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   461篇
  免费   8篇
  国内免费   1篇
安全科学   16篇
废物处理   16篇
环保管理   89篇
综合类   71篇
基础理论   104篇
污染及防治   119篇
评价与监测   22篇
社会与环境   30篇
灾害及防治   3篇
  2024年   4篇
  2023年   6篇
  2022年   6篇
  2021年   9篇
  2020年   5篇
  2019年   8篇
  2018年   9篇
  2017年   7篇
  2016年   21篇
  2015年   12篇
  2014年   15篇
  2013年   35篇
  2012年   26篇
  2011年   27篇
  2010年   17篇
  2009年   22篇
  2008年   23篇
  2007年   19篇
  2006年   21篇
  2005年   15篇
  2004年   20篇
  2003年   16篇
  2002年   12篇
  2001年   10篇
  2000年   3篇
  1999年   11篇
  1998年   4篇
  1997年   3篇
  1996年   8篇
  1995年   1篇
  1994年   10篇
  1993年   6篇
  1992年   5篇
  1991年   5篇
  1989年   5篇
  1988年   5篇
  1987年   3篇
  1986年   1篇
  1985年   3篇
  1984年   4篇
  1983年   5篇
  1982年   4篇
  1981年   2篇
  1980年   2篇
  1979年   5篇
  1978年   1篇
  1977年   2篇
  1976年   4篇
  1974年   2篇
  1965年   1篇
排序方式: 共有470条查询结果,搜索用时 15 毫秒
41.
Traffic related platinum deposits on, or near to, the roads. Platinum accumulation was studied using the method of standardised culture of grass (Lolium multiflorum) at locations with different traffic exposure in the region of Munich. Grass cultures from 6 locations with high traffic exposure, and 3 reference locations far away from traffic emissions, were analysed in 1992 and 1993. The results show a good indication of the platinum emissions byLolium multiflorum. The platinum concentrations rose with the increasing traffic. They diminished with growing distance from the verge of the road. The highest average platinum concentrations were measured at locations close to highly frequented urban roads, in the range 0.8 to 2.9 μg/kg dm. The average platinum concentration at locations far from emissions was found in the range of 0.17 to 0.51 μg/kg dm in 1992 and 1993. The good correlation between the platinum concentrations in grass cultures and the concentrations of other traffic-related elements, like antimony, chromium and lead, verifies the dependence of platinum accumulation from traffic.  相似文献   
42.
Atlantic cod stocks are subdivided into geographically and biologically discrete populations; some being locally resident, others migratory. The reasons for the variation in migration pattern and the consequences it may have for population structuring is poorly understood. We studied a group of cod from the coastal waters of the Shetland Isles in the northern North Sea. During the spawning season, electronic tags that record depth and temperature over time were implanted into 133 individuals and the fish released within a few kilometres of where they were captured. Thirty-nine cod have been recaptured up to 608 days later, throughout the year and, in all but two cases, within 15 km of their release site. Geolocation methods based on temperature and bathymetry also suggested that the cod had a limited home range, remaining resident year-round in coastal waters. The cod were deeper during the winter and moved to shallower water in late spring and summer. They showed diel, fortnightly and monthly cycles in depth movement that varied much within and between individuals over the season. Residency and the individual variability in vertical movement may reflect a combination of locally complex depth strata, variable seabed substrate and the wide range of seasonally available prey resources.  相似文献   
43.
         下载免费PDF全文
Scientists are increasingly using Twitter as a tool for communicating science. Twitter can promote scholarly discussion, disseminate research rapidly, and extend and diversify the scope of audiences reached. However, scientists also caution that if Twitter does not accurately convey science due to the inherent brevity of this media, misinformation could cascade quickly through social media. Data on whether Twitter effectively communicates conservation science and the types of user groups receiving these tweets are lacking. To address these knowledge gaps, we examined live tweeting as a means of communicating conservation science at the 2013 International Congress for Conservation Biology (ICCB). We quantified and compared the user groups sending and reading live tweets. We also surveyed presenters to determine their intended audiences, which we compared with the actual audiences reached through live tweeting. We also asked presenters how effectively tweets conveyed their research findings. Twitter reached 14 more professional audience categories relative to those attending and live tweeting at ICCB. However, the groups often reached through live tweeting were not the presenters’ intended audiences. Policy makers and government and non‐governmental organizations were rarely reached (0%, 4%, and 6% of audience, respectively), despite the intent of the presenters. Plenary talks were tweeted about 6.9 times more than all other oral or poster presentations combined. Over half the presenters believed the tweets about their talks were effective. Ineffective tweets were perceived as vague or missing the presenters’ main message. We recommend that presenters who want their science to be communicated accurately and broadly through Twitter should provide Twitter‐friendly summaries that incorporate relevant hashtags and usernames. Our results suggest that Twitter can be used to effectively communicate speakers’ findings to diverse audiences beyond conference walls.  相似文献   
44.
  总被引:1,自引:0,他引:1  
A comprehensive review of online, official, and scientific literature was carried out in 2012–13 to develop a framework of disaster social media. This framework can be used to facilitate the creation of disaster social media tools, the formulation of disaster social media implementation processes, and the scientific study of disaster social media effects. Disaster social media users in the framework include communities, government, individuals, organisations, and media outlets. Fifteen distinct disaster social media uses were identified, ranging from preparing and receiving disaster preparedness information and warnings and signalling and detecting disasters prior to an event to (re)connecting community members following a disaster. The framework illustrates that a variety of entities may utilise and produce disaster social media content. Consequently, disaster social media use can be conceptualised as occurring at a number of levels, even within the same disaster. Suggestions are provided on how the proposed framework can inform future disaster social media development and research.  相似文献   
45.
