全文获取类型
收费全文 | 1827篇 |
免费 | 149篇 |
国内免费 | 134篇 |
专业分类
安全科学 | 461篇 |
废物处理 | 38篇 |
环保管理 | 347篇 |
综合类 | 693篇 |
基础理论 | 168篇 |
环境理论 | 3篇 |
污染及防治 | 122篇 |
评价与监测 | 73篇 |
社会与环境 | 89篇 |
灾害及防治 | 116篇 |
出版年
2024年 | 3篇 |
2023年 | 19篇 |
2022年 | 16篇 |
2021年 | 32篇 |
2020年 | 44篇 |
2019年 | 49篇 |
2018年 | 40篇 |
2017年 | 73篇 |
2016年 | 82篇 |
2015年 | 73篇 |
2014年 | 94篇 |
2013年 | 142篇 |
2012年 | 112篇 |
2011年 | 121篇 |
2010年 | 103篇 |
2009年 | 93篇 |
2008年 | 75篇 |
2007年 | 120篇 |
2006年 | 128篇 |
2005年 | 104篇 |
2004年 | 83篇 |
2003年 | 97篇 |
2002年 | 67篇 |
2001年 | 59篇 |
2000年 | 59篇 |
1999年 | 46篇 |
1998年 | 28篇 |
1997年 | 18篇 |
1996年 | 13篇 |
1995年 | 14篇 |
1994年 | 11篇 |
1993年 | 8篇 |
1992年 | 6篇 |
1991年 | 6篇 |
1990年 | 8篇 |
1989年 | 5篇 |
1988年 | 8篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 7篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1980年 | 4篇 |
1978年 | 5篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1974年 | 2篇 |
1972年 | 3篇 |
1971年 | 4篇 |
排序方式: 共有2110条查询结果,搜索用时 15 毫秒
991.
In this article, a 3P sampling (Probability Proportional to Prediction) approach is presented for surveying sparse species connected to certain types of substrates. The method uses the surveyors judgement of the probability of finding the species on a substrate as the base for selection of substrates for species inventories. The method is presented together with estimators, variances and variance estimators. The method is first presented for sampling based on all substrates in a study area and then as a subsampling technique in a two-stage design in which plots or strips are selected in a first stage. The presented approach was evaluated as a subsampling technique in a strip survey of calicioid lichen species associated with coarse broadleaf trees. In comparison with a simple random subsampling without replacement, 3P subsampling was in one study area found to be an improvement with 30–55% in terms of standard errors. The improvement was more modest in the other study area, only between 10–16%. The strip survey with 3P subsampling was more cost-efficient than a strip survey without subsampling except in one case. Based on the results in the test, 3P sampling seems to have a potential for sampling sparse species. 相似文献
992.
Danz NP Regal RR Niemi GJ Brady VJ Hollenhorst T Johnson LB Host GE Hanowski JM Johnston CA Brown T Kingston J Kelly JR 《Environmental monitoring and assessment》2005,102(1-3):41-65
Understanding the relationship between human disturbance and ecological response is essential to the process of indicator development. For large-scale observational studies, sites should be selected across gradients of anthropogenic stress, but such gradients are often unknown for a population of sites prior to site selection. Stress data available from public sources can be used in a geographic information system (GIS) to partially characterize environmental conditions for large geographic areas without visiting the sites. We divided the U.S. Great Lakes coastal region into 762 units consisting of a shoreline reach and drainage-shed and then summarized over 200 environmental variables in seven categories for the units using a GIS. Redundancy within the categories of environmental variables was reduced using principal components analysis. Environmental strata were generated from cluster analysis using principal component scores as input. To protect against site selection bias, sites were selected in random order from clusters. The site selection process allowed us to exclude sites that were inaccessible and was shown to successfully distribute sites across the range of environmental variation in our GIS data. This design has broad applicability when the goal is to develop ecological indicators using observational data from large-scale surveys. 相似文献
993.
Schweiger EW Bolgrien DW Angradi TR Kelly JR 《Environmental monitoring and assessment》2005,103(1-3):21-40
Most Great River ecosystems (GREs) are extensively modified and are not receiving adequate protection to prevent further habitat
degradation and loss of biotic integrity. In the United States, ecological monitoring and assessment of GREs has lagged behind
streams and estuaries, and the management of GREs is hampered by the lack of unbiased data at appropriate spatial scales.
Properties of GREs that make them challenging to monitor and assess include difficult sample logistics and high habitat diversity.
