全文获取类型
收费全文 | 1299篇 |
免费 | 41篇 |
国内免费 | 103篇 |
专业分类
安全科学 | 160篇 |
废物处理 | 12篇 |
环保管理 | 465篇 |
综合类 | 257篇 |
基础理论 | 216篇 |
环境理论 | 3篇 |
污染及防治 | 142篇 |
评价与监测 | 71篇 |
社会与环境 | 64篇 |
灾害及防治 | 53篇 |
出版年
2023年 | 8篇 |
2022年 | 27篇 |
2021年 | 32篇 |
2020年 | 40篇 |
2019年 | 34篇 |
2018年 | 29篇 |
2017年 | 35篇 |
2016年 | 57篇 |
2015年 | 44篇 |
2014年 | 45篇 |
2013年 | 98篇 |
2012年 | 45篇 |
2011年 | 79篇 |
2010年 | 39篇 |
2009年 | 71篇 |
2008年 | 66篇 |
2007年 | 74篇 |
2006年 | 58篇 |
2005年 | 43篇 |
2004年 | 47篇 |
2003年 | 54篇 |
2002年 | 34篇 |
2001年 | 35篇 |
2000年 | 39篇 |
1999年 | 33篇 |
1998年 | 26篇 |
1997年 | 19篇 |
1996年 | 20篇 |
1995年 | 18篇 |
1994年 | 19篇 |
1993年 | 21篇 |
1992年 | 13篇 |
1991年 | 18篇 |
1990年 | 6篇 |
1989年 | 9篇 |
1988年 | 12篇 |
1987年 | 9篇 |
1986年 | 10篇 |
1985年 | 4篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 6篇 |
1978年 | 7篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1972年 | 10篇 |
1971年 | 8篇 |
1970年 | 4篇 |
排序方式: 共有1443条查询结果,搜索用时 31 毫秒
731.
A regional framework for establishing recovery criteria 总被引:6,自引:0,他引:6
Robert M. Hughes Thomas R. Whittier Christina M. Rohm David P. Larsen 《Environmental management》1990,14(5):673-683
Effective assessments of aquatic ecosystem recovery require ecologically sound endpoints against which progress can be measured.
Site-by-site assessments of end points and potential recovery trajectories are impractical for water resource agencies. Because
of the natural variation among ecosystems, applying a single set of criteria nationwide is not appropriate either. This article
demonstrates the use of a regional framework for stratifying natural variation and for determining realistic biological criteria.
A map of ecoregions, drawn from landscape characteristics, formed the framework for three statewide case studies and three
separate studies at the river basin scale. Statewide studies of Arkansas, Ohio, and Oregon, USA, streams demonstrated patterns
in fish assemblages corresponding to ecoregions. The river basin study in Oregon revealed a distinct change at the ecoregion
boundary; those in Ohio and Montana demonstrated the value of regional reference sites for assessing recovery. Ecoregions
can be used to facilitate the application of ecological theory and to set recovery criteria for various regions of states
or of the country. Such a framework provides an important alternative between site-specific and national approaches for assessing
recovery rates and conditions. 相似文献
732.
Jefferson Fox Rebekah Kanter Sanay Yarnasarn Methi Ekasingh Royce Jones 《Environmental management》1994,18(3):391-399
This research has two interrelated objectives. The first is to determine the extent to which a relationship exists between
farmer characteristics and farming practices in three villages in northern Thailand. The second is to use standard statistical
methods for incorporating spatial variables into the analysis and to assess the effects of these variables on farmer decision
making. The data base includes information on the location and size of villages, roads, streams, and fields; a digital elevation
model with information on elevation, slope, and aspect; and information keyed to individual fields on crops and cropping methods
and the ethnicity, income, and religion of farmers. The map data (517 plots) were entered into a computerized geographic information
systems (GIS). Results suggest several hypotheses about the relationships between land use and owner characteristics. More
significantly, the study concludes that spatial analysis appears to be most useful when the dependent variable is either continuous
or ordinal. The outlook is not quite as optimistic when the dependent variable is a nonordinal categorical variable. Before
spatial analysis can be applied regularly to social science data, better computational tools need to be developed. 相似文献
733.
