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   1204篇
  免费   20篇
  国内免费   11篇
安全科学   68篇
废物处理   75篇
环保管理   293篇
综合类   126篇
基础理论   221篇
环境理论   2篇
污染及防治   296篇
评价与监测   98篇
社会与环境   39篇
灾害及防治   17篇
  2023年   9篇
  2022年   7篇
  2021年   9篇
  2020年   16篇
  2019年   16篇
  2018年   20篇
  2017年   18篇
  2016年   22篇
  2015年   20篇
  2014年   26篇
  2013年   134篇
  2012年   40篇
  2011年   56篇
  2010年   53篇
  2009年   50篇
  2008年   60篇
  2007年   66篇
  2006年   68篇
  2005年   48篇
  2004年   33篇
  2003年   53篇
  2002年   46篇
  2001年   19篇
  2000年   14篇
  1999年   19篇
  1998年   21篇
  1997年   10篇
  1996年   11篇
  1995年   23篇
  1994年   12篇
  1993年   10篇
  1992年   15篇
  1991年   13篇
  1990年   17篇
  1989年   13篇
  1988年   9篇
  1987年   8篇
  1986年   8篇
  1985年   15篇
  1984年   11篇
  1983年   14篇
  1982年   19篇
  1981年   24篇
  1980年   10篇
  1979年   13篇
  1975年   4篇
  1974年   4篇
  1973年   8篇
  1972年   4篇
  1971年   4篇
排序方式: 共有1235条查询结果,搜索用时 31 毫秒
751.
752.
753.
The Critical Ecosystems Team of the US Environmental Protection Agency (EPA), Region 5, has developed an approach to prioritize and target ecologically high-quality areas for enhanced environmental protection in the Midwestern states of Illinois, Indiana, Ohio, Michigan, Minnesota and Wisconsin. Using this approach, we intend to employ a pro-active strategy to protect the environment by protecting and restoring natural ecosystems rather than the traditional EPA approach of remediating and attempting to restore already degraded habitats. The approach consists of two components: (1) partnership and (2) criteria. For the partnership component, we collected, mapped, and summarized information on ecosystems considered critical to federal and state agencies, tribes and non-profit organizations. Multi-county areas with high numbers of ecosystems identified by a variety of partners were designated as ‘Ecologically Rich Regions’. These Ecologically Rich Regions highlight broad geographic areas where there are high levels of partner interest and, correspondingly, areas with high potential for forming collaborative partnerships for enhanced environmental protection. The second component, which relies on criteria, is still under development and defines critical ecosystems as having three important properties: (1) high ecological diversity, (2) potential for long-term sustainability and (3) presence of relict native ecosystems or communities. The information compiled under both components of this ecosystem targeting approach will inform ecological risk managers and assessors about important ecosystems that should be considered in risk management and assessment processes.  相似文献   
754.
In this paper I undertake a preliminary assessment for the tropics of the relation of economic development, meaning in general increases in economic activity as measured by e.g. GDP, and its normal biophysical corollaries of increased resource use and land use change. I also examine each in relation to the intellectual concepts that underlie and guide what is commonly called economic development. Because most of the development literature is derived from economics or other social sciences, and focuses almost entirely on lifting people’s standards of living as measured in monetary units, very little examines the per unit biophysical requirements of that development, including energy or other resource use requirements, land use change or other environmental consequences of development plans. In addition there seems to be insufficient connection between those who create economic development plans and those who undertake empirical biophysical assessments to determine whether the development plan has worked or can possibly work. The problem is deeper: there exists a series of models used in the development literature that have been used to encourage and guide development. These models have received very little scrutiny as to either their efficacy or their societal or environmental impacts until quite recently. When this has been done the models have been shown to fail miserably. It is time to develop a new model of development that synthesizes conventional economic, biophysical economic and social aspects, and that is based on the scientific method rather than on perceived wisdom. This model must also take into account population growth, issues of who wins and who looses from economic development, and the implications of the incipient peak in global oil production.  相似文献   
755.
The rising rate of multiple pregnancies and its association with advanced maternal age has expanded the need for prenatal diagnosis in twins and higher order gestations. The complexity of the invasive diagnostic procedures and the risk of loss of an unaffected twin raise significant clinical, technical and ethical issues. In this review we discuss the specific issues of early scanning, counseling and determination of chorionicity prior to invasive procedures in twins. We present the available data describing the risk associated with these procedures in twins and compare data of fetal loss rate from different studies. We also discuss the issues of fetal blood sampling and late karyotyping in twin pregnancies. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   
756.
