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   2512篇
  免费   236篇
  国内免费   1101篇
安全科学   102篇
废物处理   17篇
环保管理   577篇
综合类   1849篇
基础理论   775篇
环境理论   3篇
污染及防治   127篇
评价与监测   103篇
社会与环境   212篇
灾害及防治   84篇
  2024年   28篇
  2023年   92篇
  2022年   187篇
  2021年   199篇
  2020年   172篇
  2019年   173篇
  2018年   159篇
  2017年   141篇
  2016年   151篇
  2015年   140篇
  2014年   144篇
  2013年   234篇
  2012年   168篇
  2011年   198篇
  2010年   171篇
  2009年   170篇
  2008年   143篇
  2007年   166篇
  2006年   156篇
  2005年   139篇
  2004年   105篇
  2003年   108篇
  2002年   87篇
  2001年   71篇
  2000年   75篇
  1999年   42篇
  1998年   31篇
  1997年   30篇
  1996年   29篇
  1995年   26篇
  1994年   19篇
  1993年   18篇
  1992年   13篇
  1991年   5篇
  1990年   9篇
  1989年   2篇
  1988年   10篇
  1987年   5篇
  1986年   3篇
  1985年   7篇
  1984年   3篇
  1981年   2篇
  1980年   3篇
  1978年   2篇
  1977年   2篇
  1975年   1篇
  1973年   1篇
  1972年   2篇
  1971年   3篇
  1970年   1篇
排序方式: 共有3849条查询结果,搜索用时 15 毫秒
991.
The escalating illegal wildlife trade (IWT) is one of the most high‐profile conservation challenges today. The crisis has attracted over US$350 million in donor and government funding in recent years, primarily directed at increased enforcement. There is growing recognition among practitioners and policy makers of the need to engage rural communities that neighbor or live with wildlife as key partners in tackling IWT. However, a framework to guide such community engagement is lacking. We developed a theory of change (ToC) to guide policy makers, donors, and practitioners in partnering with communities to combat IWT. We identified 4 pathways for community‐level actions: strengthen disincentives for illegal behavior, increase incentives for wildlife stewardship, decrease costs of living with wildlife, and support livelihoods that are not related to wildlife. To succeed the pathways, all require strengthening of enabling conditions, including capacity building, and of governance. Our ToC serves to guide actions to tackle IWT and to inform the evaluation of policies. Moreover, it can be used to foster dialogue among IWT stakeholders, from local communities to governments and international donors, to develop a more effective, holistic, and sustainable community‐based response to the IWT crisis.  相似文献   
992.
对φ(N)32°14′~32°56′,λ(E)104°36′~104°51′范围内400~1400m稻田小气候进行了观测,发现海拔(halt)不同,稻田生态环境相差很大:halt每升高100m,平均气温(θar)递减0.72℃,年降雨量递增63.0mm(400~600m)~106.8mm(800~1400m),相对湿度递增1%,日照时数呈抛物线上升变化.halt400m日均温稳定通过12.0℃的初期为3月中旬,halt每升高100m,该时间延迟5~7d.不同halt>12℃的有效积温分别为3621.2℃(400m)、3245.0℃(600m)、3149.9℃(800m)、2804.8℃(1000m)、2082.1℃(1200m)、1950.1℃(1400m).在相对较高的halt,存在明显的逆温和南北坡效应,相应存在杂交水稻局部高产区.本研究结果为四川不同海拔区杂交水稻品种合理布局和应用高产优质栽培技术提供了基础理论依据  相似文献   
993.
The number and diversity of civil society or third sector sustainability organisations (TSSOs) have increased in recent decades. TSSOs play a prominent role in local approaches to sustainability. However, the contributions made by TSSOs are not fully understood, beyond a limited suite of quantifiable outputs and impacts. In this qualitative study, we examine how four TSSOs from two Australian regions, Tasmania and Queensland's Sunshine Coast, contribute to social transformation beyond discrete outputs. We examine the operation, ethos, scope and influence of these organisations over time. In so doing, we identify three common ways in which these organisations facilitate social change: by (i) enhancing social connectivity through boundary work; (ii) mobilising participatory citizenship and (iii) contributing to social learning. We conclude that TSSOs contribute significantly to the systemic social conditions that enable change for sustainability and the development of community resilience and well-being, but do so in ways undervalued by existing metrics, formal evaluation processes and funding models. Clearer recognition of, and strategic emphasis on, these qualitative contributions to social transformation is vital in ensuring that TSSOs remain viable and effective over the long term.  相似文献   
994.
