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   5422篇
  免费   408篇
  国内免费   1939篇
安全科学   181篇
废物处理   202篇
环保管理   763篇
综合类   3597篇
基础理论   2027篇
环境理论   2篇
污染及防治   387篇
评价与监测   286篇
社会与环境   181篇
灾害及防治   143篇
  2023年   15篇
  2022年   69篇
  2021年   56篇
  2020年   43篇
  2019年   42篇
  2018年   49篇
  2017年   60篇
  2016年   39篇
  2015年   64篇
  2014年   104篇
  2013年   313篇
  2012年   271篇
  2011年   130篇
  2010年   137篇
  2009年   144篇
  2008年   119篇
  2007年   295篇
  2006年   301篇
  2005年   241篇
  2004年   182篇
  2003年   217篇
  2002年   275篇
  2001年   292篇
  2000年   436篇
  1999年   511篇
  1998年   395篇
  1997年   400篇
  1996年   487篇
  1995年   399篇
  1994年   355篇
  1993年   253篇
  1992年   175篇
  1991年   210篇
  1990年   133篇
  1989年   95篇
  1988年   64篇
  1987年   65篇
  1986年   33篇
  1985年   34篇
  1984年   73篇
  1983年   52篇
  1982年   26篇
  1981年   5篇
  1980年   9篇
  1979年   6篇
  1978年   4篇
  1977年   7篇
  1976年   27篇
  1975年   33篇
  1974年   11篇
排序方式: 共有7769条查询结果,搜索用时 437 毫秒
641.
The objective of this study was to investigate the impact of tourism activities on olive tree cultivation and the human population of the island of Lesbos. The presence or absence of tourism is related with the maintenance or abandonment of olive tree cultivation and population changes for each community. A spatial segregation of the island is evident, related to tourist development, olive tree cultivation, and population change. The results of the study demonstrate that in communities where tourism plays an important role olive tree cultivation is preserved and the population is stable. The preservation of the agro-ecosystem is assured while the olive groves remain productive. Simultaneously, the landscape, which provides specific attractions for tourism, is not altered.  相似文献   
642.
报道了锦蛇属团花锦蛇(E.davidi)、绿锦蛇(E.prvsina)和三索锦蛇(E.radiata)3个种的核型和Ag-NORs,团花锦蛇的型2n=36(8V+6sV+2I+20M),绿锦蛇的核型2n=36(7V+7sV+2I+20m),三索锦蛇的核型2n=40(6V+3sV+2sI+5I+24m);①团花锦蛇和绿锦蛇的染色体数目和结构与此属大多数咱的相似,;②此种为雄性,未见染色体异型。③Ag  相似文献   
643.
The results of a study on morphophysiological variation in fish inhabiting a subarctic lake exposed to chronic industrial pollution are described using an example of cisco, Coregonus lavaretus. It is shown that indices of the heart, liver, kidneys, gills, and fatness in these fish are increased significantly and have retained increased values for the past 20 years. The observed changes are analyzed on the basis of biochemical data. The results of studies on the dynamics of hematological parameters in fish are used for characterizing the development of toxicosis. Adaptive rearrangements associated with an increase in the metabolic rate and the activation of protective systems in the fish are explained in the context of S.S. Schvarts' concept. The idea is proposed that the additional energy cost of detoxification may be responsible for morphophysiological variation in fish under conditions of water pollution.  相似文献   
644.
White P  Cliffe L 《Disasters》2000,24(4):314-342
There is an ongoing debate over the value and pitfalls of the policy and practice of 'linking relief and development' or 'developmental relief' in aid responses to complex political emergencies (CPEs). Driven by concerns about relief creating dependence, sometimes doing harm and failing to address root causes of emergencies despite its high cost, pursuit of both relief and development has become a dominant paradigm among international aid agencies in CPEs as in 'natural' disasters. In CPEs a third objective of 'peace-building' has emerged, along with the logic that development can itself help prevent or resolve conflict and sustain peace. However, this broadening of relief objectives in ongoing CPEs has recently been criticised on a number of counts, central concerns being that it leads to a dilution of commitment to core humanitarian principles and is overly optimistic. This paper addresses these issues in the light of two of the CPEs studied by the COPE project: Eritrea and Somalia/Somaliland. It is argued that the debate has so far suffered from lack of clarity about what we mean by 'relief', 'development' and, for that matter, 'rehabilitation' and 'peace-building'. The wide spectrum of possible aid outcomes does not divide neatly into these categories. The relief-development divide is not always as clear-cut, technically or politically, as the critics claim. Moreover such distinctions, constructed from the point of view of aid programmers, are often of little relevance to the concerns of intended beneficiaries. Second, there has been insufficient attention to context: rather than attempting to generalise within and across CPE cases, a more productive approach would be to examine more closely the conditions under which forms of aid other than basic life support can fruitfully be pursued. This leads to consideration of collective agency capacity to respond effectively to diverse needs in different and changing circumstances.  相似文献   
645.
