全文获取类型
收费全文 | 742篇 |
免费 | 10篇 |
国内免费 | 114篇 |
专业分类
安全科学 | 47篇 |
废物处理 | 23篇 |
环保管理 | 159篇 |
综合类 | 285篇 |
基础理论 | 159篇 |
环境理论 | 1篇 |
污染及防治 | 125篇 |
评价与监测 | 32篇 |
社会与环境 | 35篇 |
出版年
2023年 | 23篇 |
2022年 | 31篇 |
2021年 | 14篇 |
2020年 | 14篇 |
2019年 | 28篇 |
2018年 | 17篇 |
2017年 | 26篇 |
2016年 | 41篇 |
2015年 | 45篇 |
2014年 | 40篇 |
2013年 | 48篇 |
2012年 | 27篇 |
2011年 | 95篇 |
2010年 | 39篇 |
2009年 | 62篇 |
2008年 | 68篇 |
2007年 | 68篇 |
2006年 | 24篇 |
2005年 | 24篇 |
2004年 | 18篇 |
2003年 | 15篇 |
2002年 | 13篇 |
2001年 | 11篇 |
2000年 | 9篇 |
1999年 | 4篇 |
1998年 | 15篇 |
1997年 | 9篇 |
1996年 | 8篇 |
1995年 | 4篇 |
1994年 | 6篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1978年 | 2篇 |
1969年 | 1篇 |
排序方式: 共有866条查询结果,搜索用时 593 毫秒
71.
Thomas V. Armentano 《Environmental management》1984,8(6):529-538
Large but feasible increases that have been projected for the production of wood energy in the United States can be expected to significantly alter the current carbon storage patterns in US forest vegetation. The 1976 net wood increment left after forest cutting equals about 136 × 106 tons of carbon/year, with about 60% of the increment found in merchantable trees, and the remainder in nonmerchantable components.Achieving 5–10 quads of wood energy beyond 1976 levels by the year 2010 can significantly change current carbon storage patterns with the magnitude of change dependent on the extent of residue harvest to meet energy goals, and the rate of future forest growth. Complete loss of the apparent net wood increment is a possible outcome.Although the future growth and harvest situation cannot be known now, a range of possible scenarios suggests that US forests in the year 2010 will store much less carbon than today, thus significantly changing their role in the global carbon cycle. 相似文献
72.
Kennett SA 《Environmental management》2002,30(5):0595-0608
Biosphere greenhouse gas (GHG) management consists of preserving and enhancing terrestrial carbon pools and producing biomass
as a fossil fuel substitute. The discussion of this topic has focused primarily on carbon-accounting and project-level issues,
particularly relating to carbon sequestration as a source of emissions credits under the Kyoto Protocol. While international
consensus on these matters is needed, this paper argues that an important domestic policy agenda also deserves attention.
National policies for biosphere GHG management are necessary to bring about large-scale changes in land-use, forestry, and
agricultural practices and can address some of the technical and policy issues that have proven to be particularly problematic
from carbon-accounting and project-level perspectives. These policies should minimize land-use and resource-management conflicts,
account for collateral benefits, and ensure institutional compatibility with existing resource-management regimes. Issues
relating to project permanence, leakage, and transaction costs should also be addressed. A range of policy instruments should
be used and biosphere GHG management should be one component of an integrated approach to environmental and resource management.
Countries promoting biosphere GHG management as an important element of their climate change strategies should be developing
these domestic policies to complement international negotiations and to demonstrate that carbon sequestration and biomass
production can make an effective contribution to the stabilization of atmospheric GHG concentrations. 相似文献
73.
