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   913篇
  免费   15篇
  国内免费   20篇
安全科学   70篇
废物处理   25篇
环保管理   183篇
综合类   139篇
基础理论   275篇
环境理论   3篇
污染及防治   156篇
评价与监测   59篇
社会与环境   29篇
灾害及防治   9篇
  2023年   7篇
  2022年   7篇
  2021年   11篇
  2020年   10篇
  2019年   18篇
  2018年   13篇
  2017年   31篇
  2016年   36篇
  2015年   24篇
  2014年   25篇
  2013年   64篇
  2012年   28篇
  2011年   50篇
  2010年   31篇
  2009年   39篇
  2008年   56篇
  2007年   44篇
  2006年   47篇
  2005年   36篇
  2004年   25篇
  2003年   33篇
  2002年   28篇
  2001年   22篇
  2000年   19篇
  1999年   13篇
  1998年   15篇
  1997年   20篇
  1996年   11篇
  1995年   14篇
  1994年   14篇
  1993年   16篇
  1992年   12篇
  1991年   9篇
  1990年   5篇
  1989年   7篇
  1988年   10篇
  1987年   13篇
  1986年   4篇
  1985年   15篇
  1984年   9篇
  1983年   7篇
  1982年   10篇
  1981年   7篇
  1980年   7篇
  1979年   7篇
  1978年   5篇
  1977年   6篇
  1976年   2篇
  1974年   3篇
  1969年   1篇
排序方式: 共有948条查询结果,搜索用时 126 毫秒
491.
Environmental knowing includes the very many bodies of formal theory which have some relevance to the environment, as well as the knowing which comes from experience in the environment. This knowing can be seen as informing action both conceptually and instrumentally. This paper presents a multidisciplinary and transdisciplinary approach which can inter-relate these many knowings in a way which is relevant to and contingent on definition of particular environmental problems. This problem-focused approach involves application of a set of questions which are implied by a taxonomy of ignorance. The paper shows how the approach can inter-relate knowings as diverse as Taoism and energy-efficiency standards, with the purpose of informating environmental action.  相似文献   
492.
Light regime, riboflavin, and pH effects on 2,4-D photodegradation in water   总被引:1,自引:0,他引:1  
A laboratory study was conducted to determine the effects of light regime, riboflavin, and pH on photodegradation of 2,4-D in aqueous solution. In controlled-environment chamber experiments, riboflavin sensitized 2,4-D photolysis in a concentration-dependent manner under both attenuated UV (-UV) and enhanced UV (+UV) light regimes. The photolysis half-life of 2,4-D in solutions containing 10 mg L-1 riboflavin was 9.7 and 12.5 h when exposed to +UV and -UV, respectively, compared to no photolysis in the absence of riboflavin. In contrast, the extrapolated half-life of 2,4-D in solutions containing 2.5 mg L-1 riboflavin was 46 h under +UV and 72 h under -UV. The rate of 2,4-D photolysis in the presence of riboflavin increased under both light regimes as initial pH of the solution was decreased from 7.5 to 4.5. The half-life of 2,4-D in the presence of 10 mg L-1 riboflavin at pH 4.5 and exposed to +UV was 1.6 h. Lumichrome, a principal photoproduct of riboflavin, did not photosensitize 2,4-D. Concentrations of 2,4-dichlorophenol formed as a result of riboflavin-sensitized 2,4-D photolysis were higher under the -UV than the +UV regime. These results indicate that riboflavin concentration, solution pH, and light regime are interacting factors that may be manipulated to enhance rates of aqueous 2,4-D photolysis.  相似文献   
493.
The development of Australia's North-West Shelf gasfield is the largest single private venture yet undertaken in Australia, with expenditure of around A$3000 million. Gas will be exported (primarily to Japan), and there will be local sales, at present confined to the state of Western Australia. Annual revenue is estimated to be A$743 million (in 1977 prices) over the life of the project, with annual tax and royalties rising to A$330 million once loans are repaid. The net effect on Australia's balance of payments is positive in most years. The project's apparent feasibility has provided an impetus to further offshore exploration in the West, with A$400 million now committed.  相似文献   
494.
Commodity export competitiveness is influenced by prices, costs, physical attributes of commodities, supply reliability and transportation. In the case of Australia, factors affecting such considerations include government export controls, environmental requirements, aboriginal rights and trade union attitudes. The author focuses on export control and the marketing of individual commodities, and emphasizes two issues of importance for the future - further processing before export and the future for long-term contracts.  相似文献   
495.
Tracer exchange kinetics were consistent with the view that microplankton of waters near Hawaii produced and assimilated dissolved orthophosphate and dissolved compounds other than orthophosphate at roughly equal rates in experiments conducted in September, 1982. Using simple exchange models plus chemical measurements, we inferred that material other than orthophosphate could sometimes dominate the soluble molybdate-reactive pool (SRP), as is frequently the case in fresh waters. Where phosphorus exchange was most rapid, the tracer kinetics suggested that some fraction of the plankton community was disproportionately responsible for dissolved phophorus exchange. Comparisons against independent measurements of rapid phytoplankton turnover in these communities supported the conclusion that dissolved compounds other than orthophosphate were rapidly cycled and formed an important substrate for plankton growth.  相似文献   
496.
