全文获取类型
收费全文 | 3242篇 |
免费 | 336篇 |
国内免费 | 820篇 |
专业分类
安全科学 | 702篇 |
废物处理 | 226篇 |
环保管理 | 411篇 |
综合类 | 2133篇 |
基础理论 | 255篇 |
环境理论 | 1篇 |
污染及防治 | 438篇 |
评价与监测 | 77篇 |
社会与环境 | 95篇 |
灾害及防治 | 60篇 |
出版年
2024年 | 10篇 |
2023年 | 43篇 |
2022年 | 80篇 |
2021年 | 122篇 |
2020年 | 109篇 |
2019年 | 111篇 |
2018年 | 99篇 |
2017年 | 118篇 |
2016年 | 140篇 |
2015年 | 150篇 |
2014年 | 199篇 |
2013年 | 223篇 |
2012年 | 295篇 |
2011年 | 298篇 |
2010年 | 236篇 |
2009年 | 220篇 |
2008年 | 182篇 |
2007年 | 290篇 |
2006年 | 264篇 |
2005年 | 182篇 |
2004年 | 159篇 |
2003年 | 136篇 |
2002年 | 124篇 |
2001年 | 109篇 |
2000年 | 103篇 |
1999年 | 86篇 |
1998年 | 70篇 |
1997年 | 55篇 |
1996年 | 39篇 |
1995年 | 35篇 |
1994年 | 21篇 |
1993年 | 16篇 |
1992年 | 26篇 |
1991年 | 9篇 |
1990年 | 8篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1985年 | 4篇 |
1982年 | 3篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 5篇 |
1971年 | 2篇 |
排序方式: 共有4398条查询结果,搜索用时 47 毫秒
711.
712.
713.
The model of random population dynamics in a sampling site returns geometric distribution of longevities of continuous presence (=persistence) and Poisson distribution of the presence–absence transitions. This discrete-time stochastic process describes the presence–absence pattern observed in the beetles surveyed 6 years on Mount Carmel, Israel. Homogeneous pools of species mostly on the Families rank, exhibit the predicted by the model patterns. Conformity to an ergodic hypothesis is the criterion of ecological homogeneity. This criterion assumes the equivalence of short-term behavior of entire pool and long-term behavior of any species from this pool. The pool of all 801 species of Order Coleoptera does not match the model. Thus a taxon of an arbitrary rank may not be considered a priory as a unit of ecological study. Determined from field data parameters of the model are biased and magnitude of the bias depends on longevity of the survey. Parameter of distribution depends also on species tolerance, which is the level adaptation of given species to given environment in given time interval. Random process of species turnover may be considered as a game of species to gain their presence against deteriorative fluctuations of environmental conditions. 相似文献
714.
在不同温度下,研究了流化填料分格式SBR工艺(简称MESBR工艺)与传统的SBR工艺的COD去除率,有机物降解速率,脱氮效果和污泥沉降性能。结果表明:MESBR系统温度下降到5℃时,COD的去除率基本稳定在90%以上,比传统SBR系统高出15%左右;MESBR系统与传统SBR系统的温度系数θ分别为1.021和1.045。温度由20℃下降至5℃时,传统SBR系统的TN和NH3-N去除率分别降低26.5%和20%,而MESBR系统分别降低18.6%和11%。传统SBR系统SVI值随温度变化较大,当温度下降到5℃时SVI值达到234.8 mL/g,而MESBR系统的SVI值没有明显的变化,基本维持在120~130 mL/g。 相似文献
715.
716.
F. Le Ber C. Lavigne K. Adamczyk F. Angevin N. Colbach J.-F. Mari H. Monod 《Ecological modelling》2009
Neutral landscape models are not frequently used in the agronomical domain, whereas they would be very useful for studying given agro-ecological or physical processes. Contrary to ecological neutral landscape models, agricultural models have to represent and manage geometrical patches and thus should rely on tessellation methods. We present a three steps approach that aimed at simulating such landscapes. Firstly, we characterized the geometry of three real field patterns; secondly, we generated simulated field patterns with two tessellation methods attempting to control the value of some of the observed characteristics and, thirdly, we evaluated the simulated field patterns. For this evaluation, we considered that good simulated field patterns should capture characteristics of real landscapes that are important for the targeted agro-ecological process. Real landscapes and landscapes simulated using either a Voronoi or a rectangular tessellation were thus compared when used as input data within a gene flow model. The results showed that neither tessellation method captured field shapes correctly, thus leading to over or (small) under estimation of gene flow. The Voronoi tessellation, though, performed better than the rectangular tessellation. Possible research directions are proposed to improve the simulated patterns, including the use of post-processing, the control of cell orientation or the implementation of other tessellation techniques. 相似文献
717.
Gorsevski PV Donevska KR Mitrovski CD Frizado JP 《Waste management (New York, N.Y.)》2012,32(2):287-296
This paper presents a GIS-based multi-criteria decision analysis approach for evaluating the suitability for landfill site selection in the Polog Region, Macedonia. The multi-criteria decision framework considers environmental and economic factors which are standardized by fuzzy membership functions and combined by integration of analytical hierarchy process (AHP) and ordered weighted average (OWA) techniques. The AHP is used for the elicitation of attribute weights while the OWA operator function is used to generate a wide range of decision alternatives for addressing uncertainty associated with interaction between multiple criteria. The usefulness of the approach is illustrated by different OWA scenarios that report landfill suitability on a scale between 0 and 1. The OWA scenarios are intended to quantify the level of risk taking (i.e., optimistic, pessimistic, and neutral) and to facilitate a better understanding of patterns that emerge from decision alternatives involved in the decision making process. 相似文献
718.
719.
720.
张水龙 《中国环境管理干部学院学报》2001,(1)
运用景观分类与评价、景观结构与功能分析、景观生态安全格局判断等景观生态学原理和方法对秦皇岛市生态环境进行了研究,结果表明:秦皇岛景观类型丰富独特,景观空间格局对主要生态过程有重要影响,对1986~1996年间景观变化定量分析的结查显示由于人工干扰指数的提高,使自然景现类型数量减少,并出现破碎化,从而降低了景观多样性和景观优势度,易导致系统的生产力、稳定性、自维持性趋向于降低。 相似文献