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   146篇
  免费   1篇
  国内免费   1篇
安全科学   1篇
废物处理   4篇
环保管理   26篇
综合类   37篇
基础理论   33篇
环境理论   2篇
污染及防治   27篇
评价与监测   14篇
社会与环境   4篇
  2023年   4篇
  2022年   2篇
  2021年   4篇
  2020年   1篇
  2019年   3篇
  2018年   5篇
  2017年   4篇
  2016年   5篇
  2015年   1篇
  2014年   6篇
  2013年   12篇
  2012年   1篇
  2011年   3篇
  2010年   3篇
  2009年   7篇
  2008年   9篇
  2007年   8篇
  2006年   4篇
  2005年   4篇
  2004年   4篇
  2003年   2篇
  2002年   5篇
  2001年   2篇
  2000年   2篇
  1999年   2篇
  1997年   3篇
  1996年   3篇
  1995年   3篇
  1994年   4篇
  1993年   2篇
  1992年   2篇
  1991年   4篇
  1990年   2篇
  1989年   1篇
  1988年   1篇
  1987年   1篇
  1985年   1篇
  1984年   3篇
  1983年   1篇
  1982年   2篇
  1981年   3篇
  1979年   1篇
  1972年   1篇
  1968年   1篇
  1967年   1篇
  1962年   1篇
  1961年   1篇
  1960年   1篇
  1959年   2篇
排序方式: 共有148条查询结果,搜索用时 484 毫秒
131.
The integration of the environmental dimension into sectoral and regional policies constitutes a dominant concern of the current EU strategy for sustainable development. Thus, physical planning as an instrument of environmental policy and its combination with environmental planning, both at a policy as well as implementation level is a key pursuit in almost all European countries. In Greece, the adoption of a concept about a rational and unified approach of physical and environmental planning has met with many difficulties. The aim of this paper is to contribute towards a critical approach of recent developments, mainly in the field of the institutional framework for spatial and environmental planning in Greece.  相似文献   
132.
133.
Junctional epidermolysis bullosa, Herlitz variant (junctional EB-Herlitz) is a lethal autosomal recessive skin disorder currently amenable to prenatal diagnosis only by direct analysis of fetal skin. However, elevated levels of alpha-fetoprotein, as well as the presence of acetylcholinesterase in amniotic fluid, have been associated with other severe fetal genodermatoses. Fetal skin samplings were performed in ten pregnancies at risk for fetal junctional EB-Herlitz, with three fetuses affected on the basis of electron microscopic detection of blisters within the lamina lucida and abnormal hemidesmosomes. In neither affected nor unaffected pregnancies were maternal serum or amniotic fluid alpha-fetoprotein levels elevated. Moreover, alphafetoprotein levels in both maternal serum and amniotic fluid were not statistically different comparing affected and unaffected fetuses. Acetylcholinesterase was not present in the amniotic fluid samples of the three affected pregnancies. Unlike other severe fetal genodermatoses, neither alpha-fetoprotein nor acetylcholinesterase was predictive of junctional EB-Herlitz.  相似文献   
134.
ABSTRACT: The quality of stream habitat varies for a variety of natural and anthropogenic reasons not identified by a condition index. However, many people use condition indices to indicate management needs or even direction. To better sort natural from livestock influences, stream types and levels of ungulate bank damage were regulated to estimates of aquatic habitat condition index and stream width parameters in a large existing stream inventory data base. Pool/riffle ratio, pool structure, stream bottom materials, soil stability, and vegetation type varied significantly with stream type. Pool/riffle ratio, soil and vegetation stability varied significantly with ungulate bank damage level. Soil and vegetation stability were highly cross-correlated. Riparian area width did not vary significantly with either stream type or ungulate bank damage. Variation among stream types indicates that riparian management and monitoring should be stream type and reach specific.  相似文献   
135.
