全文获取类型
收费全文 | 268篇 |
免费 | 6篇 |
专业分类
安全科学 | 20篇 |
废物处理 | 6篇 |
环保管理 | 68篇 |
综合类 | 32篇 |
基础理论 | 56篇 |
污染及防治 | 66篇 |
评价与监测 | 16篇 |
社会与环境 | 6篇 |
灾害及防治 | 4篇 |
出版年
2023年 | 2篇 |
2016年 | 4篇 |
2015年 | 3篇 |
2014年 | 2篇 |
2013年 | 36篇 |
2012年 | 10篇 |
2011年 | 8篇 |
2010年 | 6篇 |
2009年 | 6篇 |
2008年 | 12篇 |
2007年 | 6篇 |
2006年 | 13篇 |
2005年 | 9篇 |
2004年 | 7篇 |
2003年 | 7篇 |
2002年 | 11篇 |
2001年 | 9篇 |
2000年 | 4篇 |
1999年 | 7篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 5篇 |
1995年 | 2篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1991年 | 5篇 |
1989年 | 6篇 |
1987年 | 3篇 |
1986年 | 6篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1974年 | 6篇 |
1973年 | 2篇 |
1972年 | 3篇 |
1971年 | 2篇 |
1966年 | 3篇 |
1933年 | 2篇 |
1931年 | 1篇 |
1928年 | 1篇 |
1926年 | 1篇 |
1924年 | 1篇 |
排序方式: 共有274条查询结果,搜索用时 531 毫秒
21.
22.
Effects of restoration and reflooding on soil denitrification in a leveed Midwestern floodplain. 总被引:1,自引:0,他引:1
Cailin H Orr Emily H Stanley Karen A Wilson Jacques C Finlay 《Ecological applications》2007,17(8):2365-2376
River floodplains have the potential to remove nitrate from water through denitrification, the anaerobic microbial conversion of nitrate to nitrogen gas. An important factor in this process is the interaction of river water with floodplain soil; however, many rivers have been disconnected from their historic floodplains by levees. To test the effect of reflooding a degraded floodplain on nitrate removal, we studied changes in soil denitrification rates on the Baraboo River floodplain in Wisconsin, USA, as it underwent restoration. Prior to this study, the site had been leveed, drained, and farmed for more than 50 years. In late fall 2002, the field drainage system was removed, and a gate structure was installed to allow controlled flooding of this site with river water. Soil moisture was extremely variable among zones and months and reflected local weather. Soil organic matter was stable over the study period with differences occurring along the elevation gradient. High soil nitrate concentrations occurred in dry, relatively organic-poor soil samples and, conversely, all samples with high moisture soils characterized by low nitrate. We measured denitrification in static cores and potential denitrification in bulk samples amended with carbon and nitrogen, one year before and two years following the manipulation. Denitrification rates showed high temporal and spatial variability. Static core rates of individual sites ranged widely (from 0.00 to 16.7 microg N2O-N x [kg soil](-1) x h(-1), mean +/- SD = 1.10 +/- 3.02), and denitrification enzyme activity (DEA) rates were similar with a slightly higher mean (from 0.00 to 15.0 microg N2O-N x [kg soil](-1) x h(-1), 1.41 +/- 1.98). Denitrification was not well-correlated with soil nitrate, organic matter content, or moisture levels, the three parameters typically thought to control denitrification. Static core denitrification rates were not significantly different across years, and DEA rates decreased slightly the second year after restoration. These results demonstrate that restored agricultural soil has the potential for denitrification, but that floodplain restoration did not immediately improve this potential. Future floodplain restorations should be designed to test alternative methods of increasing denitrification. 相似文献
23.
The marine pseudomonad bacterium PL1 contains an intracellular pool of free amino acids which consist mainly of glutamate with small amounts of glutamine and aspartate when grown in a nutrient medium containing 0.2 M NaCl. When the NaCl concentration of the growth medium is increased to 0.8 M, proline becomes a major component of the intracellular pool together with glutamate—at this molarity and under suitable nutrient conditions these amino acids comprise 20% of total bacterial amino acid nitrogen. When grown in a nutrient growth medium containing a constant level of NaCl, the intracellular pool size can vary by a factor of 4 depending on the concentration of carbon and nitrogen in the medium. Experiments show that the amino acid pool can act as a nitrogen reserve but has little function as a carbon reserve. At high NaCl concentrations there is a marked dependence for growth on the presence of sufficient potassium in the medium. However, no correlation between K+ and glutamate concentration in either nitrogen or K+-limited cultures has been found. None of the enzymes associated with glutamate biosynthesis was influenced by NaCl levels between 0.2 and 0.5 M. Neither Na+ or K+ stimulated the activity of these enzymes when tested in vitro. 相似文献
24.
25.
26.
27.
