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   379篇
  免费   22篇
  国内免费   5篇
安全科学   37篇
废物处理   10篇
环保管理   97篇
综合类   44篇
基础理论   117篇
环境理论   2篇
污染及防治   52篇
评价与监测   26篇
社会与环境   16篇
灾害及防治   5篇
  2023年   9篇
  2022年   5篇
  2021年   8篇
  2020年   14篇
  2019年   11篇
  2018年   21篇
  2017年   15篇
  2016年   25篇
  2015年   19篇
  2014年   17篇
  2013年   28篇
  2012年   35篇
  2011年   26篇
  2010年   14篇
  2009年   27篇
  2008年   22篇
  2007年   20篇
  2006年   21篇
  2005年   13篇
  2004年   7篇
  2003年   10篇
  2002年   8篇
  2001年   2篇
  2000年   1篇
  1999年   2篇
  1998年   1篇
  1996年   4篇
  1995年   2篇
  1994年   2篇
  1993年   1篇
  1992年   1篇
  1991年   1篇
  1986年   1篇
  1985年   1篇
  1982年   1篇
  1981年   5篇
  1980年   4篇
  1977年   2篇
排序方式: 共有406条查询结果,搜索用时 0 毫秒
21.
Globally, urban growth will add 1.5 billion people to cities by 2030, making the difficult task of urban water provisions even more challenging. In this article, we develop a conceptual framework of urban water provision as composed of three axes: water availability, water quality, and water delivery. For each axis, we calculate quantitative proxy measures for all cities with more than 50,000 residents, and then briefly discuss the strategies cities are using in response if they are deficient on one of the axes. We show that 523 million people are in cities where water availability may be an issue, 890 million people are in cities where water quality may be an issue, and 1.3 billion people are in cities where water delivery may be an issue. Tapping into groundwater is a widespread response, regardless of the management challenge, with many cities unsustainably using this resource. The strategies used by cities deficient on the water delivery axis are different than for cities deficient on the water quantity or water quality axis, as lack of financial resources pushes cities toward a different and potentially less effective set of strategies.  相似文献   
22.
Remote sensing and geographical information systems are used to analyze landscapes important to species of conservation concern. The accuracy of the methods depends on how closely habitat mapping classes are linked to population demography. Habitat use by Florida Scrub Jays ( Aphelocoma c. coemlescens ) was quantified using circular plots. Habitat variation was mapped using high-resolution aerial photography on a site where all Florida Scrub Jays were color-banded. Nest site selection, nest success, yearling production, and breeder survival were measured within Florida Scrub Jay territories. Habitat use was lowest in areas without scrub oaks or areas within 136 m from forests. Open oak, dominated by scrub oaks and open sandy areas, had the highest use and nest success among habitats. Open oak occurred as narrow patches ( <20 m wide) in landscapes dominated by matrix habitat (palmetto-lyonia and swale marshes). Most wide patches (>50 m) of open oak were potential population sources, where reproduction exceeded mortality. Areas with patches of open oak of less than 1 ha were usually population sinks. Open oak occurred as less flammable patches in a landscape subject to frequent fires. Population sources varied temporally and spatially with fires and site potential to support scrub oaks (soils). Analyses of landscape patterns and dynamics indicated that habitat mapping should not only include patches of currently optimal habitat but should also include landscapes associated with open oak. The influences of landscape patterns on habitat use, reproductive success, survival, and territory size can be quantified at different scales starting with attributes associated with habitat patches, nest sites, and territories. Potential mapping errors occur, however, when habitats are used to quantify the areal extent of sources and sinks and similar population attributes important for species persistence.  相似文献   
23.
PROBLEM: In recent years, there has been a significant reduction in traffic crash injury among young people, but they continue to be overrepresented in the traffic crash statistics. To improve this situation, sound scientific evidence is needed to develop effective policies and programs. METHOD: The aim of the proposed study is to provide this evidence by examining early driving and driving-related experiences of newly licensed drivers as they progress through the learner-, restricted-, and full-license stages of the graduated licensing system and to determine the impact of these experiences on subsequent negative traffic-related outcomes (risky driving behavior, injury traffic crashes, noninjury traffic crashes, infringements, convictions). Given the size and complexity of the proposed study, a comprehensive pilot study was undertaken to determine the feasibility of conducting a New Zealand-wide cohort study of newly licensed drivers. RESULTS: This article describes the pilot study process and the methodology that has been developed for the New Zealand-wide study.  相似文献   
24.

