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   45篇
  免费   0篇
  国内免费   1篇
安全科学   2篇
废物处理   1篇
环保管理   5篇
综合类   6篇
基础理论   20篇
环境理论   1篇
污染及防治   6篇
评价与监测   1篇
社会与环境   3篇
灾害及防治   1篇
  2022年   1篇
  2021年   2篇
  2020年   1篇
  2019年   1篇
  2018年   2篇
  2017年   1篇
  2016年   1篇
  2015年   3篇
  2013年   3篇
  2012年   1篇
  2011年   1篇
  2010年   1篇
  2009年   2篇
  2008年   5篇
  2006年   1篇
  2002年   3篇
  2000年   2篇
  1999年   1篇
  1998年   1篇
  1994年   1篇
  1993年   2篇
  1988年   1篇
  1987年   1篇
  1986年   1篇
  1984年   1篇
  1981年   1篇
  1980年   1篇
  1978年   1篇
  1977年   1篇
  1974年   1篇
  1972年   1篇
排序方式: 共有46条查询结果,搜索用时 15 毫秒
31.
32.
Modeling diffuse phosphorus (P) loss may indicate management strategies to minimize P loss from agricultural sources. An empirical model predicting flow-weighted phosphorus concentrations (MRP) was derived using data collected from 35 Irish river catchments. Monitoring records of riverine P and stream flow data were used to calculate MRP values averaged for the years 1991-1994. These data were modeled using land use, soil type, and soil P data. Soil type in catchments was described using soil survey classifications weighted according to their P desorption properties from laboratory results. Soil test P concentrations for the studied watersheds were obtained from a national database. Soil P levels were weighted based on the results of field experiments measuring P losses in overland flow from fields at different soil test P levels. The 35 catchments were statistically clustered into two populations (A and B) based on differences in soil type, specifically, soil hydrology. Catchments in Cluster A had predominantly poorly drained soils and comparatively higher MRP concentrations (0.03-0.17 mg L(-1)) than Cluster B areas (0.01-0.7 mg L(-1)) with mostly well-drained soils. Regression equations derived for A and B type catchments predicted MRP values with 68 and 62% of the variation explained in the models, respectively. Data extracted for the rest of the country were applied to the models to delineate areas at risk on a national scale. While the models were only moderately accurate they highlighted the influence of land management, specifically, high production grassland receiving high P inputs, in conjunction with the effect of soil type and soil hydrology on the transport of P to surface waters.  相似文献   
33.
34.
The embryos of Harmothoë imbricata (L.) are protected during their early development as a mass under the scales of the female parent. Eggs are shed into the space under the scales through nephridial papillae which elongate and turn dorsally as the female matures. The mass is held together by an adhesive layer surrounding each egg. Maturation begins in September and breeding occurs during March and April, when each female spawns twice in succession. Males contain mature sperm throughout the breeding season and shed only a small proportion at each spawning. As the polychaetes mature, pairs are formed with the male resting on the dorsal surface of the female. When the female spawns, the male sheds sperm over the egg mass and the two animals then separate. The sperm has a long acrosome to penetrate the adhesive layer around the egg. Embryo-protecting species in other groups of polychaeces show parallel specialization in sperm structure and in breeding behaviour. A chronology has been established for the development of embryos up to their release from the parent, and this can be used to estimate the spawning date of females with embryo masses collected on the shore. Individuals grow at widely varying rates after settlement on the shore, and no year classes could be detected in the population. All individuals spawn in the first spring after settlement, and at least some survive to spawn again in one or more subsequent springs.  相似文献   
35.
We describe a female fetus with a de novo X chromosome rearrangement detected prenatally in both chorion villi and a pleural effusion. Chromosome painting showed the chromosome to be composed entirely of X chromosome material, while G-banding indicated a duplication of X short arms, four copies of the proximal long arm, and deletion of the distal long arm of the X. C-banding showed the presence of one active and two inactive centromeres and X-inactivation studies demonstrated the tricentric chromosome to be late replicating in all cells examined. The origin of this complex de novo rearrangement appears to have involved two separate breakage events, the first leading to the production of a dicentric X chromosome and the second generating the tricentric X.  相似文献   
36.
