全文获取类型
收费全文 | 2413篇 |
免费 | 104篇 |
国内免费 | 320篇 |
专业分类
安全科学 | 106篇 |
废物处理 | 10篇 |
环保管理 | 733篇 |
综合类 | 1046篇 |
基础理论 | 389篇 |
污染及防治 | 66篇 |
评价与监测 | 98篇 |
社会与环境 | 354篇 |
灾害及防治 | 35篇 |
出版年
2024年 | 19篇 |
2023年 | 33篇 |
2022年 | 62篇 |
2021年 | 65篇 |
2020年 | 71篇 |
2019年 | 76篇 |
2018年 | 71篇 |
2017年 | 110篇 |
2016年 | 103篇 |
2015年 | 110篇 |
2014年 | 98篇 |
2013年 | 151篇 |
2012年 | 117篇 |
2011年 | 188篇 |
2010年 | 136篇 |
2009年 | 131篇 |
2008年 | 127篇 |
2007年 | 174篇 |
2006年 | 147篇 |
2005年 | 117篇 |
2004年 | 98篇 |
2003年 | 112篇 |
2002年 | 72篇 |
2001年 | 51篇 |
2000年 | 52篇 |
1999年 | 44篇 |
1998年 | 23篇 |
1997年 | 26篇 |
1996年 | 26篇 |
1995年 | 15篇 |
1994年 | 16篇 |
1993年 | 11篇 |
1992年 | 11篇 |
1991年 | 9篇 |
1990年 | 12篇 |
1989年 | 13篇 |
1988年 | 10篇 |
1987年 | 9篇 |
1986年 | 7篇 |
1985年 | 9篇 |
1984年 | 8篇 |
1983年 | 10篇 |
1981年 | 15篇 |
1980年 | 16篇 |
1979年 | 13篇 |
1978年 | 6篇 |
1977年 | 8篇 |
1975年 | 9篇 |
1972年 | 4篇 |
1971年 | 5篇 |
排序方式: 共有2837条查询结果,搜索用时 15 毫秒
31.
陡坡地灌桑垄槽栽培研究结果,免除土壤侵蚀的危害,其50cm、100cm土壤中,比对照区持水量高10.20%~33.67%、8.27%~65.37%,含全氮率为对照的90%,含全磷率高2.9%、26.2%,含全钾率高3.18%、8.01%,而水解氮均为对照的61.5%,速效磷高较对照39.02%、97.72%,速效钾为对照的91.48%、92.54%。公顷产桑叶量和蚕茧量均较对照高5~10倍,经济效益较对照高11.88倍。 相似文献
32.
33.
34.
35.
36.
37.
Robert France 《Environmental management》1996,20(2):249-255
Due to assimilation of recycled CO2 from litter decomposition and photosynthetic changes in carbon fractionation at low light levels, the foliage at the base of a forest is often more depleted in13C compared to that exposed to the atmosphere in either the canopy or in open clearings. This is referred to as the canopy effect. African research has indicated that these habitat differences in foliar 13C can be substantial enough to affect the carbon isotope ratios of resident fauna. Previous work documenting a 30-year chronology on moose teeth from Isle Royale National Park indicated a progressive depletion in13C and suggested that this could be due to forest regrowth following extensive burning. The present study examined the assumption implicit in this hypothesis that foliar 13C varies between open and closed boreal forest sites. I found a marginal canopy effect of 2 13C difference between upper canopy and ground flora for a forest in northwestern Ontario and an average difference of 1.2 in under- and mid-story vegetation between closed forests and open clear-cuts. Because of these small differences, the utility of carbon isotope analysis in quantifying temporally integrated exploitation of deforested habitats will be low for northern boreal locations. In denser forests, such as those in the tropics or western North American where the canopy effect can be expected to be much greater, 13C analysis may still offer some promise for determining selection by wildlife of disturbed habitats. 相似文献
38.