Many of todays agricultural landscapes once held vast amounts of wetland habitat for waterbirds and other wildlife. Successful restoration of these landscapes relies on access to accurate maps of the wetlands that remain. We used C-band (5.6-cm-wavelength), HH-polarized radar remote sensing (RADARSAT) at a 38° incidence angle (8-m resolution) to map the distribution of winter shorebird (Charadriiformes) habitat on agricultural lands in the Willamette Valley of western Oregon. We acquired imagery on three dates (10 December 1999, 27 January 2000, and 15 March 2000) and simultaneously collected ground reference data to classify radar signatures and evaluate map accuracy of four habitat classes: (1) wet with 50% vegetation (considered optimal shorebird habitat), (2) wet with > 50% vegetation, (3) dry with 50% vegetation, and (4) dry with > 50% vegetation. Overall accuracy varied from 45 to 60% among the three images, but the accuracy of focal class 1 was greater, ranging from 72 to 80%. Class 4 coverage was stable and dominated maps (40% of mapped study area) for all three dates, while class 3 coverage decreased slightly throughout the study period. Among wet classes, class 1 was most abundant (30% coverage) in December and January, decreasing in March by 15%. Conversely, class 2 increased dramatically from January to March, likely due to transition from class 1 as vegetation grew. This approach was successful in detecting optimal habitat for shorebirds on agricultural lands. For modest classification schemes, radar remote sensing is a valuable option for wetland mapping in areas where cloud cover is persistent. Also, Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon 97331, USA  相似文献   
497.
Red light running is a frequent cause of motor vehicle crashes and injuries. A primary countermeasure for red light running crashes is police traffic enforcement. In recent years, many police agencies have begun using automated red light cameras as a supplement to conventional enforcement methods. The present study reviewed and evaluated available evidence in the international literature regarding the effectiveness of cameras to reduce both red light violations and crashes. Camera enforcement generally reduces violations by an estimated 40-50%. In terms of crash effects, most studies contain methodological flaws that, to varying degrees, either overestimate (failure to adjust for regression to the mean) or underestimate (comparison with nearby signalized intersections affected by cameras) crash effects. Mindful of these limitations, the research generally indicates that camera enforcement can significantly reduce injury crashes at signalized intersections, in particular right-angle injury crashes. Most studies reported increases in rear-end crashes following camera installation. Taken together the studies indicate that, overall, injury crashes, including rear-end collisions, were reduced by 25-30% as a result of camera enforcement.  相似文献   
498.
ABSTRACT: Maintenance of the more than 24 million septic tanks in the U.S. requires removal and disposal of septage. Disposal options include application to agricultural lands where the nutrients and organic matter can provide soil benefits. However, pathogens and contaminants are also contained in septage. An extensive search turned up very few data on septage quality, and those reveal high variability. The data used by the U.S. Environmental Protection Agency (EPA) in developing regulations had the lowest metal concentrations among the nine data sets that could be compared. Based on these data, EPA assumed that septage could be applied to agricultural land for more than 100 applications before reaching unacceptable cumulative loading of metals. They thus did not establish federal standards for metals in septage, and no monitoring is required under federal rules governing septage disposal. Analysis of the nine data sets we found showed that field site life would be reached in less than 100 applications for most septage and cumulative loading limits established by EPA for sewage sludges will be exceeded in 16 applications for some septage as opposed to the 100 application estimate used by EPA. Determination of acceptable cumulative loading depends on numerous technical and policy considerations. All septage sources reached the more restrictive loading limits such as those established by the New York State Department of Environmental Conservation (NYSDEC) and the recommendations in Cornell publications in less than 100 applications. In one case the cumulative limit for copper was exceeded in a single application. These findings suggest additional data are needed on septage quality and that the federal and state agencies responsible for regulating application of septage to agricultural land should reassess their standards.  相似文献   
499.
In February 2000, the EuropeanCommission adopted a Communication on theprecautionary principle. This states how theCommission intends to apply the principle andestablishes guidelines for its application. Thedocument is intended to inform discussions oninternational agreements. In particular, itprovides a defense of European Union (EU)precautionary policies in case of tradedisputes, for example, in case the EU isaccused of imposing unfair trade barriers onexports of genetically-modified (GM) productsfrom the United States under the rules of theWorld Trade Organisation. In the communication,the Commission emphasizes the scientificaspects of the precautionary principle, perhapspartly to counter claims from US officials thatthe EU's reluctance to accept GM imports is notbased on science but is politically-motivated.However, a principle is by definition a moralguide to behavior. In other words, it is anethic. The precautionary principle should beviewed as a complement to science, to beinvoked when a lack of scientific evidencemeans that outcomes are uncertain. Anyinterpretation of this principle needs to placeat least as much emphasis on its ethical andvalue-based aspects as on its scientificjustification. The Commission's interpretationrisks undermining the painstaking progress madeamong European Union member states inresponding to public concern about GM crops andfood by adopting increased precaution. Thispaper explores the balance between thescientific and ethical/value-based aspects ofthe precautionary principle as set out in theCommission's communication, to make the casethat it is the ethical and value-based aspectsrather than the scientific aspects of theguidelines that need strengthening.  相似文献   
500.
Current planning policy places increased emphasis on the protection of the natural environment. The negotiation of planning agreements between local authorities and developers has emerged as one route through which the private sector has sought to compensate for the loss of environmental resources arising from development. We argue that the utilization of conservation gain mirrors the valuation procedures for public goods found within cost — benefit techniques, which may be inappropriate for the treatment of natural environmental systems. The paper examines the negotiation of these gains from the perspective of different actors in the land development process. Both quantitative and interview material from four local planning authorities are used. The paper concludes by considering the scope for a broader use of conservation gain.  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