全文获取类型
收费全文 | 780篇 |
免费 | 9篇 |
国内免费 | 14篇 |
专业分类
安全科学 | 37篇 |
废物处理 | 41篇 |
环保管理 | 214篇 |
综合类 | 80篇 |
基础理论 | 160篇 |
污染及防治 | 188篇 |
评价与监测 | 54篇 |
社会与环境 | 28篇 |
灾害及防治 | 1篇 |
出版年
2022年 | 4篇 |
2021年 | 3篇 |
2020年 | 10篇 |
2019年 | 7篇 |
2018年 | 9篇 |
2017年 | 16篇 |
2016年 | 14篇 |
2015年 | 15篇 |
2014年 | 20篇 |
2013年 | 94篇 |
2012年 | 20篇 |
2011年 | 45篇 |
2010年 | 24篇 |
2009年 | 35篇 |
2008年 | 44篇 |
2007年 | 46篇 |
2006年 | 49篇 |
2005年 | 17篇 |
2004年 | 20篇 |
2003年 | 36篇 |
2002年 | 29篇 |
2001年 | 17篇 |
2000年 | 11篇 |
1999年 | 8篇 |
1998年 | 8篇 |
1997年 | 9篇 |
1996年 | 14篇 |
1995年 | 7篇 |
1994年 | 9篇 |
1993年 | 6篇 |
1992年 | 6篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 8篇 |
1986年 | 8篇 |
1985年 | 9篇 |
1984年 | 15篇 |
1983年 | 14篇 |
1982年 | 13篇 |
1981年 | 18篇 |
1980年 | 5篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1974年 | 7篇 |
1973年 | 3篇 |
1970年 | 3篇 |
排序方式: 共有803条查询结果,搜索用时 719 毫秒
391.
Agroecosystems,nitrogen-use efficiency,and nitrogen management 总被引:11,自引:0,他引:11
The global challenge of meeting increased food demand and protecting environmental quality will be won or lost in cropping systems that produce maize, rice, and wheat. Achieving synchrony between N supply and crop demand without excess or deficiency is the key to optimizing trade-offs amongst yield, profit, and environmental protection in both large-scale systems in developed countries and small-scale systems in developing countries. Setting the research agenda and developing effective policies to meet this challenge requires quantitative understanding of current levels of N-use efficiency and losses in these systems, the biophysical controls on these factors, and the economic returns from adoption of improved management practices. Although advances in basic biology, ecology, and biogeochemistry can provide answers, the magnitude of the scientific challenge should not be underestimated because it becomes increasingly difficult to control the fate of N in cropping systems that must sustain yield increases on the world's limited supply of productive farm land. 相似文献
392.
Herbel MJ Johnson TM Tanji KK Gao S Bullen TD 《Journal of environmental quality》2002,31(4):1146-1156
Selenium stable isotope ratios are known to shift in predictable ways during various microbial, chemical, and biological processes, and can be used to better understand Se cycling in contaminated environments. In this study we used Se stable isotopes to discern the mechanisms controlling the transformation of oxidized, aqueous forms of Se to reduced, insoluble forms in sediments of Se-affected environments. We measured 80Se/76Se in surface waters, shallow ground waters, evaporites, digested plants and sediments, and sequential extracts from several sites where agricultural drainage water is processed in the San Joaquin Valley of California. Selenium isotope analyses of samples obtained from the Tulare Lake Drainage District flow-through wetland reveal small isotopic contrasts (mean difference 0.7%) between surface water and reduced Se species in the underlying sediments. Selenium in aquatic macrophytes was very similar isotopically to the NaOH and Na2SO3 sediment extracts designed to recover soluble organic Se and Se(0), respectively. For the integrated on-farm drainage management sites, evaporite salts were slightly (approximately 0.6%) enriched in the heavier isotope relative to the inferred parent waters, whereas surface soils were slightly (approximately 1.4%) depleted. Bacterial or chemical reduction of Se(VI) or Se(IV) may be occurring at these sites, but the small isotopic contrasts suggest that other, less isotopically fractionating mechanisms are responsible for accumulation of reduced forms in the sediments. These findings provide evidence that Se assimilation by plants and algae followed by deposition and mineralization is the dominant transformation pathway responsible for accumulation of reduced forms of Se in the wetland sediments. 相似文献
393.
An inventory was conducted to assess the number, type, spatial distribution, and costs of microbiological monitoring programs
in southern California marine waters from Point Conception to the US/Mexico International Border. The location of each sampling
site was determined using global positioning system (GPS), and estimates of geographic coverage were determined using geographic
information system (GIS) techniques. Twenty-one programs conducted 87,007 tests annually at 576 sites in the study area. The
largest number of sites was sampled in Orange County, whereas the largest number of analyses was performed in Los Angeles
County because monitoring programs in this area focused on daily monitoring. Fifteen of the 21 programs were managed by National
Pollutant Discharge Elimination System (NPDES) permitted sewage effluent dischargers who sampled both offshore and shoreline
waters and typically tested for three indicator bacteria (total coliform, fecal coliform, and enterococcus). Their combined
efforts comprised 82% of all of the microbiological indicator analyses conducted on an annual basis. Five of the remaining
monitoring organizations were public health agencies, which typically focus their efforts on testing only total coliforms.
Laboratory methodology also varied considerably, with NPDES permittees predominantly utilizing membrane filtration while public
health agencies generally used multiple tube fermentation or premanufactured test kits. Nearly three quarters of all the effort
expended in southern California occurred along the shoreline as opposed to offshore locations. Two thirds of this shoreline
effort was focused on high-use sandy beaches and in proximity to perennial freshwater outlets (storm drains and creeks). Most
sampling occurred at a set of fixed sites that were revisited frequently, but only represented about 7% of the total shoreline.
