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   38605篇
  免费   349篇
  国内免费   176篇
安全科学   1083篇
废物处理   1371篇
环保管理   5441篇
综合类   6542篇
基础理论   10797篇
环境理论   27篇
污染及防治   9662篇
评价与监测   2259篇
社会与环境   1689篇
灾害及防治   259篇
  2022年   265篇
  2021年   286篇
  2020年   266篇
  2019年   347篇
  2018年   515篇
  2017年   489篇
  2016年   732篇
  2015年   650篇
  2014年   882篇
  2013年   2821篇
  2012年   1097篇
  2011年   1622篇
  2010年   1318篇
  2009年   1381篇
  2008年   1622篇
  2007年   1689篇
  2006年   1487篇
  2005年   1304篇
  2004年   1244篇
  2003年   1194篇
  2002年   1159篇
  2001年   1558篇
  2000年   1096篇
  1999年   703篇
  1998年   525篇
  1997年   551篇
  1996年   566篇
  1995年   626篇
  1994年   569篇
  1993年   512篇
  1992年   520篇
  1991年   496篇
  1990年   493篇
  1989年   508篇
  1988年   433篇
  1987年   379篇
  1986年   361篇
  1985年   372篇
  1984年   372篇
  1983年   400篇
  1982年   404篇
  1981年   351篇
  1980年   313篇
  1979年   352篇
  1978年   284篇
  1977年   248篇
  1976年   240篇
  1975年   247篇
  1973年   216篇
  1972年   238篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
771.
A fetus with multiple structural defects was seen at prenatal ultrasound examination. After termination of the pregnancy a bilateral cleft lip, alveolus, and palate; micrognathia; and webbed joints were seen. Fetal tissues showed indications of infection, intranuclear inclusion bodies, chronic stress, haemolysis, arterial wall damage, and profuse haemorrhage. Parvovirus B19 DNA was detected in fetal tissues by dot hybridization after polymerase chain reaction. The possibility of parvovirus B19 infection leading to congenital malformations is discussed.  相似文献   
772.
773.
774.
775.
776.
    
Many species that inhabit seasonally ponded wetlands also rely on surrounding upland habitats and nearby aquatic ecosystems for resources to support life stages and to maintain viable populations. Understanding biological connectivity among these habitats is critical to ensure that landscapes are protected at appropriate scales to conserve species and ecosystem function. Biological connectivity occurs across a range of spatial and temporal scales. For example, at annual time scales many organisms move between seasonal wetlands and adjacent terrestrial habitats as they undergo life‐stage transitions; at generational time scales, individuals may disperse among nearby wetlands; and at multigenerational scales, there can be gene flow across large portions of a species’ range. The scale of biological connectivity may also vary among species. Larger bodied or more vagile species can connect a matrix of seasonally ponded wetlands, streams, lakes, and surrounding terrestrial habitats on a seasonal or annual basis. Measuring biological connectivity at different spatial and temporal scales remains a challenge. Here we review environmental and biological factors that drive biological connectivity, discuss implications of biological connectivity for animal populations and ecosystem processes, and provide examples illustrating the range of spatial and temporal scales across which biological connectivity occurs in seasonal wetlands.  相似文献   
777.
778.
779.
The climate change problem calls for a continuously responding society. This raises the question: Do our institutions allow and encourage society to continuously adapt to climate change? This paper uses the Adaptive Capacity Wheel (ACW) to assess the adaptive capacity of formal and informal institutions in four sectors in the Netherlands: spatial planning, water, agriculture and nature. Formal institutions are examined through an assessment of 11 key policy documents and informal institutions are analysed through four case studies covering each sector. Based on these ACW analyses, both sector-specific and more general strengths and weaknesses of the adaptive capacity of institutions in the Netherlands are identified. The paper concludes that the most important challenge for increasing institutional adaptive capacity lies in combining decentralized, participatory approaches with more top-down methods that generate leadership (visions, goals) standards, instruments, resources and monitoring.  相似文献   
780.
Lake Victoria is a crucial ecosystem for over 25 million people in Kenya, Uganda, Tanzania, Rwanda and Burundi who live in the basin, and for the greater Nile river system downstream of the lake. Ecosystem management in the Lake Victoria basin has been highly extractive for most of the last 60 years, with the 1990s a period of marked decline in food production, economic contraction, rising poverty, increased burden of human disease, and more frequent floods. Lake Victoria itself is becoming eutrophic, with related problems of species extinctions and invasive species. There is evidence of poverty–environment traps: some households and areas appear to be caught in vicious cycles of low income, low investment in soil management, declines in soil fertility, and soil loss, while other households and areas are able to achieve higher incomes and investments, maintain soil fertility, and conserve soil on their farms.Concepts and approaches from the Millenium Ecosystem Assessment (MA) were applied in a study of ecosystem service tradeoffs, synergies and traps in two of the river basins that flow into Lake Victoria from Kenya (Yala and Nyando). Hydrologic units are the main geographic unit used in the analysis, with predictions of sediment yield serving as the main measure of regulating services. Provisioning services are evaluated through a spatially disaggregated analysis of agricultural production, yield and area that combines spatial data from aerial photographs with division-level price and yield estimates.The results illustrate considerable year-to-year variation in land use, agricultural production and sediment yield in the two basins. While overall production appears to be relatively stable at the basin level, there have been shifts in the geographic locus of production toward the upper parts of both basins. A spatial overlay of production and sediment yield indicates that different parts of the basins exhibit tradeoffs, synergies and traps. Results from this study have multiple uses in rural planning, agricultural investment, and watershed management. The results also suggest that the poverty traps conceptual framework may help to enrich the interpretative content of the MA approach.  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