全文获取类型
收费全文 | 138篇 |
免费 | 5篇 |
专业分类
安全科学 | 8篇 |
废物处理 | 3篇 |
环保管理 | 38篇 |
综合类 | 10篇 |
基础理论 | 41篇 |
污染及防治 | 30篇 |
评价与监测 | 6篇 |
社会与环境 | 3篇 |
灾害及防治 | 4篇 |
出版年
2021年 | 1篇 |
2020年 | 2篇 |
2019年 | 1篇 |
2018年 | 1篇 |
2017年 | 7篇 |
2016年 | 5篇 |
2015年 | 3篇 |
2014年 | 2篇 |
2013年 | 7篇 |
2012年 | 9篇 |
2011年 | 11篇 |
2010年 | 10篇 |
2009年 | 5篇 |
2008年 | 6篇 |
2007年 | 5篇 |
2006年 | 6篇 |
2005年 | 4篇 |
2004年 | 1篇 |
2003年 | 7篇 |
2002年 | 5篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1992年 | 5篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1971年 | 1篇 |
1968年 | 1篇 |
1965年 | 2篇 |
排序方式: 共有143条查询结果,搜索用时 6 毫秒
141.
US Federal law mandates that mined land be returned by mine operators to a condition capable of supporting its pre-mining use or a higher use. Previously forested lands have commonly been reclaimed to hayland/pasture or wildlife habitat, and most of these lands have been abandoned from management and rendered non-productive. This situation has left landowners in the position of converting these reclaimed mined lands to forests at a later date, if they choose to make them economically productive. Such land-use conversion, however, comes with a substantial up-front cost to the landowner, which makes the financial viability of such a conversion questionable. We examine the financial viability of reforestation of these previously reclaimed mine lands by calculating land expectation value (LEV) under a range of conditions that include forest type, site quality, and reforestation intensity. We find that conversion to white pine is viable on higher quality sites under low to moderate interest rates with low or high timber prices, but conversion to mixed hardwoods is only profitable under the high price scenario with low interest rates, and only on higher quality sites. We also consider the implications of a shift in reforestation burden from the landowner to the mine operator, and results suggest that including costs of reforestation as part of the mining operation creates a financially viable forest enterprise for landowners under all scenarios for both white pine and mixed hardwoods. Two forms of carbon payments that could encourage reforestation of previously reclaimed mined lands also are examined: an annual payment based upon the total accumulated carbon found on-site in a given year, and an annual payment based on only the increment of carbon storage each year. Our carbon payment results indicate that annual values of up to $5.17 per ton of carbon stored in hardwoods and $9.39 per ton of carbon stored in pines would be required to make reforestation profitable under the poorest conditions (high interest rates, low prices, and poor quality site) when the payment is based on accumulated on-site carbon, although lower values are required under more favorable scenarios. Payments that are based upon the annual increment of carbon must fall in the range of $8.66–$71.88 per ton of carbon stored in hardwoods and $0–$83.29 per ton of carbon stored in pines to make reforestation financially viable. 相似文献
142.
Intracellular and extracellular granules are found in most bivalve kidneys. We examined the composition of kidney granules from the infaunal bivalveMercenaria mercenaria (L.) collected in 1985 from Cataumet Bay, Bourne, and Waquoit Bay, Falmouth, Massachusetts, USA. Small granules are numerically dominant, but large granules dominate the samples on the basis of weight. Large granules (estimated diam. >15 m) are composed primarily of metals (28% by weight) with Mn (8%), Ca (8%), Zn (4%) and Fe (4%) as the major contributors. Non-metal elements (P, C, H, N, S) together constituted 21% of the granule dry weight, though organic content (0.02% protein, 0.3% carbohydrate and 0.5% lipid) was low. Small kidney granules (10 m diam.) and digestive gland granules fromM. mercenaria had significantly higher C, H, and N contents than larger kidney granules. Our results, taken together with those from other bivalve species, suggest that kidney granule formation and subsequent increase in size is a continuous process of lysosomal maturation, residual body release and extracellular accumulation of predominately inorganic elements. 相似文献
143.
A scanning electron microscope study of the mandibular morphology of boreal copepods 总被引:2,自引:0,他引:2
Morphological details of the mandibular blades of 11 species of copepods were examined with scanning electron microscopy. The micrographs improved our understanding of the complex toothed edge of the mandibular blade, which in turn aids in identification of the copepod prey of chaetognaths by gut-content analysis. Beklemishev's discovery of siliceous tooth crowns in calanoid copepods was confirmed for most of the species examined. Long, sharp projections on the crowns of herbivorous species, and the deep grooves into which they fit on the teeth of the opposite mandible, suggest a cracking rather than a grinding function for these teeth. 相似文献