首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1006篇
  免费   101篇
  国内免费   349篇
安全科学   41篇
废物处理   1篇
环保管理   139篇
综合类   568篇
基础理论   523篇
环境理论   2篇
污染及防治   69篇
评价与监测   34篇
社会与环境   76篇
灾害及防治   3篇
  2024年   14篇
  2023年   35篇
  2022年   62篇
  2021年   49篇
  2020年   49篇
  2019年   36篇
  2018年   42篇
  2017年   48篇
  2016年   52篇
  2015年   68篇
  2014年   52篇
  2013年   72篇
  2012年   78篇
  2011年   99篇
  2010年   62篇
  2009年   66篇
  2008年   73篇
  2007年   83篇
  2006年   77篇
  2005年   63篇
  2004年   37篇
  2003年   42篇
  2002年   28篇
  2001年   23篇
  2000年   21篇
  1999年   20篇
  1998年   12篇
  1997年   11篇
  1996年   15篇
  1995年   14篇
  1994年   12篇
  1993年   7篇
  1992年   4篇
  1991年   5篇
  1990年   3篇
  1989年   3篇
  1988年   1篇
  1987年   3篇
  1986年   2篇
  1985年   2篇
  1984年   1篇
  1983年   2篇
  1982年   1篇
  1981年   2篇
  1980年   1篇
  1979年   2篇
  1977年   1篇
  1973年   1篇
排序方式: 共有1456条查询结果,搜索用时 234 毫秒
991.
Data on the species composition, abundance, and biomass of macrozoobenthos in the rapids of a small river flowing in the foothills of the southwestern Kamchatka Peninsula are considered along with the results of quantitative analysis of structural rearrangements in the lithophilic community under the effects of changes in the granulometric composition of bottom sediments. Groups of lithophilic and pelophilic invertebrates typical of the metarithral of such rivers (e.g., chironomids of subfamilies Diamesinae and Prodiamesinae) are identified.Translated from Ekologiya, No. 2, 2005, pp. 120–125.Original Russian Text Copyright © 2005 by Leman, Chebanova.  相似文献   
992.
生物多样性保护与可持续发展   总被引:1,自引:0,他引:1  
本文就生物多样性保护的重要性进行了论述,并介绍了我国生物多样性特点,强调了生物多样性保护的迫切性,阐明了生物多样性对可持续发展的重要性。  相似文献   
993.
以云南丽江为例,指出类似丽江的诸多西部多民族交错聚居区在文化旅游二次创业过程中突出自身区域主体民族文化特色的同时,必须要重视非主体民族文化资源的保护与开发,让各民族社区参与能力的塑造和培育都能在旅游开发中得到协调发展。这既是文化多样性对区域文化旅游资源整合重构的内在发展要求,也是区域旅游在二次创业中发挥扩散效应的重要导向。  相似文献   
994.
土地的集约利用对社会发展具有重要的意义,研究土地集约利用空间差异可以更有效地提高土地利用水平。根据新一轮土地利用规划大纲要求和各区域土地利用实际,建立土地集约利用评价指标体系,确定土地集约利用评价的计算方法,包括数据的量化、标准化及综合计算模型,最后得出各地区土地集约利用程度。运用上述方法对孝感市建设用地集约利用空间差异进行分析,找出了其土地利用方面的问题和优势,为下一步改造提供依据和方向。  相似文献   
995.
This study investigated the genetic relationships between the rare terrestrial orchid Diuris fragrantissima and three closely related purple flowered species using Amplified Fragment Length Polymorphisms. The purple-flowered species were found to form individual phenetic clusters confirming recognition of D. fragrantissima at the rank of species. Levels of genetic variation were lower within D. fragrantissima than within its closest relatives but were higher than expected for severely bottlenecked species. Gene flow was detected among all species (Nm = 2.34) and populations (Nm = 0.65) however low among population gene flow indicates that populations may be at risk of divergence. This study has implications for the conservation of D. fragrantissima.  相似文献   
996.
雅玛里克山植被类型及物种多样性的特征   总被引:6,自引:0,他引:6  
采用典型样地法对雅玛里克山进行了植被调查,结果表明,该区的植物群落类型有14种;植物种类有223种植物.分属37科147属,植物生活型有9类;短命和类短命植物获得一定发育,旱生类型的植物占绝对优势,一年生植物占有一定比例等。  相似文献   
997.
