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   31166篇
  免费   327篇
  国内免费   284篇
安全科学   908篇
废物处理   1227篇
环保管理   4381篇
综合类   4563篇
基础理论   8419篇
环境理论   8篇
污染及防治   8559篇
评价与监测   1946篇
社会与环境   1553篇
灾害及防治   213篇
  2022年   221篇
  2021年   263篇
  2020年   191篇
  2019年   273篇
  2018年   422篇
  2017年   429篇
  2016年   689篇
  2015年   528篇
  2014年   795篇
  2013年   2596篇
  2012年   945篇
  2011年   1288篇
  2010年   1033篇
  2009年   1120篇
  2008年   1355篇
  2007年   1425篇
  2006年   1290篇
  2005年   1027篇
  2004年   1100篇
  2003年   1009篇
  2002年   977篇
  2001年   1270篇
  2000年   904篇
  1999年   530篇
  1998年   437篇
  1997年   391篇
  1996年   441篇
  1995年   476篇
  1994年   464篇
  1993年   409篇
  1992年   406篇
  1991年   365篇
  1990年   411篇
  1989年   397篇
  1988年   341篇
  1987年   307篇
  1986年   280篇
  1985年   282篇
  1984年   329篇
  1983年   328篇
  1982年   323篇
  1981年   309篇
  1980年   250篇
  1979年   275篇
  1978年   221篇
  1977年   201篇
  1975年   189篇
  1974年   166篇
  1973年   187篇
  1972年   219篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
As a consequence of decreases in the emission rate of sulphur in eastern North America in the late 1970s and early 1980s, sulphate deposition in central Ontario declined by about 40%, but has remained constant for about six years. Plastic Lake, a small, dilute lake on the Precambrian shield that the authors have studied since 1979, acidified between the start of the study and about 1986, but since then has not changed. The authors also monitored the chemistry of streamwater draining the Plastic Lake catchment. Water quality of runoff from an upland site improved rapidly (pH and alkalinity increased, SO4(2-) and Al decreased), but two factors offset these improvements. A small wetland area downstream reversed most of these changes, resulting in a constant output of strong acid from the catchment. In addition, in extremely dry years (1983, 1987, 1989) there were very high concentrations of SO4(2-) in the streamwater, suggesting substantial re-oxidation of reduced S in the catchment.  相似文献   
112.
Benson C  Clay EJ 《Disasters》1986,10(4):303-316
This paper documents the rapid expansion and changes in food aid flows to Sub-Saharan Africa up to mid-1985. Trends for Sub-Saharan Africa as a whole and for the more seriously affected countries are examined, as are the comparative experiences of food aid of individual countries in the region. Table 11 lists the Sub-Saharan African countries and indicates the most seriously affected food-short countries, as defined by the WFP/FAO task force. It should be borne in mind that some practical problems exist in compiling data on food aid. These include lack of availability of reliable data, especially of most recent data; lack of common terminology and definitions; and different accounting systems. These data problems are sometimes a source of confusion. However, the basic facts are clear: food aid gradually emerged during the early 1980s as a resource too often of considerable significance to many countries of Sub-Saharan Africa. These trends were only accelerated with the crisis of 1984-1985. These facts provide a point of reference for further analysis of the sources of the crisis, its actual dimensions and consequences.  相似文献   
113.
Death and injury in earthquakes   总被引:1,自引:0,他引:1  
Alexander D 《Disasters》1985,9(1):57-60
The assumption that the ratio of mortality to morbidity will approximate 1:3 in earthquake disasters is investigated. When it occurs, a 1:3 ratio is most likely to coincide with a Richter magnitude in the range 6.5–7.4, but many other ratios of death to injuries may instead be probable. For each individual disaster the pattern of casualties is likely to be very heterogeneous, but it would be easier to discover regularities if a more standardized definition of 'injury' could be found.  相似文献   
114.
Environment, Development and Sustainability - Environmental deterioration and global warming has created a substantial impact on international companies to incorporate eco-friendly, green supply...  相似文献   
115.
Russian Journal of Ecology - Populations at the border of ranges are considered more vulnerable than those in the center. However, some recent reviews contradict this hypothesis. We have studied...  相似文献   
116.
Russian Journal of Ecology - Abstract—We tested a hypothesis about the different abilities of alien and native plants to form arbuscular mycorrhizae. The studies were carried out in the...  相似文献   
117.
Rate-temperature responses in scyphozoan medusae and polyps   总被引:1,自引:0,他引:1  
The effects of temperature on oxygen consumption and spontaneous rhythmic activity have been investigated in various stages of the life histories of 3 species of jellyfish from the Chesapeake Bay, USA. All 3 species clearly show the ability to acclimate positively to temperature change. Thermal sensitivity of metabolism in the winter medusa Cyanea capillata fulva is fairly low at temperature intervals which are experienced in nature. Polyps of the two summer medusae, Chrysaora quinquecirrha and Aurelia aurita, show reduced metabolic sensitivity at temperatures normally accompanying high developmental activity and the onset of strobilation.  相似文献   
118.
119.
120.
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