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   1530篇
  免费   466篇
  国内免费   14篇
安全科学   171篇
废物处理   1篇
环保管理   59篇
综合类   119篇
基础理论   1578篇
污染及防治   24篇
评价与监测   25篇
社会与环境   19篇
灾害及防治   14篇
  2023年   93篇
  2022年   89篇
  2021年   125篇
  2020年   118篇
  2019年   118篇
  2018年   95篇
  2017年   128篇
  2016年   118篇
  2015年   146篇
  2014年   152篇
  2013年   135篇
  2012年   111篇
  2011年   129篇
  2010年   135篇
  2009年   41篇
  2008年   65篇
  2007年   21篇
  2006年   28篇
  2005年   27篇
  2004年   17篇
  2003年   21篇
  2002年   18篇
  2001年   11篇
  2000年   7篇
  1999年   11篇
  1998年   7篇
  1997年   8篇
  1996年   8篇
  1995年   4篇
  1993年   3篇
  1992年   2篇
  1991年   4篇
  1990年   2篇
  1989年   1篇
  1987年   1篇
  1984年   1篇
  1983年   1篇
  1982年   5篇
  1975年   2篇
  1973年   1篇
  1971年   1篇
排序方式: 共有2010条查询结果,搜索用时 31 毫秒
991.
992.
993.
Every action in a conservation plan has a different level of effect and consequently contributes differentially to conservation. We examined how several community-based, marine, management actions differed in their contribution to national-level conservation goals in Fiji. We held a workshop with experts on local fauna and flora and local marine management actions to translate conservation goals developed by the national government into ecosystem-specific quantitative objectives and to estimate the relative effectiveness of Fiji's community-based management actions in achieving these objectives. The national conservation objectives were to effectively manage 30% of the nation's fringing reefs, nonfringing reefs, mangroves, and intertidal ecosystems (30% objective) and 10% of other benthic ecosystems (10% objective). The experts evaluated the contribution of the various management actions toward national objectives. Scores ranged from 0 (ineffective) to 1 (maximum effectiveness) and included the following management actions: permanent closures (i.e., all extractive use of resources prohibited indefinitely) (score of 1); conditional closures harvested once per year or less as dictated by a management plan (0.50-0.95); conditional closures harvested without predetermined frequency or duration (0.10-0.85); other management actions, such as regulations on gear and species harvested (0.15-0.50). Through 3 gap analyses, we assessed whether the conservation objectives in Fiji had been achieved. Each analysis was based on a different assumption: (1) all parts of locally managed marine areas (including closures and other management) conserve species and ecosystems effectively; (2) closures conserve species and ecosystems, whereas areas outside closures, open to varying levels of resource extraction, do not; and (3) actions that allow different levels of resource extraction vary in their ability to conserve species and ecosystems. Under assumption 1, Fiji's national conservation objectives were exceeded in all marine ecosystems; under assumption 2, none of Fiji's conservation objectives were met; and under assumption 3, on the basis of the scores assigned by experts, Fiji achieved the 10% but not the 30% objectives for ecosystems. Understanding the relative contribution of management actions to achieving conservation objectives is critical in the assessment of conservation achievements at the national level, where multiple management actions will be needed to achieve national conservation objectives.  相似文献   
994.
Abstract: Graduate education in conservation biology has been assailed as ineffective and inadequate to train the professionals needed to solve conservation problems. To identify how graduate education might better fit the needs of the conservation workplace, we surveyed practitioners and academics about the importance of particular skills on the job and the perceived importance of teaching those same skills in graduate school. All survey participants (n = 189) were alumni from the University of California Davis Graduate Group in Ecology and received thesis‐based degrees from 1973 to 2008. Academic and practitioner respondents clearly differed in workplace skills, although there was considerably more agreement in training recommendations. On the basis of participant responses, skill sets particularly at risk of underemphasis in graduate programs are decision making and implementation of policy, whereas research skills may be overemphasized. Practitioners in different job positions, however, require a variety of skill sets, and we suggest that ever‐increasing calls to broaden training to fit this multitude of jobs will lead to a trade‐off in the teaching of other skills. Some skills, such as program management, may be best developed in on‐the‐job training or collaborative projects. We argue that the problem of graduate education in conservation will not be solved by restructuring academia alone. Conservation employers need to communicate their specific needs to educators, universities need to be more flexible with their opportunities, and students need to be better consumers of the skills offered by universities and other institutions.  相似文献   
995.
996.
