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   1466篇
  免费   181篇
  国内免费   126篇
安全科学   269篇
废物处理   17篇
环保管理   338篇
综合类   584篇
基础理论   188篇
污染及防治   39篇
评价与监测   171篇
社会与环境   88篇
灾害及防治   79篇
  2024年   5篇
  2023年   32篇
  2022年   55篇
  2021年   78篇
  2020年   59篇
  2019年   65篇
  2018年   47篇
  2017年   76篇
  2016年   103篇
  2015年   56篇
  2014年   67篇
  2013年   92篇
  2012年   89篇
  2011年   102篇
  2010年   68篇
  2009年   90篇
  2008年   59篇
  2007年   108篇
  2006年   75篇
  2005年   54篇
  2004年   45篇
  2003年   45篇
  2002年   42篇
  2001年   28篇
  2000年   34篇
  1999年   21篇
  1998年   19篇
  1997年   24篇
  1996年   16篇
  1995年   9篇
  1994年   17篇
  1993年   8篇
  1992年   9篇
  1991年   8篇
  1990年   6篇
  1989年   5篇
  1988年   7篇
  1987年   4篇
  1986年   5篇
  1985年   6篇
  1984年   2篇
  1983年   2篇
  1981年   5篇
  1980年   6篇
  1978年   3篇
  1977年   3篇
  1974年   2篇
  1973年   6篇
  1971年   3篇
  1970年   1篇
排序方式: 共有1773条查询结果,搜索用时 281 毫秒
341.
本文介绍了格尔木井的基本情况及所架数字仪器的技术系统构成,对水位、地热、气氡等主测项2003年1月1日-2004年12月31日的数字化资料进行了初步分析,发现地热数据基本稳定;气氡数据由原集气装置的不合理,数据上下波动较大,基本无法使用,经改造后,数据趋于稳定;水位受到调节集气装置出水量的影响,但排除该影响后数据基本可以使用。  相似文献   
342.
用灰色组合模型预测环保投资   总被引:6,自引:0,他引:6  
针对环保投资变化的非平稳性,采用灰以GM(1,1)模型分析环保投资的趋势项并与历史环保投资比较得一系列残差,然后应用人工神经网络模型进行了正以提高精度。  相似文献   
343.
Abstract:  Demographic data of rare and endangered species are often too sparse to estimate vital rates and population size with sufficient precision for understanding population growth and decline. Yet, the combination of different sources of demographic data into one statistical model holds promise. We applied Bayesian integrated population modeling to demographic data from a colony of the endangered greater horseshoe bats (Rhinolophus ferrumequinum) . Available data were the number of subadults and adults emerging from the colony roost at dusk, the number of newborns from 1991 to 2005, and recapture data of subadults and adults from 2004 and 2005. Survival rates did not differ between sexes, and demographic rates remained constant across time. The greater horseshoe bat is a long-lived species with high survival rates (first year: 0.49 [SD 0.06]; adults: 0.91 [SD 0.02]) and low fecundity (0.74 [SD 0.12]). The yearly average population growth was 4.4% (SD 0.1%) and there were 92 (SD 10) adults in the colony in year 2005. Had we analyzed each data set separately, we would not have been able to estimate fecundity, the estimates of survival would have been less precise, and the estimate of population growth biased. Our results demonstrate that integrated models are suitable for obtaining crucial demographic information from limited data.  相似文献   
344.
Abstract:  We are now entering a time of immense environmental upheaval in which, increasingly, experts are required to provide conservation assessments. Quantitative assessment of trends in species' range and abundance is costly, requiring extensive field studies over a long period of time. Unfortunately, many species are only known through a few "chance" sightings or a handful of specimens, and therefore extinction may be even harder to ascertain. Several methods have been proposed for estimating the probability of extinction. However, comparison within and between species is difficult because of variations in sighting rates. We applied a probabilistic method that incorporates sighting rate to the sighting record of Vietnamese slipper orchids ( Paphiopedilum ). The method generates a probability that another sighting will occur given the previous sighting rate and the time since last observation. This allows greater comparability between species discovered at different times. Its predictions were more highly correlated with the World Conservation Union criteria than previous methods. Trends in data collection and the political climate of a country, which affects access to material, are important potential sources of variation that affect sighting rates. A lack of understanding of the process by which data are generated makes inferring extinction from sighting records difficult because extinction status depends on how the sighting rate varies. However, such methods allow rapid conservation prioritization of taxa that are poorly known and would otherwise go unassessed.  相似文献   
345.
