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   2088篇
  免费   153篇
  国内免费   434篇
安全科学   186篇
废物处理   96篇
环保管理   317篇
综合类   933篇
基础理论   442篇
环境理论   1篇
污染及防治   395篇
评价与监测   146篇
社会与环境   116篇
灾害及防治   43篇
  2024年   7篇
  2023年   32篇
  2022年   113篇
  2021年   104篇
  2020年   97篇
  2019年   68篇
  2018年   81篇
  2017年   96篇
  2016年   94篇
  2015年   110篇
  2014年   149篇
  2013年   215篇
  2012年   157篇
  2011年   165篇
  2010年   123篇
  2009年   119篇
  2008年   116篇
  2007年   110篇
  2006年   120篇
  2005年   77篇
  2004年   51篇
  2003年   57篇
  2002年   50篇
  2001年   38篇
  2000年   33篇
  1999年   16篇
  1998年   23篇
  1997年   19篇
  1996年   20篇
  1995年   18篇
  1994年   15篇
  1993年   13篇
  1992年   11篇
  1991年   10篇
  1990年   12篇
  1989年   8篇
  1988年   8篇
  1987年   8篇
  1986年   9篇
  1985年   7篇
  1984年   12篇
  1983年   6篇
  1982年   9篇
  1981年   8篇
  1980年   10篇
  1979年   7篇
  1978年   9篇
  1976年   5篇
  1974年   5篇
  1973年   5篇
排序方式: 共有2675条查询结果,搜索用时 218 毫秒
11.
传统方法对青年群体绿色生态文化回归的影响分析中,存在青年群体分析影响片面,影响分析计算准确率较低的问题。为此提出青年群体对传统绿色生态文化回归的影响与思考。通过勒布朗斯回归数学影响方程确定影响因子,建立青年群体主观因子与客观因子之间的动态关联;采用大数据分析,构建大数据影响因子数据分析模型;依托绿色生态文化回归影响算法,从而完成青年群体对传统绿色生态文化回归的影响分析。该影响分析方法比传统方法平均准确度提升3.55倍,且能够实现青年群体对传统绿色生态文化回归的影响分析。  相似文献   
12.
During the last 10–15 years heuristic methods have been developed for problems in optimal reserve selection. Unfortunately, there is no guarantee that heuristics will find optimal solutions. In recognizing this limitation, analysts have formulated reserve selection problems as set covering problems, for which matrix reduction and integer (0/1) programming can be used to find optimal solutions. In this paper we restate the set covering formulation and review solution techniques. A new 0/1 programming model, which is a generalization of the set covering model, is then presented and applied to a hypothetical reserve selection problem. Objectives of minimizing the number of sites selected and maximizing the number of species represented are addressed. Solutions which characterize the tradeoffs between these objectives provide a rich set of information for planners and decision makers. Applications of mathematical programming to related problems in land use planning and forestry are also discussed.  相似文献   
13.
Monitoring long-term change in forested landscapes is an intimidating challenge with considerable practical, methodological, and theoretical limitations. Current field approaches used to assess vegetation change at the plot-to-stand scales and nationwide forest monitoring programs may not be appropriate at landscape scales. We emphasize that few vegetation monitoring programs (and, thus, study design models) are designed to detect spatial and temporal trends at landscape scales. Based primarily on advice from many sources, and trial and error, we identify 14 attributes of a reliable long-term landscape monitoring program: malpractice insurance for landscape ecologists. The attributes are to: secure long-term funding and commitment; develop flexible goals; refine objectives; pay adequate attention to information management; take an experimental approach to sampling design; obtain peer-review and statistical review of research proposals and publications; avoid bias in selection of long-term plot locations; insure adequate spatial replication; insure adequate temporal replication; synthesize retrospective, experimental, and related studies; blend theoretical and empirical models with the means to validate both; obtain periodic research program evaluation; integrate and synthesize with larger and smaller scale research, inventory, and monitoring programs; and develop an extensive outreach program. Using these 14 attributes as a guide, we describe one approach to assess the potential effect of global change on the vegetation of the Front Range of the Colorado Rockies. This self-evaluation helps identify strengthes and weaknesses in our program, and may serve the same role for other landscape ecologists in other programs.  相似文献   
14.
