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   7693篇
  免费   651篇
  国内免费   890篇
安全科学   2034篇
废物处理   127篇
环保管理   1185篇
综合类   3501篇
基础理论   621篇
污染及防治   347篇
评价与监测   400篇
社会与环境   570篇
灾害及防治   449篇
  2024年   13篇
  2023年   79篇
  2022年   166篇
  2021年   236篇
  2020年   259篇
  2019年   205篇
  2018年   161篇
  2017年   254篇
  2016年   295篇
  2015年   282篇
  2014年   339篇
  2013年   417篇
  2012年   600篇
  2011年   615篇
  2010年   470篇
  2009年   511篇
  2008年   350篇
  2007年   542篇
  2006年   511篇
  2005年   440篇
  2004年   390篇
  2003年   343篇
  2002年   315篇
  2001年   202篇
  2000年   229篇
  1999年   197篇
  1998年   131篇
  1997年   132篇
  1996年   91篇
  1995年   115篇
  1994年   95篇
  1993年   61篇
  1992年   61篇
  1991年   31篇
  1990年   19篇
  1989年   15篇
  1988年   10篇
  1987年   5篇
  1986年   3篇
  1985年   2篇
  1982年   6篇
  1980年   4篇
  1979年   4篇
  1978年   6篇
  1977年   3篇
  1976年   3篇
  1974年   2篇
  1972年   4篇
  1971年   4篇
  1970年   1篇
排序方式: 共有9234条查询结果,搜索用时 70 毫秒
411.
基于岩体质量指标Q分类系统,应用Monte-Carlo模拟技术,研究了岩体质量风险分析方法。该方法视Q分类系统中各单因素取值为随机变量,建立了各单因素取值概率模型;通过对所建模型的抽样计算,可获取所评价岩体实际Q值小于设计所采用Q值的概率;通过对比分析Q值累计曲线和岩体质量分布图,可得到任意Q值对应的风险概率,查清岩体中可能出现的质量等级以及每个质量等级所占百分比的情况。本文研究成果已在青岛胶州湾海底隧道工程中得到应用,并获得良好效果。  相似文献   
412.
基于现代信息技术的城市灾害应急管理系统   总被引:6,自引:0,他引:6  
城市灾害应急管理系统是一项复杂的大系统工程。本文着重从应急管理过程中的应急资源调配、应急预案制定等方面阐述了现代信息技术在城市灾害应急管理中的应用与优势。认为应急管理信息系统的建立目的不是为了预测和估算,而应是当灾害发生时,对已造成的灾情局面做出快速的辅助决策支持。基于此,利用SuperMapObject5.0,Visual Basic6.0,SQL Server2000等现代信息技术软件,以辅助决策、资源快速查询以及生命线管网易损处调查为目的,本文建立了一个局部地区灾害应急管理信息系统。系统的数据库建立更突出了为应急管理服务所需的基础信息、空间数据、应急预案和应急资源等信息划分方式;结合已有的震害预测理论和方法,开发了供水系统和交通系统的震害预测模块,事先为灾害应急决策提供可能的震害信息。系统的开发过程进一步证明了GIS在城市灾害应急管理中有着直观显示、容易操作、辅助准确决策等优势。  相似文献   
413.
城市震后救灾系统救灾决策研究   总被引:6,自引:2,他引:4  
论述了震后救灾系统模型及评估方法,采用Monte Carlo模拟和最优化技术理论,建立了城市震后救灾、救护、运输网络系统的可靠性分析方法和以失效概率为控制参数的最佳路径优化方法,并以某城市网络系统为例通过分析研究,给出了震后救灾决策方法。  相似文献   
414.