    
Extracts of 19 of 24 species of sponge collected from Queensland. Australia, inhibited the growth of test microorganisms in in-vitro assays. A similar result has been obtained by earlier workers for extracts of species of sponge obtained from temperate waters. Some of the extracts, including extracts of Thorecta vasiforis, Arenochalina mirabilis and Acanthella kleutha, showed activity against bacterial strains that was comparable with that exhibited by penicillin G and streptomycin against these strains. Gram-positive bacteria were expecially sensitive to many extracts. Little activity was exhibited by any extract against four species of fungi tested. Some of the extracts were markedly toxic to one or more of the test organisms (a fish, a crustacean and a hydroid) used, but no clear pattern linking toxicity to these organisms with antimicrobial properties of the extracts emerged. In general, there bas a negative correlation between antimicrobial activity and surface-fouling, raising the possibility of using freedom from surface-fouling as an indicator of antimicrobial activity. Four of five encrusting species from the undersides of coral boulders showed antimicrobial activity. This study confirmed the value of using methanol-toluene extracts in field-based screening programmes, but emphasised the need to use additional extracting media such as methylene chloride in order to augment the number of antimicrobial compounds detected. There are indications that antimicrobial activity may be widespread in the order Dictyoceratida, in the order Verongida and in the order Axinellida, but sporadic in other orders of Porifera.  相似文献   
46.
Juvenile gray snapper, Lutjanus griseus, are believed to use bays and estuaries in southern Florida as nurseries before moving out to the adjoining reef tract as adults. Using high-resolution sector field-inductively coupled plasma-mass spectrometry (SF-ICP-MS), the elemental chemistry of the otoliths of juveniles from five nursery regions was resolved by establishing elemental “signatures” for each region. In this study we simultaneously analyzed 32 elements including a suite of rare earth elements. A stepwise variable selection procedure retained a subset of eight elements that contributed substantially to separating otolith samples, including two rare earth elements; this is one of the first studies in which rare earth elements in otoliths have contributed to separation of fish stocks. The classification success rate in assigning fishes to the correct region of origin was 82%. Resolution of sites less than 10 km apart suggested high site fidelity in juvenile gray snapper and little mixing of water masses between sites. The juvenile nursery signatures will be used to determine the relative contribution of different nurseries to the adult population on an adjoining reef tract.  相似文献   
47.
48.
Coastal zones around the world have experienced urban growth in the last 50 years. This landscape change brings new aspects for those zones and the environment. Real estate speculation is a decisive factor that changes landscape, with urban growth that occurs both in the extent and volume of construction. Boa Viagem (BV) beach at Recife, Northeast Brazil was just a sand bar covered by an Atlantic Forest until middle of the 1800s. Today, it has turned into a busy area of the city where residences, services and commerce co-exist in a densely packed arrangement. This work demonstrates and analyses vertical growth in BV and urban changes from 1961 to 2011. It was developed using digital image processing and visual analysis of satellite imagery and aerial photos. A GIS was created using SPRING and ArcScene, to calculate variations in area and volume creating a Volumetric Index (VI). The Minimal Mapping Area was used in sixteen census tract as samples of the area. Occupation and vertical growth were especially accentuated from 1981 to 1996 with the peak at 2011. Increases in vertical growth from shore to inland are evident in all parts of the district. This finding was confirmed by three-dimensional GIS representations of the study area and the VI during the period of this work, showing the potential of 3D GIS models for studying dense urbanization areas in coastal zones.  相似文献   
49.
A study of marine boring and fouling organisms in the vicinity of the thermal effluent from the Oyster Creek Nuclear Generating Station, Barnegat Bay, New Jersey, USA has been conducted since 1971. Two subtropical species of shipworms have been found in significant numbers in the effluent. These are Teredo bartschi Clapp and Teredo furcifera von Martens. The shipworm Lyrodus sp. and the flatworm Taenioplana teredini Hyman, which is predatory on teredinids, were also found, but on only one occasion. The polychaete Ficopomatus enigmaticus (Fauvel) has been found for the first time on the Atlantic Coast of North America. Three other polychaetes, Potamilla (Potamethus) spathiferus (Ehlers), Loimia medusa (Savigny), and Sphaerosyllis sp., have been newly identified from Barnegat Bay, but probably are not recent range extensions. Only T. bartschi, T. furcifera, and F. enigmaticus have established breeding populations. Their distributions and abundances are probably related to the thermal effluent; this is most clear in the case of T. bartschi and least clear in the case of F. enigmaticus. T. bartschi was confined at first to the heated effluent in Oyster Creek, but has spread to Forked River. It has become a major faunal element in Oyster Creek. The impact of the other exotic species has been negligible. The primary mechanism of the range extensions is by boat transport.  相似文献   
50.
    
In-situ feeding habits of the copepods Temora turbinata and T. stylifera were investigated by scanning electron microscope examination of fecal pellets, the contents of which reflected copepod gut contents upon capture. Pellet contents were compared with assemblages of available phytoplankton in the water column at the times of zooplankton sampling. Samples were collected in continental shelf and slope waters of the Gulf of Mexico near the mouth of the Mississippi River. Both species ingested a wide size range and taxonomic array of phytoplankters, and to a lesser extent, other crustaceans. Fecal pellets contained primarily the remains of the phytoplankters that were most abundant in the water at times of collection. There was considerable overlap in the food items ingested by adult females of both copepod species, or two stages of T. turbinata copepodites. Thus, T. turbinata and T. stylifera are omnivores, but primarily opportunistic herbivores.  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