全文获取类型
收费全文 | 299篇 |
免费 | 8篇 |
国内免费 | 4篇 |
专业分类
安全科学 | 26篇 |
废物处理 | 8篇 |
环保管理 | 82篇 |
综合类 | 29篇 |
基础理论 | 84篇 |
环境理论 | 5篇 |
污染及防治 | 49篇 |
评价与监测 | 17篇 |
社会与环境 | 9篇 |
灾害及防治 | 2篇 |
出版年
2021年 | 3篇 |
2020年 | 2篇 |
2019年 | 5篇 |
2018年 | 6篇 |
2017年 | 8篇 |
2016年 | 12篇 |
2015年 | 5篇 |
2014年 | 6篇 |
2013年 | 20篇 |
2012年 | 17篇 |
2011年 | 17篇 |
2010年 | 9篇 |
2009年 | 13篇 |
2008年 | 13篇 |
2007年 | 12篇 |
2006年 | 23篇 |
2005年 | 12篇 |
2004年 | 15篇 |
2003年 | 11篇 |
2002年 | 10篇 |
2001年 | 4篇 |
2000年 | 8篇 |
1999年 | 6篇 |
1998年 | 3篇 |
1997年 | 8篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 6篇 |
1993年 | 5篇 |
1992年 | 2篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1965年 | 1篇 |
1964年 | 1篇 |
1958年 | 1篇 |
排序方式: 共有311条查询结果,搜索用时 15 毫秒
111.
112.
The International Union for Conservation of Nature's Red List of Threatened Species (RLS) is the key global tool for objective, repeatable assessment of species’ extinction risk status, and plays an essential role in tracking biodiversity loss and guiding conservation action. Satellite remote sensing (SRS) data sets on global ecosystem distributions and functioning show exciting potential for informing range-based RLS assessment, but their incorporation has been restricted by low temporal resolution and coverage of data sets, lack of incorporation of degradation-driven habitat loss, and noninclusion of assumptions related to identification of changing habitat distributions for taxa with varying habitat dependency and ecologies. For poorly known mangrove-associated Cuban hutias (Mesocapromys spp.), we tested the impact of possible assumptions regarding these issues on range-based RLS assessment outcomes. Specifically, we used annual (1985–2018) Landsat data and land-cover classification and habitat degradation analyses across different internal time series slices to simulate range-based RLS assessments for our case study taxa to explore potential assessment uncertainty arising from temporal SRS data set coverage, incorporating proxies of (change in) habitat quality, and assumptions on spatial scaling of habitat extent for RLS parameter generation. We found extensive variation in simulated species-specific range-based RLS assessments, and this variation was mostly associated with the time series over which parameters were estimated. However, results of some species-specific assessments differed by up to 3 categories (near threatened to critically endangered) within the same time series, due to the effects of incorporating habitat quality and the spatial scaling used in RLS parameter estimation. Our results showed that a one-size-fits-all approach to incorporating SRS information in RLS assessment is inappropriate, and we urge caution in conducting range-based assessments with SRS for species for which habitat dependence on specific ecosystem types is incompletely understood. We propose novel revisions to parameter spatial scaling guidelines to improve integration of existing time series data on ecosystem change into the RLS assessment process. 相似文献
113.
Junjie Guan Kent M. Eskridge Milford A. Hanna 《Journal of Polymers and the Environment》2004,12(3):113-121
Acetylated starches, with degrees of substitution (DS) of 2, 2.5 and 3, were blended with 3%, 7.5% and 12% -cellulose and 14%, 17% or 20% (d.b.) ethanol and twin-screw extruded at 165°C barrel temperature and 225 rpm screw speed. A response surface methodology experimental design was applied to the sub-plot and a completely randomized design to the whole plot design to test the differences among the acetylated starches and the effects of cellulose and ethanol. DS, cellulose and ethanol contents significantly affected the functional properties and specific mechanical energy requirement. DS had positive effects on radial expansion ratio (RER), compressibility and specific mechanical energy requirement and a negative effect on bulk density. Highest (RER) was obtained from 20% ethanol content. Extrudates containing 12% cellulose had the highest bulk density and the highest compressibility. Higher cellulose contents required more specific mechanical energy. 相似文献
114.
