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   71篇
  免费   3篇
  国内免费   2篇
  2023年   1篇
  2021年   5篇
  2020年   1篇
  2019年   1篇
  2018年   2篇
  2017年   2篇
  2016年   3篇
  2015年   2篇
  2014年   3篇
  2013年   5篇
  2012年   3篇
  2011年   3篇
  2009年   1篇
  2008年   2篇
  2007年   1篇
  2005年   1篇
  1998年   1篇
  1997年   1篇
  1994年   2篇
  1993年   4篇
  1992年   4篇
  1991年   4篇
  1989年   10篇
  1988年   6篇
  1987年   1篇
  1986年   1篇
  1974年   2篇
  1972年   1篇
  1970年   2篇
  1967年   1篇
排序方式: 共有76条查询结果,搜索用时 15 毫秒
1.
Since the 1970's the management of aquatic habitats has changed from piecemeal monitoring to the ecosystem approach; this was initiated in the North American Great Lakes, comprising social, economic, and environmental aspects. The information included in this paper is based on the presentation made at the Seminar On Ecosystem Approach To Water Management held in Oslo, Norway during 1991. Recently, the multidisciplinary, holistic, and integrated concept of ecosystem health has emerged, and is being advanced for the implementation of an ecosystem approach to environmental management, which has resulted in the formation of an international society (Aquatic Ecosystem Health & Management Society) and the publication of a primary journal (Journal of Aquatic Ecosystem Health). The information has been updated to incorporate new developments and recent progress about the Society and the journal since the Oslo Seminar.  相似文献   
2.
The phytoplankton productivity of Georgian Bay was studied during 1974. Lakewide samples were collected at 16 stations during monthly cruises from April to December and identification and enumeration was carried out by the Utermohl technique. Contaminant bioassays with metals added singly and as a mixture were performed in 1980 and 1981. Based on an overall average, Diatomeae (36–73%) was the most prevalent component of phytoplankton biomass followed by Chrysophyceae (5–38%), and Cyanophyta (3–27%). Biomass means of all stations by cruise indicated a range of 0.35 to 0.61 g·m–3 with a bimodal seasonal pattern. Although ultraplankton made the highest mean percent contribution to the biomass (37%), the other size assemblages such as < 5 µm (26%) and netplankton (29%) were not unimportant.Size fractionation of primary productivity during 1974 revealed that a major portion of photosynthesis (39–70%) was in the <20 µm size fraction. Algal Fractionation Bioassays conducted during 1980 and 1981 indicated a significant inhibition of ultraplankton productivity. Additional bioassays with single metals and in combination showed differential toxicity to various phytoplankton size assemblages.The phytoplankton biomass and floristic composition indicate the Georgian Bay ecosystem to be oligotrophic. This ecosystem appears to be controlled by the physical dynamics of thermal and flow regimes. Compared with other Great Lakes, the low P/B quotients recorded in oligotrophic Georgian Bay is enigmatic and may be attributable to the observed sensitivity of phytoplankton to contaminants originating from anthropogenic and natural sources.  相似文献   
3.
The phytoplankton of North Channel in Lake Huron and its productivity was studied at 8 stations distributed across the channel during May to October, 1974. The phytoplankton analysis was conducted using the Utermohl technique. The mean percent biomass at each station indicated Diatomeae (59–77%) and phytoflagellates such as Chrysophyceae (4–21%) and Cryptophyceae (7–19%) as the dominant contributors. Seasonal variations of biomass ranged from 0.2 to 0.35 g·m–3 with a single peak during stratified conditions. Diatomeae dominated throughout the period of investigation followed by Chrysophyceae and Cryptophyceae. Biomass composition by size revealed the dominance of ultraplankton (5–20 m) which contributed 29–68% to the total biomass. Species such as Fragilaria crotonensis, Tabellaria fenestrata, Synedra acus var. radians, Cyclotella comta and C. bodanica made substantial contributions during the unstratified and stratified conditions.Ultraplankton contributed overwhelmingly to the primary productivity as measured by carbon-14 uptake. The contaminant bioassays with single metals, metals in combination and a mixture of metals demonstrated that the ultraplankton's carbon assimilation was inhibited significantly, revealing their sensitivity to contaminants. Phytoplankton ecology of the Channel appears to be affected by tributary inflows, industrial/municipal inputs, and short flushing rates. However, statistical treatment of the ultraplankton biomass showed correlations with temperature and nutrients. Based on phycological and limnological characteristics, the Channel appears to be oligotrophic. The chlorophyll/biomass ratios and Activity Coefficient (P/B) align it with the most oligotrophic Lake Superior in its metabolic efficiency.  相似文献   
4.
