全文获取类型
收费全文 | 3253篇 |
免费 | 14篇 |
国内免费 | 179篇 |
专业分类
安全科学 | 83篇 |
废物处理 | 159篇 |
环保管理 | 313篇 |
综合类 | 598篇 |
基础理论 | 1148篇 |
污染及防治 | 733篇 |
评价与监测 | 200篇 |
社会与环境 | 193篇 |
灾害及防治 | 19篇 |
出版年
2023年 | 7篇 |
2022年 | 25篇 |
2021年 | 22篇 |
2020年 | 15篇 |
2019年 | 11篇 |
2018年 | 130篇 |
2017年 | 140篇 |
2016年 | 197篇 |
2015年 | 75篇 |
2014年 | 35篇 |
2013年 | 51篇 |
2012年 | 453篇 |
2011年 | 249篇 |
2010年 | 55篇 |
2009年 | 50篇 |
2008年 | 76篇 |
2007年 | 96篇 |
2006年 | 91篇 |
2005年 | 408篇 |
2004年 | 545篇 |
2003年 | 422篇 |
2002年 | 49篇 |
2001年 | 57篇 |
2000年 | 29篇 |
1999年 | 41篇 |
1998年 | 12篇 |
1997年 | 19篇 |
1996年 | 5篇 |
1995年 | 21篇 |
1994年 | 7篇 |
1993年 | 6篇 |
1992年 | 6篇 |
1991年 | 11篇 |
1990年 | 5篇 |
1989年 | 7篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1981年 | 1篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1966年 | 2篇 |
1961年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有3446条查询结果,搜索用时 600 毫秒
981.
Quantifying the Effects of Conservation Practices on Soil,Water, and Nutrients in the Loess Mesa Ravine Region of the Loess Plateau,China 总被引:1,自引:0,他引:1
A large number of soil and water conservation programs have been implemented on the Loess Plateau of China since the 1950s.
To comprehensively assess the merits and demerits of the conservation practices is of great importance in further supervising
the conservation strategy for the Loess Plateau. This study calculates the impact factors of conservation practices on soil,
water, and nutrients during the period 1954–2004 in the Nanxiaohegou Catchment, a representative catchment in the Loess Mesa
Ravine Region of the Loess Plateau, China. Brief conclusions could be drawn as follows: (1) Soil erosion and nutrient loss
had been greatly mitigated through various conservation practices. About half of the total transported water and 94.8 % of
the total transported soil and nutrients, had been locally retained in the selected catchment. The soil retained from small
watersheds do not only form large-scale fertile farmland but also safeguard the Yellow River against overflow. (2) Check dam
was the most appropriate conservation practice on the Loess Plateau. In the selected catchment, more than 90 % of the retained
soil and water were accomplished by the dam farmland, although the dam farmland occupied only 2.3 % of the total area of all
conservation measures. Retention abilities of the characteristic conservation practices were in the following order: dam farmland > terrace
farmland > forest land and grassland. (3) The conservation practices were more powerful in retaining sediment than in reducing
runoff from the Loess Plateau, and the negative effects of the conservation practices on reducing water to the Yellow River
were relatively slight. 相似文献
982.
Management of forests, rangelands, and wetlands on public lands, including the restoration of degraded lands, has the potential
to increase carbon sequestration or reduce greenhouse gas (GHG) emissions beyond what is occurring today. In this paper we
discuss several policy options for increasing GHG mitigation on public lands. These range from an extension of current policy
by generating supplemental mitigation on public lands in an effort to meet national emissions reduction goals, to full participation
in an offsets market by allowing GHG mitigation on public lands to be sold as offsets either by the overseeing agency or by
private contractors. To help place these policy options in context, we briefly review the literature on GHG mitigation and
public lands to examine the potential for enhanced mitigation on federal and state public lands in the United States. This
potential will be tempered by consideration of the tradeoffs with other uses of public lands, the needs for climate change
adaptation, and the effects on other ecosystem services. 相似文献
983.