John L. Hammen Philip J. Gerla 《Journal of the American Water Resources Association》1994,30(5):833-840
ABSTRACT: The 1986 Amendments to the Safe Drinking Water Act mandate a multifaceted approach to wellhead protection. This approach includes: (1) delineating wellhead protection areas; (2) identifying and managing potential contaminants; (3) developing contingency plans in the event of weilfield contamination; (4) siting new wells; and (5) encouraging public participation. These elements encompass technical, administrative, and educational considerations. In functioning both as a research tool and as a decision support system, a geographic information system (GIS) is shown to have proven utility in addressing these issues. This article describes the application of common GIS functionality in facilitating a comprehensive wellhead protection scheme for an agricultural municipality in North Dakota. 相似文献
734.
Jiansheng Yan Keith R. Smith 《Journal of the American Water Resources Association》1994,30(5):879-890
ABSTRACT: The unique characteristics of the hydrogeologic system of south Florida (flat topography, sandy soils, high water table, and highly developed canal system) cause significant interactions between ground water and surface water systems. Interaction processes involve infiltration, evapotranspiration (ET), runoff, and exchange of flow (seepage) between streams and aquifers. These interaction processes cannot be accurately simulated by either a surface water model or a ground water model alone because surface water models generally oversimplify ground water movement and ground water models generally oversimplify surface water movement. Estimates of the many components of flow between surface water and ground water (such as recharge and ET) made by the two types of models are often inconsistent. The inconsistencies are the result of differences in the calibration components and the model structures, and can affect the confidence level of the model application. In order to improve model results, a framework for developing a model which integrates a surface water model and a ground water model is presented. Dade County, Florida, is used as an example in developing the concepts of the integrated model. The conceptual model is based on the need to evaluate water supply management options involving the conjunctive use of surface water and groundwater, as well as the evaluation of the impacts of proposed wellfields. The mathematical structure of the integrated model is based on the South Florida Water Management Model (SFWMM) (MacVicar et al., 1984) and A Modular Three-Dimensional Finite-Difference Groundwater Flow Model (MODFLOW) (McDonald and Harbaugh, 1988). 相似文献
735.
D. W. Bacon O. T. Coomes A. A. Marsan N. Rowlands 《Journal of the American Water Resources Association》1986,22(1):29-38
ABSTRACT: A comparative study of the concentration of asbestos fibers in drinking water supplies of southeastern Quebec was undertaken to assess the relative contributions of fibers by asbestos-bearing railway ballast and naturally occurring asbestos deposits. Water samples were taken from areas where one or the other potential sources or neither potential source was present. In addition, rainwater samples were taken to assess the importance of atmospheric contributions. The sampling design accounted for potential variations in fiber counts due to the season, location and analytical procedures. Fiber concentrations were estimated from counts made on a JEOL 100CX scanning transmission electron microscope and statistically compared among areas. These levels were then compared with levels found in other areas of Canada and the United States. The results indicate that the rail ballast could be contributing statistically (albeit marginally) significant quantities of fibers to water supplies during the summer but not in the spring. Estimated concentrations in water supplies ranged between 1.7 × 106fibers/liter and 147.8 × 106fibers/liter. Fiber levels in samples taken during the spring were significantly higher and more variable than those taken during the summer. The presence of fibers in rainwater samples at concentrations of 1.9 × 106fibers/liter, 18.3 × 106fibers/liter and 23.7 × 106fibers/liter suggests that atmospheric transport may play an important role in contributing fibers to regional systems. Fiber levels found in these systems are not unique when compared to levels observed elsewhere in North America. 相似文献
736.
