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   247篇
  免费   19篇
  国内免费   27篇
安全科学   10篇
废物处理   4篇
环保管理   33篇
综合类   160篇
基础理论   34篇
污染及防治   3篇
评价与监测   5篇
社会与环境   14篇
灾害及防治   30篇
  2023年   4篇
  2022年   7篇
  2021年   6篇
  2020年   6篇
  2019年   7篇
  2018年   4篇
  2017年   7篇
  2016年   11篇
  2015年   9篇
  2014年   12篇
  2013年   14篇
  2012年   21篇
  2011年   19篇
  2010年   9篇
  2009年   11篇
  2008年   11篇
  2007年   10篇
  2006年   9篇
  2005年   11篇
  2004年   13篇
  2003年   14篇
  2002年   11篇
  2001年   9篇
  2000年   9篇
  1999年   5篇
  1998年   5篇
  1997年   3篇
  1996年   5篇
  1995年   4篇
  1994年   5篇
  1993年   2篇
  1992年   1篇
  1991年   2篇
  1990年   2篇
  1989年   2篇
  1988年   2篇
  1987年   3篇
  1986年   2篇
  1985年   3篇
  1984年   1篇
  1983年   2篇
排序方式: 共有293条查询结果,搜索用时 609 毫秒
191.
The isotope ratios δ13C and δ15N and the contents of nitrogen, carbon, and mineral substances have been studied in the leaves of Ephedra sinica, Allium polyrhizum, and Stipa glareosa plants growing separately or together under arid conditions of the Gobi (Mongolia). The contents of nitrogen, mineral substances, and δ15N have proved to decrease when these species grow together, providing evidence that they compete for environmental resources. The nitrogen content decreases to the greatest extent in E. sinica due to the low competitiveness of this species. The direction of change in δ13C in E. sinica is opposite to that in A. polyrhizum and S. glareosa. Differences in physiological mechanisms of adaptation to stress between these species provides a basis for attributing them to different functional groups and for predicting the result of their competition upon changes in climatic conditions.  相似文献   
192.
As drivers of terrestrial ecosystems, humans have replaced large carnivores in most areas, and human influence not only exerts striking ecological pressures on biodiversity at local scales but also has indirect effects in distant corners of the world. We suggest that the multibillion dollar cashmere industry creates economic motivations that link western fashion preferences for cashmere to land use in Central Asia. This penchant for stylish clothing, in turn, encourages herders to increase livestock production which affects persistence of over 6 endangered large mammals in these remote, arid ecosystems. We hypothesized that global trade in cashmere has strong negative effects on native large mammals of deserts and grassland where cashmere‐producing goats are raised. We used time series data, ecological snapshots of the biomass of native and domestic ungulates, and ecologically and behaviorally based fieldwork to test our hypothesis. In Mongolia increases in domestic goat production were associated with a 3‐fold increase in local profits for herders coexisting with endangered saiga (Saiga tatarica).That increasing domestic grazing pressure carries fitness consequences was inferred on the basis of an approximately 4‐fold difference in juvenile recruitment among blue sheep (Pseudois nayaur)in trans‐Himalayan India. Across 7 study areas in Mongolia, India, and China's Tibetan Plateau, native ungulate biomass is now <5% that of domestic species. Such trends suggest ecosystem degradation and decreased capacity for the persistence of native species, including at least 8 Asian endemic species: saiga, chiru (Pantholops hodgsoni), Bactrian camel (Camelus bactrianus), snow leopard(Panthera uncia), khulan(Equus hemionus), kiang (E. kiang), takhi (E. przewalski), and wild yak (Bos mutus). Our results suggest striking yet indirect and unintended actions that link trophic‐level effects to markets induced by the trade for cashmere. Globalización del Mercado de Cachemira y la Declinación de Mamíferos Mayores en Asia Central  相似文献   
193.
In the vast majority of cases studied to date, rapid changes in indigenous resource management institutions and traditional ecological knowledge (TEK) have been reported with profound implications for indigenous livelihoods, biodiversity, and system resilience worldwide. In this case study, we examined how policy changes in China over the past 60 years have influenced indigenous resource management institutions designed to manage common pool pastoral systems in eastern Inner Mongolia. Based on semi-structured interviews (n = 91), focus group discussions (64 participants involved), and participant observation, we found that for over half a century rescaling efforts by the Chinese government shifted the focus to national level development planning, which led to the degradation of indigenous institutions that managed common pool pastoral systems in the region. However, we also highlight how local actors have used recent changes in government policies to revitalize traditional herding institutions. This provides a rare glimpse at the re-emergence of the commons from the bottom up.  相似文献   
194.
