全文获取类型
收费全文 | 296篇 |
免费 | 12篇 |
国内免费 | 54篇 |
专业分类
安全科学 | 8篇 |
废物处理 | 13篇 |
环保管理 | 42篇 |
综合类 | 89篇 |
基础理论 | 115篇 |
污染及防治 | 35篇 |
评价与监测 | 11篇 |
社会与环境 | 48篇 |
灾害及防治 | 1篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 3篇 |
2021年 | 6篇 |
2020年 | 5篇 |
2019年 | 4篇 |
2018年 | 5篇 |
2017年 | 6篇 |
2016年 | 12篇 |
2015年 | 12篇 |
2014年 | 14篇 |
2013年 | 42篇 |
2012年 | 19篇 |
2011年 | 25篇 |
2010年 | 10篇 |
2009年 | 22篇 |
2008年 | 18篇 |
2007年 | 14篇 |
2006年 | 18篇 |
2005年 | 14篇 |
2004年 | 14篇 |
2003年 | 14篇 |
2002年 | 12篇 |
2001年 | 14篇 |
2000年 | 12篇 |
1999年 | 3篇 |
1998年 | 4篇 |
1997年 | 4篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1993年 | 1篇 |
1992年 | 3篇 |
1991年 | 7篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 4篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1980年 | 1篇 |
1977年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有362条查询结果,搜索用时 15 毫秒
71.
The decomposition of leaf litter is controlled by several factors. One factor that may play an important role is the content
of condensed tannins (proanthocyanidins). Here we designed a combined method to isolate proanthocyanidins from leaf extracts,
to convert them to anthocyanidins, and to quantify individual anthocyanidins exactly with a new, simple, but sensitive high-performance
liquid chromatography method. We used this method to show composition of proanthocyanidins and to monitor degradation of proanthocyanidins
and individual constituents in leaf litter in an aquatic environment over time. Despite the rapid decrease in the initial
concentrations, a fraction of the proanthocyanidins remained detectable for several weeks. 相似文献
72.
以南亚热带常见的先锋乡土树种藜蒴(Castanopsis fissa)为研究对象.通过室内萌发试验,分析了种子质量、凋落物覆盖和掩埋对种子萌发及幼苗早期生长的影响.结果表明,藜蒴种子能否成功萌发并形成幼苗的决定性因素是种子的掩埋深度.掩埋显著抑制了藜蒴种子萌发及形成幼苗的过程,随掩埋深度的增大,这种抑制作用越明显.掩埋对幼苗的存活和生物量没有显著影响,但可提高幼苗根部生物量的分配.深度掩埋时,质量大的种子在幼苗形成过程中具明显优势;而置于土壤表层或浅埋的种子成苗率与种子质量的相关性较低.大质量种子形成的幼苗更易于存活,在生物量的积累方面也表现H{一定的优势.凋落物覆盖未抑制幼苗的出土,且对幼苗的存活和生长具有明显的促进作用,表现在可提高幼苗的相对生长率以及生物量的积累.另外,凋落物的覆盖明显提高了幼苗生物量在其冠部的分配.因而,若利用直接播撒藜蒴种子的方式改造南亚热带退化草坡.理论上应尽可能选用大质量的种子直接播种于地表,并覆以原有的地表凋落物,以促进藜蒴幼苗成功建立. 相似文献
73.
E. N. Ikkonen V. K. Kurets S. I. Grabovik S. N. Drozdov 《Russian Journal of Ecology》2001,32(6):382-385
Carbon dioxide exchange in the intact and reclaimed sites of a woodless mesooligotrophic dwarf shrub–cotton grass–sphagnum bog was studied in field experiments. The average values of gross respiration in the ecosystem over the warm period (including respiration of plant cover, CO2emission from peat, and CO2flow from the litter) were 3.17 and 6.11 g CO2/m2per day in the natural and drained sites, respectively. 相似文献
74.
We demonstrate an approach for evaluating the level of protection attained using a variety of forms and levels of past, current,
and proposed Air Quality Standards (AQSs). The U.S. Clean Air Act requires the establishment of ambient air quality standards
to protect health and public welfare. However, determination of attainment of these standards is based on ambient pollutant
concentrations rather than prevention of adverse effects. To determine if a given AQS protected against adverse effects on
vegetation, hourly ozone concentrations were adjusted to create exposure levels that “just attain” a given standard. These
exposures were used in combination with a physiologically-based tree growth model to account for the interactions of climate
and ozone. In the evaluation, we used ozone concentrations from two 6-year time periods from the San Bernardino Mountains
in California. There were clear differences in the level of vegetation protection achieved with the various AQSs. Based on
modeled plant growth, the most effective standards were the California 8-hr average maximum of 70 ppb and a seasonal, cumulative,
concentration-weighted index (SUM06), which if attained, resulted in annual growth reductions of 1% or less. Least effective
was the 1-hr maximum of 120 ppb which resulted in a 7% annual reduction. We conclude that combining climate, exposure scenarios,
and a process-based plant growth simulator was a useful approach for evaluating effectiveness of current or proposed air quality
standards, or evaluating the form and/or level of a standard based on preventing adverse growth effects. 相似文献
75.
