全文获取类型
收费全文 | 323篇 |
免费 | 16篇 |
国内免费 | 32篇 |
专业分类
安全科学 | 37篇 |
废物处理 | 7篇 |
环保管理 | 41篇 |
综合类 | 139篇 |
基础理论 | 66篇 |
污染及防治 | 19篇 |
评价与监测 | 29篇 |
社会与环境 | 11篇 |
灾害及防治 | 22篇 |
出版年
2023年 | 5篇 |
2022年 | 3篇 |
2021年 | 5篇 |
2020年 | 3篇 |
2019年 | 4篇 |
2018年 | 2篇 |
2017年 | 4篇 |
2016年 | 9篇 |
2015年 | 5篇 |
2014年 | 5篇 |
2013年 | 11篇 |
2012年 | 18篇 |
2011年 | 13篇 |
2010年 | 17篇 |
2009年 | 22篇 |
2008年 | 25篇 |
2007年 | 34篇 |
2006年 | 34篇 |
2005年 | 30篇 |
2004年 | 20篇 |
2003年 | 18篇 |
2002年 | 7篇 |
2001年 | 13篇 |
2000年 | 1篇 |
1999年 | 11篇 |
1998年 | 5篇 |
1997年 | 8篇 |
1996年 | 8篇 |
1995年 | 4篇 |
1994年 | 7篇 |
1993年 | 4篇 |
1992年 | 4篇 |
1991年 | 5篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1986年 | 2篇 |
1984年 | 1篇 |
排序方式: 共有371条查询结果,搜索用时 125 毫秒
71.
利用神经网络法对广西山口红树林保护区2003年1月8日获取的Landsat TM 卫星图像进行分类.Landsat TM5卫星数据的3、4、5假彩色合成图像空间分辨率比较好,影像层次丰富,地物界限清晰.因此,采用3、4、5波段作为输入层.经过目视判读和现场调查,将输出层单元设置为5个,包括是红树林、陆地植被、裸地(其他建筑用地)、水体和虾池.经过流程实际运算和精度对比,设定训练阈值的贡献是0.9,训练率是0.2,训练次数是1000,最大个体允许误差为0.1.分类精度达到86.86%,高于最大似然分类(50.79%)和光谱角分类精度(75.39%),从而最终获取红树林生态系统的景观格局指标.结果显示研究区红树林均匀度(1.7789)和聚集度指数(0.6854)较高;红树林种类的优势度指数是-1.5850,为弱势群体;红树林的斑块破碎化指数是0.0325,破碎化程度较低. 相似文献
72.
73.
复合生态系统非线性累积效应响应因子的阈值模型 总被引:7,自引:0,他引:7
基于流域系统累积环境效应的产生机理,以系统动力学特征和累积环境效应-反应过程特征曲线为依据,分析了复合生态环境承载力及其适应性,提出并建立了非线性累积效应响应的指标阈值模型及因子响应程度的客观、动态量化方法。模型的建立对系统可持续发展的评估决策具有一定的指导作用。 相似文献
74.
李安民 《湖南环境生物职业技术学院学报》2001,(4)
在社会主义市场经济条件下,为什么要大力发展高等职业教育?文章认为,发展高等职业是市场经济发展和科教兴国的客观要求,并通过对高职教育的定位分析,阐明了发展高职教育的重要性.文章从高等教育的特点和“三改一补”的发展途征两方面论述了高职教育的发展方向. 相似文献
75.
A.D. Bhanarkar S.K. Goyal R. Sivacoumar C.V. Chalapati Rao 《Atmospheric environment (Oxford, England : 1994)》2005,39(40):7745-7760
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
76.
John?YangEmail author Jianguo?Sun David?Hammer Robert?Blanchar 《Environmental Chemistry Letters》2004,2(3):159-162
Soil pH, a log-transformed form of hydrogen ion (H+) activity, is often used for various statistics. However whether soil pH meets the requirement of distribution normality for statistical analyses is unknown. We studied the statistical suitability of both soil pH and H+ activity by examining their distribution normalities. Results show that the variability of H+ activity is higher and its distribution is skewer, which is significantly different from the normal and soil pH, regardless of soil conditions and analytical methods. Here we demonstrate that soil pH is more appropriate than the H+ activity for performing statistical analysis in terms of distribution normality. 相似文献
77.
A methodology for simulating climate change impacts on tree growth was introduced into a statistical growth and yield model in relation to variations in site fertility and location implemented with current temperature sum. This was based on a procedure in which the relative enhancement in stem volume growth was calculated from short-term runs of a physiological simulation model for Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies (L.) Karst.) and silver birch (Betula pendula Roth.) stands. These simulations were made for a set of stands with species-specific variations in stand characteristics, location and fertility type first in current climatic conditions and then in different combinations of CO2 and temperature elevations. Based on these simulations, the relative enhancement of volume growth induced by the climate change (relative scenario effect, RSEv) was calculated and modelled in relation to: (i) CO2 and temperature elevation, stand density and the competition status of the tree in its stand, and (ii) variations in site fertility type and current temperature sum of a stand. Finally, these transfer functions for RSEv were applied to adapt the stem volume growth in the statistical growth and yield model to reflect the response to climate change. 相似文献
78.
豪猪消化系统的解剖研究 总被引:3,自引:0,他引:3
为了了解豪猪的消化生理,为豪猪的人工饲养技术研究提供基础依据,以达到高效饲养豪猪的目的,笔者对豪猪的消化器官进行了系统解剖研究.结果表明:豪猪的胃为单室胃.盲肠很发达,这与其能够消化植物纤维有关.豪猪肝脏很发达,其重量为402 g,是其体重的4.59%,肝脏分叶多而明显. 相似文献
79.
菰和菖蒲在污水中的生长特性及其净化效果比较 总被引:9,自引:0,他引:9
通过漂浮栽植菰(Zizania latifolia)和菖蒲(Acoruscalamus),研究了它们在低、中、高3种浓度污水中的生长特性及其对这3种浓度污水的净化效果.结果表明,菰和菖蒲均在中浓度污水中生长最好.菰在中浓度污水中的生物量显著高于低浓度和高浓度中;菖蒲在中浓度污水中的生物量略高于低浓度和高浓度中,但差异不显著.菰对中浓度污水中TN、NH3-N、TP和CODCr的去除率分别为97.4%、95.3%、98.5%和71.4%,对高浓度污水中TN、NH3-N、TP和CODCr的去除率分别为96.4%、97.7%、88.2%和76.1%,净化效果均显著高于低浓度中.菰可作为中、高浓度污水的净化植物.菖蒲净化中浓度污水的效果最好,对TN、NH3-N、TP和CODCr的去除率分别为97.5%、94.1%、98.5%和72.7%;对高浓度污水中的NH3-N和CODCr去除效果也较好,去除率分别为97.8%和86.7%,但对TN和TP的去除率分别为89.5%和70.9%,显著低于对低浓度和中浓度污水中TN和TP的去除率.图1表4参13 相似文献
80.