Dearing JA Bullock S Costanza R Dawson TP Edwards ME Poppy GM Smith GM 《Environmental management》2012,49(4):767-775
The ‘Perfect Storm’ metaphor describes a combination of events that causes a surprising or dramatic impact. It lends an evolutionary
perspective to how social-ecological interactions change. Thus, we argue that an improved understanding of how social-ecological
systems have evolved up to the present is necessary for the modelling, understanding and anticipation of current and future
social-ecological systems. Here we consider the implications of an evolutionary perspective for designing research approaches.
One desirable approach is the creation of multi-decadal records produced by integrating palaeoenvironmental, instrument and
documentary sources at multiple spatial scales. We also consider the potential for improved analytical and modelling approaches
by developing system dynamical, cellular and agent-based models, observing complex behaviour in social-ecological systems
against which to test systems dynamical theory, and drawing better lessons from history. Alongside these is the need to find
more appropriate ways to communicate complex systems, risk and uncertainty to the public and to policy-makers. 相似文献
984.
The present study was conducted to compare the 137Cs, 40K, 232Th, and 238U activity concentrations in epigeic moss (Hypnum cupressiforme) and lichen (Cladonia rangiformis). The activity levels in 37 moss and 38 lichen samples collected from the Marmara region of Turkey were measured using a gamma spectrometer equipped with a high purity germanium (HPGe) detector. The activity concentrations of 137Cs, 40K, 232Th, and 238U in the moss samples were found to be in the range of 0.36-8.13, 17.1-181.1, 1.51-6.17, and 0.87-6.70 Bq kg−1 respectively, while these values were below detection limit (BDL)-4.32, 16.6-240.0, 1.32-6.47, and BDL-3.57 Bq kg−1 respectively in lichen. The average moss/lichen activity ratios of 137Cs, 40K, 232Th, and 238U were found to be 1.32 ± 0.57, 2.79 ± 1.67, 2.11 ± 0.82, and 2.19 ± 1.02, respectively. Very low 137Cs concentrations were observed in moss and lichen samples compared to soil samples collected from the same locations in a previous study. Seasonal variations of the measured radionuclide activities were also examined in the three sampling stations. 相似文献
985.
The pyrolysis characteristics of six representative organic components of municipal solid waste (MSW) and their mixtures were studied in a specially designed thermogravimetric analysis apparatus with a maximum recorded heating rate of 864.8 degrees Cmin(-1). The pyrolysis behavior of individual components was described by the Avrami-Erofeev equation. The influence of final temperature on individual components was studied, and it was concluded that final temperature was a factor in reaction speed and intensity, but that it played only a limited role in determining the reaction mechanism. The interactions between different components were evaluated, and it was concluded that the interaction between homogeneous materials was minimal, whereas the interaction between polyethylene and biomass was significant. 相似文献
986.
987.
利用响应面方法(RSM)对光催化/臭氧氧化深度处理炼油废水工艺进行优化,考察了臭氧通量、光催化剂投加量、初始p H和反应时间对于处理效果的影响,提出采用该工艺的数学模型及优化后的工艺参数。结果表明,各影响因子对COD去除率影响顺序为反应时间>光催化剂投加量>初始p H>臭氧通量,方程的F值为11.54,相关系数为0.9537,调整相关系数为0.915,说明数学模型可以较好地模拟真实的反应曲面。优化得到最佳的工艺参数:臭氧通量1.05 L/min、光催化剂投加量0.33 g/L、初始p H 7.51、反应时间96.95 min,在该条件下,对COD去除率为97.88%,与预测值99.49%接近。采用95%处理水和5%新鲜水混合,水质达到了循环冷凝水的补充水水质指标要求。 相似文献
988.