Energy and carbon balances of wood cascade chains 总被引:1,自引:0,他引:1
In this study we analyze the energy and carbon balances of various cascade chains for recovered wood lumber. Post-recovery options include reuse as lumber, reprocessing as particleboard, pulping to form paper products, and burning for energy recovery. We compare energy and carbon balances of chains of cascaded products to the balances of products obtained from virgin wood fiber or from non-wood material. We describe and quantify several mechanisms through which cascading can affect the energy and carbon balances: direct cascade effects due to different properties and logistics of virgin and recovered materials, substitution effects due to the reduced demand for non-wood materials when wood is cascaded, and land use effects due to alternative possible land uses when less timber harvest is needed because of wood cascading. In some analyses we assume the forest is a limiting resource, and in others we include a fixed amount of forest land from which biomass can be harvested for use as material or biofuel. Energy and carbon balances take into account manufacturing processes, recovery and transportation energy, material recovery losses, and forest processes. We find that land use effects have the greatest impact on energy and carbon balances, followed by substitution effects, while direct cascade effects are relatively minor. 相似文献
74.
Horacio?Alejandro?Turno?OrellanoEmail author Federico?Ignacio?Isla 《Regional Environmental Change》2004,4(1):70-76
Since the 1940s, some sectors of the sand dune barriers of Buenos Aires Province have been forested to fix the sand in the neighborhoods of resort villages. Man took advantage of the maritime climate and the shallow groundwater to introduce pine forests. Today, these forests reach more than 20 m in height and have developed soils of more than 0.05 m in thickness on former arid sands. Field data were referred to Landsat (TM) composite and Normalized Difference of Vegetation Index, NDVI, images to calculate forest density and covered area. Considering published tables of wood density for each species, the amount of total carbon storage was estimated on 318 t C ha-1 (Mg=106 g) in biomass and 86 t C ha-1 in soils. The three areas analyzed at Miramar, Necochea and Claromecó have captured 658,868 t of carbon in the last 50 years. It is estimated that 150,000,000 t C could be sequestered within temperate dune barriers of Argentina, Uruguay and Brazil. Besides this ecological point of view, there is an important socio-economic factor that cannot be excluded.Presented at and revised subsequent to the 4th LOICZ Open Science Meeting, Bahía Blanca, Argentina. October 1999. 相似文献
75.
Response of Organic and Inorganic Carbon and Nitrogen to Long-Term Grazing of the Shortgrass Steppe 总被引:3,自引:0,他引:3
We investigated the influence of long-term (56 years) grazing on organic and inorganic carbon (C) and nitrogen (N) contents of the plant–soil system (to 90 cm depth) in shortgrass steppe of northeastern Colorado. Grazing treatments included continuous season-long (May–October) grazing by yearling heifers at heavy (60–75% utilization) and light (20–35% utilization) stocking rates, and nongrazed exclosures. The heavy stocking rate resulted in a plant community that was dominated (75% of biomass production) by the C4 grass blue grama (Bouteloua gracilis), whereas excluding livestock grazing increased the production of C3 grasses and prickly pear cactus (Opuntia polycantha). Soil organic C (SOC) and organic N were not significantly different between the light grazing and nongrazed treatments, whereas the heavy grazing treatment was 7.5 Mg ha–1 higher in SOC than the nongrazed treatment. Lower ratios of net mineralized N to total organic N in both grazed compared to nongrazed treatments suggest that long-term grazing decreased the readily mineralizable fraction of soil organic matter. Heavy grazing affected soil inorganic C (SIC) more than the SOC. The heavy grazing treatment was 23.8 Mg ha–1 higher in total soil C (0–90 cm) than the nongrazed treatment, with 68% (16.3 Mg ha–1) attributable to higher SIC, and 32% (7.5 Mg ha–1) to higher SOC. These results emphasize the importance in semiarid and arid ecosystems of including inorganic C in assessments of the mass and distribution of plant–soil C and in evaluations of the impacts of grazing management on C sequestration. 相似文献
76.
