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   8945篇
  免费   656篇
  国内免费   640篇
安全科学   1655篇
废物处理   139篇
环保管理   3132篇
综合类   2724篇
基础理论   1215篇
环境理论   12篇
污染及防治   300篇
评价与监测   364篇
社会与环境   417篇
灾害及防治   283篇
  2024年   20篇
  2023年   146篇
  2022年   190篇
  2021年   237篇
  2020年   299篇
  2019年   227篇
  2018年   207篇
  2017年   265篇
  2016年   358篇
  2015年   320篇
  2014年   363篇
  2013年   535篇
  2012年   525篇
  2011年   640篇
  2010年   435篇
  2009年   531篇
  2008年   416篇
  2007年   540篇
  2006年   527篇
  2005年   412篇
  2004年   423篇
  2003年   334篇
  2002年   302篇
  2001年   287篇
  2000年   283篇
  1999年   223篇
  1998年   141篇
  1997年   144篇
  1996年   119篇
  1995年   110篇
  1994年   60篇
  1993年   68篇
  1992年   58篇
  1991年   49篇
  1990年   36篇
  1989年   29篇
  1988年   35篇
  1987年   35篇
  1986年   28篇
  1985年   25篇
  1984年   27篇
  1983年   19篇
  1982年   23篇
  1981年   19篇
  1980年   25篇
  1979年   35篇
  1978年   21篇
  1973年   15篇
  1972年   16篇
  1971年   14篇
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
141.
Wildlife management is limited by uncontrolled and often unrecognized environmental variation, by limited capabilities to observe and control animal populations, and by a lack of understanding about the biological processes driving population dynamics. In this paper I describe a comprehensive framework for management that includes multiple models and likelihood values to account for structural uncertainty, along with stochastic factors to account for environmental variation, random sampling, and partial controllability. Adaptive optimization is developed in terms of the optimal control of incompletely understood populations, with the expected value of perfect information measuring the potential for improving control through learning. The framework for optimal adaptive control is generalized by including partial observability and non-adaptive, sample-based updating of model likelihoods. Passive adaptive management is derived as a special case of constrained adaptive optimization, representing a potentially efficient suboptimal alternative that nonetheless accounts for structural uncertainty.  相似文献   
142.
微生物群落结构和多样性解析技术研究进展   总被引:15,自引:1,他引:15  
微生物群落结构和多样性是微生物生态学和环境科学研究的热点内容,对于开发微生物资源,阐明微生物群落与其生境的关系,揭示群落结构与功能的联系,从而指导微生物群落功能的定向调控具有重要意义。基本按照年代顺序概述了常用的微生物群落结构及多样性解析技术,同时也体现了解析技术由片面向全面、由低分辨水平向高分辨水平的发展过程。20世纪70年代以前,对环境微生物群落结构及多样性的认识依赖传统的培养分离方法,方法的分辨水平低,认识是不全面的和有选择性的;20世纪70年代和80年代,在微生物化学成分分析的基础上建立了生物标记物方法(醌指纹法、磷脂脂肪酸法等),对微生物群落结构和多样性的认识进入到较客观的层次上;在80和90年代,以DNA为目标物的现代分子生物学技术(rRNA基因测序技术、基因指纹图谱等)比较精确地揭示了微生物种类和遗传的多样性,并给出了关于群落结构的直观信息。指出了每种解析技术的功能特点和局限性,并展望了解析技术的发展趋势是原位、快速、灵敏、高通量和准确定量。  相似文献   
143.
山西高原油松种群遗传多样性   总被引:2,自引:2,他引:2  
李毳  柴宝峰  王孟本 《生态环境》2005,14(5):719-722
用酸性聚丙烯酰胺凝胶电泳(A-PAGE)技术,分析了山西高原9个油松种群在醇溶蛋白水平上的遗传多样性。135份材料共分离出23条带,其中3条为共有带,多态性高达86.95%。全部材料共出现53种带型,9个不同油松种群的带型有差异,同一种群不同个体的带型也有所不同,说明山西高原的油松在遗传上已产生一定程度分化,在醇溶蛋白水平上呈现出遗传多态性。从供试材料的带型计算出油松遗传分化系数为0.1547。即在种群间的变异占总变异的15.47%,种群内变异为84.53%,大部分的遗传变异存在于种群内,但种群间的分化程度在松属树种中也属于较高水平。根据23个多态位点计算遗传相似系数和遗传距离,进行聚类分析,将山西高原9个油松种群聚为3个类群。  相似文献   
144.
We develop a landscape stewardship classification which distinguishes between farmers’ understanding of landscape stewardship, their landscape values, and land management actions. Forty semi-structured interviews were conducted with small-holder (<5 acres), medium-holders (5–100 acres), and large-holders (>100 acres) in South-West Devon, UK. Thematic analysis revealed four types of stewardship understandings: (1) an environmental frame which emphasized the farmers’ role in conserving or restoring wildlife; (2) a primary production frame which emphasized the farmers’ role in taking care of primary production assets; (3) a holistic frame focusing on farmers’ role as a conservationist, primary producer, and manager of a range of landscape values, and; (4) an instrumental frame focusing on the financial benefits associated with compliance with agri-environmental schemes. We compare the landscape values and land management actions that emerged across stewardship types, and discuss the global implications of the landscape stewardship classification for the engagement of farmers in landscape management.  相似文献   
145.
