全文获取类型
收费全文 | 593篇 |
免费 | 86篇 |
国内免费 | 85篇 |
专业分类
安全科学 | 120篇 |
废物处理 | 21篇 |
环保管理 | 140篇 |
综合类 | 271篇 |
基础理论 | 77篇 |
污染及防治 | 34篇 |
评价与监测 | 37篇 |
社会与环境 | 23篇 |
灾害及防治 | 41篇 |
出版年
2024年 | 3篇 |
2023年 | 10篇 |
2022年 | 12篇 |
2021年 | 22篇 |
2020年 | 19篇 |
2019年 | 12篇 |
2018年 | 20篇 |
2017年 | 20篇 |
2016年 | 34篇 |
2015年 | 26篇 |
2014年 | 39篇 |
2013年 | 43篇 |
2012年 | 52篇 |
2011年 | 51篇 |
2010年 | 28篇 |
2009年 | 30篇 |
2008年 | 23篇 |
2007年 | 41篇 |
2006年 | 40篇 |
2005年 | 24篇 |
2004年 | 25篇 |
2003年 | 28篇 |
2002年 | 16篇 |
2001年 | 10篇 |
2000年 | 10篇 |
1999年 | 8篇 |
1998年 | 16篇 |
1997年 | 11篇 |
1996年 | 11篇 |
1995年 | 9篇 |
1994年 | 9篇 |
1993年 | 3篇 |
1992年 | 6篇 |
1991年 | 5篇 |
1990年 | 2篇 |
1989年 | 6篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1977年 | 1篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1971年 | 3篇 |
1970年 | 1篇 |
排序方式: 共有764条查询结果,搜索用时 593 毫秒
51.
Steven R. Greb David J. Graczyk 《Journal of the American Water Resources Association》1995,31(3):431-438
ABSTRACT: Historically, dissolved-oxygen (DO) data have been collected in the same manner as other water-quality constituents, typically at infrequent intervals as a grab sample or an instantaneous meter reading. Recent years have seen an increase in continuous water-quality monitoring with electronic dataloggers. This new technique requires new approaches in the statistical analysis of the continuous record. This paper presents an application of frequency-duration analysis to the continuous DO records of a cold and a warm water stream in rural southwestern Wisconsin. This method offers a quick, concise way to summarize large time-series data bases in an easily interpretable manner. Even though the two streams had similar mean DO concentrations, frequency-duration analyses showed distinct differences in their DO-concentration regime. This type of analysis also may be useful in relating DO concentrations to biological effects and in predicting low DO occurrences. 相似文献
52.
The flood frequency characteristics of 18 watersheds in southeastern Arizona were studied using the log-Boughton and the log-Pearson Type 3 distribution. From the flood frequency study, a generalized envelope for Q100 for watersheds 0.01 to 4000 mi2 in area has been produced for southeastern Arizona. The generalized envelope allows comparisons to be made among the relative flood characteristics of the watersheds used in the study and provides a conservative estimate of Q100 for ungaged watersheds in the region. 相似文献
53.
She-Kong Chong Stephen M. Moore 《Journal of the American Water Resources Association》1983,19(2):277-282
ABSTRACT: Twenty-two gaging stations were selected for developing a regional flood frequency curve for small (area less than 2 square miles) watersheds in southern Illinois. Five probability functions were compared, and the extreme value type I function was selected to develop the regional flood curve. The curve was generated with the index flood method and also another empirical method that related the function parameters to the watershed area. Estimated peak discharges with various return periods were compared with the results obtained from multiple regression analysis. 相似文献
54.
55.
