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   1297篇
  免费   32篇
  国内免费   18篇
安全科学   54篇
废物处理   68篇
环保管理   128篇
综合类   279篇
基础理论   228篇
环境理论   1篇
污染及防治   346篇
评价与监测   144篇
社会与环境   79篇
灾害及防治   20篇
  2023年   10篇
  2022年   16篇
  2021年   30篇
  2020年   17篇
  2019年   17篇
  2018年   38篇
  2017年   49篇
  2016年   43篇
  2015年   31篇
  2014年   59篇
  2013年   93篇
  2012年   44篇
  2011年   80篇
  2010年   54篇
  2009年   64篇
  2008年   73篇
  2007年   69篇
  2006年   51篇
  2005年   53篇
  2004年   60篇
  2003年   69篇
  2002年   49篇
  2001年   53篇
  2000年   30篇
  1999年   25篇
  1998年   16篇
  1997年   12篇
  1996年   5篇
  1995年   12篇
  1994年   10篇
  1993年   14篇
  1992年   16篇
  1991年   3篇
  1990年   4篇
  1989年   6篇
  1988年   6篇
  1987年   2篇
  1986年   5篇
  1985年   8篇
  1984年   4篇
  1983年   8篇
  1982年   8篇
  1981年   4篇
  1980年   2篇
  1979年   2篇
  1976年   2篇
  1970年   2篇
  1962年   5篇
  1961年   2篇
  1938年   1篇
排序方式: 共有1347条查询结果,搜索用时 15 毫秒
501.
In this methodological study, the applicability of aerial photographs for monitoring mangrove vegetation dynamics at high resolution was investigated. Vegetation maps of three mangrove forests in Sri Lanka (Galle, Rekawa and Pambala) were produced based on visual analysis of aerial photographs. The visual analysis was aided by applying an interpretation key constructed during a first fieldwork mission. Image attributes used for the identification of individual trees included: gray values, texture, form and size of the crowns and the presence or absence of a shaded side. For the identification of species assemblages, the vegetation structure (i.e. the distribution of individual trees) appeared to be an important attribute. The accuracy and reliability of the vegetation maps were investigated during a second fieldwork mission. The aerial photographs proved to be very useful for the production of genus-based vegetation maps. The error analysis showed that density estimations (quantitative identification) based on aerial photography was not sufficiently accurate for the objectives of the study, but that the overall identification of vegetation assemblages (qualitative identification) coincided most satisfactory with the ground-truth data. In addition to the applicability of aerial photography in monitoring mangroves, the importance of aerial photography in the management of the mangrove ecosystem is clearly highlighted.  相似文献   
502.
503.
Marfan syndrome (MFS) is an autosomal dominant disorder with a prevalence of 2–3 per 10 000 individuals. Symptoms range from skeletal overgrowth, cutaneous striae to ectopia lentis and aortic dilatation leading to dissection. Prenatal diagnosis was until recently mainly performed in familial cases by linkage analysis. However, mutation detection has become available with thorough screening methods. The phenotypic variability observed in MFS makes reproductive options difficult, as molecular diagnosis cannot predict clinical severity of the disease. Data are presented on 15 prenatal and/or preimplantation genetic diagnoses (PGD) in nine families, originating from Belgium, the Netherlands, Spain and France. In four families data from linkage analysis were used, whereas in five other families the causative FBN1 mutation was characterised. Four PGD cycles in two couples led to one ongoing pregnancy. In addition, two amniocenteses and nine chorionic villus (CV) samplings were performed. In five pregnancies an affected fetus was diagnosed. In one of them, the couple chose to continue the pregnancy and an affected child was born, whereas the other four couples decided to terminate the pregnancy. It is expected that the greater availability of mutation testing of the FBN1 gene will increase requests for prenatal diagnosis. PGD appears to be an acceptable alternative for couples facing ethical reproductive dilemmas. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   
504.
505.