The hazardous waste management (HWM) practice at Tehran University of Medical Sciences Central Campus, Iran, was investigated in this study. Four schools were selected and the required information such as type and amount of wastes, temporary storage methods, waste discharge frequency, and final waste disposal methods using sampling, questionnaires, interviews with laboratory staff, and reference to available documents were gathered. The quantity of hazardous waste generation per year excluding the uncontrolled wastewater was found to be 2.072 tons per year. The obtained results show that wastes having features of being infectious, toxic, ignitable, carcinogenic, corrosive, and reactive were present at 32%, 28%, 16%, 14%, 8%, and 2%, respectively. In the central campus, hazardous solid wastes managed with household solid wastes and hazardous liquid waste were discharged into the sinks without any kind of control; improper HWM practices are evident from the point of waste production to final disposal.  相似文献   
146.
Benthic communities on soft bottoms off Barcelona, at and around two main pollution sources, the mouth of the Besòs River and the outlet of the submarine pipeline draining wastewater and organic sludges from the wastewater treatment plant of Sant Adrià del Besòs, have been studied. Samples were obtained with a Van Veen grab from 36 stations covering a 100 km2 grid, between 10 and 70 m in depth. The effect of both pollution sources is clearly seen both at the species (the following macrofauna groups have been studied: Polychaeta, Mollusca, Echinodermata and Crustacea Decapoda) and community levels. The distribution of species and individuals numbers, species diversity and a pollution index, and of some selected (indicator) polychaeta species, all clearly define the degree of environmental degradation and the extent of the areas under the influence of the organic pollution.  相似文献   
147.
Over the past several decades a growing interest has emerged in the relationship between forest dependent communities and their use of non-timber forest resources (NTFR—i.e. berries, roots, barks). Motivated in large part by international concerns over the loss of biological and cultural diversity, efforts are now being made to conserve the world's remaining forests by repositioning NTFR to the forefront of the forest management process. Together with the Little Salmon Carmacks First Nation, we have undertaken an assessment that: 1) addresses the role of NTFR in fulfilling basic human necessities and well-being of community members, and 2) identifies the perceptual differences that exist among First Nation and non-First Nation community members regarding the security and future availability of forest resources. Based on our findings, we argue that if the true value of the forest is to be understood, and thus sustained, those involved in management must consider the full array of products and services the forest provides. Thus the conventional and over-simplified view that the forest is to provide primarily for commercial timber must be challenged in light of the multiplicity of values community members gain from forest use.  相似文献   
148.
Ecological regionalization is a base for rational management and sustainable utilization of ecosystems and natural resources. It can provide a scientific basis for constructing healthy ecological environments and making policies of environmental management. In this paper, based on synthetic analysis of the characteristics of the ecology and environments of China, the principles of ecological regionalization are discussed, and indices and nomenclature of ecological regionalization are proposed. The ecoregions on a national scale are divided. The results show that there are 3 domains, 13 ecoregions and 57 ecodistricts. The present scheme can be used as a framework for ecosystem assessment and management. Based on the ecoregions, measurements of management for forest, grassland, agriculture and wetland ecosystems are recommended. The experience and information can be used within and beyond the national scale for land-use planning, biodiversity conservation and ecosystem restoration.  相似文献   
149.
Environmental management and planning is now considered as a new field of professional expertise. There are even professional associations for interested professionals. To date, urban environmental management has been regarded as a subdiscipline of environmental management, but since the Rio Conference in 1992, with the new focus of urban management on environmental problems, it can itself be considered as a professional field. This paper traces the emergence of the field and tries to identify the new skills required for it. The question of formal training, in higher education, for a new type of professional is raised and discussed. It refers at length to an initiative taken by the Asian Institute of Technology (Bangkok) to propose and offer a new graduate programme in this discipline, and draws on the author's experience of an Asian workshop (Bangkok, May 1993) aimed at defining the need for such a new profession in Asia.  相似文献   
150.

Recognizing the limitations common to both centralized and privatized management regimes, institutionalized resource management is beginning to incorporate the knowledge and skills of local resource users, coupled with the enabling policies and legislation of state systems, to arrive at cooperative approaches to resource management. These varying and dynamic approaches to resource management have been compelled largely through the recognition of the limited capabilities of existing management systems to adapt effectively to ecosystem change and the evolving needs of resource users. These cooperative approaches to management should not, however, be considered an institutional end-point, but rather a phase in the perpetual transition of a social system; each unique in character and individually variable depending on the resource being managed, the political climate in which management occurs, as well as the differing strategies employed by resource users to enact institutional change. Drawing from the experiences of the Whitefish Lake First Nation of Alberta, Canada, this paper presents a brief overview of the evolution of resource management theory, grounded in the real-world formation of the Whitefish Lake First Nation — Province of Alberta Cooperative Management Agreement.  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