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   151篇
  免费   2篇
  国内免费   1篇
安全科学   4篇
废物处理   8篇
环保管理   38篇
综合类   12篇
基础理论   36篇
环境理论   1篇
污染及防治   40篇
评价与监测   9篇
社会与环境   4篇
灾害及防治   2篇
  2022年   4篇
  2021年   1篇
  2020年   2篇
  2019年   6篇
  2018年   3篇
  2017年   4篇
  2016年   8篇
  2015年   5篇
  2014年   4篇
  2013年   24篇
  2012年   8篇
  2011年   7篇
  2010年   2篇
  2009年   7篇
  2008年   10篇
  2007年   6篇
  2006年   11篇
  2005年   6篇
  2004年   2篇
  2003年   11篇
  2002年   3篇
  2001年   3篇
  2000年   4篇
  1999年   2篇
  1998年   3篇
  1997年   1篇
  1994年   1篇
  1993年   1篇
  1992年   1篇
  1991年   1篇
  1990年   2篇
  1988年   1篇
排序方式: 共有154条查询结果,搜索用时 718 毫秒
61.
Sleeper sharks are a poorly studied group of deep-sea sharks. The subgenus, Somniosus, contains three morphologically similar species: S. microcephalus found in the Arctic and North Atlantic; S. pacificus in the North Pacific; and S. antarcticus in the Southern Ocean. These sharks have been reported mainly in temperate to polar waters and occasionally in subtropical locations. They have not been recorded in tropical waters. This study investigates the relationships among the accepted species of Somniosus through analysis of mitochondrial cytochrome b sequence variation. Seventy-five samples were examined from four sampling locations in the North Pacific, Southern Ocean and North Atlantic. Twenty-one haplotypes were found. A minimum spanning parsimony network separated these haplotypes into two divergent clades, an S. microcephalus and an S. pacificus/antarcticus clade, strongly supporting the distinction of S. microcephalus as a separate species from the Pacific sleeper shark species. Analysis of genetic structure within the S. pacificus/antarcticus clade (analysis of molecular variance, allele frequency comparisons, and a nested clade analysis) showed limited or no differences amongst three populations. Further examination of genetic variation at more variable mtDNA and nuclear markers is needed to examine the species status of S. pacificus and S. antarcticus.  相似文献   
62.
In this policy perspective, we outline several conditions to support effective science–policy interaction, with a particular emphasis on improving water governance in transboundary basins. Key conditions include (1) recognizing that science is a crucial but bounded input into water resource decision-making processes; (2) establishing conditions for collaboration and shared commitment among actors; (3) understanding that social or group-learning processes linked to science–policy interaction are enhanced through greater collaboration; (4) accepting that the collaborative production of knowledge about hydrological issues and associated socioeconomic change and institutional responses is essential to build legitimate decision-making processes; and (5) engaging boundary organizations and informal networks of scientists, policy makers, and civil society. We elaborate on these conditions with a diverse set of international examples drawn from a synthesis of our collective experiences in assessing the opportunities and constraints (including the role of power relations) related to governance for water in transboundary settings.  相似文献   
63.
Chromium speciation in the blood of metal-on-metal hip implant patients   总被引:1,自引:0,他引:1  
The objective of this study was to determine the valence state of chromium (Cr) in the blood of individuals with Cr-containing metal hip implants. Serum and red blood cell (RBC) Cr concentrations from 52 patients with Cr-containing total hip arthroplasties were measured preoperatively and at 3, 12, and 24 months postoperatively. Geometric mean and median pre-surgery serum Cr concentrations were consistently below 0.2 µg/L, while geometric mean and median pre-op RBC Cr concentrations were typically about four- to six-fold higher than the serum values. A significant 5- to 13-fold increase was found in the mean and median serum Cr concentrations three months post-surgery, with an 8- to 18-fold rise at 12 and 24 months, respectively. Steady-state serum concentrations were reached between 3 and 12 months. In contrast, there were no marked differences in mean and median RBC Cr concentrations pre- and post-surgery. Slope regression analysis for our data was similar to those reported for Cr(III) in spiked blood samples. The analysis showed that Cr released from hip implants preferentially distributed into serum and not RBC, indicating that the form of Cr present in blood of hip implant patients was in the form of non-toxic Cr(III). Our findings indicate that blood Cr concentrations Cr(III) associated with metal implants do not pose an adverse health risk to patients, which is in agreement with findings published by most investigators.  相似文献   
64.