Gradients of genetic distances (GGDs) between 26 adjacent cenopopulations of Scotch pine (Pinus sylvestris L.) along the transects through the distinct landscape-ecotopic isolation borders were analyzed graphically. The results
made it possible to reveal and quantitatively estimate gradients and borders of gene-pool structural patterns in populations
of this species in the central part of Northern Eurasia. In lowland areas, the most distinct borders were found between pine
populations growing on dry lands and bogs (Pineta sphagnosa) in the forest zone of the Transural region, as well as between the Arakaragaiskii and Amankaragaiskii island pine forests
in the steppe zone (Northern Turgai). In highland areas (the Urals and the Carpathians), the greatest GGDs were observed between
low-mountain (about 600 m above sea level) and middle-mountain (850–900 m) populations. Analysis of GGDs is a promising gene-geographic
method for determining population borders and studying the chorogenetic structure of species. 相似文献
76.
Boxman AW Peters RC Roelofs JG 《Environmental pollution (Barking, Essex : 1987)》2008,156(3):1252-1259
In a Scots pine forest the throughfall deposition and the chemical composition of the soil solution was monitored since 1984. (Inter)national legislation measures led to a reduction of the deposition of nitrogen and sulphur. The deposition of sulphur has decreased by approximately 65%. The total mineral-nitrogen deposition has decreased by ca. 25%, which is mainly due to a reduction in ammonium-N deposition (−40%), since nitrate-N deposition has increased (+50%). The nitrogen concentration in the upper mineral soil solution at 10 cm depth has decreased, leading to an improved nutritional balance, which may result in improved tree vitality. In the drainage water at 90 cm depth the fluxes of NO3− and SO42− have decreased, resulting in a reduced leeching of accompanying base cations, thus preserving nutrients in the ecosystem. It may take still several years, however, before this will meet the prerequisite of a sustainable ecosystem. 相似文献
77.
The competition of hydrogen and manganese ions for adsorption sites in Sitka spruce litter was investigated in a factorial design, simulated acid rain experiment, which involved leaching of litter with simulated throughfall solutions at three pH levels (5.3, 4.3 and 3.3) and three manganese concentrations (0 to 0.2 mg1-1). the throughfall solution at the lowest pH was the most efficient in removing exchangeable manganese from litter. the manganese concentration in the leachates was approximately proportional to the hydrogen ion concentration in the simulated throughfall solution. Under field conditions, throughfall manganese concentration also naturally tends to increase as a consequence of enhanced foliar leaching of manganese in response to increasing precipitation acidity. the manganese concentration in the simulated throughfall also affected manganese concentration in the leachates, however, and contributed to a buildup of exchangeable manganese in litter, thus counteracting to some extent possible adverse effects of excess leaching due to increased throughfall acidity. 相似文献
78.
Paul Schroeder 《Environmental management》1991,15(4):475-481
A possible response to increasing atmospheric CO2 concentration is to attempt to increase the amount of carbon stored in terrestrial vegetation. One approach to increasing
the size of the terrestrial carbon sink is to increase the growth of forests by utilizing intensive forest management practices.
This article uses data from the literature and from forest growth and yield models to analyze the impact of three management
practices on carbon storage: thinning, fertilization, and control of competing vegetation. Using Douglas-fir (Pseudotsuga menziesii) and loblolly pine (Pinus taeda) as example species, results from experiments with computer simulation models suggest that, for these two species, thinning
generally does not increase carbon storage and may actually cause a decrease. The exception is thinning of very dense young
stands. Fertilization generally increases carbon storage, although the response can be quite variable. The largest gains in
carbon storage are likely to come from fertilizing lower-quality sites and from fertilizing thinned or less dense stands.
Forests usually show increased growth in response to fertilization over a wide range of ages. Simulation of the growth of
loblolly pine indicates that controlling competing vegetation at an early age helps to maximize stand growth and carbon storage.
The research described in this article has been funded by the US Environmental Protection Agency. This document has been prepared
at the EPA Environmental Research Laboratory in Corvallis, Oregon, through contract number 68-C8-0006 to NSI Technology Inc.
It has been subjected to the agency’s peer and administrative review and approved for publication. Mention of trade names
or commercial products does not constitute endorsement or recommendation for use. 相似文献
79.
黄土高原人工油松林枯枝落叶截留动态研究 总被引:16,自引:1,他引:16
用定位观测的方法研究了人工油松林枯枝落叶的截流量及其截留的动态过程。结果表明,黄土高原人工油松林枯枝落叶的截流量年均为49.3mm,截留率为12.5%。枯枝落叶截留的动态过程受大气降水和环境因子的影响较大,也与其自身湿润程度有关。在次降水过程中,其截留的过程是当降水开始时,截留量增加迅速;降水持续到一定时间后,截流量的增量变小,达到最大值后,截流量在此处上下增减。枯枝落叶截留的动态过程可用直线和正弦函数的组合描述,且该函数能揭示枯枝落叶截留的生物学特性和环境因素对其过程的影响。该模型在计算森林水文及其水土保持效应评价中有广泛的应用前景。 相似文献
80.
Litter at beaches can come from more than one source and determining the proportions to assign pollution to different sources
is very complex. There is no widely accepted methodology at present that links litter items to their source. The aim of this
study was to create a method of assigning a source to litter found on beaches of the Bristol Channel but which could equally
be used on any beach. Various methods that attempt to establish the source of beach litter were evaluated; their strengths,
weaknesses, applicability and reliability for use on Bristol Channel, UK beaches were considered. Elements of existing methods
coupled with new ideas were utilized in the production of a ‘refined’ methodology: consequently a new method of assigning
a source to beach litter was developed. The developed ‘Matrix Scoring Technique’ was applied to data collected at Minehead
beach on the Bristol Channel, UK. Several numerical and nomenclature variations were used to produce a system that reflected
the various sources and eliminated as much bias as possible. This cross-tabulated matrix scoring system can produce an insight
into the contribution of different source groups to litter found on beaches. This novel approach requires further testing
with emphasis on a control data set. 相似文献