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   643篇
  免费   10篇
  国内免费   1篇
安全科学   20篇
废物处理   15篇
环保管理   209篇
综合类   54篇
基础理论   156篇
污染及防治   150篇
评价与监测   23篇
社会与环境   23篇
灾害及防治   4篇
  2023年   3篇
  2021年   7篇
  2020年   6篇
  2019年   9篇
  2018年   6篇
  2017年   8篇
  2016年   25篇
  2015年   14篇
  2014年   23篇
  2013年   61篇
  2012年   29篇
  2011年   26篇
  2010年   15篇
  2009年   24篇
  2008年   22篇
  2007年   26篇
  2006年   17篇
  2005年   19篇
  2004年   29篇
  2003年   26篇
  2002年   18篇
  2001年   19篇
  2000年   13篇
  1999年   7篇
  1998年   16篇
  1997年   6篇
  1996年   8篇
  1994年   16篇
  1993年   11篇
  1992年   5篇
  1991年   8篇
  1990年   12篇
  1989年   7篇
  1988年   8篇
  1987年   6篇
  1986年   11篇
  1985年   7篇
  1984年   6篇
  1983年   10篇
  1982年   8篇
  1981年   8篇
  1980年   10篇
  1979年   5篇
  1978年   6篇
  1977年   5篇
  1976年   4篇
  1975年   2篇
  1973年   3篇
  1972年   2篇
  1967年   2篇
排序方式: 共有654条查询结果,搜索用时 804 毫秒
351.
ABSTRACT: Previous reports based on climate change scenarios have suggested that California will be subjected to increased wintertime and decreased summertime streamflow. Due to the uncertainty of projections in future climate, a new range of potential climatological future temperature shifts and precipitation ratios is applied to the Sacramento Soil Moisture Accounting Model and Anderson Snow Model in order to determine hydrologic sensitivities. Two general circulation models (GCMs) were used in this analysis: one that is warm and wet (HadCM2 run 1) and one that is cool and dry (PCM run B06.06), relative to the GCM projections for California that were part of the Third Assessment Report of the Intergovernmental Panel on Climate Change. A set of specified incremental temperature shifts from 1.5°C to 5.0°C and precipitation ratios from 0.70 to 1.30 were also used as input to the snow and soil moisture accounting models, providing for additional scenarios (e.g., warm/dry, cool/wet). Hydrologic calculations were performed for a set of California river basins that extend from the coastal mountains and Sierra Nevada northern region to the southern Sierra Nevada region; these were applied to a water allocation analysis in a companion paper. Results indicate that for all snow‐producing cases, a larger proportion of the streamflow volume will occur earlier in the year. The amount and timing is dependent on the characteristics of each basin, particularly the elevation. Increased temperatures lead to a higher freezing line, therefore less snow accumulation and increased melting below the freezing height. The hydrologic response varies for each scenario, and the resulting solution set provides bounds to the range of possible change in streamflow, snowmelt, snow water equivalent, and the change in the magnitude of annual high flows. An important result that appears for all snowmelt driven runoff basins, is that late winter snow accumulation decreases by 50 percent toward the end of this century.  相似文献   
352.
Many government agencies and other organizations hold large tracts of surplus land. Some are investigating ways to lower expenses by selling the land or transferring management responsibility. There is no generally recognized process used to decide what land can be decommissioned and what future use would be best. This paper provides guidance for land‐use decisions in the form of a checklist. The checklist questions address both the socio‐economic resources and current land use in the region, and the ecological resources and suitability of the tract itself. The answers will clarify regional public needs and the economic and ecological values of the land.  相似文献   
353.
354.
There is a continuing debate about the proper role of analytical (positivist) science in natural resource decision making. Two diametrically opposed views are evident, arguing for and against a more extended role for scientific information. The debate takes on a different complexion if one recognizes that certain kinds of problem, referred to here as “wicked” or “trans-science” problems, may not be amenable to the analytical process. Indeed, the mistaken application of analytical methods to trans-science problems may not only be a waste of time and money but also serve to hinder policy development. Since many environmental issues are trans-science in nature, then it follows that alternatives to analytical science need to be developed. In this article, the issues involved in the debate are clarified by examining the impact of the use of analytical methods in a particular case, the spruce budworm controversy in New Brunswick. The article ends with some suggestions about a “holistic” approach to the problem.  相似文献   
355.
Summary An increased role for citizen participation in natural resource decision-making has been advocated by, amongst others, the United Nations (Brundtland Commission) as a means of initiating fundamental changes in the way we exploit natural resources. However, attempts at meaningful participation by the public are met with resistance, commonly by the dominant elites who control environmental and economic policies. Citizen groups press for involvement, only to be dismissed by local establishments as ill-informed amateurs. The resulting conflicts seldom lead to innovations in policy or to constructive cooperation in the face of new environmental problems. This leads the author to feelings of pessimism about prospects for genuine public participation in the absence of political change. In arguing in support of such change, a case study is offered which illustrates the unfortunate consequences that ensue when participation is sought and rejected. The paper closes with recommendations for the way in which citizen groups could contribute in a meaningful way to natural resource decision-making, were they to be given the opportunity.Dr Alan Miller is currently Professor of Psychology at the University of New Brunswick. He has published previously in this journal on the topic of Ideology and Environmental Risk Management (The Environmentalist,5(1), 21–30.)  相似文献   
356.
