全文获取类型
收费全文 | 8325篇 |
免费 | 568篇 |
国内免费 | 305篇 |
专业分类
安全科学 | 1701篇 |
废物处理 | 140篇 |
环保管理 | 3069篇 |
综合类 | 2195篇 |
基础理论 | 818篇 |
环境理论 | 10篇 |
污染及防治 | 256篇 |
评价与监测 | 336篇 |
社会与环境 | 344篇 |
灾害及防治 | 329篇 |
出版年
2023年 | 106篇 |
2022年 | 134篇 |
2021年 | 199篇 |
2020年 | 266篇 |
2019年 | 196篇 |
2018年 | 167篇 |
2017年 | 226篇 |
2016年 | 315篇 |
2015年 | 275篇 |
2014年 | 324篇 |
2013年 | 473篇 |
2012年 | 459篇 |
2011年 | 580篇 |
2010年 | 387篇 |
2009年 | 499篇 |
2008年 | 361篇 |
2007年 | 471篇 |
2006年 | 473篇 |
2005年 | 364篇 |
2004年 | 395篇 |
2003年 | 303篇 |
2002年 | 279篇 |
2001年 | 275篇 |
2000年 | 272篇 |
1999年 | 208篇 |
1998年 | 135篇 |
1997年 | 143篇 |
1996年 | 114篇 |
1995年 | 123篇 |
1994年 | 55篇 |
1993年 | 67篇 |
1992年 | 59篇 |
1991年 | 51篇 |
1990年 | 36篇 |
1989年 | 27篇 |
1988年 | 34篇 |
1987年 | 36篇 |
1986年 | 28篇 |
1985年 | 25篇 |
1984年 | 28篇 |
1983年 | 17篇 |
1982年 | 22篇 |
1981年 | 18篇 |
1980年 | 25篇 |
1979年 | 33篇 |
1978年 | 21篇 |
1975年 | 14篇 |
1973年 | 14篇 |
1972年 | 16篇 |
1971年 | 14篇 |
排序方式: 共有9198条查询结果,搜索用时 15 毫秒
251.
Quantifying and Evaluating Ecosystem Health: A Case Study from Moreton Bay, Australia 总被引:1,自引:0,他引:1
As part of the program monitoring the ecosystem health of Moreton Bay, Queensland, Australia, we developed a means for assessing
ecosystem health that allows quantitative evaluation and spatial representations of the assessments. The management objectives
for achieving ecosystem health were grouped into ecosystem objectives, water quality objectives, and human health objectives.
For the first two groups, aspects of the ecosystem (e.g., trophic status) were identified, and an indicator was chosen for
each aspect. Reference values for each indicator were derived from management objectives and compared with the mapped survey
values. Subregions for which the indicator statistic was equal to or better than the assigned reference value are referred
to as “compliant zones.” High-resolution surface maps were created from spatial predictions on a fine hexagonal grid for each
of the indicators. Eight reporting subregions were established based on the depth and predicted residence times of the water.
Within each reporting subregion, the proportion that was compliant was calculated. These results then were averaged to create
an integrated ecosystem health index. The ratings by a team of ecosystem experts and the calculated ecosystem health indices
had good correspondence, providing assurance that the approach was internally consistent, and that the management objectives
covered the relevant biologic issues for the region. This method of calculating and mapping ecosystem health, relating it
directly to management objectives, may have widespread applicability for ecosystem assessment. 相似文献
252.
We examined the principal effects of different information network topologies for local adaptive management of natural resources.
We used computerized agents with adaptive decision algorithms with the following three fundamental constraints: (1) Complete
understanding of the processes maintaining the natural resource can never be achieved, (2) agents can only learn by experimentation
and information sharing, and (3) memory is limited. The agents were given the task to manage a system that had two states:
one that provided high utility returns (desired) and one that provided low returns (undesired). In addition, the threshold
between the states was close to the optimal return of the desired state. We found that networks of low to moderate link densities
significantly increased the resilience of the utility returns. Networks of high link densities contributed to highly synchronized
behavior among the agents, which caused occasional large-scale ecological crises between periods of stable and high utility
returns. A constructed network involving a small set of experimenting agents was capable of combining high utility returns
with high resilience, conforming to theories underlying the concept of adaptive comanagement. We conclude that (1) the ability
to manage for resilience (i.e., to stay clear of the threshold leading to the undesired state as well as the ability to re-enter
the desired state following a collapse) resides in the network structure and (2) in a coupled social–ecological system, the
systemwide state transition occurs not because the ecological system flips into the undesired state, but because managers
lose their capacity to reorganize back to the desired state.
An erratum to this article can be found at . 相似文献
253.
