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   689篇
  免费   179篇
安全科学   94篇
废物处理   66篇
环保管理   265篇
基础理论   316篇
污染及防治   67篇
评价与监测   5篇
灾害及防治   55篇
  2022年   1篇
  2021年   5篇
  2020年   8篇
  2019年   35篇
  2018年   54篇
  2017年   32篇
  2016年   54篇
  2015年   44篇
  2014年   55篇
  2013年   212篇
  2012年   30篇
  2011年   39篇
  2010年   49篇
  2009年   28篇
  2008年   30篇
  2007年   21篇
  2006年   23篇
  2005年   14篇
  2004年   19篇
  2003年   22篇
  2002年   27篇
  2001年   19篇
  2000年   20篇
  1999年   11篇
  1998年   1篇
  1997年   1篇
  1994年   4篇
  1993年   1篇
  1992年   2篇
  1991年   2篇
  1990年   1篇
  1988年   1篇
  1983年   2篇
  1966年   1篇
排序方式: 共有868条查询结果,搜索用时 15 毫秒
711.
The consensus is that both ecological and social factors are essential dimensions of conservation research and practice. However, much of the literature on multiple disciplinary collaboration focuses on the difficulties of undertaking it. This review of the challenges of conducting multiple disciplinary collaboration offers a framework for thinking about the diversity and complexity of this endeavor. We focused on conceptual challenges, of which 5 main categories emerged: methodological challenges, value judgments, theories of knowledge, disciplinary prejudices, and interdisciplinary communication. The major problems identified in these areas have proved remarkably persistent in the literature surveyed (c.1960–2012). Reasons for these failures to learn from past experience include the pressure to produce positive outcomes and gloss over disagreements, the ephemeral nature of many such projects and resulting lack of institutional memory, and the apparent complexity and incoherence of the endeavor. We suggest that multiple disciplinary collaboration requires conceptual integration among carefully selected multiple disciplinary team members united in investigating a shared problem or question. We outline a 9‐point sequence of steps for setting up a successful multiple disciplinary project. This encompasses points on recruitment, involving stakeholders, developing research questions, negotiating power dynamics and hidden values and conceptual differences, explaining and choosing appropriate methods, developing a shared language, facilitating on‐going communications, and discussing data integration and project outcomes. Although numerous solutions to the challenges of multiple disciplinary research have been proposed, lessons learned are often lost when projects end or experienced individuals move on. We urge multiple disciplinary teams to capture the challenges recognized, and solutions proposed, by their researchers while projects are in process. A database of well‐documented case studies would showcase theories and methods from a variety of disciplines and their interactions, enable better comparative study and evaluation, and provide a useful resource for developing future projects and training multiple disciplinary researchers. Cazando la Quimera de la Multidisciplina en la Ciencia de la Conservación  相似文献   
712.
Offsets are a novel conservation tool, yet using them to achieve no net loss of biodiversity is challenging. This is especially true when using conservation offsets (i.e., protected areas) because achieving no net loss requires avoiding equivalent loss. Our objective was to determine if offsetting the impacts of mining achieves no net loss of native vegetation in Brazil's largest iron mining region. We used a land‐use change model to simulate deforestation by mining to 2020; developed a model to allocate conservation offsets to the landscape under 3 scenarios (baseline, no new offsets; current practice, like‐for‐like [by vegetation type] conservation offsetting near the impact site; and threat scenario, like‐for‐like conservation offsetting of highly threatened vegetation); and simulated nonmining deforestation to 2020 for each scenario to quantify avoided deforestation achieved with offsets. Mines cleared 3570 ha of native vegetation by 2020. Under a 1:4 offset ratio, mining companies would be required to conserve >14,200 ha of native vegetation, doubling the current extent of protected areas in the region. Allocating offsets under current practice avoided deforestation equivalent to 3% of that caused by mining, whereas allocating under the threat scenario avoided 9%. Current practice failed to achieve no net loss because offsets did not conserve threatened vegetation. Explicit allocation of offsets to threatened vegetation also failed because the most threatened vegetation was widely dispersed across the landscape, making conservation logistically difficult. To achieve no net loss with conservation offsets requires information on regional deforestation trajectories and the distribution of threatened vegetation. However, in some regions achieving no net loss through conservation may be impossible. In these cases, other offsetting activities, such as revegetation, will be required. Compensación de los Impactos de la Minería para Obtener Ninguna Pérdida Neta de la Vegetación Nativa  相似文献   
713.
