全文获取类型
收费全文 | 981篇 |
免费 | 63篇 |
国内免费 | 144篇 |
专业分类
安全科学 | 23篇 |
废物处理 | 10篇 |
环保管理 | 199篇 |
综合类 | 475篇 |
基础理论 | 232篇 |
污染及防治 | 24篇 |
评价与监测 | 73篇 |
社会与环境 | 121篇 |
灾害及防治 | 31篇 |
出版年
2024年 | 6篇 |
2023年 | 17篇 |
2022年 | 41篇 |
2021年 | 25篇 |
2020年 | 29篇 |
2019年 | 33篇 |
2018年 | 29篇 |
2017年 | 33篇 |
2016年 | 40篇 |
2015年 | 43篇 |
2014年 | 43篇 |
2013年 | 70篇 |
2012年 | 43篇 |
2011年 | 65篇 |
2010年 | 66篇 |
2009年 | 55篇 |
2008年 | 53篇 |
2007年 | 48篇 |
2006年 | 63篇 |
2005年 | 48篇 |
2004年 | 33篇 |
2003年 | 45篇 |
2002年 | 40篇 |
2001年 | 27篇 |
2000年 | 26篇 |
1999年 | 27篇 |
1998年 | 15篇 |
1997年 | 12篇 |
1996年 | 12篇 |
1995年 | 12篇 |
1994年 | 9篇 |
1993年 | 8篇 |
1992年 | 8篇 |
1991年 | 7篇 |
1990年 | 6篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 5篇 |
1985年 | 4篇 |
1983年 | 4篇 |
1981年 | 2篇 |
1980年 | 8篇 |
1979年 | 4篇 |
1978年 | 1篇 |
1977年 | 4篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1972年 | 3篇 |
1971年 | 1篇 |
排序方式: 共有1188条查询结果,搜索用时 15 毫秒
971.
The methodological principles of making a phytoecological map reflecting the degree of anthropogenic transformation of the plant cover are described. 相似文献
972.
长江淡水潮汐湿地植物特性和植物群落演替研究——以镇江北固山湿地为例 总被引:3,自引:0,他引:3
镇江北固山湿地属于长江近河口段淡水潮汐湿地,植物群落基本保持原生演替的前期状况。根据对该湿地的实地观测研究,描述了河滨湿地植物的生长特性;结合湿地的水文特征刻画了湿地高等水生植物在时间、空间和景观上的生态过程;综合河滨湿地植物的生长特性及湿地的水文特征探讨了镇江淡水潮汐湿地的演变趋势。对湿地面临的问题进行了讨论,从而为长江淡水潮汐湿地的生态修复和增加生物多样性及湿地保护提供参考。 相似文献
973.
Naisargi Dave Aaron Mittelstet Jesse Korus Michele Waszgis 《Journal of the American Water Resources Association》2020,56(3):528-541
The 2010 dam breach and consequent anomalous flood event on the Cedar River in Nebraska, USA provided an opportunity to study the following objectives: (1) evaluate the impact of an extreme flood event on streambank retreat along a 45 km stretch relative to the average annual retreat; (2) quantify the changes in streambank retreat for each km segment downstream of the breach; and (3) examine the influence of riparian vegetation and radius of curvature on meander bank erosion rate. During the hydrologic event, discharge peaked at nearly three times greater than the next highest recorded rate and equated to a return period of 2,000 years. Aerial images and ArcGIS were utilized to calculate the average annual streambank retreat for each year during the preflood (2006–2010), flood (2010), and postflood (2010–2016) periods. The 2010 flood period had a significantly higher average annual streambank retreat of 2,820 m2/km/yr than the preflood and postflood periods, which, respectively, measured 576 and 384 m2/km/yr. From 2006 to 2016, 29% of all streambank erosion was from this one extreme flood event, thus demonstrating the impact that one extreme flood event can have on streambank retreat and the geomorphology of a stream system. 相似文献
974.