The small watershed approach is well-suited but underutilized in mercury research. We applied the small watershed approach to investigate total mercury (THg) and methylmercury (MeHg) dynamics in streamwater at the five diverse forested headwater catchments of the US Geological Survey Water, Energy, and Biogeochemical Budgets (WEBB) program. At all sites, baseflow THg was generally less than 1ng L(-1) and MeHg was less than 0.2ng L(-1). THg and MeHg concentrations increased with streamflow, so export was primarily episodic. At three sites, THg and MeHg concentration and export were dominated by the particulate fraction in association with POC at high flows, with maximum THg (MeHg) concentrations of 94 (2.56)ng L(-1) at Sleepers River, Vermont; 112 (0.75)ng L(-1) at Rio Icacos, Puerto Rico; and 55 (0.80)ng L(-1) at Panola Mt., Georgia. Filtered (<0.7microm) THg increased more modestly with flow in association with the hydrophobic acid fraction (HPOA) of DOC, with maximum filtered THg concentrations near 5ng L(-1) at both Sleepers and Icacos. At Andrews Creek, Colorado, THg export was also episodic but was dominated by filtered THg, as POC concentrations were low. MeHg typically tracked THg so that each site had a fairly constant MeHg/THg ratio, which ranged from near zero at Andrews to 15% at the low-relief, groundwater-dominated Allequash Creek, Wisconsin. Allequash was the only site with filtered MeHg consistently above detection, and the filtered fraction dominated both THg and MeHg. Relative to inputs in wet deposition, watershed retention of THg (minus any subsequent volatilization) was 96.6% at Allequash, 60% at Sleepers, and 83% at Andrews. Icacos had a net export of THg, possibly due to historic gold mining or frequent disturbance from landslides. Quantification and interpretation of Hg dynamics was facilitated by the small watershed approach with emphasis on event sampling.  相似文献   
65.
Despite a heavy reliance on scientific knowledge as the primary source of information in resource management, many resources are in decline, particularly in fisheries. To try and combat this trend, researchers have drawn upon the knowledge of local resource users as an important supplement to scientific knowledge in designing and implementing management strategies. The integration of local knowledge with scientific knowledge for marine species management, however, is problematic stemming primarily from conflicting data types. This paper considers the use of spatial information technology as a medium to integrate and visualise spatial distributions of both quantitative scientific data and qualitative local knowledge for the purposes of producing valid and locally relevant fisheries management plans. In this context, the paper presents a detailed protocol for the collection and subsequent use of local knowledge in fisheries management planning using geographic information systems (GIS). Particular attention is paid to the use of local knowledge in resource management, accuracy issues associated with the incorporation of qualitative data into a quantitative environment, base map selection and construction, and map bias or errors associated with the accuracy of recording harvest locations on paper map sheets, given the complications of map scale.  相似文献   
66.
