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   184篇
  免费   1篇
  国内免费   2篇
安全科学   3篇
废物处理   1篇
环保管理   7篇
综合类   119篇
基础理论   31篇
污染及防治   18篇
评价与监测   3篇
社会与环境   5篇
  2017年   3篇
  2016年   2篇
  2015年   5篇
  2014年   5篇
  2013年   4篇
  2011年   6篇
  2010年   2篇
  2009年   6篇
  2008年   2篇
  2006年   4篇
  2005年   4篇
  2002年   6篇
  2001年   3篇
  2000年   2篇
  1999年   8篇
  1998年   4篇
  1996年   3篇
  1995年   4篇
  1994年   3篇
  1993年   2篇
  1974年   2篇
  1970年   3篇
  1969年   2篇
  1968年   2篇
  1967年   4篇
  1966年   5篇
  1965年   3篇
  1964年   8篇
  1963年   2篇
  1962年   5篇
  1961年   4篇
  1960年   3篇
  1959年   4篇
  1958年   2篇
  1957年   4篇
  1956年   5篇
  1955年   5篇
  1954年   5篇
  1953年   2篇
  1952年   4篇
  1948年   1篇
  1943年   2篇
  1941年   2篇
  1939年   1篇
  1936年   3篇
  1933年   1篇
  1930年   2篇
  1929年   1篇
  1928年   3篇
  1920年   1篇
排序方式: 共有187条查询结果,搜索用时 15 毫秒
151.
During September/October 2012, a norovirus gastroenteritis outbreak affecting about 11,000 people occurred in Germany. Epidemiological studies suggested that frozen strawberries represented the vehicle of infection. We describe here the analysis of frozen strawberries for the presence of norovirus. Samples were taken by applying a stratified subsampling scheme. Two different methods for virus extraction from strawberries were compared. First, viruses were eluted from strawberries under alkaline conditions and concentrated using a polyethylene glycol precipitation. Second, ultrafiltration was applied for concentration of viruses rinsed off of the berries. In both cases, RNA was extracted and analyzed by real-time RT-PCR. Application of the ultrafiltration method generally resulted in a lower detection rate. Noroviruses were detected in 7/11 samples derived from the lot of strawberries implicated in the outbreak using the precipitation method. Typing of norovirus revealed three different genotypes including a combination of norovirus genotype II.16 (viral polymerase) and II.13 (viral capsid). This genotype combination was also found in some of the patients that were involved in the outbreak, but that had not been reported in Germany so far. In conclusion, heterogeneously distributed noroviruses in frozen strawberries can be detected by applying an optimized combination of sampling procedures, virus extraction methods, and real-time RT-PCR protocols. The detection of several different genotypes in the strawberries may suggest contamination from sewage rather than from a single infected food handler.  相似文献   
152.
153.
In Europe, socio-economic enterprises such as charities, voluntary organisations and not-for-profit companies are involved in the repair, refurbishment and reuse of various products. This paper characterises and analyses the operations of socio-economic enterprises that are involved in the reuse of Information and Communication Technology (ICT) equipment. Using findings from a survey, the paper specifically analyses the reuse activities of socio-economic enterprises in the UK from which Europe-wide conclusions are drawn. The amount of ICT products handled by the reuse organisations is quantified and potential barriers and opportunities to their operations are analysed. By-products from reuse activities are discussed and recommendations to improve reuse activities are provided. The most common ICT products dealt with by socio-economic enterprises are computers and related equipment. In the UK in 2010, an estimated 143,750 appliances were reused. However, due to limitations in data, it is difficult to compare this number to the amount of new appliances that entered the UK market or the amount of waste electrical and electronic equipment generated in the same period. Difficulties in marketing products and numerous legislative requirements are the most common barriers to reuse operations. Despite various constraints, it is clear that organisations involved in reuse of ICT could contribute significantly to resource efficiency and a circular economy. It is suggested that clustering of their operations into “reuse parks” would enhance both their profile and their products. Reuse parks would also improve consumer confidence in and subsequently sales of the products. Further, it is advocated that industrial networking opportunities for the exchange of by-products resulting from the organisations’ activities should be investigated. The findings make two significant contributions to the current literature. One, they provide a detailed insight into the reuse operations of socio-economic enterprises. Previously unavailable data has been presented and analysed. Secondly, new evidence about the by-products/materials resulting from socio-economic enterprises’ reuse activities has been obtained. These contributions add substantially to our understanding of the important role of reuse organisations.  相似文献   
154.
155.
In declining forests of the Vosges mountains (northeast of France), we previously observed that the yellowing of spruce (Picea abies L. cv. Karsten) needles was associated with impairment of the free radical scavenging capacity of the cells and coincided with chronic exposure to ozone. Chloroplasts of yellow needles were characterized by an abnormal accumulation of photosystem II (PSII) D1-protein in the thylakoids. Further experiments carried out on declining and decline-resistant individual spruce trees characterized in previous studies showed that needle yellowing was associated with impairment of the overall anti-oxidative defense in both the cytosol and the chloroplasts. Both enzymic (peroxidases) and non-enzymic (carotenoids) oxidant scavengers were shown to be affected in the declining spruce. PSII D1-protein accumulation seemed to result from a stabilization of the polypeptide, which led us to hypothesize that oxidative processes might interfere with the specific degradation of this protein in declining spruce, with destructive consequences for the photosystems.  相似文献   
156.
King brown snakes or mulga snakes (Pseudechis australis) are the largest and among the most dangerous and wide-ranging venomous snakes in Australia and New Guinea. They occur in diverse habitats, are important predators, and exhibit considerable morphological variation. We infer the relationships and historical biogeography of P. australis based on phylogenetic analysis of 1,249 base pairs from the mitochondrial cytochrome b, NADH dehydrogenase subunit 4 and three adjacent tRNA genes using Bayesian, maximum-likelihood, and maximum-parsimony methods. All methods reveal deep phylogenetic structure with four strongly supported clades comprising snakes from New Guinea (I), localities all over Australia (II), the Kimberleys of Western Australia (III), and north-central Australia (IV), suggesting a much more ancient radiation than previously believed. This conclusion is robust to different molecular clock estimations indicating divergence in Pliocene or Late Miocene, after landbridge dispersal to New Guinea had occurred. While members of clades I, III and IV are medium-sized, slender snakes, those of clade II attain large sizes and a robust build, rendering them top predators in their ecosystems. Genetic differentiation within clade II is low and haplotype distribution largely incongruent with geography or colour morphs, suggesting Pleistocene dispersal and recent ecomorph evolution. Significant haplotype diversity exists in clades III and IV, implying that clade IV comprises two species. Members of clade II are broadly sympatric with members of both northern Australian clades. Thus, our data support the recognition of at least five species from within P. australis (auct.) under various criteria. We discuss biogeographical, ecological and medical implications of our findings.Electronic Supplementary Material  Supplementary material is available in the online version of this article at  相似文献   
157.
Some aspects of comparative sensory physiology are reviewed in the context of the historical development. Emphasis is placed on the concepts how spatial and temporal stimulus patterns are processed into nervous excitation patterns and projected in the brain: Both receptor organs and neuron networks may act as selective filters for certain features of the stimulus situation. Neural projections represent not only the spatial distribution of the stimulus pattern but also other parameters. Excitation patterns resulting from the stimulus situation are compared in the neuronal networks with patterns inherited, learned, or inherited and modified by learning. The result of this comparison may then trigger the behavior necessary under the conditions present.  相似文献   
158.
159.
160.
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