Munawar  M.  Weisse  T. 《Hydrobiologia》1989,188(1):163-174
Various components of the Microbial loop such as bacteria, heterotrophic nanoflagellates and autotrophic picoplankton were analyzed, for the first time across the Great Lakes, during a cruise in the summer of 1988. In addition, the size fractionated primary productivity using carbon-14 techniques was also determined. The statistical analysis indicated that bacteria, autotrophic picoplankton and ultraplankton/picoplankton productivity were significantly higher in Lakes Ontario and Erie than Lakes Huron and Michigan. The autotrophic picoplankton and ultraplankton/picoplankton productivity was higher in Lake Erie compared to Lake Ontario.The autotrophic picoplankton showed sensitivity to nutrients and contaminants in various types of environments. A dramatic decrease of autotrophic picoplankton in eutrophic-contaminated areas, such as Ashbridges Bay, Hamilton Harbour and western Lake Erie was observed. Conversely, in Saginaw Bay, another eutrophic environment, the autotrophic picoplankton were significantly higher than in Lake Huron. The sensitivity of autotrophic picoplankton to nutrients/contaminants might have implications to trophic interactions. Our results suggest that structural and functional characteristics of the microbial loop may be operating differently in stressed versus unstressed ecosystems. The possibility of using autotrophic picoplankton as an early warning indicator of environmental perturbation is proposed.  相似文献   
5.
Munawar  M.  Norwood  W. P.  McCarthy  L. H.  Mayfield  C. I. 《Hydrobiologia》1989,(1):601-618
The contamination of Toronto Harbour is a very serious problem. The major sources of pollution are the Don River and sewer outflows, as well as industrial, and municipal effluents. The problem is further compounded by perturbations of the toxic sediment caused by dredging, dredge-disposal, navigation, and recreational activities. The impact of contamination and nutrient enrichment was reflected in the size-fractionated primary productivity experiments. Generally, microplankton/netplankton (> 20 µm) productivity was enhanced whereas ultraplankton (< 20 µm) productivity was inhibited. These observations are attributable to interactions between ameliorating nutrients and toxic contaminants as well as to the differential sensitivity of natural phytoplankton size assemblages to the bioavailable chemical regime. In situ environmental techniques applied in Toronto Harbour were effective, sensitive, and rapid, and provided a better understanding of the impact of dredging/disposal activities under natural conditions. These techniques have great potential in the assessment of the ecotoxicology of harbours and other stressed environments.  相似文献   
6.
The use of a multi-trophic assay strategy is now being encouraged in toxicological investigations which provides for rapid and sensitive tests. Such a strategy, a microcomputer-based algal fluorescence technique, was applied for the bioassessment of Lake St. Clair and St. Clair River ecosystems. The technique was found to be rapid, sensitive, and relatively inexpensive. In addition, it permitted microscopic examination of the impact of contaminants on individual cells/organisms, a feature which is not possible by other tests using radioisotopes and enzymes. The algal fluorescence technique appears to have a considerable potential for fast screening of large numbers of environmental samples.  相似文献   
7.
