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   859篇
  免费   21篇
  国内免费   46篇
安全科学   72篇
废物处理   15篇
环保管理   202篇
综合类   380篇
基础理论   81篇
污染及防治   45篇
评价与监测   90篇
社会与环境   38篇
灾害及防治   3篇
  2024年   3篇
  2023年   7篇
  2022年   12篇
  2021年   22篇
  2020年   23篇
  2019年   11篇
  2018年   14篇
  2017年   15篇
  2016年   21篇
  2015年   25篇
  2014年   42篇
  2013年   41篇
  2012年   45篇
  2011年   60篇
  2010年   41篇
  2009年   48篇
  2008年   49篇
  2007年   50篇
  2006年   43篇
  2005年   24篇
  2004年   26篇
  2003年   31篇
  2002年   29篇
  2001年   29篇
  2000年   30篇
  1999年   22篇
  1998年   31篇
  1997年   19篇
  1996年   10篇
  1995年   8篇
  1994年   16篇
  1993年   11篇
  1992年   11篇
  1991年   6篇
  1989年   1篇
  1988年   2篇
  1987年   7篇
  1986年   8篇
  1985年   4篇
  1984年   6篇
  1983年   2篇
  1982年   5篇
  1981年   4篇
  1980年   4篇
  1979年   5篇
  1978年   2篇
  1973年   1篇
排序方式: 共有926条查询结果,搜索用时 15 毫秒
851.
Evaluation of conservation education programs can: (1) provide accountability in demonstrating a program's worth, (2) offer an opportunity for receiving feedback and improving programs, (3) further our understanding of the process of program development, and (4) promote conservation education by substantiating claims about its benefits. The Planning-Process-Product systems evaluation model provides feedback needed for making decisions about the development, implementation, and outcome of a program. Planning evaluation was useful in assessing the needs, goals, opportunities, and constraints of a number of programs in Costa Rica and Belize, such as a forestry education project and a zoo outreach program. It provided a basis for making planning decisions incorporating specific objectives, such as the reforestation of a region or a change in knowledge and attitudes in program participants. Process evaluation provided a Costa Rican sustainable development program with feedback during its implementation and enabled it to modify and improve its newsletter for local farmers and its ecology classes for school children. Product evaluation assessed project accomplishments, such as the $700,000 raised by the Children's Rainforest group and the 20 miles of riparian land under conservation management as part of the Belize Community Baboon Sanctuary project. Outcomes are compared with the programs original monetary or land management objectives to determine the success of the programs and to provide feedback for improvement.  相似文献   
852.
Cross-boundary issues for national parks: What works “on the ground”   总被引:1,自引:0,他引:1  
In recent years, cross-boundary management has become an essential part of park management. In this article we compare the perspectives of managers of several US national parks to the advice on this issue presented in the published literature. Data were obtained from interviews of the superintendents, assistant superintendents and resources managers of five major western national parks and from a survey of participants in a NPS workshop attended by park superintendents, scientists, and resource managers; law enforcement personnel; and interpreters. Three themes related to boundary management were consistently stressed by park managers: (10 a lack of sufficient funds and personnel within the parks; (2) the need for reliable information on both political and natural processes; and, (3) the importance of personal interactions between park staff and individuals from the surrounding area. Basic data collection, the documentation of trends, cooperative groups and personal contacts, educational programs, and land acquisition were the most useful strategies. A lack of funds and information, ineffective communication, enforcement problems, and a lack of motivation for parties to reach a negotiated agreement were the most serious obstacles. A wide range of valuable institutional knowledge concerning boundary management exists within the National Park Service; however, there appears to be a gap between published strategies and the approaches that work “on the ground”.  相似文献   
853.
Wastewater irrigation is an environmentally sound wastewater disposal practice, but sewage is more saline than the supplied fresh water and the salts are recycled together with the water. Salts have negative environmental effects on crops, soils, and groundwater. There are no inexpensive ways to remove the salts once they enter sewage, and the prevention of sewage salt enrichment is the most immediately available solution. The body of initiatives presently structured by the Ministry of the Environment of Israel are herein described, with the aim to contribute to the search for a long-term solution of salinity problems in arid countries. The new initiatives are based on: (1) search for new technologies to reduce salt consumption and discharge into sewage; (2) different technologies to cope with different situations; (3) raising the awareness of the public and industry on the environmental implications of salinity pollution; and (4) an elastic legal approach expressed through new state-of-the-art regulations. The main contributor to the salinity of sewage in Israel is the watersoftening process followed by the meat koshering process. Some of the adopted technical solutions are: the discharge of the brine into the sea, the substitution of sodium by potassium salts in the ion-exchangers, the construction of centralized systems for the supply of soft water in industrial areas, the precipitation of Ca and Mg in the effluents from ion-exchangers and recycling of the NaCI solution, a reduction of the discharge of salts by the meat koshering process, and new membrane technology for salt recovery.  相似文献   
854.
Specific industrial processes and its waste characteristics should be known for proper management and control of the wastes produced from industries. Some industrial processes and waste characteristics are introduced to explain how to deal with the wastes for waste characterization. Evaluation methods of biodegradability of industrial wastewater were introduced in order for environmental engineers to be able to decide the proper treatment method of the industrial wastewaters. Industrial processes and characterization discussed in this section might be useful for the selection of suitable methods to prevent pollutant discharge from industrial processes.  相似文献   
855.
