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   6215篇
  免费   123篇
  国内免费   62篇
安全科学   335篇
废物处理   222篇
环保管理   1677篇
综合类   576篇
基础理论   1496篇
环境理论   9篇
污染及防治   1422篇
评价与监测   382篇
社会与环境   232篇
灾害及防治   49篇
  2023年   30篇
  2022年   42篇
  2021年   55篇
  2020年   56篇
  2019年   72篇
  2018年   98篇
  2017年   116篇
  2016年   172篇
  2015年   128篇
  2014年   141篇
  2013年   730篇
  2012年   232篇
  2011年   325篇
  2010年   235篇
  2009年   262篇
  2008年   290篇
  2007年   332篇
  2006年   260篇
  2005年   191篇
  2004年   224篇
  2003年   223篇
  2002年   187篇
  2001年   117篇
  2000年   115篇
  1999年   92篇
  1998年   94篇
  1997年   79篇
  1996年   105篇
  1995年   105篇
  1994年   101篇
  1993年   91篇
  1992年   70篇
  1991年   66篇
  1990年   70篇
  1989年   53篇
  1988年   69篇
  1987年   53篇
  1986年   67篇
  1985年   53篇
  1984年   63篇
  1983年   64篇
  1982年   77篇
  1981年   73篇
  1980年   42篇
  1979年   44篇
  1978年   36篇
  1977年   38篇
  1976年   22篇
  1974年   17篇
  1972年   19篇
排序方式: 共有6400条查询结果,搜索用时 78 毫秒
981.
982.
983.
984.
985.
986.
International negotiations on the inclusion of land use activities into an emissions reduction system for the UN Framework Convention on Climate Change (UNFCCC) have been partially hindered by the technical challenges of measuring, reporting, and verifying greenhouse gas (GHG) emissions and the policy issues of leakage, additionality, and permanence. This paper outlines a five-part plan for estimating forest carbon stocks and emissions with the accuracy and certainty needed to support a policy for Reducing Emissions from Deforestation and forest Degradation, forest conservation, sustainable management of forests, and enhancement of forest carbon stocks (the REDD-plus framework considered at the UNFCCC COP-15) in developing countries. The plan is aimed at UNFCCC non-Annex 1 developing countries, but the principles outlined are also applicable to developed (Annex 1) countries. The parts of the plan are: (1) Expand the number of national forest carbon Measuring, Reporting, and Verification (MRV) systems with a priority on tropical developing countries; (2) Implement continuous global forest carbon assessments through the network of national systems; (3) Achieve commitments from national space agencies for the necessary satellite data; (4) Establish agreed-on standards and independent verification processes to ensure robust reporting; and (5) Enhance coordination among international and multilateral organizations.  相似文献   
987.
The fungicide vinclozolin and insecticide λ-cyhalothrin are widely used to control canola (Brassica spp.) diseases and insect pests, respectively, in Canada. We investigated non-target effects of these pesticides, applied at recommended rates, on soil microbial biomass, functional bacterial diversity and functional community structure of soil bacteria (by evaluating patterns of C substrate utilization) in canola rhizosphere and bulk soil at three locations in Alberta from 2002 to 2004. Experimental treatments were (a) untreated control, (b) vinclozolin fungicide foliar application, (c) λ-cyhalothrin insecticide foliar application, and (d) vinclozolin and λ-cyhalothrin applications. No significant pesticide effects on soil microbial biomass or functional bacterial diversity were observed, but the functional structures of soil bacteria were altered. In 1 of 12 cases, the control treatment had a different soil bacterial community structure from the 3 pesticide treatments. The fungicide treatment had different bacterial community structures from the control or insecticide treatments in 3 of 12 cases, the insecticide treatment had different community structures from the control or fungicide treatments in 4 of 12 cases, and the combined fungicide and insecticide treatment had different community structures from the other treatments in 3 of 12 cases. Therefore, evaluating soil bacterial functional structures revealed pesticide effects that were not detected when bacterial diversity or microbial biomass were measured in canola rhizosphere or bulk soil.  相似文献   
988.