Charles P. Newcombe 《Environmental management》1985,9(4):277-288
The problem of acid deposition and its harmful effects on aquatic ecosystems has created a new branch of science that is called upon to provide the knowledge on which legislative controls can be based. However, because of the nature of existing legislation, which requires evidence of cause and effect between industrial emissions and pollution, and because of science's inability to provide this information over the short term, considerable controversy has arisen about whether sufficient information exists to warrant control measures at this time. Among those who advocate controls, there is genuine divergence of opinion about how stringent the controls must be to achieve any desired level of protection.The controversy has led to an impasse between the scientific and political participants, which is reflected in the slow pace of progress toward an effective management strategy. Resolution of the impasse, at least in the short term, may demand that science and politics rely on empirical models rather than explanatory ones. The empirical model, which is the major proposal in this article, integrates all of the major variables and many of the minor ones, and constructs a three-dimensionally curved surface capable of representing the status of any waterbody subjected to the effects of acid deposition. When suitably calibrated—a process involving the integration of knowledge and data from aquatic biology, geochemistry, meteorology, and limnology—it can be used to depict limits to the rate of acid deposition required for any level of environmental protection. Because it can generate a pictorial display of the effects of management decisions and legislative controls, the model might serve as a basis for enhancing the quality of communication among all the scientific and political participants and help to resolve many of their controversies. 相似文献
737.
This paper examines opportunities to improve the environmental and economic performance of cropping systems through intensified
application of information in agrichemical management. Through intensified application of information, both net farm income
and environmental quality may increase through more closely matching the specific needs of the crop with the type, timing,
and volume of chemical inputs used in crop production.
This study examines the current status and future prospect of agrichemical dealers offering information intensive agrichemical
management services to producers.
Agrichemical dealers are the focus of this study because: (1) farmers are perceived as ill-prepared to substantially upgrade
the sophistication of their agrichemical management without off-farm support, and (2) dealers enjoy a close relationship with
farmers, which potentially could be expanded to include a variety of information-based services. A mail survey was conducted
of all agrichemical suppliers/applications in Wisconsin. The response rate was 76% (172 of 225).
Substantial numbers of services were found to be offered by many dealers. The majority of these services were related to traditional
yield-enhancement function. Services that have a greater potential to mitigate the negative environmental impacts of inefficient
agrichemical use and have higher on-farm data requirements were found to be less widely offered by dealers. Analysis of constraints
to further development of information-intensive services indicates that dealers offering significant numbers of services are
concerned with constraints external to the dealership, while dealers offering relatively few services perceive internal constraints
as most limiting. This relationship indicates that efforts to accelerate dealerships' development of information-intensive
agrichemical management services should focus on specific constraints operating on targeted dealerships. 相似文献
738.
A watershed disturbance index developed by the USDA Forest Service called equivalent roaded area (ERA) was used to assess
the cumulative effect from forest management in California's Sierra Nevada and Klamath mountain ranges. The basins' ERA index
increased as logging and road-building occurred and then decreased over time as management ceased and vegetation recovered.
A refinement of the standard index emphasized disturbances in sensitive, near-channel areas, and evaluated recovery periods
of 20, 30, and 50 years. Shorter recovery periods yielded better correlations between recovering forest systems and aquatic
response than the longer recovery period, as represented by ERA and diversity or dominance, respectively. The refined ERA
index correlated more closely with macroinvertebrate dominance and diversity information that was available for part of the
study period. A minimum ERA threshold of 5% was detected, below which no effect to the macroinvertebrate community was observed.
Above this threshold, elevated ERA values were associated with a decline in macroinvertebrate diversity and an increase in
dominance of the top five taxa. Use of an ERA technique that emphasizes near-channel areas and biological thresholds would
contribute to the Forest Service's implementation of ecosystem management. 相似文献
739.
740.
以某大型危险化学品储运企业为背景,对重大危险源应急救援信息系统进行研究,首先对重大危险源应急救援过程中各种信息需求进行分析,将信息分为基础信息、预防信息和救援信息3个方面;然后在单机和网络两种版本硬件结构比较的基础上,以工艺参数传感器、泄漏传感器、火灾报警器、应急设备控制器等主要设备为基础构建了单机版的硬件结构;最后,采用C/S软件结构,运用组件式GIS技术,从系统的总体结构、数据库结构以及功能设计等几个方面对应急救援信息系统进行了研究。 相似文献