From aquatic science to ecosystem health: a philosophical perspective   总被引:1,自引:0,他引:1  
The development of an ecosystem (social, economic, environmental) approach to water management is traced from its origins in the Great Lakes of North America. The focus on health and integrity of ecosystems is an outgrowth of the Lamarckian concept of The Biosphere as a global system of matter, life, and mind. The driving forces behind the development of an ecosystem approach have been negative feedback from excessive demotechnic growth and faith that we can maintain a healthy relationship with Mother Earth.  相似文献   
8.
A general mathematical framework has been proposed in this work for scheduling of a multiproduct and multipurpose facility involving manufacturing of biotech products. The specific problem involves several batch operations occurring in multiple units involving fixed processing time, unlimited storage policy, transition times, shared units, and deterministic and fixed data in the given time horizon. The different batch operations are modeled using state‐task network representation. Two different mathematical formulations are proposed based on discrete‐ and continuous‐time representations leading to a mixed‐integer linear programming model which is solved using General Algebraic Modeling System software. A case study based on a real facility is presented to illustrate the potential and applicability of the proposed models. The continuous‐time model required less number of events and has a smaller problem size compared to the discrete‐time model. © 2014 American Institute of Chemical Engineers Biotechnol. Prog., 30:1221–1230, 2014  相似文献   
9.
Munawar  M.  Munawar  I. F.  Leppard  G. G. 《Hydrobiologia》1989,(1):237-246
The use of phytoplankton as test organisms in bioassays has recently gained momentum due to their simplicity, availability, sensitivity, rapidity of analysis, and cost-effectiveness. Increasing emphasis is currently being given to field and in situ experiments using indigenous populations, particularly ultraplankton/picoplankton (2–20 m) which play a key role in the microbial loop and food chain dynamics. Impact evaluation can be determined at the structural, ultra-structural, and functional level. An array of techniques is available for toxicity testing including the use of either algal cultures or natural assemblages in laboratory or in situ experiments, the selection of which depends on the objectives, precision required, and project budget of the particular study. An overview is presented of the various procedures using algae in toxicity testing with a focus on the Great Lakes and an emphasis on field techniques. The effective use and application of such sensitive technology has tremendous potential for early warning detection of ecosystem perturbations in concert with a multi-trophic battery of tests.  相似文献   
10.
Using historical (1970) and more recent (1996) Lake Erie plankton and trophic status data, we developed a Planktonic Index of Biotic Integrity (P-IBI) to measure changes in lake ecosystem health. We used discriminant analysis to determine phytoplankton and zooplankton community characteristics (metrics) that distinguished among levels of impairment. Traditional measures of lake trophic status classes (i.e., oligotrophic, mesotrophic, eutrophic), such as chlorophyll a and total phosphorus concentrations, were used to classify sites on a gradient of impairment. We then judged the ability of plankton metrics to distinguish among trophic status classes. Because of the temporal variability found in plankton communities, we conducted analyses on a monthly basis (May–September). For June, July and August we found five unique metrics that could distinguish among trophic status classes. The P-IBI showed an increase in water quality in Lake Erie between 1970 (<3 = eutrophic) and the mid-1990s (1996 and 1997) (3–4 = mesotrophic) (which reflected mean (±standard error) total phosphorus concentrations (μg/L) 1970 > 1996; western basin (41.53 ± 2.68 > 29.75 ± 1.39), eastern basin (14.84 ± 0.82 > 7.74 ± 0.28) and mean (±standard error) chlorophyll a concentrations (μg/L) uncorrected for pheophytin 1970 > 1996; western basin (12.58 ± 1.82 > 5.40 ± 0.22), central basin (5.90 ± 0.36 > 3.17 ± 0.54), and eastern basin (5.17 ± 0.38 > 1.67 ± 0.18)), with declining water quality in the late 1990s (1998 and 1999) (3) and 2002 (<3). We recommend that the techniques used in creating the P-IBI be investigated for determining ecosystem health of other lakes.  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