Cliffe L  Luckham R 《Disasters》2000,24(4):291-313
It is now part of received wisdom that humanitarian assistance in conflict and post-conflict situations may be ineffective or even counterproductive in the absence of an informed understanding of the broader political context in which so-called 'complex political emergencies' (CPEs) occur. Though recognising that specific cases have to be understood in their own terms, this article offers a framework for incorporating political analysis in policy design. It is based on a programme of research on a number of countries in Africa and Asia over the last four years. It argues that the starting-point should be an analysis of crises of authority within contemporary nation-states which convert conflict (a feature of all political systems) into violent conflict; of how such conflict may in turn generate more problems for, or even destroy, the state; of the deep-rooted political, institutional and developmental legacies of political violence; and of the difficulties that complicate the restoration of legitimate and effective systems of governance after the 'termination' of conflict. It then lists a series of questions which such an analysis would need to ask--less in order to provide a comprehensive check-list than to uncover underlying political processes and links. It is hoped these may be used not only to understand the political dynamics of emergencies, but also to identify what kinds of policy action should and should not be given priority by practitioners.  相似文献   
646.
Rashid SF 《Disasters》2000,24(3):240-253
Bangladesh experienced one of the worst floods in recorded history in 1998. This paper focuses on the needs and coping strategies of the urban poor in Dhaka City, which had been very badly affected. The city's roads were completely under water, and most areas were water-logged with drainage and sewage systems blocked. Rising water levels compelled many slum dwellers to move to temporary shelters and relief camps. Women and children were the worst affected. The lack of sanitation facilities and privacy forced women and children to defecate in their own homes. There was an acute scarcity of safe drinking-water, and food prices rose dramatically. Diarrhoea, fever and colds were the most common illnesses affecting the poor. The floods left many of them unemployed, and in some families, the result was increased tension and incidents of domestic violence. In some areas, members felt pressured to repay micro-credit loans. Most NGOs, however, suspended loan repayments. During this period, a committee was set up to co-ordinate and work towards addressing some of the main post-flood problems.  相似文献   
647.
氯离子选择性电极法测定钻井废水氯离子含量   总被引:1,自引:0,他引:1  
利用氯离子选择性电极测定钻井废水中的氯离子含量,分别用两种方法对钻井废水进行了预处理,氯离子在0-250mg/L的范围内线形关系良好,相关系数为0.9968,并且重现性和选择性良好、精密度与准确度较理想。  相似文献   
648.
649.
If the objective of the United Nations Framework Convention on Climate Change (UNFCCC) is to be achieved, Parties must commit themselves to meeting meaningful long‐term targets that, based on current knowledge, would minimize the possibility of irreversible climate change. Current indications are that a global mean temperature rise in excess of 2–3 °C would enhance the risk of destabilizing the climate system as we know it, and possibly lead to catastrophic change such as a shutdown of the deep ocean circulation, and the disintegration of the West Arctic Ice Sheet. Observations have shown that for many small island developing States (SIDS), life‐sustaining ecosystems such as coral reefs, already living near the limit of thermal tolerance, are highly climate‐sensitive, and can suffer severe damage from exposure to sea temperatures as low as 1 °C above the seasonal maximum. Other natural systems (e.g., mangroves) are similarly susceptible to relatively low temperature increases, coupled with small increments of sea level rise. Economic and social sectors, including agriculture and human health, face similar challenges from the likely impacts of projected climate change. In light of known thresholds, this paper presents the view that SIDS should seek support for a temperature cap not exceeding 1.5–2.0 °C above the pre‐industrial mean. It is argued that a less stringent post‐Kyoto target would frustrate achievement of the UNFCCC objective. The view is expressed that all countries which emit significant amounts of greenhouse gases should commit to binding reduction targets in the second commitment period, but that targets for developing countries should be less stringent than those agreed for developed countries. Such an arrangement would be faithful to the principles of equity and would ensure that the right of Parties to attain developed country status would not be abrogated.  相似文献   
650.
在系统安全理论中,确定各基本事件的可靠度以实现所给定的系统安全目标值问题一直没有得到很好解决。笔者将可靠性分配理论与故障树分析方法相结合,提出了2个层次可靠度分配法:最小割集之间采取可靠度再分配法,对构成最小割集的各个基本事件之间采取等分配法。从而建立系统中各单元可靠度再分配量化模型。为便于应用,通过实例,详述系统各单元可靠性分配的计算过程。研究表明,运用该模型可准确、简便地计算出各单元的可靠度,使系统在给定的目标值条件下达到系统的安全性优化。  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