ABSTRACT: Water surface temperatures can be obtained from satellite thermal remote sensing. Landsat and other satellites sense emitted thermal infrared radiation on a regular basis over much of the earth's surface. Evaporation is accomplished by the net transport of mass from the water surface to the atmosphere. The evaporative transfer predominantly determines the water surface temperature. Hence, there should be good correlations between evaporation and surface temperatures. Previous investigations on Utah Lake with satellite-derived temperatures and pan- and model-derived evaporation values have produced good correlations. However, more study was required with additional satellite data and evaporation measurements for saltwater conditions. The applicability of this method for estimating evaporation on Utah's Great Salt Lake was of particular interest at this time because of the unprecedented rise of this terminal lake. Satellite thermal data and evaporation data from four different years were obtained for the Great Salt Lake and the surrounding region. More than 350 correlation and linear regression analyses were performed on the temperature and evaporation data. The lake salt concentrations were also factored into the analyses in several different ways. The correlation results were generally very good and a methodology for using satellite-derived water surface temperatures along with salt concentrations was developed to estimate evaporation.  相似文献   
357.
358.
ABSTRACT: Outflow from the Sacramento-San Joaquin river system (Delta outflow) provides about 90 percent of the freshwater flow to San Francisco Bay. Because this river system also supplies most of the water used in California, some believed that annual freshwater flow to the Bay had declined by as much as 50 to 60 percent as water use increased. Consequently, we studied trends in actual Delta outflow and precipitation for the period 1921 to 1986, which is when Delta outflow data are available. We found that there has been no decrease in the annual Delta outflow over this period. In fact, a statistically significant increase in annual Delta outflow of 87 cfa/yr has occurred during the period 1921 to 1986. One reason that Delta outflow has increased is because precipitation has increased faster than water use. Other contributing factors include increased runoff from land use changes, water imports from other areas, and the redistribution of ground water. In addition, statistically significant seasonal trends in Delta outflow were found. Over the period 1921–1986 Delta outflow decreased in April and May and increased from July through November. Changes in other months were not statistically significant. These seasonal changes result primarily from the operation of upstream flood control and water development projects, which store water in the spring and release it in the summer and fall. These seasonal changes are also influenced by a climatic shift that has decreased spring snowmelt runoff and increased late summer through winter precipitation.  相似文献   
359.
Recent years have seen the environment emerge as one of the most pressing issues facing American business. Eventually, environmental costs will affect the bottom line of every American company. A recent study in the National Law Journal estimates that cleanup of the nation's known hazardous wastes sites will cost $752 billion over thirty years under current environmental policies. Environmental legislation and regulations impose annual compliance costs estimated by the Environmental Protection Agency at more than $30 billion. In the near future, environmental expenses for cleanup, regulatory compliance, and management are anticipated to grow to between 2.5 and 3 percent of GNP. Corporations that wish to be competitive must successfully manage these costs while maintaining or improving their role as responsible corporate citizens. Implementing a comprehensive system for identifying and managing environmental costs requires a multidisciplinary team effort. Environmental costs impact product selection, design and pricing, capital budgeting, and future strategic direction. In order to make informed and meaningful managerial decisions on environmental programs, real cost data are vital. An environmental management systems (EMS) requires information to set goals and then monitor progress towards those goals over time. This article will discuss the current cost accounting systems (CASs) available to support the myriad goals of environmental management systems. In addition, the article will outline a framework for plotting the location of your current EMS on a matrix of regulatory and information requirements and evaluating whether your corporation's CAS is adequate to support the goals and objectives set by your environmental management program. By anticipating future regulatory and information requirements, flexible systems can be developed to adapt to new and more stringent regulations and more complex information requirements.  相似文献   
360.
ABSTRACT: An integrated, multi-disciplinary effort to model land processes affecting Mayaguez Bay in western Puerto Rico is described. A modeling strategy was developed to take advantage of remotely sensed data. The spatial, interannual, and seasonal variability of sediment discharges to the bay were also evaluated. Classified images of remotely sensed data revealed the spatial distribution and quantities of land use classes in the region and aided in the discretization of the watershed into homogeneous regions. These regions were modeled using a geomorphic modeling technique based upon spatially averaged parameters. Simulation results from the modeling effort compared favorably with observations at two locations within the watershed. Results showed that runoff and sediment loads from the area exhibit a marked seasonal trend and that deforested areas located in the foothill regions of the watershed contribute a disproportionate share of the sediment load to the bay. In years when rainfall distributions are uniformly distributed over the area, the sediment yields may be up to 100 percent higher than years when the rainfall is concentrated in the heavily forested mountainous regions.  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