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   725篇
  免费   9篇
  国内免费   6篇
安全科学   33篇
废物处理   20篇
环保管理   173篇
综合类   66篇
基础理论   214篇
环境理论   1篇
污染及防治   113篇
评价与监测   60篇
社会与环境   48篇
灾害及防治   12篇
  2022年   4篇
  2021年   3篇
  2020年   7篇
  2019年   8篇
  2018年   19篇
  2017年   13篇
  2016年   24篇
  2015年   12篇
  2014年   18篇
  2013年   37篇
  2012年   24篇
  2011年   44篇
  2010年   23篇
  2009年   37篇
  2008年   35篇
  2007年   32篇
  2006年   31篇
  2005年   27篇
  2004年   20篇
  2003年   21篇
  2002年   28篇
  2001年   17篇
  2000年   23篇
  1999年   14篇
  1998年   13篇
  1997年   9篇
  1996年   14篇
  1995年   18篇
  1994年   16篇
  1993年   13篇
  1992年   9篇
  1991年   7篇
  1990年   10篇
  1989年   6篇
  1988年   11篇
  1987年   7篇
  1985年   11篇
  1984年   9篇
  1983年   14篇
  1982年   8篇
  1981年   5篇
  1980年   4篇
  1979年   8篇
  1977年   3篇
  1976年   2篇
  1975年   3篇
  1974年   3篇
  1972年   4篇
  1968年   2篇
  1967年   2篇
排序方式: 共有740条查询结果,搜索用时 849 毫秒
551.
Mitochondrial DNA (mtDNA) genotypes were examined in 1989 in threeCrassostrea virginica (Gmelin) populations native to Chesapeake Bay, USA, and in one population selectively inbred for rapid growth for ten generations. We wished to determine whether this character would be useful as a genetic marker for distinguishing between the inbred line and the native oysters and to determine whether detectable genetic differences exist among present-day native populations ofC. virginica. Thirty mtDNA haplotypes were identified. The average percentage nucleotide difference between native haplotypes was 1.8%. Inbred oysters were characterized by mtDNA haplotypes distinctly different from ancestral native oysters, indicating a high degree of genetic differentiation between the two groups (average percentage mtDNA nucleotide sequence divergence,=21.8%). The common native haplotype was not present in the selectively inbred sample, and six of the seven haplotypes detected in the inbred oysters were not found in the survey of native oysters. Chi-square tests on haplotype frequencies indicated that the native populations were not significantly different from one another. However, the distribution and relatedness of haplotypes suggest that significant change in the oyster gene pool may have occurred over the past few decades.  相似文献   
552.
Climate change presents additional challenges to a diverse country like Cameroon that shares the Congo Basin rainforest. Not only is the population vulnerable to the direct effects of climate change, forest-dependent communities are also vulnerable to changing environmental policy that may affect their access to forest resources. Using a qualitative approach to data collection through semi-structured interviews and content analysis of relevant documents, the perception of decision-makers within, and the response of the institutions of the state, the private sector and civil society to the complex challenges of climate change in the Congo Basin forest of Cameroon were analysed. Results indicate that while decision-makers’ awareness of climate change is high, a concrete institutional response is at a very early stage. Cameroon has low adaptive capacity that is further constrained by weak linkages among government institutions nationally and between different levels of government and with communities. Civil society institutions play a role in enhancing government capacity to respond, particularly in relation to new international policies on climate change and forests. Adaptive capacity would be further enhanced by facilitating institutional linkages and coordinating multilevel responses across all boundaries of government, private sector and civil society. A collaborative capacity builder could foster the transfer, receipt and integration of knowledge across the networks, and ultimately build long-term collaborative problem-solving capacity in Cameroon.  相似文献   
553.
Climate change is occurring with greater speed and intensity that previously anticipated. All effective environmentally and socially sound mitigation efforts need to be employed to effectively address this global crisis. Land Use, Land Use Change and Forestry (LULUCF) projects can provide significant climate change mitigation benefits as well as poverty alleviation and biodiversity conservation benefits. The policies of the European Union Emissions Trading Scheme (EU-ETS), the world’s largest carbon market exclude LULUCF. Scientific support for this exclusion was presented in a briefing paper published by the Climate Action Network—Europe (CAN) that puts forward the proposition that land based storage of carbon is ineffective. A careful review of the scientific papers cited in support of CAN’s position indicates that, while the papers themselves are scientifically sound, they do not support the continued exclusion of LULUCF projects from the EU-ETS. At the same time some important recent research papers that describe the carbon storage and social benefit potential of such projects are not included in the analysis. An in-depth consideration of the scientific evidence is necessary in evaluating this policy option. Based on this evidence a case can be made for the inclusion of LULUCF projects in the EU-ETS.  相似文献   
554.
Demersal 0-group Atlantic cod (Gadus morhua L.) were collected in Trinity Bay, Newfoundland, Canada, between August 1993 and January 1994. Diet composition and simple indices of condition (hepato-somatic index, condition factors and body ash content) were determined. Laboratory experiments were also conducted to determine whether simple indices of condition reflect differences in energy intake (ration level) and to determine minimum index of condition values, assessed from 0-group cod that died due to exhaustion of their energy reserves. Determination of lower critical indices of condition provided a meaningful interpretation of field data on feeding, condition and survival of 0-group cod. In the wild, indices of condition reflecting variation in liver and muscle energy reserves of cod increased rapidly with the consumption of Calanus finmarchicus, which exhibited a high incidence of oil sacs, and declined abruptly when this lipid-rich prey was no longer consumed. Liver and muscle condition of 0-group cod from the field varied seasonally, but their condition was consistently above that of cod that died in the laboratory. Laboratory studies, using three ration levels, revealed that condition indices differed over time and among ration levels. Indices of condition representing variation in muscle energy reserves exhibited a steady decline once the hepato-somatic index fell below about 2.0. We interpret this as evidence for depletion of lipids first and then proteins, a pattern similar to that of larger juveniles and adults. We conclude that as long as 0-group cod are above a “safe” level of condition their body length can still increase even when condition is declining. Received: 2 September 1997 / Accepted: 8 December 1998  相似文献   
555.
