全文获取类型
收费全文 | 5835篇 |
免费 | 449篇 |
国内免费 | 582篇 |
专业分类
安全科学 | 1266篇 |
废物处理 | 138篇 |
环保管理 | 1124篇 |
综合类 | 2884篇 |
基础理论 | 382篇 |
环境理论 | 1篇 |
污染及防治 | 327篇 |
评价与监测 | 294篇 |
社会与环境 | 179篇 |
灾害及防治 | 271篇 |
出版年
2024年 | 15篇 |
2023年 | 60篇 |
2022年 | 101篇 |
2021年 | 169篇 |
2020年 | 234篇 |
2019年 | 139篇 |
2018年 | 83篇 |
2017年 | 192篇 |
2016年 | 171篇 |
2015年 | 253篇 |
2014年 | 262篇 |
2013年 | 303篇 |
2012年 | 378篇 |
2011年 | 476篇 |
2010年 | 330篇 |
2009年 | 314篇 |
2008年 | 210篇 |
2007年 | 373篇 |
2006年 | 417篇 |
2005年 | 284篇 |
2004年 | 278篇 |
2003年 | 284篇 |
2002年 | 235篇 |
2001年 | 205篇 |
2000年 | 179篇 |
1999年 | 163篇 |
1998年 | 125篇 |
1997年 | 96篇 |
1996年 | 95篇 |
1995年 | 82篇 |
1994年 | 62篇 |
1993年 | 54篇 |
1992年 | 46篇 |
1991年 | 21篇 |
1990年 | 15篇 |
1989年 | 8篇 |
1987年 | 12篇 |
1986年 | 14篇 |
1985年 | 9篇 |
1984年 | 6篇 |
1983年 | 10篇 |
1982年 | 10篇 |
1981年 | 8篇 |
1980年 | 16篇 |
1979年 | 10篇 |
1978年 | 10篇 |
1977年 | 7篇 |
1974年 | 6篇 |
1973年 | 5篇 |
1971年 | 9篇 |
排序方式: 共有6866条查询结果,搜索用时 328 毫秒
541.
Expansion of the distribution of exotic rainbow trout is thought to be a leading cause for the decline of native brook trout since the 1930s in Great Smoky Mountains National Park, USA. An experimental rehabilitation project was conducted from 1976 to 1981 using backpack electrofish shockers on four remnant brook trout populations sympatric with rainbow trout. The objectives were to evaluate the effectiveness of the technique to remove the exotic rainbow trout, to determine the population responses by native brook trout, and to evaluate the usefulness of the technique for trout management in the park.Rainbow trout populations were greatly reduced in density after up to six years of electrofishing, but were not eradicated. Rainbow trout recruitment, however, was essentially eliminated. Brook trout populations responded by increasing in density (including young-of-the-year), but rates of recovery differed among streams. The maximum observed densities ir each stream occurred at the end of the project.The findings suggest that electrofishing had a major negative impact on the exotic species, which was followed by positive responses from the native species in the second and third order study streams. The technique would probably be less effective in larger (fourth-order) park streams, but as an eradication tool the technique may have its highest potential in small first order streams. Nonetheless, the technique appears useful for population control without causing undue impacts on native aquatic species, although it is labor intensive, and capture efficiency is greatly influenced by fish size and stream morphology. To completely remove the exotic fish from selected streams, different technologies will have to be explored and developed. 相似文献
542.
Andrew Charles Gross 《Environmental management》1986,10(1):25-39
This article analyzes water quality on a global scale. An overview of the global water supply and demand situation is presented first, including regional and country information, as well as data on selected water use patterns. The focus then shifts to a discussion of water pollution, its various causes, impact, and remedies, with emphasis on legal and administrative solutions. Water pollution control expenditures and the resultant achievements are dealt with in the final third of the article, with projections to 1995. A wide variety of published sources was dovetailed to obtain a composite picture and most likely scenario; this was supplemented with primary interviews by the author conducted in North America, Western and Eastern Europe, and Oceania at the start of the 1980s. 相似文献
543.
本文报道了沱江上游青白江区水环境管理的现状,分析了水环境管理中存在的问题,提出了防治对策。 相似文献
544.
545.
546.
城市防洪工程风险决策方法 总被引:2,自引:2,他引:2
本文着重讨论了与城市防洪工程决策制定密切相关的几个问题:①城市防洪工程设计标准的确定;②现有防洪工程的性能评估,③最优防洪工程对策的确定等,并在风险分析的基础上,给出了解决上述问题的方法。所得结论可为城市防洪工程决策的制定提供较为科学的理论依据。 相似文献
547.
本文以定量分析为主要手段,详细研究了吉林省农业病虫害发生的时间过程规律和空间分布规律,深入探讨了环境因子对农业病虫害的影响,综合评价了病虫害防治工作的效果。 相似文献
548.
江苏沿海滩涂开发现状分析 总被引:6,自引:0,他引:6
本文作者根据多年的江苏滩涂开发利用调查资料,着重分析了江苏滩涂开发成就,开发潜力和制约因素三方面的现状,提出了加快滩涂开发的重要措施。 相似文献
549.
Agriculture and stream water quality: A biological evaluation of erosion control practices 总被引:4,自引:0,他引:4
David R. Lenat 《Environmental management》1984,8(4):333-343
Agricultural runoff affects many streams in North Carolina. However, there is is little information about either its effect on stream biota or any potential mitigation by erosion control practices. In this study, benthic macroinvertebrates were sampled in three different geographic areas of North Carolina, comparing control watersheds with well-managed and poorly managed watersheds. Agricultural streams were characterized by lower taxa richness (especially for intolerant groups) and low stability. These effects were most evident at the poorly managed sites. Sedimentation was the apparent major problem, but some changes at agricultural sites implied water quality problems. The groups most intolerant of agricultural runoff were Ephemeroptera, Plecoptera and Trichoptera. Tolerant species were usually filter-feeders or algal grazers, suggesting a modification of the food web by addition of particulate organic matter and nutrients. This study clearly indicates that agricultural runoff can severely impact stream biota. However, this impact can be greatly mitigated by currently recommended erosion control practices. 相似文献
550.
Barry A. Pierce 《Environmental management》1983,7(2):151-160
Grass carp (Ctenopharyngodon idella Val.) were introduced into the United States in 1963 as potential biological control agents for nuisance aquatic weeds. Since that time an oftentimes bitter controversy has raged over its effects on sportfishing, and its possible natural reproduction and naturalization in North America. This review considers the history, ecology, and present status of grass carp in the United States in light of the voluminous scientific research conducted since its importation. Particular attention is given to the role of grass carp in the fisheries management plans of Arkansas. Recent development of a sterile, triploid grass carp hybrid may lead to widespread use of grass carp to control nuisance aquatic weeds in culturally eutrophicated waters of the United States. 相似文献