We characterize and compare water challenges confronting the 28 megacities of the world in 2014. Relying on existing literature and diverse primary data sources, we present a unique portrait at a global scale of the water implications of the rapid growth in megacities. We find that differentiating and analyzing the complexity of megacities' water problems based on geographic contexts, historical development trajectories, urban population growth rates, and forms of urban expansion helps explain the nature of the various water management problems they confront. Two governance features also shed light on megacity water challenges: fragmentation resulting from forms of megacity urban expansion; and, urban dualism resulting from contradictions between historical and cultural legacies and the rise of global engineering and technological norms for water management. The increasing vulnerability of megacities to climate change poses risks as well as opportunities for a more collective response to address this global phenomenon. Our analysis raises important questions and offers guidance about the future trajectories of many more large cities around the world that are on their way to becoming megacities.  相似文献   
714.
Using questionnaire and interview data, this study attempted to find out whether the organizational loose (participative) and tight (directive) practices are compatible with or contradict each other. Using the theoretical framework of Sagie's ( 1997 ) loose–tight leadership approach, our hypotheses concerned the effects of both practices on the employee's work‐related attitudes, and the mediating role of two variables, cognitive (information sharing) and motivational (exerting effort), in these effects. Data were analysed using two methodological approaches, quantitative and qualitative. Based on a quantitative analysis of the questionnaires given to 101 professional employees of a textile company, partial support was provided for the study hypotheses. A qualitative analysis of in‐depth, semi‐structured interviews with all the employees (n = 20) in one of the company divisions led to similar conclusions. Specifically, we found that although the loose and tight practices affected work attitudes, the interviewees attributed more impact to the tight practice. In addition, none of the study variables mediated the loose impact on attitudes, whereas information sharing (but not exerting effort) mediated the influence of tight practice. Finally, the qualitative analysis revealed a deeper insight into the nature of both leader practices and their possible integration in the decision‐making processes in organizations. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   
715.
This study tested three contrasting theories about the sequential process of the three dimensions of burnout (i.e., exhaustion, cynicism and professional efficacy) as measured by the Maslach Burnout Inventory—General Survey (MBI‐GS). The causal order of the burnout components was investigated by including job stressors as antecedents of burnout in structural equation models (LISREL). The predictive effect of exhaustion on burnout dimensions eight years later was also investigated. The longitudinal models were then tested in two occupational subgroups. The participants were 713 Finnish employees (415 white‐collar and 298 blue‐collar workers) from an international industry enterprise. The best fitting model of the associations between the three burnout dimensions was obtained by a path model where exhaustion predicted cynicism, and cynicism in turn predicted lack of professional efficacy. The symptoms of exhaustion were persistent over time. There were no differences between the two occupational groups in the process of burnout. Also the work‐related antecedents of burnout (job stressors) were very similar in both groups. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   
716.
Abstract: Climate‐change scenarios project significant temperature changes for most of South America. We studied the potential impacts of predicted climate‐driven change on the distribution and conservation of 26 broad‐range birds from South America Cerrado biome (a savanna that also encompass tracts of grasslands and forests). We used 12 temperature or precipitation‐related bioclimatic variables, nine niche modeling techniques, three general circulation models, and two climate scenarios (for 2030, 2065, 2099) for each species to model distribution ranges. To reach a consensus scenario, we used an ensemble‐forecasting approach to obtain an average distribution for each species at each time interval. We estimated the range extent and shift of each species. Changes in range size varied across species and according to habitat dependency; future predicted range extent was negatively correlated with current predicted range extent in all scenarios. Evolution of range size under full or null dispersal scenarios varied among species from a 5% increase to an 80% decrease. The mean expected range shifts under null and full‐dispersal scenarios were 175 and 200 km, respectively (range 15–399 km), and the shift was usually toward southeastern Brazil. We predicted larger range contractions and longer range shifts for forest‐ and grassland‐dependent species than for savanna‐dependent birds. A negative correlation between current range extent and predicted range loss revealed that geographically restricted species may face stronger threat and become even rarer. The predicted southeasterly direction of range changes is cause for concern because ranges are predicted to shift to the most developed and populated region of Brazil. Also, southeastern Brazil is the least likely region to contain significant dispersal corridors, to allow expansion of Cerrado vegetation types, or to accommodate creation of new reserves.  相似文献   
717.