Environmental Auditing and the Role of the Accountancy Profession: A Literature Review 总被引:3,自引:0,他引:3
This review of the literature on environmental auditing and the potential role of accountants distinguishes between compliance audits and audits of the environmental management system. After an extensive introduction to the concept, this review focuses on the similarities and differences between an environmental audit and a financial statement audit. The general approach to both types of audits is similar, except that environmental audits are largely unregulated. Both audits place an emphasis on the evaluation of control systems, which is an argument in favor of external auditors playing a role in environmental audits. Another argument for including external accountants is their code of ethics. However, these professionals seem to be reluctant to enter the field of environmental auditing. It is argued that this reluctance is because of a lack of generally accepted principles for conducting environmental audits. If external accountants are engaged in environmental auditing, they should be part of multidisciplinary teams that also include scientists and engineers to avoid a too strong focus on procedures. Rather than treating these audits as totally different, it is proposed that there be a move towards integrated, or even universal, audits. 相似文献
254.
A multi-objective optimisation approach to water management 总被引:3,自引:0,他引:3
The management of river basins is complex especially when decisions about environmental flows are considered in addition to those concerning urban and agricultural water demand. The solution to these complex decision problems requires the use of mathematical techniques that are formulated to take into account conflicting objectives. Many optimization models exist for water management systems but there is a knowledge gap in linking bio-economic objectives with the optimum use of all water resources under conflicting demands. The efficient operation and management of a network of nodes comprising storages, canals, river reaches and irrigation districts under environmental flow constraints is challenging. Minimization of risks associated with agricultural production requires accounting for uncertainty involved with climate, environmental policy and markets. Markets and economic criteria determine what crops farmers would like to grow with subsequent effect on water resources and the environment. Due to conflicts between multiple goal requirements and the competing water demands of different sectors, a multi-criteria decision-making (MCDM) framework was developed to analyze production targets under physical, biological, economic and environmental constraints. This approach is described by analyzing the conflicts that may arise between profitability, variable costs of production and pumping of groundwater for a hypothetical irrigation area. 相似文献
255.
Thora Martina Herrmann 《Natural resources forum》2005,29(2):120-134
One of the most important endemic tree species of Chile and at the same time one of the most endangered ones is Araucaria araucana (Mol.) C. Koch, the monkey‐puzzle tree. It grows in the Andes Mountains, homeland of the indigenous Mapuche Pewenche people who depend on this tree. This paper is based on field research that investigated the ecological knowledge, uses and management of the Araucaria araucana forest by indigenous Mapuche Pewenche people based on the socio‐cultural, spiritual and ecological relationships they have with the Araucaria forest, to find out how indigenous people and their knowledge could contribute to sustainable Araucaria forest management. A Mapuche Pewenche community located in the IX region of Chile contributed to this study. Based on the analyses this paper illustrates the nature of indigenous ecological knowledge of Araucaria araucana on the one hand, and its utility in native forest management on the other. The research shows that the Mapuche Pewenche hold ecological knowledge and conduct practices to manage their Araucaria forest in a balanced way. They conserve and use forest biodiversity at one and the same time. This paper provides recommendations for sustainable Araucaria forest management and conservation strategies ex‐situ and in‐situ incorporating indigenous knowledge and scientific knowledge and for promoting a collaborative natural resources management. 相似文献
256.
A recent comprehensive review of the characteristics and utilization of copper slags encourages (properly) several applications for this important pyrometallurgical byproduct. However, the review does not include possible environmental effects from these slags. The United Nations Basel Convention on the Transboundary Movement of Hazardous Wastes and Their Disposal characterizes copper compounds that exhibit specified hazard characteristics as hazardous wastes. In 1996, the Convention considered further characterization of these and other compounds and substances. The final characterization of copper slags is as non-hazardous, i.e., exempt from control. This decision was based in part (if not largely) on the data that are presented here. Literature reports were used to accumulate data describing the chemical composition and acid leaching of commercial copper slags from three countries. From these data, average values of chemical composition and their statistical confidence limits (95%) were calculated. The variability of the chemical analyses of three commercial slags produced over 19 or 20 months were statistically analyzed and shown to be small. The concentrations of toxic heavy metals in the slags are low and the frequency distributions of the values are narrow. Most of the data are normally distributed, validating the use of the statistics used and permitting predictions of likely values. The amounts of heavy metals extracted by an aggressive standard acid leach procedure are low and well below the United States. regulatory levels derived from drinking water standards. The results for total composition and leaching illustrate why the U.S. Environmental Protection Agency made a regulatory determination that such slags are not hazardous wastes. Later, in 1996, the Basel Convention Technical Working Group concurred and the Parties to the Convention adopted their recommendation. 相似文献
257.