五孔测针标定曲线数学模型的计算机控制   总被引:1,自引:0,他引:1  
由于三维流场测试工作及计算量繁重 ,采用传感技术实现三维流场的自动测试 ,计算机选出最优拟合曲线与实测数据相比较 ,因而达到测试三维流场风流目的。利用回归分析原理 ,将感压元件五孔测针的一系列标定曲线建立了相应的数学模型 ,采用MATLAB语言 ,实现了对标定曲线的拟合 ,用PLOT函数实现了对拟合标定曲线的自动绘制。同时考虑高次多项式 (拟合次数n >10 )易出现振荡的特点 ,故在拟合次数n从 1~ 10可能拟合多项式中 ,选出最优多项式。通过数学模型的应用实现了由计算机控制 ,从而为有效利用传感技术对三维流场的自动化测试提供了可能性。  相似文献   
997.
Boundary organizations are situated between science, policy, and practice and have a goal of supporting communication and collaboration among these sectors. They have been promoted as a way to improve the effectiveness of conservation efforts by building stronger relationships between scientists, policy makers, industry, and practitioners (Cook et al. 2013). Although their promise has been discussed in theory, the work of and expectations for boundary organizations are less defined in practice. Biodiversity conservation is characterized by complexity, uncertainty, dissent, and tight budgets, so boundary organizations face the challenging task of demonstrating their value to diverse stakeholders. We examined the challenges boundary organizations face when seeking to evaluate their work and thus aimed to encourage more productive conversations about evaluation of boundary organizations and their projects. Although no off‐the‐shelf solution is available for a given boundary organization, we identified 4 principles that will support effective evaluation for boundary organizations: engage diverse stakeholders, support learning and reflection, assess contribution to change, and align evaluation with assumption and values.  相似文献   
998.
Finding ways to increase financial support is critical to conservation efforts. We used conservation fundraising data, unprecedented in their resolution, to reveal spatial patterns in philanthropic giving to a major land protection organization in the United States. We also quantified the relationship between the amount of effort devoted to fundraising and donations received. Around 40% of the variation in the propensity to give and overall value of gifts was explained by sociodemographic and other predictors. For example, education level had greater predictive capacity than income, political views, and other factors often considered important. Fundraising effort was strongly predictive of the amount donated in an area. Our model estimated a doubling of funds raised with a 5-fold increase of effort. Conservation organizations could use our statistical framework to inform efforts aimed at increasing philanthropic giving by identifying locations with large model residuals. An example application of our framework showed an almost 40% increase (US$200 million) in fundraising revenue for the case-study conservation organization.  相似文献   
999.
Urban sprawl and the rising popularity of water-sensitive urban design of urban landscapes has led to a global surge in the number of wetlands constructed to collect and treat stormwater runoff in cities. However, contaminants, such as heavy metals and pesticides, in stormwater adversely affect the survival, growth, and reproduction of animals inhabiting these wetlands. A key question is whether wildlife can identify and avoid highly polluted wetlands. We investigated whether pond-breeding frogs are attempting to breed in wetlands that affect the fitness of their offspring across 67 urban wetlands in Melbourne, Australia. Frog species richness and the concentration of contaminants (heavy metals and pesticides) were not significantly related, even in the most polluted wetlands. The proportion of fringing vegetation at a wetland had the greatest positive influence on the number of frog species present and the probability of occurrence of individual species, indicating that frogs inhabited wetlands with abundant vegetation, regardless of their pollution status. These wetlands contained contaminant levels similar to urban wetlands around the world at levels that reduce larval amphibian survival. These results are, thus, likely generalizable to other areas, suggesting that urban managers could inadvertently be creating ecological traps in countless cities. Wetlands are important tools for the management of urban stormwater runoff, but their construction should not facilitate declines in wetland-dependent urban wildlife.  相似文献   
1000.
The Dodo was last sighted on the inshore island of Ile d'Ambre in 1662, nearly 25 years after the previous sighting on the mainland of Mauritius. It has been suggested that its survival on the inshore island is representative of the refuge effect. Understanding what constitutes significant persistence is fundamental to conservation. I tested the refuge‐effect hypothesis for the persistence of the Dodo (Raphus cucullatus) on an inshore island beyond that of the mainland population. For a location to be considered a refuge, most current definitions suggest that both spatial and temporal isolation from the cause of disturbance are required. These results suggest the island was not a refuge for the Dodo because the sighting in 1662 was not temporally isolated from that of the mainland sightings. Furthermore, with only approximately 350 m separating Ile d'Ambre from the mainland of Mauritius, it is unlikely this population of Dodos was spatially isolated. Hipótesis del Efecto Refugio y la Desaparición del Dodo  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