Marek K. Jarecki Timothy B. Parkin Alvarus S.K. Chan Thomas C. Kaspar Thomas B. Moorman Jeremy W. Singer Brian J. Kerr Jerry L. Hatfield Raymond Jones 《Agriculture, ecosystems & environment》2009,134(1-2):29-35
Agriculture contributes 40–60% of the total annual N2O emissions to the atmosphere. Development of management practices to reduce these emissions would have a significant impact on greenhouse gas levels. Non-leguminous cover crops are efficient scavengers of residual soil NO3, thereby reducing leaching losses. However, the effect of a grass cover crop on N2O emissions from soil receiving liquid swine manure has not been evaluated. This study investigated: (i) the temporal patterns of N2O emissions following addition of swine manure slurry in a laboratory setting under fluctuating soil moisture regimes; (ii) assessed the potential of a rye (Secale cereale L.) cover crop to decrease N2O emissions under these conditions; and (iii) quantified field N2O emissions in response to either spring applied urea ammonium nitrate (UAN) or different rates of fall-applied liquid swine manure, in the presence or absence of a rye/oat winter cover crop. Laboratory experiments investigating cover crop effects N2O emissions were performed in a controlled environment chamber programmed for a 14 h light period, 18 °C day temperature, and 15 °C night temperature. Treatments with or without a living rye cover crop were treated with either: (i) no manure; (ii) a phosphorus-based manure application rate (low manure): or (iii) a nitrogen-based manure application rate (high manure). We observed a significant reduction in N2O emissions in the presence of the rye cover crop. Field experiments were performed on a fine-loamy soil in Central Iowa from October 12, 2005 to October 2, 2006. We observed no significant effect of the cover crop on cumulative N2O emissions in the field. The primary factor influencing N2O emission was N application rate, regardless of form or timing. The response of N2O emission to N additions was non-linear, with progressively more N2O emitted with increasing N application. These results indicate that while cover crops have the potential to reduce N2O emissions, N application rate may be the overriding factor. 相似文献
28.
There are always conflicts between the need for conservation and economic growth in the developing countries. Planning plays a primary role in balancing these conflicts. This is particularly obvious in Chinese cities since China adopted its open door policy in 1978. Foreign investment has been a major driving force for rapid growth of the Chinese economy. Planners in China have been facing the dilemma of protecting the natural environment on the one hand while, on the other hand, supporting the overall national goal of attracting foreign investment to maintain continuous economic growth. The planning system in China, which has been largely based on a planned economy, soon found itself handicapped in safeguarding the environment from rapid industrialization and urbanization fostered by market forces. This paper takes Guangzhou as an example to study challenges to the planning system in Chinese cities in the past two decades of rapid economic growth and urbanization. By means of a case study on an industrial development within a protected orchard area in Guangzhou, this study illustrates the conflict between the need for rural conservation and the pressure for economic development in the Chinese cities. In particular, it analyzes the pressures on the present urban planning system in China in terms of the following categories: the emergence of private investors in urban development; the goal of pursuing a high economic growth rate; the implications of a transitional economy for urban planning; and the weakness of the present urban planning system. It concludes that the role of urban planning in China should change from simply providing guidelines on board land-use strategy, to a combination of a strategic plan with specific development control laws at the operational level. Finally, some recommendations are suggested as to how to improve the planning system in China. 相似文献
29.
Schmidt TS Clements WH Wanty RB Verplanck PL Church SE San Juan CA Fey DL Rockwell BW DeWitt EH Klein TL 《Ecological applications》2012,22(3):870-879
Geologic processes strongly influence water and sediment quality in aquatic ecosystems but rarely are geologic principles incorporated into routine biomonitoring studies. We test if elevated concentrations of metals in water and sediment are restricted to streams downstream of mines or areas that may discharge mine wastes. We surveyed 198 catchments classified as "historically mined" or "unmined," and based on mineral-deposit criteria, to determine whether water and sediment quality were influenced by naturally occurring mineralized rock, by historical mining, or by a combination of both. By accounting for different geologic sources of metals to the environment, we were able to distinguish aquatic ecosystems limited by metals derived from natural processes from those due to mining. Elevated concentrations of metals in water and sediment were not restricted to mined catchments; depauperate aquatic communities were found in unmined catchments. The type and intensity of hydrothermal alteration and the mineral deposit type were important determinants of water and sediment quality as well as the aquatic community in both mined and unmined catchments. This study distinguished the effects of different rock types and geologic sources of metals on ecosystems by incorporating basic geologic processes into reference and baseline site selection, resulting in a refined assessment. Our results indicate that biomonitoring studies should account for natural sources of metals in some geologic environments as contributors to the effect of mines on aquatic ecosystems, recognizing that in mining-impacted drainages there may have been high pre-mining background metal concentrations. 相似文献
30.
Paul A. Read Janet R. Stanley Dianne A. Vella-Brodrick Dave J. Griggs 《Environment, Development and Sustainability》2013,15(5):1173-1187
This paper explores a finding that emerged in the early phases of a multidisciplinary project applying population health and psychology to issues of social progress and sustainability. Across 180 countries and half a century of data, the levels of carbon emissions per capita that maximise life expectancy fall within a tight band averaging only 6.6 tonnes—considerably less than wealthier countries emit per person. Various tests fail to break down the curves and, although the authors remain cautious, the stability since 1960 offers implications for the carbon budget leading up to 2050. This is the first time these curves have been contextualised against established climate science, with timely implications for international negotiations on sustainability and development. 相似文献