Coal fly ash (CFA) is dumped at a deep sea disposal site (1,500m water depth) in the eastern Mediterranean, ca. 70km off the Israeli shore. Since 1989, about one million tons of CFA were dumped at the 200km2 allocated area. Six years of monitoring at the dump-site shows that the CFA is heterogeneously distributed; there are areas where CFA covers about 1.3cm depth of the sea floor while at others no CFA is found. CFA is present as a fine powder, small aggregates and even as large blocks both in the dump-site as well as at its peripheries. Cadmium, copper and zinc concentrations in the CFA decreased as a result of the prolonged contact with sea water at in situ conditions while inconclusive changes in mercury, iron and manganese were detected. No changes were observed for lead, iron and aluminium concentrations. A controlled long term field experiment, now in progress at the site, is expected to clarify further chemical changes occurring in the CFA.  相似文献   
195.
In order to improve the sustainability of the Asian concrete industry, it is important to understand the effect of regional context considering the widely varying socio-economic conditions present in Asia. This research in Mongolia and Singapore was conducted as a continuation of previous studies in Japan, Thailand and South Korea in order to further contribute to understanding regional context, particularly geographic, climate, and economic factors. Geography and climate were found to strongly affect the means by which durability should be assured in each country, as Singapore has a tropical climate whereas Mongolia experiences a large temperature variation with extremely cold winters. The ability to access construction materials and resources was also related to geography, as Singapore, while resource poor, is an international shipping center, whereas Mongolia has abundant resources but few access routes for imports. Quality control issues in Mongolia could be understood in the context of the lower level of economic development, whereas in Singapore the high level of development has lead to an emphasis on green construction, with the government taking the lead in implementing new systems and technologies.  相似文献   
196.
A revival of interest among professional people in central and inner city residence appears to have occurred in West Germany since the late 1970s. In recent years, a selective programme of central area rehabilitation has successfully wedded public and private funding in Nürnberg, with consequent displacement of low‐income tenants. The further spread of upgrading and social change appears to have been halted in parts of the inner city designated as Urban Renewal Areas, where the federal and local authorities are apparently intent on stabilising and improving the much‐neglected housing and environmental conditions of the poorest “guestworker” communities.  相似文献   
197.
内蒙古主要畜牧气象灾害减灾对策研究   总被引:5,自引:0,他引:5  
针对内蒙古自治区草地畜牧业生产中长期存在的实际问题,从草地雪灾、暴风雪、风冷灾害、旱灾等方面讨论了气象灾害对草地畜牧业生产的影响,并提出了相应的减灾对策,为草原牧区防灾减灾决策提供科学依据。  相似文献   
198.
利用陇东1971~2000年的冰雹资料,分析了冰雹的气候特征,归纳了产生冰雹天气过程的3种主要环流背景.  相似文献   
199.
构造环境对幔源岩中稀有气体同位素比值的制约   总被引:1,自引:0,他引:1  
稀有气体是地球化学研究中有效的物源示踪剂。在广泛收集资料的基础上,通过对He、Ne、Ar同位素数据的统计分析,总结、对比了不同构造环境幔源物质中轻稀有气体同位素的组成特征。统计表明,大洋中脊玄武岩(MORB)中3He/4He=7 0~10 0Ra者约占统计样品的90%;洋岛幔源物质(OIB)的3He/4He值变化范围大,但>10 0Ra者占65%;消减带幔源岩的3He/4He值总体略低于MORB;大陆幔源岩的3He/4He值主要变化于6 0~10 0Ra间,但环太平洋大陆边缘低于MORB者普遍;大陆热点地幔流体具有类似OIB的3He/4He值分布特征。MORB与OIB的40Ar/36Ar值分布范围类似(主要范围为296~12000),但低于1000者在MORB中仅24 5%,而在OIB中约43 4%;板块俯冲区幔源岩的40Ar/36Ar值总体较低,<1000者约占67%;大陆各类地幔流体的40Ar/36Ar值普遍偏低,主要在4000以下。大陆、大洋幔源岩中20Ne/22Ne值主要介于9 8~12 5间,但<9 8者在各大陆地幔普遍存在。幔源物质的上述组成特征与大气、地壳等源区对其影响有关。我国东部幔源物质稀有气体同位素组成具有大气 地幔混合源区特征。  相似文献   
200.
内蒙古有着独特的发展有机食品所应当具备的条件和资源,本文介绍了有机食品的概念及发展情况,对内蒙古有机食品产业的发展作出展望和探讨。  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