ABSTRACT: We compared the recovery from abusive grazing of aquatic habitat due to different range management on two geomorphically similar rangeland streams in northwest Nevada. Managers excluded livestock from the Mahogany Creek watershed from 1976 to 1990 while allowing rotation of rest grazing on its tributary Summer Camp Creek. Bank stability, defined as the lack of apparent bank erosion or deposition, improved through the study period on both streams, but periodic grazing and flooding decreased stability more on Summer Camp Creek than flooding alone on Mahogany Creek. Pool quantity and quality on each stream decreased because of coarse woody debris removal and sediment deposition during a drought. Fine stream bottom sediments decreased five years after the removal of livestock, but sedimentation increased during low flows in both streams below road crossings. Tree cover increased 35 percent at both streams. Thus, recovery of stability and cover and decreased sedimentation are compatible with rotation of rest grazing on Summer Camp Creek. Width/depth ratio and gravel/cobble percent did not change because they are inherently stable in this stream type. Management activities such as coarse woody debris removal limited pool recover and road crossings increased sedimentation.  相似文献   
136.
137.
Abstract: Stream and riparian managers must effectively allocate limited financial and personnel resources to monitor and manage riparian ecosystems. They need to use management strategies and monitoring methods that are compatible with their objectives and the response potential of each stream reach. Our objective is to help others set realistic management objectives by comparing results from different methods used to document riparian recovery across a diversity of stream types. The Bureau of Land Management Elko Field Office, Nevada, used stream survey, riparian proper functioning condition (PFC) assessment, repeat photographic analysis, and stream and ecological classification to study 10 streams within the Marys River watershed of northeast Nevada during all or parts of 20 years. Most riparian areas improved significantly from 1979 to 1992‐1993 and then additionally by 1997‐2000. Improvements were observed in riparian and habitat condition indices, bank cover, and stability, pool quality, bank angle, and depth of undercut bank. Interpretation of repeat photography generally confirmed results from stream survey and should be part of long‐term riparian monitoring. More attributes of Rosgen stream types C and E improved than of types B and F. A and Gc streams did not show significant improvement. Alluvial draws and alluvial valleys improved in more ways than V‐erosional canyons and especially V‐depositional canyons. Stream survey data could not be substituted for riparian PFC assessment. Riparian PFC assessments help interpret other data.  相似文献   
138.
139.
ABSTRACT: The objective of this study was to characterize the sources, concentrations, and distribution of total and methylmer‐cury in water, and channel and bank sediments of Steamboat Creek, Nevada. This information was needed to begin to assess the potential impacts of stream restoration on mercury pollution in this tributary to the Truckee River. The Truckee River flows into Pyramid Lake, a terminal water body home to one endangered and one threatened fish species, where stable pollutants will accumulate over time. Mercury in Steamboat Creek was originally derived from its headwaters, Washoe Lake, where several gold and silver mills that utilized mercury were located. In the 100 plus years since ore processing occurred, mercury‐laden alluvium has been deposited in the stream channel and on streambanks where it is available for remobilization. Total mercury concentrations measured in unfiltered water from the creek ranged from 82 to 419 ng/L, with greater than 90 percent of this mercury being particle‐bound (> 0.45 (m). Mercury in sediments ranged from 0.26 to 10.2 μg/g. Methylmercury concentrations in sediments of Steamboat Creek were highest in wetlands, lower in the stream channel, and still lower in streambank settings. Methylmercury concentrations in water were 0.63 to 1.4 ng/L. A streambank restoration plan, which includes alterations to channel geometry and wetland creation or expansion, has been initiated for the creek. Data developed indicate that streambank stabilization could reduce the mercury loading to the Creek and that wetland construction could exacerbate methylmercury production.  相似文献   
140.
The lethal effects of aluminum ion (Al3+) in tilapia (Oreochromis niloticus) raised in concrete tanks were investigated. Tilapias were fed daily with commercial feed enriched with known concentrations of Al3+ and analyzed by differential pulse anodic stripping voltammetry (DPASV). The concentrations of Al3+ in feces, water, muscle tissue, viscera, and heads were determined every 3 months for a period of 365 days. The Tilapia head was the most affected tissue by Al3+. In general, Al3+ bioaccumulation reached the lethal dose (LD50) after 335 days of experiment as follows: 34.9?mg?kg?1 (muscle tissue), 88.2?mg?kg?1 (viscera), and 126.9?mg?kg?1 (head without gills). After determining Cu2+, Zn2+, and Ca2+ by absorption spectrometry, a decrease in the Ca2+ concentration was noted in the head during the experimental period. These observations were associated with the occurrence of a decalcification in the bone tissue in the presence of Al3+. In contrast, it was found that Zn2+ ions may act as a protective agent against Al3+-induced contamination.  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