Background

Falls are a common, serious, and often unrecognized problem facing older adults. The objective of this study was to provide an initial clinical and statistical validation for a public health strategy of fall risk self-assessment by older adults using a Fall Risk Questionnaire (FRQ).

Methods

Adults age 65 + (n = 40) were recruited at a Los Angeles Veterans Affairs (VA) medical facility and at a local assisted living facility. Participants completed the FRQ self-assessment and results were compared to a “gold standard” of a clinical evaluation of risks using the American/British Geriatrics Society guidelines to assess independent predictors of falls: history of previous falls, fear of falling, gait/balance, muscle weakness, incontinence, sensation and proprioception, depression, vision, and medications. For the comparison, we used an iterative statistical approach, weighing items based on relative risk.

Results

There was strong agreement between the FRQ and clinical evaluation (kappa = .875, p < .0001). Individual item kappa values ranged from .305-.832. After dropping one FRQ item (vision risk) because of inadequate agreement with the clinical evaluation (kappa = .139, p = .321), the final FRQ had good concurrent validity.

Conclusions

The FRQ goes beyond existing screening tools in that it is based on both evidence and clinical acceptability and has been initially validated with clinical examination data. A larger validation with longitudinal follow-up should determine the actual strength of the FRQ in predicting future falls.  相似文献   
25.
Recent “green” planning initiatives envision food production, including urban agriculture and livestock production, as desirable elements of sustainable cities. We use an integrated urban political ecology and human–plant geographies framework to explore how foraging for “wild” foods in cities, a subversive practice that challenges prevailing views about the roles of humans in urban green spaces, has potential to also support sustainability goals. Drawing on research from Baltimore, New York City, Philadelphia, and Seattle, we show that foraging is a vibrant and ongoing practice among diverse urban residents in the USA. At the same time, as reflected in regulations, planning practices, and attitudes of conservation practitioners, it is conceptualised as out of place in urban landscapes and an activity to be discouraged. We discuss how paying attention to urban foraging spaces and practices can strengthen green space planning and summarise opportunities for and challenges associated with including foragers and their concerns.  相似文献   
26.
Managers of the nearly 0.5 million ha of public lands in North and South Dakota, USA rely heavily on manual measurements of canopy height in autumn to ensure conservation of grassland structure for wildlife and forage for livestock. However, more comprehensive assessment of vegetation structure could be achieved for mixed-grass prairie by integrating field survey, topographic position (summit, mid and toeslope) and spectral reflectance data. Thus, we examined the variation of mixed-grass prairie structural attributes (canopy leaf area, standing crop mass, canopy height, nitrogen, and water content) and spectral vegetation indices (VIs) with variation in topographic position at the Grand River National Grassland (GRNG), South Dakota. We conducted the study on a 36,000-ha herbaceous area within the GRNG, where randomly selected plots (1?km2 in size) were geolocated and included summit, mid and toeslope positions. We tested for effects of topographic position on measured vegetation attributes and VIs calculated from Landsat TM and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data collected in July 2010. Leaf area, standing crop mass, canopy height, nitrogen, and water content were lower at summits than at toeslopes. The simple ratio of Landsat Band 7/Band 1 (SR71) was the VI most highly correlated with canopy standing crop and height at plot and landscape scales. Results suggest field and remote sensing-based grassland assessment techniques could more comprehensively target low structure areas at minimal expense by layering modeled imagery over a landscape stratified into topographic position groups.  相似文献   
27.
A framework for analyzing climate change adaptations as actions   总被引:1,自引:0,他引:1  
Developing generalized theories about adaptation to climate change requires common concepts to map different adaptation situations. The paper aims to contribute to this endeavor by presenting a novel framework that conceptualizes adaptations to climate change as actions. The framework is intended to systematically analyze the actor relations involved in adaptations and the barriers to their implementation. By combining established scientific action theories with terminology from the Intergovernmental Panel on Climate Change (IPCC) in an innovative way, it can be used to clarify the notion of adaptation used in adaptation assessments. The framework’s potential is illustrated by a case study on cooling water management in the river Rhine catchment and by the elucidation of some prominent concepts in adaptation research. We show that by framing adaptations as actions, the purpose of adaptations and how they tend to connect up in means-ends-chains becomes crucial. Actors can take different functional roles as exposure unit, operator and receptor of adaptation. A mismatch of these roles can lead to barriers to adaptation, of which we deduce four types: complex actor relations, missing operators, missing means and unemployed means. The case study yields a complex bundle of adaptations, and shows that the potential barriers involved are quite diverse. There is thus no blueprint solution. Although we identify entry points for adaptation, the analysis leads to a skeptical conclusion for adapting cooling water management in the whole Rhine catchment.  相似文献   