This paper provides a review and justification of the minimum data needed to characterize soils for hazardous waste site assessments and to comply with the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA). Scientists and managers within the regulatory agency and the liable party need to know what are the important soil characteristics needed to make decisions about risk assessment, what areas need remediation and what remediation options are available. If all parties involved in characterizing a hazardous waste site can agree on the required soils data set prior to starting a site investigation, data can be collected in a more efficient and less costly manner. Having the proper data will aid in reaching decisions on how to address concerns at, and close-out, hazardous waste sites.This paper was prepared to address two specific concerns related to soil characterization for CERCLA remedial response. The first concern is the applicability of traditional soil classification methods to CERCLA soil characterization. The second is the identification of soil characterization data type required for CERCLA risk assessment and analysis of remedial alternatives. These concerns are related, in that the Data Quality Objective (DQO) process addresses both. The DQO process was developed in part to assist CERCLA decision-makers in identifying the data types, data quality, and data quantity required to support decisions that must be made during the remedial investigation/feasibility study (RI/FS) process. Data Quality Objectives for Remedial Response Activities: Development Process (US EPA, 1987a) is a guidebook on developing DQOs. This process as it relates to CERCLA soil characterization is discussed in the Data Quality Objective Section of this paper.  相似文献   
15.
Molecular methods, including DNA probes, were used to identify and enumerate pathogenic Vibrio species in the Chesapeake Bay; our data indicated that Vibrio vulnificus exhibits seasonal fluctuations in number. Our work included a characterization of total microbial communities from the Bay; development of microarrays that identify and quantify the diversity of those communities; and observation of temporal changes in those communities. To identify members of the microbial community, we amplified the 16S rDNA gene from community DNA isolated from a biofilm sample collected from the Chesapeake Bay in February, 2000. The resultant 75 sequences were 95% or more similar to 7 species including two recently described Shewanella species, baltica and frigidimarina, that have not been previously isolated from the Chesapeake. When the genera of bacteria from biofilm after culturing are compared to those detected by subcloning amplified 16S fragments from community DNA, the cultured sample exhibited a strong bias. In oysters collected in February, the most common bacteria were previously unknown. Based on our 16S findings, we are developing microarrays to detect these and other microbial species in these estuarine communities. The microarrays will detect each species using four distinct loci, with the multiple loci serving as an internal control. The accuracy of the microarray will be measured using sentinel species such as Aeromonas species, Escherichia coli, and Vibrio vulnificus. Using microarrays, it should be possible to determine the annual fluctuations of bacterial species (culturable and non-culturable, pathogenic and non-pathogenic). The data may be applied to understanding patterns of environmental change; assessing the health of the Bay; and evaluating the risk of human illness associated with exposure to and ingestion of water and shellfish.  相似文献   
16.
哈尔滨市交通噪声监测与评价   总被引:3,自引:0,他引:3  
本文结合哈尔滨市历年交通噪声的状况及变化趋势,探讨了其近几年交通噪声的状况,并对部分路段进行了实际监测.根据调查结果和实际监测结论,本文综合系统地分析了哈尔滨市交通噪声强度和主要影响因素的发展变化趋势,对哈尔滨市交通噪声进行了初步评价,提出了全市交通噪声控制对策.  相似文献   
17.
无盘网络系统是一种很适合在计算机配置较固定、软件程序较划一的网络环境中运行的网络系统,随着电脑教育的规模扩大,网络教室的普及,发展也非常快.本文简述了其产生环境、功能介绍,针对其优势和不足说明了无盘网络系统的应用前景是非常广阔的.  相似文献   
18.
分散式小区污水回用分析研究   总被引:5,自引:0,他引:5  
污水回用处理可分为分散式和集中式,本文着重就分散式小区污水回用处理模式进行探讨,比较分析国内外典型国家或城市的技术和应用现状,在此基础上,指出我国分散式小区污水回用模式当前实施存在的问题及今后的发展趋势.  相似文献   
19.
利用"3S"技术对古日格斯台自然保护区植被类型的空间分布进行了分析,绘制了古日格斯台自然保护区植被图,讨论了其生态多样性和脆弱性,以此作为植被监测与管理的依据,进而对古日格斯台自然保护区的植被进行有效的保护.  相似文献   
20.
The invertebrate neuromodulator octopamine is known to be involved in bees' associative learning, enhancing the responsiveness of a bee to a conditioned stimulus. In this study, we tested the effect of octopamine on the choice behavior of free-flying bumblebees using a two-phase experiment in an array of artificial flowers. During the first phase of the experiment, the bee was allowed to collect octopamine-laden sugar water from two types of equally rewarding flowers (yellow versus blue). In the second phase, one type of flower was set to be unrewarding. The behavior of the bee (proportion of visits to the unrewarding flowers) over the two phases was fitted to a sigmoid regression model. Our results show that octopamine had no significant effect on the bees' equilibrium choice or on the overall rate of the behavioral change in response to the change in reward. Rather, octopamine significantly affected the time interval between the change in reward status and the initiation of behavioral change in the bee.  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