Monitoring Forest Carbon Sequestration with Remote Sensing and Carbon Cycle Modeling 总被引:1,自引:0,他引:1
Sources and sinks of carbon associated with forests depend strongly on the management regime and spatial patterns in potential productivity. Satellite remote sensing can provide spatially explicit information on land cover, stand-age class, and harvesting. Carbon-cycle process models coupled to regional climate databases can provide information on potential rates of production and related rates of decomposition. The integration of remote sensing and modeling thus produces spatially explicit information on carbon storage and flux. This integrated approach was employed to compare carbon flux for the period 1992–1997 over two 165-km2 areas in western Oregon. The Coast Range study area was predominately private land managed for timber production, whereas the West Cascades study area was predominantly public land that was less productive but experienced little harvesting in the 1990s. In the Coast Range area, 17% of the land base was harvested between 1991 and 2000. Much of the area was in relatively young, productive-age classes that simulations indicate are a carbon sink. Mean annual harvest removals from the Coast Range were greater than mean annual net ecosystem production. On the West Cascades study area, a relatively small proportion (< 1%) of the land was harvested and the area as a whole was accumulating carbon. The spatially and temporally explicit nature of this approach permits identification of mechanisms underlying land base carbon flux.
Published online 相似文献
77.
Forest Protection and Reforestation in Costa Rica: Evaluation of a Clean Development Mechanism Prototype 总被引:9,自引:1,他引:8
Subak S 《Environmental management》2000,26(3):283-297
/ Costa Rica has recently established a program that provides funds for reforestation and forest protection on private lands, partly through the sale of carbon certificates to industrialized countries. Countries purchasing these carbon offsets hope one day to receive credit against their own commitments to limit emissions of greenhouse gases. Costa Rica has used the proceeds of the sale of carbon offsets to Norway to help finance this forest incentive program, called the Private Forestry Project, which pays thousands of participants to reforest or protect forest on their lands. The Private Forestry Project is accompanied by a monitoring program conducted by Costa Rican forest engineers that seeks to determine net carbon storage accomplished on these lands each year. The Private Forestry Project, which is officially registered as an Activity Implemented Jointly, is a possible model for bundled projects funded by the Clean Development Mechanism (CDM) established by the 1997 Kyoto Protocol to the UN Framework Convention on Climate Change. It also serves as an interesting example for the CDM because it was designed by a developing country host-not by an industrialized country investor. Accordingly, it reflects the particular "sustainable development" objectives of the host country or at least the host planners. Early experience in implementing the Private Forestry Project is evaluated in light of the main objectives of the CDM and its precursor-Activities Implemented Jointly. It is concluded that the project appears to meet the criteria of global cost-effectiveness and financing from non-ODA sources. The sustainable development implications of the project are specific to the region and would not necessarily match the ideals of all investing and developing countries. The project may be seen to achieve additional greenhouse gas abatement when compared against some (although not all) baselines. 相似文献
78.
Antoine Longieras Jean-Baptiste Tanchette Damien Erre Christian Braud Alain Copinet 《Journal of Polymers and the Environment》2007,15(3):200-206
Commercial poly(lactide) degradation was studied in an inert solid medium simulating compost conditions, with the aim to achieve
a complete carbon balance of the polymer degradation. The mineralisation rate at the end of the test was compared to those
obtained for poly(lactide) degradation in compost. It was shown that the mineralisation rate after 45 days of degradation
was quite lower in inert solid medium than in compost but the standard deviation of data was enhanced. A protocol for both
extraction and quantification of the carbon included in the different degradation by-products was proposed and the carbon
balance of the polymer degradation was followed during the test with a satisfactory accuracy. The non-degraded PLA material
was recovered during the test, hence the evolution of the glass transition temperature and the molecular weight was followed.
A two-step degradation mechanism was highlighted in inert solid medium, showing the fundamental role of abiotic reactions
for PLA degradation in compost. 相似文献
79.
The information presented in this paper is directed to air pollution engineers who are concerned with monitoring Carbon Monoxide. This paper evaluates systems for CO sampling under conditions where the receptor is located at intersections within 40 meters of the road edge. Non-Dispersive Infrared and electrochemical analysis techniques are used in conjunction with continuous recording, continuous bag sampling, and meter readings at 5 second intervals. The relative accuracy of each system is examined and the conditions for which each system is best suited are described. 相似文献
80.
Abstract This paper describes the development of apparatus suitable for direct supercritical fluid extraction of organics from water. Results are presented for the extraction of pentachlorophenol present in water at concentrations of the order of 0.1 ppm. The effect of changes in apparatus design and supercritical fluid flow rate on recovery are discussed. 相似文献