A statistical model for longitudinal count data is used to examine the potential adverse health effects of ambient air pollution. Daily respiratory admissions to 164 acute care hospitals in Ontario are obtained for the period 1983 to 1988. Estimates of ozone levels in the vicinity of each hospital are determined from air pollution monitoring stations maintained by the Ontario Ministry of the Environment. Generalized estimating equation methods are used to make inferences about the regression and overdispersion parameters. The admission data display little evidence of serial correlation and extra Poisson variation. However, admission rates vary considerably among hospitals. This latter source of variation needs to be taken into account in examining the effects of air pollution on respiratory health status.  相似文献   
346.
讨论了BP网络模型存在的不足及建模条件,提出了建立合理的BP网络模型的基本原则和步骤.针对水质评价问题,通过在各类水质污染指标浓度区间内生成随机分布样本的方法,组成足够多用于BP网络训练、检验和测试用的样本,建立了辽河水质综合评价的BP网络模型;给出了区分不同类别水质的模型分界值样本和模型输出分界值.  相似文献   
347.
Contribution of pollution from different types of sources in Jamshedpur, the steel city of India, has been estimated in winter 1993 using two approaches in order to delineate and prioritize air quality management strategies for the development of region in an environmental friendly manner. The first approach mainly aims at preparation of a comprehensive emission inventory and estimation of spatial distribution of pollution loads in terms of SO2 and NO2 from different types of industrial, domestic and vehicular sources in the region. The results indicate that industrial sources account for 77% and 68% of the total emissions of SO2 and NO2, respectively, in the region, whereas vehicular emissions contributed to about 28% of the total NO2 emissions. In the second approach, contribution of these sources to ambient air quality levels to which the people are exposed to, was assessed through air pollution dispersion modelling. Ambient concentration levels of SO2 and NO2 have been predicted in winter season using the ISCST3 model. The analysis indicates that emissions from industrial sources are responsible for more than 50% of the total SO2 and NO2 concentration levels. Vehicular activities contributed to about 40% of NO2 pollution and domestic fuel combustion contributed to about 38% of SO2 pollution. Predicted 24-h concentrations were compared with measured concentrations at 11 ambient air monitoring stations and good agreement was noted between the two values. In-depth zone-wise analysis of the above indicates that for effective air quality management, industrial source emissions should be given highest priority, followed by vehicular and domestic sources in Jamshedpur region.  相似文献   
348.
空气自动监测系统的仪器仪表多样化,以及数据采集装置和数据格式的差异,给系统软硬件的集成,以及数据应用和管理带来了不便,也是构成空气自动监测信息化进程中的技术瓶颈之一,通过对空气自动监测系统软件开发和数据整合模式的对比分析,探讨了解决问题的途径。  相似文献   
349.
Incorporating Collateral Data in Conservation Biology   总被引:1,自引:0,他引:1  
Abstract:  Conservation biologists often need to set ecological modeling assumptions or estimate parameters from sparse data. In some cases this problem can be addressed by incorporating data from closely related species or from the same species at different sites (i.e., collateral data). Currently no structured methods exist for incorporating such information. An analogous problem in Actuarial science is to set premium rates in situations with little direct data on claim frequency or size. The rates are estimated using actuarial credibility theory, which incorporates collateral data with the direct data. actuarial credibility theory combined with the actuarial control cycle financial management process also provides an adaptive mechanism for updating assumptions. This theory may have some utility for ecologists wanting to incorporate collateral data in an adaptive management framework, a companion to approaches such as Bayesian updating. We describe the historical development of actuarial credibility theory from early ad hoc methods to empirical Bayes approaches. We explore some of the theory's strengths, such as relative simple formulae for incorporation collateral data, and we explore some of the theory's weaknesses, such as the use of the best linear approximation to the Bayes estimate. We illustrate potential applications of the theory using an example on the mortality rate of the Powerful Owl (  Ninox strenua ).  相似文献   
350.
Hierarchical models are considered for estimating the probability of agreement between two outcomes or endpoints from an environmental toxicity experiment. Emphasis is placed on generalized regression models, under which the prior mean is related to a linear combination of explanatory variables via a monotone function. This function defines the scale over which the systematic effects are modelled as additive. Specific illustration is provided for the logistic link function. The hierarchical model employs a conjugate beta prior that leads to parametric empirical Bayes estimators of the individual agreement parameters. An example from environmental carcinogenesis illustrates the methods, with motivation derived from estimation of the concordance between two species carcinogenicity outcomes. Based on a large database of carcinogenicity studies, the inter-species concordance is seen to be reasonably informative, i.e. in the range 67–84%. Stratification into pertinent potency-related sub-groups via the logistic model is seen to improve concordance estimation: for environmental stimuli at the extremes of the potency spectrum, concordance can reach well above 90%.  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