Bärbel Langmann Bryan Duncan Christiane Textor Jörg Trentmann Guido R. van der Werf 《Atmospheric environment (Oxford, England : 1994)》2009,43(1):107-116
Gaseous and particulate emissions from vegetation fires substantially modify the atmospheric chemical composition, degrade air quality and can alter weather and climate. The impact of vegetation fire emissions on air pollution and climate has been recognised in the late 1970s. The application of satellite data for fire-related studies in the beginning of the 21th century represented a major break through in our understanding of the global importance of fires. Today the location and extent of vegetation fires, burned area and emissions released from fires are determined from satellite products even though many uncertainties persist. Numerous dedicated experimental and modeling studies contributed to improve the current knowledge of the atmospheric impact of vegetation fires. The motivation of this paper is to give an overview of vegetation fire emissions, their environmental and climate impact, and what improvements can be expected in the near future. 相似文献
115.
Isolated Spring Wetlands in the Great Basin and Mojave Deserts,USA: Potential Response of Vegetation to Groundwater Withdrawal 总被引:3,自引:0,他引:3
Desert springs, often the sole sources of water for wildlife and cattle, support wetland and wetland/upland transition ecosystems
including rare and endemic species. In the basin and range province in Nevada, USA, springs in the Great Basin and Mojave
deserts are sustained by interconnected deep carbonate and shallow basin-fill aquifers which are threatened by proposed groundwater
withdrawal to sustain rapidly expanding urban areas, a common problem in arid regions worldwide. This paper draws on historic
groundwater data, groundwater modeling, and studies of environmental controls of spring ecosystems to speculate on the potential
effects of groundwater withdrawal and water table decline on spring-supported vegetation. The focus is on springs in the Great
Basin and Mojave deserts representative of those that may be affected by future, planned groundwater withdrawal. Groundwater
withdrawal is expected to reduce spring discharge directly through reduced flows from the shallow basin-fill aquifer or through
reduction of the hydraulic head of the deep carbonate aquifer. This flow reduction will truncate the outflow stream, reducing
the areal cover of wetland and wetland/upland transition vegetation. Lowering the local water table may also reduce the amount
of upland phreatophytic vegetation by causing water levels to drop below plant rooting depths. Percolation of salts to surface
soils may be reduced, eventually altering desert shrub cover from halophytes to nonhalophytes. The extent of these effects
will vary among springs, based on their distance from extraction sites and location relative to regional groundwater flow
paths. On-site monitoring of biotic variables (including cover of selected hygrophytes and phreatophytes) should be a necessary
complement to the planned monitoring of local hydrologic conditions. 相似文献
116.
Richard N. DeVries Douglas C. Kent 《Journal of the American Water Resources Association》1973,9(5):998-1005
ABSTRACT: The Ogallala aquifer in the Oklahoma Panhandle is in need of better management because of increased groundwater demand which has caused declines in static water levels at an alarming rate. A groundwater management computer model was developed for the Ogallala aquifer in the Texas Panhandle and treats the aquifer as a homogeneous system. In this study, the computer model has been modified in order to evaluate the effects of vertical layering on semi-static water level changes which occur during the dewatering of a single unconfined aquifer. The modified model was applied to a study area near Guymon, Oklahoma, using both the homogeneous and the multilayered cases. The aquifer is characterized by a saturated thickness of 400 feet. The accumulated drawdown values of the homogeneous and the multilayered cases demonstrate that an average difference of approximately 22% of the original saturated thickness occurs between the two cases before the base of the aquifer is encountered. Approximately 25% more time is required to dewater the layered aquifer. Thus, vertical variations of lithology in an aquifer such as the Ogallala should be considered when prediction is made relative to groundwater management. 相似文献
117.
118.
There Is More to Biodiversity than the Tropical Rain Forests 总被引:1,自引:0,他引:1
119.
120.
Mapping the Conservation Landscape 总被引:12,自引:0,他引:12