Zhalong National Nature Reserve in the northeast of China is a large wetland and a habitat of hundreds species of fauna and flora. The rare red-crowned crane is one kind of endangered birds in it. Recently, Zhalong wetland is shrinking and it encounters many problems including occasional fires, bad water quality, human activities, etc. In order to find out a proper way to protect and restore the wetland, this study, using a geographic information system, the global positioning system and remote sensing techniques, analyses the spatial characteristics of the changes in marsh landscape pattern and examines the driving factors for these changes. Data sources include 8 Landsat Thematic Mapper satellite images of Zhalong area in the period of 1986–2002 and the investigation information on site. Based on the analysis of changes of marsh area and annual precipitation during the 16 years, it is found that there is a close correlation between annual precipitation and marsh area. It means that climate is one of driving factors of marsh pattern changes. To understand influences of other kinds of land uses on marsh spatial distribution in Zhalong wetland, this paper analyses the relationship between marsh and different kinds of land uses, such as water surface, residential area, farmland, salina land and grass land, respectively. According to the patch analysis theory, a fragmental index and a fractal dimension of the marsh are calculated with perimeter-area method. The results indicate that the marsh pattern is affected by human activities significantly. In addition, the location alteration of marsh centroid point over the 16 years is studied. The movement trace of marsh centroid point is concerned with different hydrological situation in different areas of the wetland. In summary the characteristics of the marsh landscape pattern evolution during the 16 years are affected by multiple driving factors. The main driving factors are climate, human activities, distribution of other kinds of land uses and hydrological situation in different areas.  相似文献   
415.
By using a dynamic dilution system, the atmospheric measurement of 11 selected toxics VOCs (ethylene, acetylene, propene, 1-butene, 1,3-butadiene, 1-pentene, 1-hexene, benzene, toluene, ethylbenzene, m+p-xylene) from the list WHO of 1996 and TO-14 method of US EPA by preconcentration by thermal desorption (TD), analysis by gas chromatography (GC), identification and quantification with a flame ionisation detector (FID) was developed and validated in term of metrology, especially the techniques of sampling of these VOCs with adsorbents cartridges "Air Toxics" when used with an "UMEG sampler" equipped in the inlet with a nafion membrane. In particular the influence of climatic conditions (temperature and relative humidity) and the influence of chemical factors like ozone, on the representativity of sampling were studied. Experiments made with various humidities showed that the addition of a nafion membrane in the inlet of the sampling system was required. Without this membrane, losses of compounds were observed for RH >50%. With this membrane, storage for 2 weeks in a refrigerator, as for canisters, did not induce a loss of compounds. No significative decrease of concentrations of the studied VOCs after 14 days storage, which are known to react with ozone, were observed with an ozone concentrations of 55 ppb. One explanation is that nafion membrane, placed in the inlet of the sampler, will neutralize ozone before entering the sampling tubes. This observation is in accordance with literature which states that the sampling of VOCs on Carbotrap cartridges without ozone scrubber induce a loss of compounds.  相似文献   
416.
Recent advances in both information and sensor technologies have enabled the development of Real Time Remote Monitoring (RTRM) capabilities for environmental management. An online and real time remote monitoring system for air pollution has been designed and installed at a traffic police station at Punjagutta in Hyderabad, India. The system is optimized using electrochemical sensors and a real time particulate matter analyzer. The system also monitors meteorological parameters such as temperature, humidity, rainfall, barometric pressure, wind speed and wind direction. The system periodically monitors both pollution and meteorological parameters at pre- programmed intervals of hr during peak periods and 1 hr during non peak periods of the day and continuously uploads to a predestinated web site (www.appcb.org/home.htm) using File Transfer Protocol. The web site renders a quick, simple and graphical display of air pollution levels and meteorological parameters and their significance to humans. The present paper highlights design considerations of a pollution monitoring system, system hardware and software requirements and practical limitations and future directions for real time remote monitoring of air pollution.  相似文献   
417.
This investigation conducted a full-scale survey the drinking water distribution system in Kaohsiung city, Taiwan. The aim was to investigate whether the distribution system was capable of maintaining high water quality from the water treatment facilities through to the end user. The results showed that the distribution system can maintain high water quality, except for suitable chlorine residuals. The authors plotted chlorine residual contour maps to identify areas with low chlorine residuals, helping them prioritize sections that must be flushed or renewal. The contour maps also provide sufficient and clear information for locating booster chlorination stations. Contour maps enable water facilities to identify how water quality decays in the distribution systems and the locations of such decay. Water quality decay can be caused by properties of pipeline materials, hydraulic conditions, and/or biofilm thickness. However, understanding the exact reasons is unnecessary because the contour maps provide sufficient information for trouble-shooting the distribution systems.  相似文献   
418.