Abedalrazq F. Khalil Mac McKee Mariush Kemblowski Tirusew Asefa 《Journal of the American Water Resources Association》2005,41(1):195-208
ABSTRACT: Water scarcity in the Sevier River Basin in south‐central Utah has led water managers to seek advanced techniques for identifying optimal forecasting and management measures. To more efficiently use the limited quantity of water in the basin, better methods for control and forecasting are imperative. Basin scale management requires advanced forecasts of the availability of water. Information about long term water availability is important for decision making in terms of how much land to plant and what crops to grow; advanced daily predictions of streamflows and hydraulic characteristics of irrigation canals are of importance for managing water delivery and reservoir releases; and hourly forecasts of flows in tributary streams to account for diurnal fluctuations are vital to more precisely meet the day‐to‐day expectations of downstream farmers. A priori streamflow information and exogenous climate data have been used to predict future streamflows and required reservoir releases at different timescales. Data on snow water equivalent, sea surface temperatures, temperature, total solar radiation, and precipitation are fused by applying artificial neural networks to enhance long term and real time basin scale water management information. This approach has not previously been used in water resources management at the basin‐scale and could be valuable to water users in semi‐arid areas to more efficiently utilize and manage scarce water resources. 相似文献
258.
Douglas G. Boyer 《Journal of the American Water Resources Association》2005,41(2):291-300
ABSTRACT: Water quality indicators of two agriculturally impacted karst areas in southeastern West Virginia were studied to determine the water quality effects of grazing agriculture and water quality trends following initiation of water quality improvement programs. Both areas are tributaries of the Greenbrier River and received funding for best management practices under the President's Initiative for Water Quality and then under the Environmental Quality Incentives Program (EQIP). After 11 years of study there was little evidence to suggest that water quality improved in one area. Three and a half years of study in the other area showed little evidence of consistent water quality improvement under EQIP. Lack of consistent water quality improvement at the catchment scale does not imply that the voluntary programs were failures. Increased livestock numbers as a result of successful changes in forage management practices may have overridden water quality improvements achieved through best management practices. Practices that target well defined contributing areas significantly impacting aquifer water quality might be one way to improve water quality at catchment scales in karst basins. For example, a significant decrease in fecal coliform concentrations was observed in subterranean drainage from one targeted sinkhole after dairy cattle were permanently excluded from the sinkhole. 相似文献
259.
John V. Westra Julie K.H. Zimmerman Bruce Vondracek 《Journal of the American Water Resources Association》2005,41(2):309-322
ABSTRACT: Farmers can generate environmental benefits (improved water quality and fisheries and wildlife habitat), but they may not be able to quantify them. Furthermore, farmers may reduce their incomes from managing lands to produce these positive externalities but receive little monetary compensation in return. This study simulated the relationship between agricultural practices, water quality, fish responses to suspended sediment and farm income within two small watersheds, one of a cool water stream and one of a warm water stream. Using the Agricultural Drainage and Pesticide Transport (ADAPT) model, this study related best management practices (BMPs) to calculated instream suspended sediment concentrations by estimating sediment delivery, runoff, base flow, and streambank erosion to quantify the effects of suspended sediment exposure on fish communities. By implementing selected BMPs in each watershed, annual net farm income declined $18,000 to $28,000 (1 to 3 percent) from previous levels. “Lethal” fish events from suspended sediments in the cool water watershed decreased by 60 percent as conservation tillage and riparian buffers increased. Despite reducing suspended sediments by 25 percent, BMPs in the warm water watershed did not reduce the negative response of the fisheries. Differences in responses (physical and biological) between watersheds highlight potential gains in economic efficiency by targeting BMPs or by offering performance based “green payments.” 相似文献
260.
Lee Benda Marwan A. Hassan Michael Church Christine L. May 《Journal of the American Water Resources Association》2005,41(4):835-851
Headwater streams comprise 60 to 80 percent of the cumulative length of river networks. In hilly to mountainous terrain, they reflect a mix of hillslope and channel processes because of their close proximity to sediment source areas. Their morphology is an assemblage of residual soils, landslide deposits, wood, boulders, thin patches of poorly sorted alluvium, and stretches of bedrock. Longitudinal profiles of these channels are strongly influenced by steps created by sediment deposits, large wood, and boulders. Due to the combination of small drainage area, stepped shallow gradient, large roughness elements, and cohesive sediments, headwater streams typically transport little sediment or coarse wood debris by fluvial processes. Consequently, headwaters act as sediment reservoirs for periods spanning decades to centuries. The accumulated sediment and wood may be episodically evacuated by debris flows, debris floods, or gully erosion and transported to larger channels. In mountain environments, these processes deliver significant amounts of materials that form riverine habitats in larger channels. In managed steepland forests, accelerated rates of landslides and debris flows resulting from the harvest of headwater forests have the potential to seriously impact the morphology of headwater streams and downstream resources. 相似文献