A new analytical method for determining cobalt (Co) species in human serum by size exclusion chromatography with inductively coupled plasma mass spectrometry (SEC-ICP-MS) was applied to serum samples collected from 12 human volunteers who participated in a Co(II) chloride supplement study involving ingestion of 1 mg Co/day for up to 90 consecutive days. The study protocol included determination of serum total Co by acid digestion followed by ICP-MS. Co speciation assay measurements were conducted for up to 13 time points per individual spanning from one to two weeks before dosing began to two weeks after dosing ceased. The Co speciation assay showed good recovery >91% relative to total Co measurements. Undiluted serum demonstrated uniform fractions of large molecular Co defined as Co bound to albumin and other proteins >50 kDa at 96% and the residual as small molecular Co defined as free Co(II) and <1 kDa Co-complexes for individual serum Co concentrations up to 146 μg/L. There were no dose-related changes in Co distribution. Analysis of the same serum samples with tenfold dilution in 0.1 M acetic acid led to a lower fraction of large molecular Co at 87%, with the difference between diluted and undiluted measurements being 8.4%. The difference noted between undiluted and diluted large molecular Co may be attributed to Co release from albumin. Data demonstrated that large molecular Co was the predominant Co species in both undiluted and diluted human serum over a broad range of in vivo Co concentrations, reflecting high albumin–Co binding capacity. These data validate the Co speciation assay and may be employed in understanding further the toxicokinetics and dose-response relationships for Co species.  相似文献   
67.
Studies show that Whites tend to show the lowest level of support for affirmative action (AA) policies. Opponents of AA often argue that this is because it violates principles of meritocracy. However, self‐interest (based on social identification with those adversely affected) could also explain their opposition. In three studies, we varied whether an Asian or White male is adversely affected by AA to test another explanation; namely, that Whites' fairness judgments are based on both the adversely affected person's race and the fairness evaluator's ideological beliefs. Although we found some support for the meritocratic explanation, this was not sufficient to explain why Whites view AA as (un)fair. Instead, we found strong support for our prediction that Whites who are opposed to equality perceive more unfairness when a White (vs. Asian) was harmed by AA, whereas Whites who endorse egalitarian ideologies perceive the opposite. This finding suggests that neither self‐interest nor meritocratic explanations can fully account for Whites' opposition to AA. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
68.
69.
The current downturn of the arctic cryosphere, such as the strong loss of sea ice, melting of ice sheets and glaciers, and permafrost thaw, affects the marine and terrestrial carbon cycles in numerous interconnected ways. Nonetheless, processes in the ocean and on land have been too often considered in isolation while it has become increasingly clear that the two environments are strongly connected: Sea ice decline is one of the main causes of the rapid warming of the Arctic, and the flow of carbon from rivers into the Arctic Ocean affects marine processes and the air–sea exchange of CO2. This review, therefore, provides an overview of the current state of knowledge of the arctic terrestrial and marine carbon cycle, connections in between, and how this complex system is affected by climate change and a declining cryosphere. Ultimately, better knowledge of biogeochemical processes combined with improved model representations of ocean–land interactions are essential to accurately predict the development of arctic ecosystems and associated climate feedbacks.  相似文献   
70.
Hibernating bats have undergone severe recent declines across the eastern United States, but the cause of these regional‐scale declines has not been systematically evaluated. We assessed the influence of white‐nose syndrome (an emerging bat disease caused by the fungus Pseudogymnoascus destructans, formerly Geomyces destructans) on large‐scale, long‐term population patterns in the little brown myotis (Myotis lucifugus), the northern myotis (Myotis septentrionalis), and the tricolored bat (Perimyotis subflavus). We modeled population trajectories for each species on the basis of an extensive data set of winter hibernacula counts of more than 1 million individual bats from a 4‐state region over 13 years and with data on locations of hibernacula and first detections of white‐nose syndrome at each hibernaculum. We used generalized additive mixed models to determine population change relative to expectations, that is, how population trajectories differed with a colony's infection status, how trajectories differed with distance from the point of introduction of white‐nose syndrome, and whether declines were concordant with first local observation of the disease. Population trajectories in all species met at least one of the 3 expectations, but none met all 3. Our results suggest, therefore, that white‐nose syndrome has affected regional populations differently than was previously understood and has not been the sole cause of declines. Specifically, our results suggest that in some areas and species, threats other than white‐nose syndrome are also contributing to population declines, declines linked to white‐nose syndrome have spread across large geographic areas with unexpected speed, and the disease or other threats led to declines in bat populations for years prior to disease detection. Effective conservation will require further research to mitigate impacts of white‐nose syndrome, renewed attention to other threats to bats, and improved surveillance efforts to ensure early detection of white‐nose syndrome.  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