Implications of differing input data sources and approaches upon forest carbon stock estimation 总被引:3,自引:0,他引:3
Michael A. Wulder Joanne C. White Graham Stinson Thomas Hilker Werner A. Kurz Nicholas C. Coops Ben?it St-Onge J. A. Trofymow 《Environmental monitoring and assessment》2010,166(1-4):543-561
Site index is an important forest inventory attribute that relates productivity and growth expectation of forests over time. In forest inventory programs, site index is used in conjunction with other forest inventory attributes (i.e., height, age) for the estimation of stand volume. In turn, stand volumes are used to estimate biomass (and biomass components) and enable conversion to carbon. In this research, we explore the implications and consequences of different estimates of site index on carbon stock characterization for a 2,500-ha Douglas-fir-dominated landscape located on Eastern Vancouver Island, British Columbia, Canada. We compared site index estimates from an existing forest inventory to estimates generated from a combination of forest inventory and light detection and ranging (LIDAR)-derived attributes and then examined the resultant differences in biomass estimates generated from a carbon budget model (Carbon Budget Model of the Canadian Forest Sector (CBM-CFS3)). Significant differences were found between the original and LIDAR-derived site indices for all species types and for the resulting 5-m site classes (p?<?0.001). The LIDAR-derived site class was greater than the original site class for 42% of stands; however, 77% of stands were within ±1 site class of the original class. Differences in biomass estimates between the model scenarios were significant for both total stand biomass and biomass per hectare (p?<?0.001); differences for Douglas-fir-dominated stands (representing 85% of all stands) were not significant (p?=?0.288). Overall, the relationship between the two biomass estimates was strong (R 2?=?0.92, p?<?0.001), suggesting that in certain circumstances, LIDAR may have a role to play in site index estimation and biomass mapping. 相似文献
989.
Using the analytical hierarchy process to assess the environmental vulnerabilities of basins in Taiwan 总被引:3,自引:0,他引:3
Every year, Taiwan endures typhoons and earthquakes; these natural hazards often induce landslides and debris flows. Therefore,
watershed management strategies must consider the environmental vulnerabilities of local basins. Because many factors affect
basin ecosystems, this study applied multiple criteria analysis and the analytical hierarchy process (AHP) to evaluate seven
criteria in three phases (geographic phase, hydrologic phase, and societal phase). This study focused on five major basins
in Taiwan: the Tan-Shui River Basin, the Ta-Chia River Basin, the Cho-Shui River Basin, the Tseng-Wen River Basin, and the
Kao-Ping River Basin. The objectives were a comprehensive examination of the environmental characteristics of these basins
and a comprehensive assessment of their environmental vulnerabilities. The results of a survey and AHP analysis showed that
landslide area is the most important factor for basin environmental vulnerability. Of all these basins, the Cho-Shui River
Basin in central Taiwan has the greatest environmental vulnerability. 相似文献
990.
Assessment of groundwater vulnerability in the Yinchuan Plain,Northwest China using OREADIC 总被引:13,自引:0,他引:13
Groundwater vulnerability assessments provide a measure of the sensitivity of groundwater quality to an imposed contaminant
load and are globally recognized as an essential element of all aquifer management and protection plans. In this paper, the
vulnerability of groundwaters underlying the Yinchuan Plain of Northwest China is determined using OREADIC, a GIS-based assessment
tool that incorporates the key characteristics of the universally popular DRASTIC approach to vulnerability assessment but
has been modified to consider important additional hydrogeological factors that are specific to the region. The results show
that areas of high vulnerability are distributed mainly around Qingtongxia City, Wuzhong City, Lingwu City, and Yongning County
and are associated with high rates of aquifer recharge, shallow depths to the water table, and highly permeable aquifer materials.
The presence of elevated NO3− in the high vulnerability areas endorses the OREADIC approach. The vulnerability maps developed in this study have become
valuable tools for environmental planning in the region and will be used for predictive management of the groundwater resource. 相似文献