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   246篇
  免费   5篇
安全科学   23篇
废物处理   7篇
环保管理   63篇
综合类   18篇
基础理论   65篇
污染及防治   49篇
评价与监测   15篇
社会与环境   8篇
灾害及防治   3篇
  2023年   2篇
  2017年   1篇
  2016年   4篇
  2015年   3篇
  2014年   2篇
  2013年   30篇
  2012年   8篇
  2011年   7篇
  2010年   3篇
  2009年   7篇
  2008年   17篇
  2007年   5篇
  2006年   13篇
  2005年   8篇
  2004年   8篇
  2003年   6篇
  2002年   9篇
  2001年   11篇
  2000年   7篇
  1999年   7篇
  1998年   3篇
  1997年   2篇
  1996年   6篇
  1995年   1篇
  1994年   1篇
  1993年   1篇
  1992年   4篇
  1991年   5篇
  1990年   2篇
  1989年   6篇
  1988年   1篇
  1987年   2篇
  1986年   6篇
  1985年   4篇
  1984年   2篇
  1983年   2篇
  1982年   4篇
  1981年   2篇
  1980年   3篇
  1979年   7篇
  1978年   4篇
  1977年   5篇
  1976年   3篇
  1975年   2篇
  1974年   3篇
  1973年   2篇
  1972年   2篇
  1971年   2篇
  1968年   1篇
  1966年   2篇
排序方式: 共有251条查询结果,搜索用时 203 毫秒
71.
Foraging guilds of North American birds   总被引:2,自引:0,他引:2  
We propose a foraging guild classification for North American inland, coastal, and pelagic birds. This classification uses a three-part identification for each guild—major food, feeding substrate, and foraging technique—to classify 672 species of birds in both the breeding and nonbreeding seasons. We have attempted to group species that use similar resources in similar ways. Researchers have identified foraging guilds generally by examining species distributions along one or more defined environmental axes. Such studies frequently result in species with several guild designations. While the continuance of these studies is important, to accurately describe species' functional roles, managers need methods to consider many species simultaneously when trying to determine the impacts of habitat alteration. Thus, we present an avian foraging classification as a starting point for further discussion to aid those faced with the task of describing community effects of habitat change.  相似文献   
72.
ABSTRACT: Accurate forecasting of heavy rainstorms that affect the Chicago Metropolitan area and lead to the undesirable release of storm runoff into Lake Michigan is a major objective. These releases (overflows) were found to be produced by storm events yielding 2 inches or more in a few hours, although only 24 percent of such ≥ 2-inch storms in the area during 1948-1981 produced overflows. Failure to forecast properly or to be able to react to these 2-inch overflow producing events has occurred most often in the spring and fall, although relatively often in June and July in recent years. These overflows have exhibited an inexplicable trebling during 1972-1981 without an increase in ≥ 2-inch storm events. This type of troublesome storm can be reliably predicted, using a recently developed radar man forecast system for the Chicago area.  相似文献   
73.
An immunological axis of biocontrol: infections in field-trapped insects   总被引:1,自引:1,他引:0  
Insect immunology is an active research arena, however, the vast majority of research in the area is conducted on model species taken from laboratory cultures. We tested the hypothesis that insects are regularly exposed to infections or invasions in nature and here report results of a field study designed to assess the extent of natural infections in insects collected from agrarian fields surrounding Kahramanmaraş, Turkey. Specimens were dissected to assess numbers of nodules. Formation of darkened, melanotic nodules is the predominant cellular immune reaction to microbial and parasitic infection, and once formed, the nodules are permanently attached to internal surfaces. The collected insects were healthy. Of the >400 examined specimens, at least some nodules were found in 98%. Numbers of nodules ranged from ∼2/individual to >100 nodules/individual. We conclude that insects are regularly challenged by microbial and parasitic infections from which they recover. The novel implication of our data is that insect immune systems may limit the host range and effectiveness of agents deployed in biological control programs. Knowledge of insect immune systems may contribute to increased use of biopesticides globally.  相似文献   
74.
The growing importance of the environment and its management has simultaneously emphasized the benefits of hydroelectric power and its environmental costs. In a changing policy climate, giving importance to renewable energy development and environmental protection, conflict potential between stakeholders is considerable. Navigation of conflict determines the scheme constructed, making sustainable hydropower a function of human choice. To meet the needs of practitioners, greater understanding of stakeholder conflict is needed. This paper presents an approach to illustrate the challenges that face small-scale hydropower development as perceived by the stakeholders involved, and how they influence decision-making. Using Gordleton Mill, Hampshire (UK), as an illustrative case, soft systems methodology, a systems modeling approach, was adopted. Through individual interviews, a range of problems were identified and conceptually modeled. Stakeholder bias towards favoring economic appraisal over intangible social and environmental aspects was identified; costs appeared more influential than profit. Conceptual evaluation of the requirements to meet a stakeholder-approved solution suggested a complex linear systems approach, considerably different from the real-life situation. The stakeholders introduced bias to problem definition by transferring self-perceived issues onto the project owner. Application of soft systems methodology caused a shift in project goals away from further investigation towards consideration of project suitability. The challenge of sustainable hydropower is global, with a need to balance environmental, economic, and social concerns. It is clear that in this type of conflict, an individual can significantly influence outcomes; highlighting the need for more structured approaches to deal with stakeholder conflicts in sustainable hydropower development.  相似文献   
75.
The search for ways of reducing vehicular emissions has led to numerous investigations of the relationships between fuel composition and the pollutants discharged from automobiles. The most obvious fuel effects result from evaporation of gasoline components from the fuel tanks and carburetors of vehicles which lack effective mechanical devices (such as those required on all 1971 model cars) to control evaporative losses. Thus, several laboratories and cooperative study groups (Coordinating Research Council and American Petroleum Institute) have investigated the ways in which fuel properties (especially the amounts and types of C4-C5 hydrocarbons) influence both the amount and the potential atmospheric reactivity of evaporative emissions.1–6 But fuel evaporation accounts for only a small portion of the total hydrocarbons emitted by automobiles, and gasoline modifications (such as volatility reductions) that reduce evaporative losses can lead to higher levels of hydrocarbons in automobile exhaust.4–6  相似文献   
76.
The U.S. Environmental Protection Agency's program to assess the public health significance of diesel emissions is described. The reasons for the EPA concern over diesel exhaust products are discussed. Some results of EPA research efforts over the last nine months are summarized and preliminary conclusions are drawn. Finally, the planned future health experiments which will hopefully fill some remaining gaps in our knowledge are identified.  相似文献   
77.
The National Ambient Air Quality Monitoring Program is carried out by state and local air pollution control agencies in support of their State Implementation Plans (SIP’s). The current EPA regulations which specify the characteristics of these state monitoring programs are undergoing change as a result of a comprehensive review by an independent work group. These revised regulations, which are described in the paper, are intended to improve the quality, timeliness, and usability of the data generated by the states for all data users. In addition, the revised regulations seek to bring about; (a) national consistency in monitoring site locations through standardized siting procedures; (b) improved network operations by means of a minimum quality assurance program; (c) reduced network inflexibility through an annual network review process; and (d) reduced data reporting through changed data reporting procedures.  相似文献   
78.
Abstract

