2020年   1214篇
  2019年   2450篇
  2018年   2703篇
  2017年   2887篇
  2016年   2847篇
  2015年   3339篇
  2014年   3888篇
  2013年   4660篇
  2012年   4067篇
  2011年   3822篇
  2010年   3231篇
  2009年   3256篇
  2008年   3105篇
  2007年   2915篇
  2006年   2463篇
  2005年   1833篇
  2004年   1498篇
  2003年   1368篇
  2002年   1201篇
  2001年   1111篇
  2000年   1273篇
  1999年   1210篇
  1998年   928篇
  1997年   849篇
  1996年   841篇
  1995年   732篇
  1994年   523篇
  1993年   430篇
  1992年   459篇
  1991年   361篇
  1990年   274篇
  1989年   231篇
  1988年   173篇
  1987年   92篇
  1986年   84篇
  1985年   60篇
  1984年   60篇
  1983年   46篇
  1982年   50篇
  1981年   39篇
  1979年   5篇
  1978年   7篇
  1975年   4篇
  1974年   4篇
  1972年   8篇
  1971年   6篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
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   
33.
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   
34.
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   
35.
36.
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   
37.
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   
38.
Jiao  Youzhou  Xue  Huizan  He  Chao  Wang  Zigang  Ma  Xiaoran  Liu  Xinxin  Liu  Liang  Chang  Chun  Petracchini  Francesco  Li  Panpan 《Environment, Development and Sustainability》2022,24(4):4709-4726
Environment, Development and Sustainability - Anaerobic digestion (AD) is an attractive straw resource treatment technology as it can improve the utilization efficiency of straw resource. Raw straw...  相似文献   
39.
Environment, Development and Sustainability - Sustainability assessing on agricultural production systems has developed rapidly over the last two decades, and various models are formulated from...  相似文献   
40.
Yao Huifang  Duo  Zhang  Jie  Lu  Chao  Wang  Deshui  Yu 《Russian Journal of Ecology》2022,53(4):308-317
Russian Journal of Ecology - The aim of this study is to explore the effects of the litter cover thickness and cleaning methods on seed germination and seedling growth of Pinus densata. The overall...  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