We estimated that roughly $3 million is spent annually on monitoring bathing water quality in southern California, exceeding
that spent in any other part of the country. 相似文献
394.
Habitat Assessment of Non-Wadeable Rivers in Michigan 总被引:1,自引:0,他引:1
Habitat evaluation of wadeable streams based on accepted protocols provides a rapid and widely used adjunct to biological
assessment. However, little effort has been devoted to habitat evaluation in non-wadeable rivers, where it is likely that
protocols will differ and field logistics will be more challenging. We developed and tested a non-wadeable habitat index (NWHI)
for rivers of Michigan, where non-wadeable rivers were defined as those of order ≥5, drainage area ≥1600 km2, mainstem lengths ≥100 km, and mean annual discharge ≥15 m3/s. This identified 22 candidate rivers that ranged in length from 103 to 825 km and in drainage area from 1620 to 16,860
km2. We measured 171 individual habitat variables over 2-km reaches at 35 locations on 14 rivers during 2000–2002, where mean
wetted width was found to range from 32 to 185 m and mean thalweg depth from 0.8 to 8.3 m. We used correlation and principal
components analysis to reduce the number of variables, and examined the spatial pattern of retained variables to exclude any
that appeared to reflect spatial location rather than reach condition, resulting in 12 variables to be considered in the habitat
index. The proposed NWHI included seven variables: riparian width, large woody debris, aquatic vegetation, bottom deposition,
bank stability, thalweg substrate, and off-channel habitat. These variables were included because of their statistical association
with independently derived measures of human disturbance in the riparian zone and the catchment, and because they are considered
important in other habitat protocols or to the ecology of large rivers. Five variables were excluded because they were primarily
related to river size rather than anthropogenic disturbance. This index correlated strongly with indices of disturbance based
on the riparian (adjusted R2 = 0.62) and the catchment (adjusted R2 = 0.50), and distinguished the 35 river reaches into the categories of poor (2), fair (19), good (13), and excellent (1).
Habitat variables retained in the NWHI differ from several used in wadeable streams, and place greater emphasis on known characteristic
features of larger rivers. 相似文献
395.
An examination of the curvilinear relationship between leader–member exchange and intent to turnover
Based on the theoretical identification of three different motivational forces for voluntary turnover—affective, calculative, and alternative—we hypothesize that the relationship between supervisor–subordinate relationship quality (i.e., leader–member exchange) and turnover intentions is best represented as curvilinear as opposed to linear. We test this hypothesis in two organizational samples consisting of 402 employees from a water management district and 183 employees from a distribution services organization. We found support for the hypothesis in both samples. We offer directions for future research. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
396.
397.
398.
How integrated is river basin management? 总被引:2,自引:0,他引:2
Land and water management is increasingly focused upon the drainage basin. Thirty-six terms recently used for schemes of “integrated
basin management” include reference to the subject or area and to the aims of integrated river basin management, often without
allusion to the multiobjective nature. Diversity in usage of terms has occurred because of the involvement of different disciplines,
of the increasing coherence of the drainage basin approach, and the problems posed in particular parts of the world. The components
included in 21 different approaches are analyzed, and, in addition to showing that components related broadly to water supply,
river channel, land, and leisure aspects, it is concluded that there are essentially five interrelated facets of integrated
basin management that involved water, channel, land, ecology, and human activity. Two aspects not fully included in many previous
schemes concern river channel changes and the dynamic integrity of the fluvial system. To clarify the terminology used, it
is suggested that the termcomprehensive river basin management should be used where a wide range of components is involved, whereasintegrated basin management can signify the interactions of components and the dominance of certain components in the particular area.Holistic river basin management is advocated as a term representing an approach that is both fully comprehensive and integrated but also embraces the energetics
of the river system and consideration of changes of river channels and of human impacts throughout the river system. The paradigm
of working with the river can be extended to one of working with the river in the holistic basin context. 相似文献
399.
Kenneth M. Strzepek David H. Marks 《Journal of the American Water Resources Association》1981,17(1):10-15
ABSTRACT: Simulation models constructed to estimate the physical and economic performance of alternative river basin development configurations have been widely used since the start of the Harvard Water Program in the early 1960's. These models have proved useful in choosing from among several potential river basin configurations, since they can rapidly evaluate each configuration's expected performance. However, when dealing with large scale river basin development projects, in which over 50 or 100 alternative reservoirs, irrigation areas, and other components must be considered, it is sometimes quite difficult to effectively use a simulation model to rapidly identify those combinations of projects which best satisfy the development objectives. The purpose of this paper is to describe how a simulation model was used in the analysis of a complex river basin development project in Eastern Europe, and how the problems of scale were confronted and solved. The author's experience on this projet is used to derive a set of general guidelines which may be helpful in other simulation studies. 相似文献
400.
John Cairns Kenneth W. Thompson J. David Landers Michael J. Mckee Albert C. Hendricks 《Journal of the American Water Resources Association》1980,16(3):421-427
ABSTRACT: Electronic modifications necessary to adapt an existing fish opercular movement monitor for use in salt water are described. Ten species of fresh and salt water fishes were tested for suitability as test organisms for future studies of pollutional effects. It was concluded that with proper tank design most species would provide useful data and that the system could be easily adapted for use in marine situations. 相似文献