Estimation of Cumulative Frequency Distribution for Carbon Monoxide Concentration from Wind-Speed Data, in Buenos Aires (Argentina) 总被引:2,自引:0,他引:2
In this article we apply and test a methodology to estimate cumulative frequency distribution for air pollutant concentration from wind-speed data. We use the inverse relationship after Simpson et al. (Atmospheric Environment, 19, 75–82, 1985) between the opposing percentile values in the statistical distributions for air pollutant concentrations and wind-speed data. This relationship is valid, irrespective of the statistical distributions of both variables, if an inverse relationship between them is also applicable. The available data are five years of 8-h average carbon monoxide concentration and 8-h mean wind-speed, observed in Buenos Aires (Argentina). The performance of the obtained empirical expressions in estimating cumulative frequency distributions for 8-h CO is statistically evaluated. The results show that it is possible to obtain an acceptable cumulative frequency distribution for 8-h CO concentration at the site if the cumulative frequency distribution for wind-speed is known. Q–Q plots show a good agreement between estimated and observed values. From our data, the mean relative error of the estimations was found to be as much as 8.0%. 相似文献
56.
涉及电动振动台选型的结构与技术的评价和分析 总被引:1,自引:0,他引:1
通过振动台系统组成部分(振动台体,磁场电源和功率放大器)涉及的结构与技术的分析,对振动台系统技术指标的先进性,结构设计的合理性及振动台用于振动试验的准确性和安全性的评价提供依据,可供选择振动台系统参考。 相似文献
57.
ABSTRACT: Both L-moment and nonparametric frequency analyses were performed on a series of annual maximum floods from New Brunswick, Canada. The L-moment analysis concluded that the data were generated from a unimodal Generalized Extreme Value (GEV) distribution. However, the nonparametric frequency analysis indicated that a majority of stations followed nonunimodal mixed distributions since peak flows occur during different seasons and are the result of different generating mechanisms. The coupling of L-moment and nonparametric analyses facilitates mixed distribution identification. Thus, the nonparametric method helps in identifying underlying probability distribution, especially when samples arise from mixed distributions. 相似文献
58.
长江三角洲及其附近地区两千年来水灾的研究 总被引:6,自引:1,他引:5
通过对长江三角洲及其附近地区两千年来水灾生成频率和强度的分析。认为两晋、南北朝时期和南宋、元、明、清时期是两千年来本区的主要水灾期。对照两千年来中国东部气候变化、海面升降与长江口河道变迁关系,认为在本区水灾生成事件中,气候因素起着主导控制作用。当然,人类活动对本区水灾生成的影响也不容忽视。本地区近百年来的旱涝灾害规律可用非线性科学的方法进行研究,旱涝灾害的准60年、准35年和准11年的长周期变化与地球自转速度、地极移动和太阳黑子活动的3个周期变化基本一致。本地区气候系统的行为具有混沌特征。这是线性逼近和周期叠加预报方法难以得出灾害预报正确结果的原因,但气候系统半个月的确定性预测可以实现。 相似文献
59.
Regular additions of NH4NO3 (35–140 kg N ha−1 yr−1) and (NH4)2SO4 (140 kg N ha−1 yr−1) to a calcareous grassland in northern England over a period of 12 years have resulted in a decline in the frequency of the
indigenous bryophyte species and the establishment of non-indigenous calcifuge species, with implications for the structure
and composition of this calcareous bryophyte community. The lowest NH4NO3 additions of 35 kg N ha−1 yr−1 produced significant declines in frequency of Hypnum cupressiforme, Campylium chrysophyllum, and Calliergon cuspidatum. Significant reductions in frequency at higher NH4NO3 application rates were recorded for Pseudoscleropodium purum, Ctenidum molluscum, and Dicranum scoparium. The highest NH4NO3 and (NH4)2SO4 additions provided conditions conducive for the establishment of two typical calcifuges – Polytrichum spp. and Campylopus introflexus, respectively. Substrate-surface pH measurements showed a dose-related reduction in pH with increasing NH4NO3 deposition rates of 1.6 pH units between the control and highest deposition rate, and a further significant fall in pH, of
>1 pH unit, between the NH4NO3 and (NH4)2SO4 treatments. These results suggest that indigenous bryophyte composition may be at risk from nitrogen deposition rates of
35 kg N ha−1 yr−1 or less. These effects are of particular concern for rare or endangered species of low frequency. 相似文献
60.