Future energy requirements are often estimated by prediction, as if they were beyond man's control. After stating that such predictions have, in practice, become implicit planning, the author outlines necessary steps for discussing future energy requirements and raises some basic issues which must be considered when comparing the feasibilities of 'hard' or 'soft' energy paths.  相似文献   
37.
The present study focused on the assessment of oxidative stress induction by pesticides such as carbamates which are widely used as insecticides and nematicides and contaminate aquatic ecosystems on certain biomarkers in liver of common carp (Cyprinus carpio L.). Biomarkers selected for stress monitoring were malondialdehyde (MDA), an index of lipid peroxidation, and antioxidant defence system enzymes, mainly catalase (CAT), glutathione reductase (GR), and glutathione-S-transferase (GST) activities in liver of fish exposed to 0, 10, 50, or 100?µg?L?1 of carbofuran for 4, 15, or 30 days. Oxidative stress was found in liver of common carp exposed to carbofuran which was manifested by a decrease in CAT and GR activities after 4 and 30 days of exposure. An adaptive response was probably produced since at day 15 no modifications in the CAT activity and increased GR activity were observed. In addition, a decrease in MDA content with the highest concentration of carbofuran used was found after 30 days of exposure. However, no significant changes were found in GST activity showing a varied response. The results concerning oxidative and antioxidant profiles indicate that subchronic exposure to the insecticide carbofuran is capable of inducing oxidative stress in fish.  相似文献   
38.
A response to the Nuffield Council on Bioethics Consultation from the Institute of Biology, the Association of Applied Biology, the British Crop Protection Council, the British Ecological Society, the British Electrophoresis Society, the British Grassland Society, and the Institute of Horticulture  相似文献   
39.
The focus of the studies presented in the preceding companion paper (Part A: Review) and here (Part B: Applications) is on defining representative emission rates from vegetation for determining the roles of biogenic volatile organic compound (BVOC) emissions in atmospheric chemistry and aerosol processes. The review of previously published procedures for identifying and quantifying BVOC emissions has revealed a wide variety of experimental methods used by various researchers. Experimental details become increasingly critical for quantitative emission measurements of low volatility monoterpenes (MT) and sesquiterpenes (SQT). These compounds are prone to be lost inadvertently by uptake to materials in contact with the sample air or by reactions with atmospheric oxidants. These losses become more prominent with higher molecular weight compounds, potentially leading to an underestimation of their emission rates. We present MT and SQT emission rate data from numerous experiments that include 23 deciduous tree species, 14 coniferous tree species, 8 crops, and 2 shrubs. These data indicate total, normalized (30 degrees C) basal emission rates from <10 to 5600ngCg(-1)h(-1) for MT, and from <10 to 1150ngCg(-1)h(-1) for SQT compounds. Both MT and SQT emissions have exponential dependencies on temperature (i.e. rates are proportional to e(betaT)). The inter-quartile range of beta-values for MT was between 0.12 and 0.17K(-1), which is higher than the value commonly used in models (0.09K(-1)). However many of the MT emissions also exhibited light dependencies, making it difficult to separate light and temperature influences. The primary light-dependent MT was ocimene, whose emissions were up to a factor of 10 higher than light-independent MT emissions. The inner-quartile range of beta-values for SQT was between 0.15 and 0.21K(-1).  相似文献   
40.
The terrestrial chapter of the Circumpolar Biodiversity Monitoring Programme (CBMP) has the potential to bring international multi-taxon, long-term monitoring together, but detailed fundamental species information for Arctic arthropods lags far behind that for vertebrates and plants. In this paper, we demonstrate this major challenge to the CBMP by focussing on spiders (Order: Araneae) as an example group. We collate available circumpolar data on the distribution of spiders and highlight the current monitoring opportunities and identify the key knowledge gaps to address before monitoring can become efficient. We found spider data to be more complete than data for other taxa, but still variable in quality and availability between Arctic regions, highlighting the need for greater international co-operation for baseline studies and data sharing. There is also a dearth of long-term datasets for spiders and other arthropod groups from which to assess status and trends of biodiversity. Therefore, baseline studies should be conducted at all monitoring stations and we make recommendations for the development of the CBMP in relation to terrestrial arthropods more generally.  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