Abstract: Social, economic, and ecological criteria contribute to the successful design, implementation, and management of marine protected areas (MPAs). In the context of California's Marine Life Protection Act Initiative, we developed a set of methods for collecting, compiling, and analyzing data about the spatial extent and relative economic importance of commercial and recreational fishing. We interviewed 174 commercial fishers who represented the major fisheries in the initiative's north‐central coast region, which extends from Point Arena south to Pigeon Point. These fishers provided data that we used to map the extent of each of the fishing grounds, to weight the relative importance of areas within the grounds, to characterize the operating costs of each fishery, and to analyze the potential economic losses associated with proposed marine protected areas. A regional stakeholder group used the maps and impact analyses in conjunction with other data sets to iteratively identify economic and ecological trade‐offs in designations of different areas as MPAs at regional, port, and fishery extents. Their final proposed MPA network designated 20% of state waters as MPAs. Potential net economic loss ranged from 1.7% to 14.2% in the first round of network design and totaled 6.3% in the final round of design. This process is a case study in the application of spatial analysis to validate and integrate local stakeholder knowledge in marine planning.  相似文献   
995.
Abstract: Ecosystem fragmentation and destruction can lead to restrictive administration policies on traditional harvesting by indigenous peoples from remaining ecosystem tracts. In New Zealand, concerns about endangered species and governmental policies that focus on species and ecosystem preservation have resulted in severely curtailed traditional harvesting rights. Although provision has been made for limited gathering of traditional plants from government‐administered conservation lands, it is unclear how much harvesting is undertaken on these lands and elsewhere and what this harvest might consist of. We interviewed seven expert Maori elders from the Waikato, New Zealand, to identify plant species they currently harvested and from where. We compared these data with the data we collected on permits issued for plant collecting on conservation lands in the same region. We sought to gain information on indigenous plant harvesting to determine the extent of permitted harvesting from conservation lands in the Waikato and to identify issues that might affect plant harvesting and management. Elders identified 58 species they harvest regularly or consider culturally important; over 50% of these species are harvested for medicinal use. Permit data from 1996 to 2006 indicated no apparent relationship between species of reported cultural significance and the number of permits issued for each of these species. Currently, few plant species are harvested from conservation lands, although some unofficial harvesting occurs. Elders instead reported that medicinal plants are frequently collected from urban and other public areas. They reported that plant species used for dyeing, carving, and weaving are difficult to access. Elders also discussed concerns such as spraying of roadsides, which resulted in the death of medicinal species, and use of commercial hybrids in urban planning. Local government may have an increasingly important role in supporting native traditions through urban planning, which takes account of cultural harvesting needs while potentially reducing future harvesting pressure on conservation lands. We suggest that active participation by the Māori community in the development and management of urban harvesting resources will result in positive outcomes.  相似文献   
996.
Abstract: The developing field of community genetics has the potential to broaden the contribution of genetics to conservation biology by demonstrating that genetic variation within foundation plant species can act to structure associated communities of microorganisms, invertebrates, and vertebrates. We assessed the biodiversity consequences of natural patterns of intraspecific genetic variation within the widely distributed Australian forest tree, Eucalyptus globulus. We assessed genetic variation among geographic races of E. globulus (i.e., provenances, seed zones) in the characteristics of tree‐trunk bark in a 17‐year‐old common garden and the associated response of a dependent macroarthropod community. In total, 180 macroarthropod taxa were identified following a collection from 100 trees of five races. We found substantial genetically based variation within E. globulus in the quantity and type of decorticating bark. In the community of organisms associated with this bark, significant variation existed among trees of different races in composition, and there was a two‐fold difference in species richness (7–14 species) and abundance (22–55 individuals) among races. This community variation was tightly linked with genetically based variation in bark, with 60% of variation in community composition driven by bark characteristics. No detectable correlation was found, however, with neutral molecular markers. These community‐level effects of tree genetics are expected to extend to higher trophic levels because of the extensive use of tree trunks as foraging zones by birds and marsupials. Our results demonstrate the potential biodiversity benefits that may be gained through conservation of intraspecific genetic variation within broadly distributed foundation species. The opportunities for enhancing biodiversity values of forestry and restoration plantings are also highlighted because such planted forests are increasingly becoming the dominant forest type in many areas of the world.  相似文献   
997.