ABSTRACT: A global predictive real time control strategy minimizing overflow volumes from combined sewers during rainfall was applied to control flows entering the Marigot interceptor (Laval, Canada) for 23 rain events that occurred in this urban area during the summer of 1989. Different surcharge intensities were allowed in the sewer. The duration of the control horizon as well as the location and number of control regulators were varied to assess the impact of these parameters on total overflow volumes and on control safety. Due to the high propagation speed of flow waves in pressurized conduits, it was found that five‐ minute control horizons were sufficient to ensure control performance and safety when important surcharges were permitted in the interceptor and when the controlled regulators were located where pressurized flow occurred. It was also found that it is possible to reduce the number of controlled regulators by placing them at locations intercepting the largest volumes of water during rain periods.  相似文献   
718.
Aquatic sediments often contain a large number of chemical contaminants that are potential pollutants. It is often presumed that such contaminants are released to the water column during sediment resuspension and, in there, adversely impact aquatic life and other beneficial uses of the water. However, extensive laboratory and field studies of about 100 contaminated sediments from across the United States that specifically addressed this type of release showed that of about 30 common heavy metals, organic compounds, and other potential pollutants, only manganese II and ammonia were released to then remain in the water column after sediment resuspension. These results indicated that the chemistry of aqueous iron controls the availability of many contaminants in resuspended sediment. The formation of ferric hydroxide during sediment suspension into the water column, as a result of the reaction between ferrous iron in the sediments and dissolved oxygen in the water column, leads to rapid scavenging of many contaminants in the Fe(OH)3 precipitate. The scavenged contaminants are redeposited in the sediments. This article reviews the role of the aqueous chemistry of iron as it relates to controlling the release of potential pollutants from resuspended sediments. © 2005 Wiley Periodicals, Inc.  相似文献   
719.
The impact of urbanization on groundwater is not simple to understand, as it depends on a variety of factors such as climate, hydrogeology, water management practices, and infrastructure. In semiarid landscapes, the urbanization processes can involve high water consumptions and irrigation increases, which in turn may contribute to groundwater recharge. We assessed the hydrological impacts of urbanization and irrigation rates in an Andean peri‐urban catchment located in Chile, in a semiarid climate. For this purpose, we built and validated a coupled surface–groundwater model that allows the verification of a strong stream–aquifer interaction in areas with shallow groundwater, higher than some sewers and portions of the stream. Moreover, we also identified a significant local recharge associated with pipe leaks and inefficient urban irrigation. From the evaluation of different future scenarios, we found a sustainable water conservation scenario will decrease the current groundwater levels, while the median flow reduces from 408 to 389 L/s, and the low flow (Q95%) from 43 to 22L/s. Overall, our results show the relevance of integrating the modeling of surface and subsurface water resources at different spatial and temporal scales, when assessing the effect of urban development and the suitability of urban water practices.  相似文献   
720.
Increasing reservoir storage is commonly proposed to mitigate increasing water demand and provide drought reserves, especially in semiarid regions such as California. This paper examines the value of expanding surface reservoir capacity in California using hydroeconomic modeling for historical conditions, a future warm‐dry climate, and California's recently adopted policy to end groundwater overdraft. Results show expanding surface storage capacity rarely provides sizable economic value in most of California. On average, expanding facilities north of California's Delta provides some benefit in 92% of 82 years modeled under historical conditions and in 61% of years modeled in a warm‐dry climate. South of California's Delta, expanding storage capacity provides no benefits in 14% of years modeled under historical conditions and 99% of years modeled with a warm‐dry climate. Results vary across facilities between and within regions. The limited benefit of surface storage capacity expansion to statewide water supply should be considered in planning California's water infrastructure.  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