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   556篇
  免费   7篇
  国内免费   10篇
安全科学   28篇
废物处理   13篇
环保管理   108篇
综合类   88篇
基础理论   139篇
污染及防治   114篇
评价与监测   59篇
社会与环境   20篇
灾害及防治   4篇
  2023年   2篇
  2022年   10篇
  2021年   7篇
  2020年   7篇
  2019年   5篇
  2018年   11篇
  2017年   13篇
  2016年   23篇
  2015年   11篇
  2014年   25篇
  2013年   48篇
  2012年   43篇
  2011年   37篇
  2010年   17篇
  2009年   25篇
  2008年   37篇
  2007年   24篇
  2006年   34篇
  2005年   22篇
  2004年   24篇
  2003年   24篇
  2002年   16篇
  2001年   2篇
  2000年   9篇
  1999年   4篇
  1998年   5篇
  1997年   5篇
  1996年   6篇
  1995年   4篇
  1994年   6篇
  1993年   5篇
  1992年   3篇
  1991年   1篇
  1990年   5篇
  1989年   1篇
  1988年   3篇
  1987年   2篇
  1986年   6篇
  1985年   5篇
  1984年   4篇
  1983年   7篇
  1982年   8篇
  1981年   8篇
  1978年   4篇
  1977年   4篇
  1975年   1篇
排序方式: 共有573条查询结果,搜索用时 187 毫秒
261.
Sexual conflict can result in the evolution of extreme mating strategies, including forced copulation. Forced extrapair copulation (FEPC) is generally rare among birds, but is common in re-introduced populations of the hihi (Notiomystis cincta), a socially monogamous, New Zealand endemic, endangered passerine. The aim of this study was to understand the patterns of extrapair paternity in a population where the majority of EPC is forced and to examine the factors, in particular female-specific, influencing the proportion of offspring fathered by extrapair males (EPP—extrapair paternity) and the number of males siring extrapair offspring within a brood (EPM) in this species. Using 8 years of comprehensive paternity, life-history and demographic information for 485 breeding attempts, we show that the frequency of EPP is dependent on (1) social male and female age, (2) the month the female fledged, (3) breeding density and (4) whether it was their first or second reproductive event of the season. In addition, we show that both EPP and EPM are negatively associated with breeding synchrony and clutch size is the most important predictor of EPM. Understanding the drivers of EPP and EPM in species with FECP is important because these are strong determinants of variance in reproductive success and the maintenance of extreme mating behaviour.  相似文献   
262.
Human land use is fragmenting habitats worldwide and inhibiting dispersal among previously connected populations of organisms, often leading to inbreeding depression and reduced evolutionary potential in the face of rapid environmental change. To combat this augmentation of isolated populations with immigrants is sometimes used to facilitate demographic and genetic rescue. Augmentation with immigrants that are genetically and adaptively similar to the target population effectively increases population fitness, but if immigrants are very genetically or adaptively divergent, augmentation can lead to outbreeding depression. Despite well‐cited guidelines for the best practice selection of immigrant sources, often only highly divergent populations remain, and experimental tests of these riskier augmentation scenarios are essentially nonexistent. We conducted a mesocosm experiment with Trinidadian guppies (Poecilia reticulata) to test the multigenerational demographic and genetic effects of augmenting 2 target populations with 3 types of divergent immigrants. We found no evidence of demographic rescue, but we did observe genetic rescue in one population. Divergent immigrant treatments tended to maintain greater genetic diversity, abundance, and hybrid fitness than controls that received immigrants from the source used to seed the mesocosms. In the second population, divergent immigrants had a slightly negative effect in one treatment, and the benefits of augmentation were less apparent overall, likely because this population started with higher genetic diversity and a lower reproductive rate that limited genetic admixture. Our results add to a growing consensus that gene flow can increase population fitness even when immigrants are more highly divergent and may help reduce uncertainty about the use of augmentation in conservation.  相似文献   
263.
264.
The impact of drought on the ecological and chemical status of surface and groundwaters of the River Tormes (River Duero basin, northwestern Iberian Peninsula) was studied to evaluate the evolution of the quality of the river during its passage through the city of Salamanca (Spain). The Water Quality Index (WQI) of the river revealed that the drought period of 2005 did not significantly affect water chemical quality. However, during the study period differences were found in surface water ecological quality, using phytoplankton quality as AN indicator. These differences may be accentuated as a result of regulation of the River Tormes by the Santa Teresa reservoir. Arsenic and fluoride concentrations were measured in water wells, finding higher arsenic concentrations after the drought period and no correlation between the arsenic and fluoride contents. The results are useful for an overall understanding of potential impact of climate change on the ecological and chemical status of water in regional systems.  相似文献   
265.
Atmospheric concentration of nitrous oxide (N2O), a greenhouse gas (GHG), is rising largely due to agriculture. At the plot scale, N2O emissions from crops are known to be controlled by local agricultural practices such as fertilisation, tillage and residue management. However, knowledge of greenhouse gas emissions at the scale of the cropping system is scarce, notably because N2O monitoring is time consuming. Strategies to reduce impact of farming on climate should therefore be sought at the cropping system level. Agro-ecosystem models are simple alternative means to estimate N2O emissions. Here, we combined ecosystem modelling and field measurements to assess the effect of agronomic management on N2O emissions. The model was tested with series of daily to monthly N2O emission data. It was then used to evaluate the N2O abatement potential of a low-emission system designed to halve greenhouse gas emissions in comparison with a system with high productivity and environmental performance. We found a 29 % N2O abatement potential for the low-emission system compared with the high-productivity system. Among N2O abatement options, reduction in mineral fertiliser inputs was the most effective.  相似文献   
266.
267.
IP25 is a highly branched isoprenoid and an organic geochemical biomarker that is produced by some Arctic sea ice diatoms. IP25 has previously been used in Arctic palaeo sea ice reconstruction studies and as a tracer for studying Arctic food webs. Here, the molecular structure of IP25 has been confirmed by 1H and 13C NMR spectroscopy following large-scale extraction from marine sediments obtained from the Canadian Arctic and purification using a combination of open-column and HPLC chromatographic methods. The structure of IP25 was consistent between the three different sampling locations and was identical to that found previously for this biomarker following synthesis from a closely related highly branched isoprenoid diene. Since this study represents the first structural characterisation of IP25 in sediments, future analysis of sedimentary IP25 for palaeo Arctic sea ice reconstructions can be carried out with much greater confidence.  相似文献   
268.
IntroductionThis article presents a health and safety intervention model and the use of process evaluation to assess a participatory ergonomic intervention.MethodThe effectiveness of the Ergonomic Program Implementation Continuum (EPIC) was assessed at six healthcare pilot sites in Ontario, Canada. The model provided a framework to demonstrate evaluation findings.ResultsParticipants reported that EPIC was thorough and identified improvements related to its use. Participants believed the program contributed to advancing an organizational culture of safety (COS). Main barriers to program uptake included resistance to change and need for adequate funding and resources. The dedication of organizational leaders and consultant coaches was identified as essential to the program's success.Impact on IndustryIn terms of impact on industry, findings contribute to the evidence-based knowledge of health and safety interventions and support use of the framework for creating a robust infrastructure to advance organizational COS and link staff safety and wellness with patient safety in healthcare.  相似文献   
269.
270.
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