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   1343篇
  免费   29篇
  国内免费   9篇
安全科学   59篇
废物处理   48篇
环保管理   338篇
综合类   140篇
基础理论   416篇
污染及防治   202篇
评价与监测   110篇
社会与环境   53篇
灾害及防治   15篇
  2023年   6篇
  2022年   14篇
  2021年   23篇
  2020年   16篇
  2019年   19篇
  2018年   25篇
  2017年   28篇
  2016年   49篇
  2015年   33篇
  2014年   29篇
  2013年   80篇
  2012年   76篇
  2011年   76篇
  2010年   56篇
  2009年   46篇
  2008年   67篇
  2007年   71篇
  2006年   77篇
  2005年   55篇
  2004年   49篇
  2003年   58篇
  2002年   39篇
  2001年   22篇
  2000年   29篇
  1999年   21篇
  1998年   25篇
  1997年   24篇
  1996年   23篇
  1995年   18篇
  1994年   14篇
  1993年   17篇
  1992年   16篇
  1991年   10篇
  1990年   14篇
  1989年   11篇
  1988年   11篇
  1987年   9篇
  1986年   13篇
  1985年   9篇
  1984年   15篇
  1983年   11篇
  1982年   12篇
  1981年   16篇
  1980年   6篇
  1979年   13篇
  1978年   7篇
  1977年   8篇
  1976年   4篇
  1975年   4篇
  1974年   2篇
排序方式: 共有1381条查询结果,搜索用时 0 毫秒
981.
Investments in agricultural technologies, capacity building and policy harmonization are needed to support sustainable development across Africa. Regional development projects can facilitate the adoption of agricultural technologies and innovations across nation-state borders and generate benefits for shared prosperity. This paper uses panel data from 1,160 smallholder households including beneficiaries and non-beneficiaries from five countries in East Africa - Burundi, Kenya, Rwanda, Tanzania, and Uganda. From a pool of over 90 projects implemented over a span of 15 years, 23 regional projects are included in this study. The major economic benefits to smallholder participants are higher crop productivity and income, access to adaptable technologies, access to markets, higher livestock and milk production, gender equality, enhanced food security, resilience and capacity building for uptake and scaling up of future innovation platforms. For example, the adoption of low-cost tissue culture banana by the beneficiaries increased their incomes by 15% in Rwanda while the adoption of appropriate land and water management technologies increased the potato yields from 2.8 tons (USD 2,840/ha) to over 7.5 tons (USD 7,410/ha) in Kenya. The beneficiaries ensured value added to commodities like bananas (for export) and orange-fleshed sweet potatoes (a nutrition-sensitive intervention for enhancing domestic intake of vitamin A) in Burundi, Kenya, Rwanda and Uganda. Additionally, milk production increased from 6 to 11 L per cow per day in Uganda and from 6 to 8 L per cow per day in Tanzania, with increases in sales generating USD 115 per cow per month above the non-beneficiaries. These results are supported by previous studies on technology adoption, investments in agriculture and well-being outcomes. Our findings with the higher farm income Difference-in-Differences (DiD) estimator for the female beneficiaries compared to male beneficiaries might have important implications for investing in regional development projects that will close the gender gap in agricultural productivity in Africa. Regional projects can also support post-conflict development efforts for food security and peace in fragile contexts such as in Burundi. Our findings might serve as an input to the African Union's Comprehensive Africa Agriculture Development Programme, localization of the United Nations Sustainable Development Goals related to food security and agriculture in Africa and an input to monitoring, evaluation and learning.  相似文献   
982.
Entrances to many caves occupied by the endangered Indiana bat ( Myotis sodalis ) have been modified to control human access. We show that modifying cave entrances can degrade the bats' winter habitat, we demonstrate one mechanism by which this damage occurs, and we document a restoration experiment. We compared a large bar population in an unmodified cave with a small, reduced bat population in a cave with warm winter temperatures resulting from an entrance wall that impeded air exchange. In the modified cave, mean winter temperature at the hibernation site was 5.0° C higher than in the unmodified cave, bats entered hibernation at a 5% higher body mass, bats lost 42% more mass and the frequency distribution of late-winter mass was truncated, with no bats weighing less than 5.4 g. The results describe unacceptable extremes for hibernation: subfreezing temperatures and warm temperatures causing mass-loss rates of more than 0.009 g/day. Over a decade following removal of the entrance-constricting wall, the population increased from 2,000 to 13,000 bats. Previous recommendations, based on common-sense observation, to open blocked cave entrances are confirmed by this study. The similar case of Coach Cave, Kentucky, offers the potential for recovery of 100,000 Indiana bats.  相似文献   
983.
Integrated Environmental Management: Moving from Theory to Practice   总被引:1,自引:0,他引:1  
Integrated environmental management (IEM) and related concepts promoting holistic approaches to environmental management have been evolving rapidly over the past few decades. Although considerable research has examined the substantive dimensions of these concepts, practitioners have forged ahead applying IEM without a clear operational model. The authors link elements of ecosystem management and related fields with interaction to offer a new operational definition and practice paradigm. Interaction among stakeholders and with the public generally is the key operational component for IEM. Focusing on stakeholder interactions, the authors analyse the principle communication and conflict resolution tools employed in integrated approaches. Two illustrative cases from the state of Wisconsin demonstrate the application of interaction techniques and tools in pursuing integrated environmental management.  相似文献   
984.
985.
986.
987.
988.
Two species of pulmonate snails,Lymnaea cat-ascopium andPhysa integra, were collected from Douglas and Houghton Lakes. Snail populations from the former lake (pristine) had never been exposed to copper sulfate, whereas those from the latter one (treated) had been subjected to the molluscicide for more than 40 years. Molluscs from the treated lake were more resistant to the copper at concentrations of 0.5 and 1.0 ppm than those from the pristine lake. Furthermore, larger lymnaeids had a higher survival rate than smaller ones.  相似文献   
989.
990.
A study of historical storm-induced changes along the south shore barriers of Long Island (Fire Island Inlet to Southampton), New York, USA, was undertaken in an effort to determine the relative roles of different transport processes in barrier migration. Inlets were found to have a profound effect on the barrier system, largely controlling its landward migration, based upon maps, charts, and aerial photographs from the seventeenth century to the present. Salt marshes became established principally on the broad intertidal bay shoals left by a closed or slowly migrating inlet. Inlets along this microtidal coast are now stabilized by jetties, which may have a negative effect on long-term barrier-island migration.  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