In this paper, a simulation model is presented for nutrient cycling in heathland ecosystems. The results of simulations are compared with field data of phosphorus and nitrogen accumulation in different compartments of the system in the years after burning, given in the literature on this subject (Chapman, 1967; 1970). It is shown that for the cycling of P the system returns slowly to equilibrium after an initial disturbance. The time span of about 30 years that is required to reach equilibrium is in agreement with the field data. However, P accumulation in living above-ground biomass and litter is overestimated by the model in the first years after burning. Nitrogen accumulation in biomass and litter is systematically underestimated by the model.The results are discussed with reference to the processes in nutrient cycling that are insufficiently understood, and with reference to the management of heathlands.  相似文献   
506.
草原生物多样性监测指标体系构建的探讨   总被引:1,自引:0,他引:1  
草原生物多样性监测目前已成为草原生物多样性研究和保护的热点问题。草原生物多样性监测指标则是一些简化的生物或环境特征参数,说明草原生物多样性现状和变化趋势,以及人类活动压力对草原生物多样性的影响,以促进科学界、政府和公众间的沟通,提高草原生物多样性管理水平。本文综述了草原生物多样性监测指标筛选的一般标准和指标体系构建的主要理论,梳理目前已提出或应用的主要生物多样性监测指标,以期为我国构建国家或区域尺度生物多样性监测指标体系提供参考。  相似文献   
507.
508.
In this study, we investigated the presence of enteric viruses such as norovirus (NoV), hepatitis A virus (HAV), hepatitis E virus (HEV), and adenovirus (HAdV), in vegetables available on the Italian markets. For this aim, 110 national and international ??ready to eat?? samples were collected and analyzed by biomolecular tests and positive samples were confirmed by sequencing. All samples (100?%) were negative for HAV, HEV, and HAdV, while 13.6?% (15/110) were positive for NoV. Actually there is not a formal surveillance system for NoV infections in Italy but we clearly demonstrated a potential risk associated with the consumption of ??ready to eat?? vegetables. This study confirmed for the first time in Italy the presence of norovirus in semi-dried tomatoes by PCR technique.  相似文献   
509.
After briefly reviewing key resilience engineering perspectives and summarising some green infrastructure (GI) tools, we present the contributions that GI can make to enhancing urban resilience and maintaining critical system functionality across complex integrated social–ecological and technical systems. We then examine five key challenges for the effective implementation of GI that include (1) standards; (2) regulation; (3) socio-economic factors; (4) financeability; and (5) innovation. We highlight ways in which these challenges are being dealt with around the world, particularly through the use of approaches that are both context appropriate and socially inclusive. Although progress surmounting these challenges has been made, more needs to be done to ensure that GI approaches are inclusive and appropriate and feature equally alongside more traditional ‘grey’ infrastructure in the future of urban resilience planning. This research was undertaken for the Resilience Shift initiative to shift the approach to resilience in practice for critical infrastructure sectors. The programme aims to help practitioners involved in critical infrastructure to make decisions differently, contributing to a safer and better world.  相似文献   
510.
An attempt for the spectroscopic identification of oxygenated compounds produced in combustion processes under different environmental conditions is reported in this paper. A deeper knowledge about presence and evolution of such species in dependence of the operating conditions of practical burner represents a fundamental hint to the objective of an advancement of the control of combustion process and reduction of pollutant emissions. This paper mainly focuses on species characterized by the presence of carbonyl functionality since aldehydes, ketones and diketones are among the principal intermediate species and products of hydrocarbon oxidation. They are by themselves to be considered atmospheric pollutants and are also indicators of actual pathways followed during the chemical reactions occurring in the combustion process. For these reasons they are most suitable for the exploitation of the above indicated objectives. In this paper, a classification of spectroscopic features and markers of these classes of carbonyl compounds is presented on the basis of both literature and spectra collected from sample species. This interpretative scheme is then used for the attribution of fluorescence signals collected from a tetradecane spray in different environmental conditions.  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