This research surveyed human-impacted littoral forests in southeastern Madagascar to determine (i) how forest structural features, indicative of human impact, are related to total, utilitarian, and endemic tree diversity; (ii) the distribution, abundance, and demographics of tree species groups (i.e., total, useful, endemic) across the landscape; and (iii) the amount of basal area available per human use category. We also use these data to consider issues of sustainable use and how human impact may influence littoral forest tree community composition across the landscape. Within 22 transects of 400 m2 each, we recorded a total of 135 tree species and 2155 individuals. Seventy-nine species (58%) were utilitarian and 56 (42%) were nonutilitarian species. Of the 2155 individuals, 1827 (84%) trees were utilitarian species. We recorded 23 endemic species (17% of the total species) and 17 (74%) of these were utilitarian species. Basal area was significantly correlated with Shannon Weiner Index values for total (r = 0.64, P < 0.01), utilitarian (r = 0.58, P < 0.01), and endemic tree diversity (r = 0.85, P < 0.01). Basal area was significantly correlated with the Simpson’s index values for the endemic species (r = 0.74, P < 0.01). These correlations suggest that endemic tree species, of high global conservation value, may be the species group most influenced by changes in forest structure. Utilitarian species constituted 84% of the total basal area. The use category contributing the highest amount of basal area to the landscape was firewood. The results presented herein demonstrate that the landscape of southeastern Madagascar, commonly perceived as degraded, retains high value for both global conservation purposes and for local livelihoods. Thus, valuable opportunities may exist for developing conservation incentives that leverage both global and local conservation needs.  相似文献   
998.
Urbanization and the Loss of Resource Lands in the Chesapeake Bay Watershed   总被引:3,自引:0,他引:3  
We made use of land cover maps, and land use change associated with urbanization, to provide estimates of the loss of natural resource lands (forest, agriculture, and wetland areas) across the 168,000 km2 Chesapeake Bay watershed. We conducted extensive accuracy assessments of the satellite-derived maps, most of which were produced by us using widely available multitemporal Landsat imagery. The change in urbanization was derived from impervious surface area maps (the built environment) for 1990 and 2000, from which we estimated the loss of resource lands that occurred during this decade. Within the watershed, we observed a 61% increase in developed land (from 5,177 to 8,363 km2). Most of this new development (64%) occurred on agricultural and grasslands, whereas 33% occurred on forested land. Some smaller municipalities lost as much as 17% of their forest lands and 36% of their agricultural lands to development, although in the outlying counties losses ranged from 0% to 1.4% for forests and 0% to 2.6% for agriculture. Fast-growing urban areas surrounded by forested land experienced the most loss of forest to impervious surfaces. These estimates could be used for the monitoring of the impacts of development across the Chesapeake Bay watershed, and the approach has utility for other regions nationwide. In turn, the results and the approach can help jurisdictions set goals for resource land protection and acquisition that are consistent with regional restoration goals.  相似文献   
999.
贵州山区是我国一个植物多样性较丰富的地区,仅野生观赏植物(含园林及行道绿化,美化树种)就有300多种,其中120多种属珍稀受危观赏物种。文章着重对36种主要珍稀濒危观赏植物的分布、生境、濒危类型、程度等进行了分析,并从观赏植物本身的生理生态习性、贵州山区生境本底的严酷性(土壤瘠薄,可有效利用的地表水匮乏等)、人类不合理干扰活动(如过渡采收、毁林垦荒等)方面探讨了该地区观赏植物多样性的受危原因。在此基础上,结合目前西部大开发中生态建设的要求,提出了该地区受危观赏植物的保护对策。  相似文献   
1000.
为了描述剩余污泥稳定化芦苇床系统中有机质矿化、甲烷排放及相关微生物多样性之间的内在关系,采用PCR-DGGE技术分析了不同芦苇床、不同季节的稳定化污泥中古细菌群落结构及其多样性。序列分析发现,与DGGE条带序列亲缘关系最近的种属为未培养古细菌和未培养产甲烷古细菌。古细菌群落结构呈季节性变化,且同一季节不同芦苇床的群落结构存在一定差异。具有通气结构芦苇床的剩余污泥中产甲烷古细菌的丰度较低,同时甲烷排放量也较低,因此设置通气结构的芦苇床设计更合理。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号