This paper examines the energy and carbon balance of two residential house alternatives; a typical wood frame home using more conventional materials (brick cladding, vinyl windows, asphalt shingles, and fibreglass insulation) and a similar wood frame house that also maximizes wood use throughout (cedar shingles and siding, wood windows, and cellulose insulation) in place of the more typical materials used – a wood-intensive house. Carbon emission and fossil fuel consumption balances were established for the two homes based on the cumulative total of three subsystems: (1) forest harvesting and regeneration; (2) cradle-to-gate product manufacturing, construction, and replacement effects over a 100-year service life; and (3) end-of-life effects – landfilling with methane capture and combustion or recovery of biomass for energy production.The net carbon balance of the wood-intensive house showed a complete offset of the manufacturing emissions by the credit given to the system for forest re-growth. Including landfill methane emissions, the wood-intensive life cycle yielded 20 tons of CO2e emissions compared to 72 tons for the typical house. The wood-intensive home's life cycle also consumed only 45% of the fossil fuels used in the typical house.Diverting wood materials from the landfill at the end of life improved the life cycle balances of both the typical and wood-intensive houses. The carbon balance of the wood-intensive house was 5.2 tons of CO2e permanently removed from the atmosphere (a net carbon sink) as compared to 63.4 of total CO2e emissions for the typical house. Substitution of wood fuel for natural gas and coal in electricity production led to a net energy balance of the wood-intensive house that was nearly neutral, 87.1 GJ energy use, 88% lower than the scenario in which the materials were landfilled.Allocating biomass generation and carbon sequestration in the forest on an economic basis as opposed to a mass basis significantly improves the life cycle balances of both houses. Employing an economic allocation method to the forest leads to 3–5 times greater carbon sequestration and fossil fuel substitution attributable to the house, which is doubled in forestry regimes that remove stumps and slash as fuel. Thus, wood use has the potential to create a significantly negative carbon footprint for a house up to the point of occupancy and even offset a portion of heating and cooling energy use and carbon emissions; the wood-intensive house is energy and carbon neutral for 34–68 years in Ottawa and has the potential to be a net carbon sink and energy producer in a more temperate climate like San Francisco.  相似文献   
989.
This study seeks to improve understanding of temperature patterns in reservoir outflows. We examined water temperatures in an irrigation storage reservoir, Island Park Reservoir, and its outflow, Henry’s Fork of the Snake River in eastern Idaho. Our objectives were to (1) quantify the extent to which daily temperature ranges in the reservoir outflow deviated from other reaches of the Henry’s Fork, and (2) test whether the reservoir’s net volume change during the summer — expressed as the volume of water remaining in the reservoir on September 1 — predicted mean summer temperature in the outflow. Two years of temperature data showed dampened diel temperature cycles in the reservoir outflow. Model selection with 17 years of climatic, hydrologic, and reservoir management variables found mean summer temperature in the outflow was best predicted by September 1 reservoir volume and average summer air temperature. Two years of weekly reservoir thermal profiles indicated large changes in reservoir volume eliminated cool hypolimnetic water and encouraged mixing, allowing warm epilimnetic water to be discharged into the outflow. Increases in future drought frequency and severity and increases in summer air temperatures could increase the frequency of occurrence of high mean summertime water temperatures in the outflow. Our study provides important information for local managers by quantifying influences on outflow temperatures and the downstream river ecosystem.  相似文献   
990.
Following costly repairs of a coastal landfill's shoreline protection system (SPS) within a tidal zone with additional future repairs imminent, a green and sustainable remedy optimization to eliminate the root cause of the damage was evaluated. The removal of the armored point located just north of the landfill that had been a major source of erosion to the SPS during storm events was proposed and implemented. The restoration of the beach to protect the landfill and restore natural longshore processes, while providing habitat for wildlife, was a key goal of the project. As a part of the work, the removal of a creosote‐impregnated boat ramp was incorporated into the final design at the request of stakeholders. During the process, all materials excavated from the site were either beneficially reused in the construction or reused off‐site as concrete, clean fill, or fuel. The work was implemented in the dry by working with the tides and successfully achieved the project goals. Based on the initial inspections following the repairs, no additional repairs are anticipated well into the future. © 2016 Wiley Periodicals, Inc.  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