Title III of the 1990 Clean Air Act Amendments designated methanol as a pollutant to be regulated. The U.S. Environmental Protection Agency (EPA), through a contract with Research Triangle Institute, has developed a method for measuring methanol emissions from stationary sources. The methanol sampling train (MST) consists of a glass-lined heated probe, two condensate knockout traps, and three sorbent cartridges packed with Anasorb® 747. Samples are desorbed with a 1:1 mixture of carbon disulfide (CS2) and N, N-dimethylformamide (DMF). Condensate water and CS2/ DMF samples are analyzed by gas chromatography with flame ionization detection. The MST has a practical quantitation limit of approximately 3 ppm for a 20-L sample. Samples were shown to be stable for at least two weeks after collection.

Field tests of the MST and the National Council of the Paper Industry for Air and Stream Improvement (NCASI) methanol sampling method were conducted at two pulp and paper mills. Sampling and analysis procedures followed EPA Method 301 requirements.

The sampling location for the first field test was the inlet vent to a softwood bleach plant scrubber, where the methanol concentration was approximately 30 ppm. The mean recovery of spike was 108.3% for the MST method and 81.6% for the NCASI method. Although neither method showed significant bias at the 95% confidence level, the betweenmethods bias was significantly different.

A second field test was conducted at a vent from a black liquor oxidation tank where the methanol concentration was approximately 350 ppm. Mean spike recoveries were 96.6 and 94.2% for the MST and NCASI methods, respectively. The biases of the two methods and the between-methods bias were not significantly different for the second field test.  相似文献   
79.
The Nasty Necessity: Eradicating Exotics   总被引:1,自引:0,他引:1  
  相似文献   
80.
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