基于MODIS-EVI数据的长江三角洲地区植被变化的特征 总被引:2,自引:0,他引:2
基于2001~2010年MODIS EVI植被指数产品数据,结合国家标准气象站逐月气温、降雨及日照时数资料,对长江三角洲地区植被的时空变化特征进行分析。结果表明:(1)空间分布上,该区域西南部以林地为主,而东北部以农田为主,近10 a植被变化面积占总面积的32%,以农田的转出和城镇的转入为主;(2)区域年最大EVI整体呈减少趋势(-0028/10 a),不同季节下,夏冬季均呈减少趋势(以2月和8月份最为显著),春秋季则呈增加趋势(以5月和10月份最为显著);(3)不同植被类型下,城镇和农田EVI呈不同程度减少趋势,以城镇EVI下降速度(-0076/10 a)最为显著(R2=077),而林地变化较弱;(4)研究区湿润气候环境下,农田和林地年最大EVI与日照时数和气温多呈正相关性,与降雨多呈负相关性,其中以林地EVI与2~4月份日照时数的正相关性较为显著,城镇EVI与气象因子的关系相对较弱,更多的是受城镇化等人类活动的影响 相似文献
975.
空气负离子研究进展及影响因素分析 总被引:1,自引:0,他引:1
空气负离子保健作用受到人们的普遍关注,其浓度是衡量空气清洁度的重要指标之一,在空气环境质量评价中日益受到重视。从医学健康、环境卫生、工农业、生态旅游四个方面论述了空气负离子在国内外的研究进展,并结合最新研究成果,综述了负离子在不同气象因子、海拔高度、植被、区域、时段下的浓度变化规律。在此基础上,对空气负离子未来研究方向提出建议,为空气负离子进一步研究提供参考和借鉴。 相似文献
976.
Global change affects alpine ecosystems by, among many effects, by altering plant distributions and community composition.
However, forecasting alpine vegetation change is challenged by a scarcity of studies observing change in fixed plots spanning
decadal-time scales. We present in this article a probabilistic modeling approach that forecasts vegetation change on Niwot
Ridge, CO using plant abundance data collected from marked plots established in 1971 and resampled in 1991 and 2001. Assuming
future change can be inferred from past change, we extrapolate change for 100 years from 1971 and correlate trends for each
plant community with time series environmental data (1971–2001). Models predict a decreased extent of Snowbed vegetation and
an increased extent of Shrub Tundra by 2071. Mean annual maximum temperature and nitrogen deposition were the primary a posteriori
correlates of plant community change. This modeling effort is useful for generating hypotheses of future vegetation change
that can be tested with future sampling efforts. 相似文献
977.
Changes in groundwater levels and the response of natural vegetation to
transfer of water to the lower reaches of the Tarim River 总被引:6,自引:0,他引:6
Restoration and reconstruction of the degraded Tarim River ecosystem is an important challenge.A goal of an ecological water conveyance project is to protect and restore the natural vegetation in the lower reaches of Tarim River by transferring water from Bosten Lake,through the river channel,to the lower reaches.This study describes the changes in groundwater depth during the water transfer and the respondence of riparian vegetation to alterations in groundwater levels.The results indicate that groundwater depth along the Tarim River channel has a significant spatial-temporal component.Groundwater levels closest to the river channel show the most immediate and pronounced changes as a response to water transfer while those further away respond more slowly,although the observed change appears to be longer in duration.With a rise in the groundwater level,natural vegetation responded with higher growth rates,biomass and biodiversity.These favorable changes show that it is feasible to protect and restore the degraded natural vegetation by raising the groundwater depth.Plant communities are likely to reflect the hysteresis phenomenon,requiring higher water levels to initiate and stimulate desired growth than what may be needed to maintain the plant community.Because different species have different ecologies,including different root depths and densities and water needs,their response to increasing water availability will be spatially and temporally heterogenous.The response of vegetation is also influenced by microtopography and watering style.This paper discusses strategies for the protection and restoration of the degraded vegetation in the lower reaches of the Tarim River and provides information to complement ongoing theoretical research into ecological restoration in arid or semi-arid ecosystems. 相似文献
978.
979.
980.
以野外监测数据为基础,应用模糊综合评判方法掌握大气污染物的变化规律,然后采用熏气试验测定植被对污染物的净化速率,建立大气污染物的植被控制模型,并以此提出了益阳市大气主要污染物的植被负荷及绿化设计。 相似文献