/ The valleys of European piedmonts constitute changing narrow corridors within which water, matter, nutrients, energy, and species flow. The dispersion patterns of these flows have been significantly disturbed since the end of the 18th century. Thus, western European valleys have been changed into complex mosaics by implementation of socioeconomical programs. In order to define future actions allowing the preservation of this "ecocomplex" (Blandin and Lamotte 1988), it is necessary to gather precise information of the landscape dynamics. Hence, the study of the European river valleys must be based upon two major steps: (1)the analysis of the present landscape with suitable remote sensing techniques, allowing us to map the complex mosaic of narrow corridors; and (2) the analysis of temporal landscape development patterns since the first engineering works that have transformed the braided channel system. In this paper, the efficiency of the addition of two techniques is highlighted: (1) the "wavelet merging method" from multispectral and panchromatic SPOT images for the floodplain land-cover mapping, and (2) the historical reconstruction techniques from old maps and archive documents in order to analyze the cumulative impacts of engineering works on landscape diversity. To illustrate the method, a particularly complex case study is chosen: the Arc/Isere confluence (downstream from Albertville, Savoie, France). Remote sensing, field survey, and historical reconstruction allowed us to distinguish two types of spatial units: (1) the "functional sets" characterized by independent state factors (edaphic, hydrological, and topographic) and supporting a limited number of vegetation types (spontaneous or cultivated), and (2) the functional unit (= ecotope), which corresponds to a unique combination of vegetation type/functional set.KEY WORDS: Landscape ecology; Floodplains; Vegetation; Land use; Remote sensing; Historical reconstruction; Mapping; Merging methods; Human impacts; Alps; Isere river; France 相似文献
39.
V. Krishna Prasad K.V.S. Badarinath H. Tsuruta S. Sudo S. Yonemura John Cardina Benjamin Stinner Richard Moore Deborah Stinner Casey Hoy 《The Environmentalist》2003,23(2):175-187
Forests and soils are a major sink of carbon, and land use changes can affect the magnitude of above ground and below ground carbon stores and the net flux of carbon between the land and the atmosphere. Studies on methods for examining the future consequences of changes in patterns of land use change and carbon flux gains importance, as they provide different options for CO2 mitigation strategies. In this study, a simulation approach combining Markov chain processes and carbon pools for forests and soils has been implemented to study the carbon flows over a period of time. Markov chains have been computed by converting the land use change and forestry data of India from 1997 to 1999 into a matrix of conditional probabilities reflecting the changes from one class at time t to another class time t+1. Results from Markov modeling suggested Indian forests as a potential sink for 0.94 Gt carbon, with an increase in dense forest area of about 75.93 Mha and decrease of about 3.4 Mha and 5.0 Mha in open and scrub forests, if similar land use changes that occurred during 1997–1999 would continue. The limiting probabilities suggested 34.27 percent as dense forest, 6.90 as open forest, 0.4 percent mangrove forest, 0.1 percent scrub and 58 percent as non-forest area. Although Indian forests are found to be a potential carbon sink, analysis of results from transition probabilities for different years till 2050 suggests that, the forests will continue to be a source of about 20.59 MtC to the atmosphere. The implications of these results in the context of increasing anthropogenic pressure on open and scrub forests and their contribution to carbon source from land use change and forestry sector are discussed. Some of the mitigation aspects to reduce greenhouse gas emissions from land use change and forestry sector in India are also reviewed in the study. 相似文献
40.
Traditional knowledge and practices are important in prudent resource use and biodiversity conservation. The implications of modernization and changing lifestyle are discussed in the context of agriculture and resource use, the two sectors in which maximum modernization has occurred. The information was gathered through observations and structured interviews over three years (July 1996 to July 1999) of field work in the western Himalaya. It was observed that forest based subsistence agriculture has given way to the market dependant cash crop cultivation. That apart from loss of genetic diversity, has also resulted in the degradation of forests. The use of wild plants in the day-to-day activities has also declined and dependence on high value market products has increased. Currently, wild plants are used only if no other cheap substitute is available in the market or if the use is economically beneficial to the people. Thus, the knowledge gathered through ages of experience is eroding because of the activities geared for short-term economic benefits which, in long run, may not be sustainable. 相似文献