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   711篇
  免费   16篇
  国内免费   12篇
安全科学   36篇
废物处理   16篇
环保管理   165篇
综合类   113篇
基础理论   196篇
环境理论   4篇
污染及防治   132篇
评价与监测   32篇
社会与环境   29篇
灾害及防治   16篇
  2023年   12篇
  2022年   9篇
  2021年   26篇
  2020年   13篇
  2019年   29篇
  2018年   21篇
  2017年   37篇
  2016年   35篇
  2015年   21篇
  2014年   20篇
  2013年   51篇
  2012年   38篇
  2011年   37篇
  2010年   33篇
  2009年   29篇
  2008年   42篇
  2007年   33篇
  2006年   31篇
  2005年   24篇
  2004年   26篇
  2003年   21篇
  2002年   26篇
  2001年   19篇
  2000年   9篇
  1999年   10篇
  1998年   5篇
  1997年   4篇
  1996年   5篇
  1995年   7篇
  1994年   4篇
  1993年   5篇
  1992年   3篇
  1991年   4篇
  1989年   5篇
  1988年   2篇
  1987年   6篇
  1986年   2篇
  1985年   3篇
  1984年   2篇
  1983年   5篇
  1982年   6篇
  1981年   5篇
  1980年   2篇
  1979年   2篇
  1978年   1篇
  1977年   4篇
  1976年   1篇
  1975年   1篇
  1974年   1篇
  1969年   1篇
排序方式: 共有739条查询结果,搜索用时 15 毫秒
31.
Because environmental conservation can remove scarce natural resources from competing uses, it is important to gain support for conservation programs by demonstrating that management actions have been effective in achieving their goals. One way to do this is to show that selected significant environmental variables (indicators) vary between managed and unmanaged areas or change over time following implementation of a management regime. However, identifying indicators that reflect environmental conditions relevant to management practices has proven difficult. This paper focuses on developing a framework for choosing indicators in a coral reef habitat. The framework consisted of three phases: (1) information gathering to identify candidate variables; (2) field-testing candidate variables at sites that differ in intensity of human activity, thus identifying potential indicators; and (3) evaluating potential indicators against a set of feasibility criteria to identify the most useful indicators. To identify indicators suitable to measure the success of a management strategy to reduce anchor damage to a coral reef, 24 candidate variables were identified and evaluated at sites with different intensities of anchoring. In this study, measures that reflected injuries to coral colonies were generally more efficient than traditional measures of coral cover in describing the effects of anchoring. The number of overturned colonies was identified as the single most useful indicator of coral reef condition associated with anchoring intensities. The indicator selection framework developed here has the advantages of being transparent, cost efficient, and readily transferable to other types of human activities and management strategies.  相似文献   
32.
The multi-disciplinary evaluation of a national agri-environment scheme   总被引:8,自引:0,他引:8  
With an increasing amount of public funds being spent on agri-environmental schemes effective methods have to be developed to evaluate them. As many schemes have multiple objectives there is a need for a multi-disciplinary approach to any evaluation. A method was developed to assess the degree to which ecological, landscape, historical and access objectives for the Countryside Stewardship Scheme (CSS) in England have been met. The method used a sample of 484 agreements for which data were collected from surveys, a desk study and an interview with the agreement holder. These data were then evaluated by an expert team of an ecologist, landscape architect, landscape historian, and a social scientist specializing in rural affairs. The team were subsequently brought together with a Chair to discuss their findings for each agreement, allocating scores for each of five criteria: agreement negotiation; appropriateness, environmental effectiveness, compliance and side effects. The additionality that each agreement was likely to provide was also assessed. The results of this process suggest that in the majority of cases the CSS agreements should maintain or enhance the environment in terms of ecology, landscape, and landscape history and increase public enjoyment of the countryside. Thirty-six percent of agreements showed high additionality and 38% medium additionality which demonstrates that the CSS is likely to provide a benefit to society. Agreement negotiation, predicted environmental effectiveness and predicted compliance all improved significantly over the period 1996-98. Recommendations made from this project have been implemented by the Government department to improve the CSS. The multi-disciplinary method was successful and, with further development, could be used for assessment of any agri-environment scheme, or potentially any conservation project or broader 'rural development' scheme encompassing environmental, economic and social objectives. A key to success is the need for the criteria to be tailored for the project concerned and clearly established at the beginning.  相似文献   
33.
Few disputes in the annals of US environmentalism enjoy the pedigree of the conservation-preservation debate. Yet, although many scholars have written extensively on the meaning and history of conservation and preservation in American environmental thought and practice, the resonance of these concepts outside the academic literature has not been sufficiently examined. Given the significance of the ideals of conservation and preservation in the justification of environmental policy and management, however, we believe that a more detailed analysis of the real-world use and understanding of these ideas is needed. In this paper, we describe the results of a qualitative, semantic study of the concepts of conservation and preservation undertaken in the context of the Chattahoochee National Forest (CNF), located in northern Georgia (USA). Thirty in-depth interviews were conducted with scientists and north Georgia residents either interested or involved in the future management of the forest. Respondents were asked to define conservation and preservation in their own words and to indicate which approach they felt was more appropriate for the management of the CNF. Qualitative content analysis was used to elicit a set of recurring themes for each foundational concept. Taken together, these themes help to flesh out the meaning of conservation and preservation for citizens and scientists today, and illustrate the evolving nature of two of the more significant and venerable ideas animating US environmental policy and management.  相似文献   