In the meerkat (Suricata suricatta), a cooperative mongoose, pups follow potential feeders while the group is foraging and emit incessant calls when soliciting food from them. In contrast to a ’stationary’ brood of chicks, in which nestlings are fed at a fixed location, meerkat pups are ’mobile’ and become spread out. The question arises whether meerkat pups that experience different constraints to those facing chicks have evolved similar begging strategies. This paper describes the vocalisations that meerkat pups emit in the context of begging and investigates the influence of these calls on food allocation by older group members and on the behaviour of littermates. Meerkat pups use two types of calls when soliciting food from a potential feeder. The most common is a ’repeat’ call, which pups emit continuously when following an older forager over several hours a day. In addition, when a potential feeder finds a prey item, the pups next to it emit a bout of calls with increased calling rate, amplitude and fundamental frequency, termed ’high-pitched’ calls. Observations, together with playback experiments, showed that more prey was allocated to pups that called longer and more intensely. The pup closest to a feeder was almost always fed. The probability of emitting high-pitched calls did not depend on the time since a pup had received food, and the change from repeat to high-pitched calls occurred suddenly. The main function of the high-pitched call, therefore, does not appear to be to signal a pup’s hunger state. More likely, the two calls, in the context of begging, may be an adaptation to energetic constraints in a mobile feeding system. Pups, which are dispersed during foraging, may emit repeat calls over long periods to prevent potential feeders from eating all the prey themselves. At the moment a potential feeder finds prey, pups may give the more intense high-pitched calls to direct feeders to bring the food item to them and not to a littermate. Therefore, unlike the stationary feeding system where chicks emit one type of begging call when the feeder approaches the nest, meerkats, with a mobile feeding system, have evolved two discrete types of vocalisations in the context of begging. Received: 22 November 1999 / Revised: 1 July 2000 / Accepted: 17 July 2000  相似文献   
419.
DNA fingerprinting was combined with field observations over four breeding seasons to investigate the social structure and mating system of the laughing kookaburra (Dacelo novaeguineae). Groups comprised a socially dominant pair and up to six helpers of either sex. Helpers were always recruited from young hatched in the group. Territorial inheritance, which is a feature of other cooperative breeders and an oft-cited benefit of philopatry, did not occur. Helpers only attained dominant status in an established group by dispersing into a vacant dominant position in that group. However, helpers could also form new groups by excising a new territory, often through a ”budding” process. The mating system was overwhelmingly monogamous. There were no cases of extra-group parentage in a sample of 140 nestlings; within groups of three or more birds, dominance predicted parentage almost perfectly (99.2% of 129 nestlings), irrespective of whether helpers in the group were related to one or both dominant birds. This is contrary to predictions from models of reproductive skew, possibly because they currently fail to incorporate the willingness of females to share reproduction among males. Received: 15 May 1999 / Received in revised form: 2 November 1999 / Accepted: 6 November 1999  相似文献   
420.
One of the most interesting aspects of the mating system of pied flycatchers is the regular occurrence of polygyny. Here we present data on the reproductive success of polygynously paired pied flycatcher males compared to monogamous males based on paternity analyses through DNA fingerprinting. Males paired with two females suffered a higher loss in reproductive output per female compared to monogamous males due to (1) a greater proportion of unhatched eggs in their broods, (2) greater nestling mortality and (3) a greater probability of being cuckolded. Nevertheless, the number of fledglings was significantly greater for polygynous males. Based on the number of nestlings that returned for subsequent breeding seasons, however, the reproductive success of monogamous and polygynous males did not differ significantly. These data raise the question as to why males attempt polygyny. Received: 16 August 1999 / Received in revised form: 15 March 2000 / Accepted: 18 March 2000  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