The U.S. Environmental Protection Agency’s Environmental Monitoring and Assessment Program (EMAP) has developed a comprehensive,
regional-scale, survey-based monitoring approach to assessment of streams and estuaries, but has not yet conducted research
on applying these tools to GRE monitoring. In this paper we present an overview of an EMAP research project on the Upper Missouri
River (UMR). We summarize the assessment objectives for the study, the design for selecting sample locations, the indicators
measured at these sites and the tools used to analyze data. We present an example of the type of statements that can be made
with EMAP monitoring data. With modification, the set of methodologies developed by EMAP may be well suited for assessment
of GREs in general. 相似文献
994.
Kalikhman I 《Environmental monitoring and assessment》2005,110(1-3):203-215
A mathematical model was used to compare the effects of a regular (one-pass) or interleaved (two-pass) acoustic survey on
the adequacy of reconstructing patchy distribution fields. The model simulates fish or plankton patches of different shapes
and spatial orientations, and a set of parallel or zigzag transects forming a regular or interleaved acoustic survey. The
efficiency of a survey is determined by the adequacy of a reconstructed field to that originally generated, which is evaluated
by calculating their correlations. Regarding the immovable fields, the efficiency of a regular or interleaved acoustic survey
was tested with the following two alternative assumptions: (1) the entire survey was completed; (2) the survey was interrupted
for some reason at the moment when one transect remained non-accomplished. In the former case, the efficiencies of both acoustic
surveys were nearly the same; in the latter case, the efficiency of an interleaved survey was superior to that of a regular
one. With respect to movable fields, the efficiency of the completed interleaved surveys was even higher than that of the
regular ones. Thus, the results obtained allow us to conclude that an interleaved survey is expedient in cases where there
is no preference regarding the position of a vessel for further work. 相似文献
995.
We studied the multiscale (sites, river reaches and rivers) and short-term temporal (monthly) variability in a freshwater fish assemblage. We found that small-scale spatial variation and short-term temporal variability significantly influenced fish community structure in the Macquarie and Namoi Rivers. However, larger scale spatial differences between rivers were the largest source of variation in the data. The interaction between temporal change and spatial variation in fish community structure, whilst statistically significant, was smaller than the variation between rivers. This suggests that although the fish communities within each river changed between sampling occasions, the underlying differences between rivers were maintained. In contrast, the strongest interaction between temporal and spatial effects occurred at the smallest spatial scale, at the level of individual sites. This means whilst the composition of the fish assemblage at a given site may fluctuate, the magnitude of these changes is unlikely to affect larger scale differences between reaches within rivers or between rivers. These results suggest that sampling at any time within a single season will be sufficient to show spatial differences that occur over large spatial scales, such as comparisons between rivers or between biogeographical regions. 相似文献
996.
SPSS10.0是目前功能齐全、便于应用的优秀统计软件。文章介绍了该软件在环境监测数据分析和监测网设计中的应用。文中简述了该软件的功能及优点,并通过实例,展示其在环境监测数据分析和监测网设计中的应用,这对于优化监测数据分析结果和监测网的设计均有较好的借鉴作用。 相似文献
997.
998.
Linking Ecological Sustainability and World Food Needs 总被引:1,自引:0,他引:1
Alison G. Power 《Environment, Development and Sustainability》1999,1(3-4):185-196
Ecological approaches to agriculture can provide useful guidelines for addressing world food needs, while avoiding adverse environmental and social impacts. Experiments in both natural and agricultural ecosystems suggest that systems with high plant diversity may be more productive, more stable and more resilient than species-poor systems. In addition, systems with high plant diversity support higher levels of biodiversity in other functional groups, which may enhance the productivity of the plant component. Given these benefits of diverse systems, various approaches for converting conventional high input agricultural systems to more sustainable systems are addressed. Andow and Hidaka's (1989) concept of production syndromes is considered in the context of conversion to sustainable agriculture. 相似文献
999.
Sustainability is a concept that has been widely embraced both politically and intellectually but has not been addressed in terms of practical application. In most resource sectors, the features of a sustainable future remain unclear and there are few examples that give practical expression to sustainability. This is especially true in the case of water resources management which has been conspicuous in its absence from the majority of the literature. This paper attempts to address this deficiency on two counts. First, it provides a discussion of sustainability and the application of the concept to the management of water resources. Second, the paper illustrates how the concept can be utilized for the management and planning of urban stormwater. The paper concludes by offering research opportunities to investigate the feasibility of adopting natural channel design and artificial wetlands for sustainable stormwater management. 相似文献
1000.