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   43714篇
  免费   442篇
  国内免费   350篇
安全科学   1330篇
废物处理   1965篇
环保管理   5464篇
综合类   8972篇
基础理论   10603篇
环境理论   10篇
污染及防治   10602篇
评价与监测   2798篇
社会与环境   2524篇
灾害及防治   238篇
  2022年   377篇
  2021年   404篇
  2020年   248篇
  2019年   330篇
  2018年   622篇
  2017年   633篇
  2016年   963篇
  2015年   713篇
  2014年   1133篇
  2013年   3334篇
  2012年   1320篇
  2011年   1793篇
  2010年   1492篇
  2009年   1590篇
  2008年   1863篇
  2007年   1797篇
  2006年   1623篇
  2005年   1438篇
  2004年   1439篇
  2003年   1369篇
  2002年   1262篇
  2001年   1560篇
  2000年   1093篇
  1999年   704篇
  1998年   518篇
  1997年   532篇
  1996年   538篇
  1995年   630篇
  1994年   563篇
  1993年   516篇
  1992年   547篇
  1991年   533篇
  1990年   515篇
  1989年   496篇
  1988年   431篇
  1987年   389篇
  1986年   396篇
  1985年   394篇
  1984年   423篇
  1983年   400篇
  1982年   412篇
  1981年   385篇
  1980年   305篇
  1979年   330篇
  1978年   288篇
  1977年   249篇
  1974年   246篇
  1973年   284篇
  1972年   257篇
  1967年   274篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
151.
Historical records from Ontario's Provincial Water Quality Monitoring Network (PWQMN) for rivers and streams were analyzed to assess the feasibility of mapping regional water quality patterns in southeastern Ontario which spans two major geologic zones, the Precambrian Shield and the St. Lawrence Lowlands, thus serving as a paradigm for much of Ontario. Despite biases toward the populated Lowlands and associated pollution problems, general spatial trends are evident via the analysis of intervariable relations, individual parameter maps and multivariate analysis. Using a robust algorithm designed to identify outliers and abstract underlying bivariate relations, a linear regional hardness-alkalinity relation was derived, where most anomalies proved to be mine drainage impacted sites. Regionally, multivariate ordination reveals that central tendencies of common indicators of ionic strength and nutrient richness correlate positively and that site clusters broadly reflect the transition from oligotrophic Shield waters to eutrophic conditions of heavily agricultural Lowland streams. Results suggest that on the Shield more precisely delineated aquatic regions may be realized by applying GIS to integrate river and synoptic lake survey data. Further synthesis with bedrock and surficial geology, physiography, pedology and other temporally invariant spatial attributes should yield regional patterns of background quality from which locally attainable water objectives might be defined. Additional synoptic surveys of sedimentary Lowland streams may be required as most available sites relflect anthropogenic pollution.  相似文献   
152.
The relation between mortality of young fish and recruitment is important for assessment of the environmental effects of facilities that kill large numbers of young fish, such as electric power stations and hydropower plants. A simulation model with a bioenergetic growth component was applied to examine the relation between mortality of young and recruitment for walleye (Stizostedion vitreum) with different forms of population regulation, including: food limited growth, food limited growth with size-dependent mortality, and food limited growth with age at maturity dependent on size. With food limited growth small increases in mortality of young reduced recruitment considerably, but the population slowly approached a new equilibrium. If mortality of young increased when growth was food limited, the population approached a new equilibrium of natality and mortality because with fewer individuals there was more food per individual, and individuals were larger in size and produced more eggs; this feedback adjusted natality to equal mortality. With either mortality or age at maturity dependent on size, large increases in mortality of young resulted in only small decreases in recruitment.  相似文献   
153.
Green RH 《Disasters》1986,10(4):288-302
Frustrations and failures will continue to mount if we do not immediately summon the courage to revise the ways we think and take action-as well as maintaining essential services to support life and health … Saving hundreds of thousands … who are at risk of dying from malnutrition or infection is an immediate imperative. But it must be only one stage in the progress toward other activities, and one element in the truly comprehensive approach… The main intent of this paper is to explore aspects of the nature and evolution of poverty in Sub-Saharan Africa with special reference to food and hunger and their interaction with macro-economic policy. An attempt is made to outline the overall context within which food aid needs to be used in order to have a greater developmental impact. Following an Introductory Section I, Section II provides a sketch map of how recession and lagging food production - with cyclical weather crises superimposed - affect the human condition of poor people. Section III reviews die interaction between "standard" IMF stabilization and World Bank structural adjustment strategies and poverty/hunger. Improvements in the design of stabilization and adjustment programmes, and of the inter-relationship with them of emergency programmes, can be identified. A number turn on the broadened and more innovative or catalytic use of food aid. Section IV reviews aspects of facing a continuing series of emergencies and of designing life support programmes to facilitate rehabilitation of the households directly affected as well as of the national economies. From this base it explores a series of elements in achieving renewed development. The concluding Section seeks to explore the strengths, limitations and potentials of food aid in the context set by the previous sections. The standard criticisms of food aid appear to be overstated and/or to relate to particular modalities or approaches rather than to anything intrinsic. A number of criteria for improving the effectiveness of food aid - especially in respect to rehabilitation, recovery and renewed development - are set out.  相似文献   
154.
Taylor AJ 《Disasters》1986,10(1):70-73
This paper was prepared in 1978 on the basis of a review of sociological and anthropological fieldwork conducted up to that time. Although theoretical in presentation its conclusions are formulated in accordance with the author's own extensive observations of organizational response to natural disasters in developing countries, especially those having sudden onset. Practical implications for co-ordination agencies and pre-disaster training are drawn.  相似文献   
155.
Environment, Development and Sustainability - Realisation of the sustainable development goals (SDGs) will provide improvements to people's lives and longevity of the planet. The architectural,...  相似文献   
156.
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   
157.
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   
158.
159.
160.
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