Why Economics Matters for Endangered Species Protection   总被引:3,自引:0,他引:3  
Abstract: We offer three reasons why economics matters more to species protection than many people think and what this implies for the ongoing debate over the reauthorization of the Endangered Species Act of 1973. Economics matters because (1) human behavior generally, and economic parameters in particular, help determine the degree of risk to a species; (2) in a world of scarce resources, the opportunity cost of species protection—the costs of reduced resources for other worthwhile causes—must be taken into account in decision making; and (3) economic incentives are critical in shaping human behavior, and consequently the recovery of species. Endangered species protection that explicitly addresses these basic principles can avoid wasting valuable resources that yield no gain in species protection.  相似文献   
556.
The ability to acquire information about predators allows prey to better balance threat-sensitive tradeoffs by responding only to ecologically relevant predation threats. However, predation risk is highly variable through time and responding to predators that no longer represent a threat would likely prove costly to prey. While a wealth of studies have examined the way in which prey learn, little attention has been paid to retention of acquired information. Recent studies suggest that retention is indeed plastic and shaped by a suite of intrinsic factors such as strength of initial conditioning and individual growth rate. Here, we investigated if the duration of retention of acquired information is influenced by individual behavioral tactics (i.e., ‘personality’). We recorded latency to escape an opaque acclimation chamber of juvenile rainbow trout (Oncorhynchus mykiss) as a measure of behavioral tactic. We then immediately conditioned individual trout to recognize pumpkinseed (Lepomis gibbosus) and tested for recognition 24 h or 8 days postconditioning. Our results demonstrate that while shy versus bold trout exhibited no difference in the strength of conditioned response to pumpkinseed odor during conditioning trials or when tested for recognition 24 h postconditioning, there was a significant effect of individual behavioral tactic on the retention of learned predator recognition. While shy trout continued to exhibit a learned response to pumpkinseed odor when tested 8 days postconditioning, bold trout were not different from our pseudoconditioned controls. These data suggest that the behavioral tactic employed at the time of conditioning influences the ‘memory window’ of acquired information.  相似文献   
557.
In this Comment we refer to our strong reservations concerning the paper by Powell et al. J Coast Conserv, (2012) recently published on the Online First web site of the Journal of Coastal Conservation. The paper makes a number of comments on data obtained from the Permanent Service for Mean Sea Level (PSMSL) and British Oceanographic Data Centre (BODC) which are incorrect or misleading. In addition, some of their comments on sea-level science in general need to be challenged and corrected.  相似文献   
558.
Psychological ownership is increasingly recognized as a core feeling in the experience of work. Within jobs and the work context, there is a wide range of opportunities to experience psychological ownership. Yet empirical work on how feelings of ownership develop is lacking, and thus ways to develop psychological ownership in the workplace are not well understood. We explore the routes traveled to feelings of ownership by using job complexity as one example of work environment structure that affects the formation of psychological ownership. In two studies, we develop measures of the routes and confirm that perceived differences in one's work meaningfully predict psychological ownership. Collectively, the two studies provide insight into and offer suggestions for how ownership develops and ways in which managers might foster employee feelings of ownership toward their work. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   
559.
In recent years, investigations into major incidents often highlight poor safety culture as one of the key causal factors. These investigations are often assisted by causal analysis tools that help to ensure that the investigation and the information captured are systematic. However, current causal analysis tools are not designed to analyse dynamic complexity of major incidents and safety culture, which arises from the interactions between actors and the temporal and spatial gaps between actions and consequences. This is because most causal analysis tools model events and causal factors linearly. In contrast, systems thinking, a discipline of seeing systems holistically, emphasises the circular nature of complex systems, i.e. cause and effect are not distinguishable. This paper proposes that traditional causal analysis tools and investigation should be enhanced with the use of systems thinking tools.One of the systems thinking tools that is particularly useful in analysing major incidents and safety culture is causal loop diagrams. The diagrams can be used to explain the systemic structure sustaining a safety culture and identify effective interventions to improve the safety culture and prevent a recurrence of a major incident. The paper demonstrates the use of systems thinking and causal loop diagrams through a case study on Bellevue hazardous waste fire in Western Australia. The case study shows how different actors in the system, each acting in reaction to pressures that they are facing, produced and sustained a poor safety culture that was a major contributory factor to the fire in 2001.  相似文献   
560.
The Building Research Establishment (BRE) has been using diffusive samplers for the study of VOCs in indoor and outdoor air since 1989. The Perkin Elmer type sampler packed with Tenax TA adsorbent is used for the diffusive sampling of C6-C16 organic compounds. This method was applied in a major study of relationships between the environment and child health carried out during 1990-1993 in the Avon area of the UK. The present paper reports results of an investigation into the repeatability of the sampler in outdoor air and measurements of 6 aromatic hydrocarbons inside and outside a home over a 5 year period and inside and outside an office building over a 12 month period. Both the home and the office were located in Hertfordshire, England. Concentrations of VOCs recorded are similar to those found in the Avon area. Higher concentrations of each of the six compounds were recorded inside the home than outside, whilst greater amounts of benzene and toluene were found inside the office than outside. Seasonal variations in concentrations are observed and measurements recorded outdoors are similar to those recorded by other workers.  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