Each National Park Service unit in the United States produces a resources management plan (RMP) every four years or less. The plans commit budgets and personnel to specific projects for four years, but they are prepared with little quantitative and analytical rigor and without formal decision-making tools. We have previously described a multiple objective planning process for inventory and monitoring programs (Schmoldt and others 1994). To test the applicability of that process for the more general needs of resources management planning, we conducted an exercise on the Olympic National Park (NP) in Washington State, USA. Eight projects were selected as typical of those considered in RMPs and five members of the Olympic NP staff used the analytic hierarchy process (AHP) to prioritize the eight projects with respect to their implicit management objectives. By altering management priorities for the park, three scenarios were generated. All three contained some similarities in rankings for the eight projects, as well as some differences. Mathematical allocations of money and people differed among these scenarios and differed substantially from what the actual 1990 Olympic NP RMP contains. Combining subjective priority measures with budget dollars and personnel time into an objective function creates a subjective economic metric for comparing different RMP’s. By applying this planning procedure, actual expenditures of budget and personnel in Olympic NP can agree more closely with the staff’s management objectives for the park.  相似文献   
856.
工业雷管在生产、贮运、使用过程中存在意外发火或爆炸事故。为了防止这种突然事件和避免带来的伤害与损失,笔者就可能导致意外起爆的各种原因进行了分析,提出了各种相应的防范措施和意见  相似文献   
857.
The main goal of this paper was to explore the relationship between living in industrial areas and individual’s level of psychological health. Using a quasi-experimental design main findings suggest that, regardless of the type of industry that is operating, there was a significant association between living in industrialized areas and decreased levels of well being, optimism and use of active coping strategies. However, results on anxiety and depression were especially high in areas associated with air pollution. Moreover, there was also a significant association between more subjective meanings of place and psychological health. According to a reality-orientation criterion, evidences showed that when individuals live in industrial areas perceptions of their places as industrial are associated with lower depression, anxiety and psychiatric symptoms.  相似文献   
858.
Abstract: Tree basal growth in response to flooding regime was evaluated at a 5.2‐ha bottomland forest along the Olentangy River in central Ohio. Tree‐ring analysis was used to develop a 14‐year basal area increment (BAI) (cm2/year) series for 42 canopy trees (representing 10 species) throughout the bottomland. Mean annual BAI was evaluated relative to the frequency and duration of bankfull (>70 m3/s) and high‐flood (>154 m3/s) river discharge for a given water year (October 1‐September 30) and growing season (April 1‐September 30). A significant polynomial relationship was detected between the number of days of high‐flood river discharge over a combined two‐year period (Year i + Year i ? 1) and mean annual BAI. No significant relationships were detected when only the concurrent‐year or previous‐year flood regimes were considered or when growing season was considered. A similar relationship was detected when duration of high‐flood discharge days and BAI were both evaluated in two‐year increments (Year i + Year i ? 1). Mean annual BAI was most influenced by boxelder (Acer negundo) which was the dominant species and exhibited strong agreement with the overall BAI series. In each case, the resulting parabolic curve of tree basal growth in response to flooding suggests an optimal number of flooding days, a response to perturbation consistent with the subsidy‐stress model. Dendrochronology may be a useful tool for managers looking to restore environmental flows to regulated rivers.  相似文献   
859.
Beaver–willow (Castor-Salix) communities are a unique and vital component of healthy wetlands throughout the Holarctic region. Beaver selectively forage willow to provide fresh food, stored winter food, and construction material. The effects of this complex foraging behavior on the structure and function of willow communities is poorly understood. Simulation modeling may help ecologists understand these complex interactions. In this study, a modified version of the SAVANNA ecosystem model was developed to better understand how beaver foraging affects the structure and function of a willow community in a simulated riparian ecosystem in Rocky Mountain National Park, Colorado (RMNP). The model represents willow in terms of plant and stem dynamics and beaver foraging in terms of the quantity and quality of stems cut to meet the energetic and life history requirements of beaver. Given a site where all stems were equally available, the model suggested a simulated beaver family of 2 adults, 2 yearlings, and 2 kits required a minimum of 4 ha of willow (containing about10 stems m−2) to persist in a steady-state condition. Beaver created a willow community where the annual net primary productivity (ANPP) was 2 times higher and plant architecture was more diverse than the willow community without beaver. Beaver foraging created a plant architecture dominated by medium size willow plants, which likely explains how beaver can increase ANPP. Long-term simulations suggested that woody biomass stabilized at similar values even though availability differed greatly at initial condition. Simulations also suggested that willow ANPP increased across a range of beaver densities until beaver became food limited. Thus, selective foraging by beaver increased productivity, decreased biomass, and increased structural heterogeneity in a simulated willow community.  相似文献   
860.
Impediments to refractory recycling decision-making   总被引:1,自引:0,他引:1  
This paper focuses on organizational impediments to the successful implementation of industrial recycling programs. Even if a technologically viable and mutually beneficial solution were to exist, there are a number of organizational impediments that make it unlikely to succeed unless the benefits are very large and apparent. These impediments stem from the difficulty in identifying potential partners and involving the appropriate individuals within the firms that understand the technical requirements, value the strategic benefits and are receptive towards establishing the industrial recycling relationship. This dilemma applies to many industrial recycling opportunities, but solutions do exist. One way to avoid some of these obstacles is to use a middleman, or broker, who can play several crucial roles to establish the relationship. This paper describes the impediments and key broker roles, and provides a case study dealing with refractory recycling. It provides a case study that documents a recycling relationship between an aluminum-manufacturing firm that produces a large volume of spent refractories and a regional portland cement producer that is using the spent refractories as an alternative raw material source. This paper also provides a thorough literature search in the area of refractory recycling. Finally, the case study provides an opportunity for analysis and reflection on the implications of these findings to industrial firms, industrial societies and governmental agencies that seek to encourage successful recycling operations.  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