CORRESPONDENCE     
Charles Kelly 《Disasters》1996,20(3):276-277
  相似文献   
757.
Estimating contaminant distributions in environmental media is necesary to evaluate human and ecological hazards. Because of uncertainties in release histories and transport, traditional sampling and statistical techniques applicable to the experimental sciences may not be suitable for exploratory studies at hazardous waste sites. An approach that relies on cluster analysis of principal components (PCA) was used to identify contaminated wild asparagus (Asparagus officinalis) growing in the vicinity of waste disposal sites along the Columbia River at the U.S. Department of Energy's Hanford Site in southeast Washington state. Metals in soil samples taken from the sites contained elevated levels of Ag, Al, Ba, Cd, Cr, Cu, Hg, Ni, Pb, Sb, Zn, and V. Samples of asparagus tissue were collected from the river near the waste site, from Hanford old fields abandoned 52 years ago, and from commercial fields in the neighboring communities. Dried tissues were analyzed for metals content by ICP-mass spectrometry, furnace AA, and cold vapor AA. Tissue concentrations of elements varied over 5 orders of magnitude, from K at 46 900 ppm to As and Ag at maximum concentrations below 1 ppm. PCA produced four components that accounted for 66.2% of the metals variance. Subsequent cluster analysis using Ward's minimum variance separated the data into Columbia River and old-field groups, with the River group further divided into three clusters: plants primarily upriver from the waste sites, plants primarily downriver, and plants growing in or near the waste sites. The clustering showed that the more soluble components of the discharges (Ba and Ca) showed a pattern of distribution in the asparagus plants consistent with the ground water flow pattern, in that these elements were found far downriver of the disposal sites themselves. In contrast, the less mobile elements Al, Cd, Cr, Fe, Mn, Tl, and Zn were elevated only near the most-recently used waste disposal area. Asparagus from agricultural fields, including fields abandoned 50 years ago, contained higher concentrations of Fe, Cu, Pb, K, and Ni than did the wild riverine plants.The U.S. Governments right to retain a non-exclusive royalty free licence in and to any copyright is acknowledged.  相似文献   
758.
759.
Infiltration and runoff from manured agricultural fields can result in livestock pathogens reaching groundwater and surface waters. Here, we measured the effectiveness of glass wool filters to simultaneously concentrate enteric viruses and bacteria of bovine origin from water. The recovery efficiencies were determined for bovine viral diarrhea virus types 1 and 2, bovine rotavirus group A, bovine coronavirus, poliovirus Sabin III, toxigenic Escherichia coli ,and Campylobacter jejuni seeded into water with three different turbidity levels (0.5, 215, and 447 NTU). Twenty liters of dechlorinated tap water (pH 7) were seeded with the test organisms, and then passed through a glass wool filter using a peristaltic pump (flow rate = 1 liter min?1). Retained organisms were eluted from the filters by passing beef extract-glycine buffer (pH 9.5) in the direction opposite of sample flow. Recovered organisms were enumerated by qPCR except for C. jejuni, which was quantified by culture. Mean recovery efficiencies ranged from 55 to 33 % for the bacteria and 58 to 16 % for the viruses. Using bootstrapping techniques combined with Analysis of Variance, recovery efficiencies were found to differ among the pathogen types tested at the two lowest turbidity levels; however, for a given pathogen type turbidity did not affect recovery except for C. jejuni. Glass wool filtration is a cost-effective method for concentrating several waterborne pathogens of bovine origin simultaneously, although recovery may be low for some specific taxa such as bovine viral diarrhea virus 1.  相似文献   
760.
In the prior‐appropriation water rights regimes that prevail in the arid western United States, claims to annually variable surface water flows are fulfilled based on the order of their establishment. The two‐step process used to establish an appropriative water right in all 17 conterminous western states creates a temporary phase, or conditional water right, which has a priority date but no actual water use. We provide a review of the legal basis for these conditional water rights and demonstrate the potential uncertainty they introduce to current water users. We then present a complete census of conditional water rights in Colorado, including their amounts, ages, and uses. At the end of 2012 there were a large number of conditional water rights in Colorado (some over 90 years old) equal to 61% of the perfected water rights. Many of the controversial conditional water rights in Colorado have been associated with unconventional oil production in the northwestern portion of the state; however, conditional water rights are ubiquitous across the state and across many use types. In several basins, their existence can introduce uncertainty to some of the most senior water rights holders. Nevertheless, in most of the state, the effects of conditional water rights are restricted to a relatively junior class of water users. This work quantifies for the first time the result, in one state, of a peculiar aspect of water law common across all western prior‐appropriation states.  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