Forest management in south eastern Nigeria has changed hands from the forest communities to foreign technology. As a result the sustainable, conservative and cyclical use that characterised the communities that lived in balance with their forest resources are no longer practised. Consequently, a great deal of the region's valuable timber trees has been lost and the environmental influences of the forest grossly reduced. The local communities have not only been deprived of a multitude of non-timber forest resources upon which they depend for their survival and well-being but have also lost their knowledge of traditional forest management. Although these consequences are far-reaching, the neglected majority in the rural areas bear the brunt. To save what is left of the once vast forest areas, communities in and around the biome need to be empowered to manage their forest resources. Empowerment will challenge their responsibility and their ability to function for the common good—themselves, the State and the world at large.  相似文献   
998.
Glyphosate, the most extensively used herbicide globally, has raised ecotoxicological concerns because it can be transported into the aquatic environment and cause adverse effects on the aquatic system. However, the functional mechanism of glyphosate on cyanobacteria are not completely disentangled. In this study, we selected six common cyanobacteria to evaluate glyphosate effects on cyanobacterial growth in monoculture experiment. Results showed that the growth of five tested cyanobacterial species were promoted under different degrees, and only Pseudanabaena was inhibited by glyphosate. In the phylogenetic tree based on gene sequences of 5-enol-pyruvylshikimate-3-phosphate synthase (EPSPS), a target for glyphosate, we found that the position of Pseudanabaena is the closest to plant, which was sensitive to glyphosate, thereby explaining the inhibitory effect of Pseudanabaena following glyphosate exposure. The primary degraded metabolites or analogs did not induce cyanobacterial growth, laterally demonstrating that glyphosate was used as a source of phosphorus to accelerate cyanobacterial growth because phosphorus levels increased in the medium of glyphosate treatment. Overall, this study provides a better understanding of the influence of glyphosate on the composition of aquatic microbiota and explains the mechanism of cyanobacterial response to glyphosate.  相似文献   
999.
Conformity assessment procedures prescribed by European legislation are presented and their concrete implementation is illustrated by the example of personal protective equipment (PPE). The different categories of PPE defined by Council Directive 89/686/EEC are explained with reference to the applicable conformity assessment elements. Quality assurance of production is presented as the central element of the conformity assessment procedure for complex PPE. Special emphasis is put on the necessity of having a regular exchange of views and information among notified bodies in Europe. Ways in which third countries can eventually carry out conformity assessment on the basis of a contract with the European Community Commission are explained.  相似文献   
1000.
三峡工程于2010年10月26日达到三期正常蓄水位,为了研究三期蓄水后初期长江口的生态环境特征,于2011年4月对长江口水域24个站位进行了浮游动物的采集,分析了其种类、丰度、优势种及其与环境的关系.结果表明,调查海域共发现浮游动物97种(含20种浮游幼体),其中,桡足类33种,水母类13种,介形类5种,毛颚类5种,还有一些其它浮游种类.夜光虫和中华哲水蚤是该水域的绝对优势种.根据各站位浮游动物种类组成及其丰度,采用聚类分析法将该水域的浮游动物分为4组群落区域:外海高盐区、冲淡水和外海水混合区、长江口南支附近、长江口北支附近.物种丰度和多样性在空间分布上呈相反的趋势,在长江冲淡水和外海水的混合水域丰度最高,多样性指数最低.物种与环境的CCA(典范对应分析)显示,影响长江口春季浮游动物群落结构的主要环境因子为盐度、营养盐和水温.  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