34.
ABSTRACT: Interbasin water transfer is one of the most controversial water-resources-planning topics. Local communities, particularly those from which the water is to be taken (donor regions), generate enough opposition to doom many projects to failure. The opposition often arises because planners have traditionally considered excess water a free commodity rather than a marketable resource. To make transfer schemes mutually acceptable to donor and recipient regions, visible benefits must be offered. Agreement must be made on an acceptable purchase price and/or on other benefits such as a substantial amount of low flow augmentation or possibly some degree of flood control on the donor source stream. The hydrologic and economic feasibility of water transfer from the East Susquehanna River basin to the Delaware Reservoir System for supplemental supply to the New York City area was investigated. Nine alternative schemes for diversions up to 400 cfs and compensations in the form of low flow augmentation and/or flood control were considered resulting in unit costs to the recipient region between $90 and $380/mg. If only the minimum state-mandated flow is released to the Susquehanna River, the savings to the water recipients would be sufficient to pay a purchase price of about $21/mg, which would be equivalent to a total amount of $420,000/year for an average export of 100 cfs.  相似文献   
35.
This article assesses the possibilities of establishing more efficient patterns of energy use in Haiti, a country increasingly dependent on imported petroleum products to fuel its economy. The author examines the various consuming sectors of the economy and the options for the use of indigenous fuels in place of petroleum. She next describes the potential roles national energy planning and foreign assistance can play in solving the more pressing of Haiti's energy problems. Four functions are urgently needed: collection of basic energy data, co-ordination of alternative energy development, establishment of an energy office in the government and an effort to co-ordinate bilateral and multilateral assistance in the energy field. Cet article évalue les possibilités d'établir des modèles d'utilisation d'énergie plus efficaces en Haïti, pays de plus en plus dépendant des importations de produits pétroliers pour son économie. L'auteur examine les divers secteurs de consommation de l'économie et les choix qui existent en ce qui concerne l'utilisation des combustibles domestiques à la place du pétrole. L'auteur décrit ensuite les rôles potentiels que peuvent jouer la planification nationale de l'énergie et l'assistance extérieure dans la résolution des problèmes énergétiques les plus urgents du pays. Quatre lignes d'action sont requises d'urgence: le rassemblement des données énergétiques de base, la coordination du développement de sources d'énergie de remplacement, la création d'une direction de l'énergie à l'échelon gouvernemental et la mise en oeuvre d'une politique coordonnée d'assistance bilatérale et multilatérale dans le domaine de l'énergie. Este articulo evalúa las posibilidades de establecer estructuras de consumo de energía mas eficientes en Haiti, pais que tiene una dependencia creciente en el petróleo importado. El autor examina varios sectores consumidores de energia y las opciones existentes para sustituir el petróleo por fuentes energéticas nacionales. Luego examina el rol potencial de la planificación energética nacional y la asistencia extranjera en resolver los problemas energéticos más agudos en Haiti. Se establece la necesidad urgente de las siguientes funciones: colección de información básica sobre energía, coordinación del desarrollo energético, establecimiento de una institución que se ocupe de energía en el gobierno y coordinación de la asistencia bilateral y multilateral en el campo de la energía.  相似文献   
36.
ABSTRACT: Several methods for synthetic unit hydrographs are available in the literature. Most of these methods involve the hand fitting of a curve over a set of a few hydrograph points, which can sometimes be a subjective task. Besides, the user often finds it difficult or simply neglects to adjust the generated unit graph to a runoff volume of one unit (inch, cm, or mm). It is the purpose of this paper to present to the design hydrologist a simple method to fit a smooth gamma distribution over a single point specified by the unit hydrograph peak and the time to peak with a guaranteed unit depth of runoff.  相似文献   
37.

Objectives

To develop a flexible droplet digital PCR (ddPCR) workflow to perform non-invasive prenatal diagnosis via relative mutation dosage (RMD) for maternal pathogenic variants with a range of inheritance patterns, and to compare the accuracy of multiple analytical approaches.

Methods

Cell free DNA (cfDNA) was tested from 124 archived maternal plasma samples: 88 cases for sickle cell disease and 36 for rare Mendelian conditions. Three analytical methods were compared: sequential probability ratio testing (SPRT), Bayesian and z-score analyses.

Results

The SPRT, Bayesian and z-score analyses performed similarly well with correct prediction rates of 96%, 97% and 98%, respectively. However, there were high rates of inconclusive results for each cohort, particularly for z-score analysis which was 31% overall. Two samples were incorrectly classified by all three analytical methods; a false negative result predicted for a fetus affected with sickle cell disease and a false positive result predicting the presence of an X-linked IDS variant in an unaffected fetus.

Conclusions

ddPCR can be applied to RMD for diverse conditions and inheritance patterns, but all methods carry a small risk of erroneous results. Further evaluation is required both to reduce the rate of inconclusive results and explore discordant results in more detail.  相似文献   
38.
39.
40.
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