28.
Coalitionary aggression occurs when at least two individuals jointly direct aggression at one or more conspecific targets. Scientists have long argued that this common form of cooperation has positive fitness consequences. Nevertheless, despite evidence that social bond strength (which is thought to promote coalition formation) is correlated with fitness in primates, cetaceans, and ungulates, few studies have directly examined whether coalitionary aggression improves reproductive success. We tested the hypothesis that among free-ranging chimpanzees (Pan troglodytes schweinfurthii), participation in coalitionary aggression increases reproductive output. Using 14 years of genetic and behavioral data from Gombe National Park, Tanzania, we found that coalitionary aggression increased a male’s chances of (A) siring offspring, compared to other males of similar dominance rank, and (B) ascending in rank, a correlate of future reproductive output. Because male chimpanzees form coalitions with many others within a complex network, we used social network analysis to identify the types of connections correlated with these fitness benefits. The beneficiaries of coalitionary aggression were males with the highest “betweenness”—that is, those who tended to have coalition partners who themselves did not form coalitions with each other. This suggests that beyond simply recognizing third-party relationships, chimpanzees may use this knowledge to choose coalition partners. If so, this is a significant step forward in our knowledge of the adaptive value of social intelligence. Regardless of mechanism, however, this is the first evidence of genetic benefits of coalitionary aggression in this species, and therefore has important implications for understanding the evolution of cooperation.  相似文献   
29.
Rebecca Pearse 《环境政策》2016,25(6):1079-1101
Reporting on the origins and directions of social movement strategy on climate and energy issues in the last decade, the shifts in ‘climate movement’ practice are discussed using a neo-Polanyian account of the political economy of climate change combined with sociological analysis of the strategic decisions campaigners reported making. Since the mid-2000s, Australia’s climate movement has been engaged in three concurrent arenas of political contestation. The longest-standing arena of movement activity has been negotiations over climate policy. More recently, activists and communities are engaged in a struggle over the expansion of fossil fuels. A third contest has been waged over the present and future position of renewable energy technologies in Australia’s electricity market. In the wake of climate policy failure, energy campaigns have been deepened, and it seems that a broader energy justice agenda is being forged. New strategic dilemmas are visible in the field.  相似文献   
30.
Pair-bonded males often make substantial contributions to the care of their offspring. Male parental behavior may be affected by a range of factors, including previous experience (parental or alloparental), genetic influences, and contributions by the female partner. Previous studies have shown that a microsatellite polymorphism in the regulatory region of the avpr1a gene influences aspects of paternal behavior in male prairie voles (Microtus ochrogaster). Specifically, males with longer avpr1a microsatellites groomed offspring more than did males with shorter avpr1a microsatellites. Previous experience with alloparental care also appears to influence subsequent paternal care in prairie voles. We investigated the influence of avpr1a microsatellite length and previous parental experience on paternal behavior in prairie voles two generations from the field and specially bred to exaggerate differences in avpr1a microsatellite length. We found that avpr1a microsatellite length alone did not affect any of the paternal behaviors that we measured. In contrast, males differed in parental behavior between first and second litters. Regardless of avpr1a microsatellite length, males licked/groomed the second litter less, and retrieved pups more quickly during the second compared to the first litter. Our results show that previous paternal experience may play a more important role than the length of the microsatellite in the regulatory region of the avpr1a gene in influencing paternal care.  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