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   1404篇
  免费   135篇
  国内免费   411篇
安全科学   133篇
废物处理   47篇
环保管理   187篇
综合类   871篇
基础理论   200篇
污染及防治   216篇
评价与监测   200篇
社会与环境   65篇
灾害及防治   31篇
  2024年   16篇
  2023年   25篇
  2022年   62篇
  2021年   58篇
  2020年   75篇
  2019年   59篇
  2018年   78篇
  2017年   81篇
  2016年   87篇
  2015年   80篇
  2014年   94篇
  2013年   151篇
  2012年   109篇
  2011年   127篇
  2010年   69篇
  2009年   98篇
  2008年   69篇
  2007年   94篇
  2006年   76篇
  2005年   64篇
  2004年   43篇
  2003年   46篇
  2002年   44篇
  2001年   31篇
  2000年   31篇
  1999年   22篇
  1998年   25篇
  1997年   20篇
  1996年   21篇
  1995年   20篇
  1994年   5篇
  1993年   11篇
  1992年   9篇
  1991年   9篇
  1990年   5篇
  1989年   6篇
  1988年   6篇
  1987年   4篇
  1985年   1篇
  1984年   1篇
  1983年   2篇
  1982年   3篇
  1981年   3篇
  1980年   3篇
  1979年   2篇
  1978年   1篇
  1975年   2篇
  1972年   1篇
  1971年   1篇
排序方式: 共有1950条查询结果,搜索用时 328 毫秒
401.
安徽省地下水观测及群测群防管理信息系统   总被引:1,自引:0,他引:1  
建立安徽省地下水观测及群测群防网管理信息系统,有利于实现市县地震监测预报工作信息化、规范化管理。本文系统地介绍了安徽省地下水观测及群测群防管理信息系统的主要内容、研制思路和研究成果。该系统的完成对推进安徽省地下水观测及群测群防网管理乃至全省地震监测预报信息管理将发挥积极作用。  相似文献   
402.
对现代科学技术所出现的“生态化”现象进行了初步探讨。首先,对生态学涵义的扩展和生态化研究方法进行了研究,认为其涵义已从生态学的生物学含义发展到现代生态学的新涵义,其方法就是研究在科学技术中的“对象”与“环境”的关系问题;在此基础上,对科学技术研究目标作了生态化表述,即要建设生态-经济-社会优质复合群;然后,对科学技术所出现的生态化理论与方法进行了初步研究,并对建设普遍优质的生态-经济-社会复合群理论及其应用进行了分析;最后,对生态化的研究方法进行了总结。  相似文献   
403.
城市垃圾焚烧发电系统热平衡分析与优化方案   总被引:2,自引:0,他引:2  
以城市垃圾焚烧过程的热工计算为基础,深入研究了热平衡分析与能量回收之间的关系。针对国内在垃圾焚烧发电领域存在的主要问题,提出了传统工艺的优化方案,并对我国城市垃圾焚烧发电的能量回收利用前景进行了预测分析。  相似文献   
404.
城市绿化树木碳氧平衡效应研究   总被引:21,自引:0,他引:21  
本文通过实测广州市内几种常见绿化树木的光合强度和呼吸强度以及叶面积指数,计算城市绿地吸收二氧化碳和释放氧气的能力。得出各种树木的叶片光合强度。由于各树木的叶面积指数不同,绿地的吸碳放氧能力也不同。据此,从人类呼吸的基本需要考虑,探讨了城市地定额指标问题。  相似文献   
405.
Do female roe deer in good condition produce more sons than daughters   总被引:2,自引:0,他引:2  
In polygynous roe deer Capreolus capreolus, males are only slightly heavier than females and the overall sex ratio at birth is close to unity. We studied offspring sex ratio and litter size (range 1–4, n = 74) of culled females, in utero, which provided an opportunity to examine responses of sex ratio to maternal condition. Male embryos were heavier than their sisters, and male fawns (9 months old) heavier than female fawns, suggesting a higher growth rate in males. There was no evidence for differential mortality between the sexes from birth to 9 months old. Heavier adult females produced larger embryos than lighter, or primiparous females. The overall sex ratio of embryos did not differ from unity, but adult does had more male embryos (55%) than primiparous does (32%), and the proportion of male embryos in a litter increased with the mother's body mass. Litter size also tended to increase with maternal age and body mass. We argue that this pattern reflects adaptive variation in offspring sex ratio.  相似文献   
406.
根据城市生活垃圾的特点和性质,利用物料平衡和热力学原理进行好氧堆肥实验装置的设计,并对堆肥发酵仓容积的确定和配套辅助设备进行了研究,得出当堆肥装置直径小于225m时,需采取保温措施。通过强制通风静态仓式堆肥小试实验进行的城市生活垃圾堆肥结果表明,通过30℃及以上的水浴加热,可实现固体废物的堆肥化。  相似文献   
407.
GOAL, SCOPE AND BACKGROUND: Air pollution has been of a major problem in the Pearl River Delta of south China, particularly during the last two decades. Emissions of air pollutants from industries have already led to damages in natural communities and environments in a wide range of the Delta area. Leaf parameters such as chlorophyll fluorescence, leaf area (LA), dry weight (DW) and leaf mass per area (LMA) had once been used as specific indexes of environmental stress. This study aims to determine in situ if the daily variation of chlorophyll fluorescence and other ecophysiological parameters in five seedlings of three woody species, Ilex rotunda, Ficus microcarpa and Machilus chinensis, could be used alone or in combination with other measurements for sensitivity indexes to make diagnoses under air pollution stress and, hence, to choose the correct tree species for urban afforestation in the Delta area. METHODS: Five seedlings of each species were transplanted in pot containers after their acclimation under shadowing conditions. Chlorophyll fluorescence measurements were made in situ by a portable fluorometer (OS-30, Opti-sciences, U.S.A). Ten random samples of leaves were picked from each species for LA measurements by area-meter (CI-203, CID, Inc., U.S.A). DW was determined after the leaf samples were dried to a constant weight at 65 degrees C. LMA was calculated as the ratio of DW/LA. Leaf N content was analyzed according to the Kjeldhal method, and the extraction of pigments was carried out according Lin et al. RESULTS AND DISCUSSION: The daily mean Fv/Fm (Fv is the variable fluorescence and Fm is the maximum fluorescence) analysis showed that Ilex rotunda and Ficus microcarpa were more highly resistant to pollution stress, followed by Machilus chinensis, implying that the efficiency of photosystem II in I. rotunda was less affected by air pollutants than the other two species. Little difference in daily change of Fv/Fm in I. rotunda between the polluted and the clean site was also observed. However, a relatively large variation of Fv/Fm appeared in the other two species, particularly in M. chinensis, suggesting that they were more sensitive to air pollutants than I. rotunda. The mean LA was reduced for all species growing at the polluted site. The mean LMA for all species exceeded the sclerophylly threshold given by Cowling and Campbell and increased for those under pollution stress, which could be explained as one of the acclimation strategies for plants to air pollution stress. Little difference in leaf chlorophyll content was observed in F. microcarpa and M. chinensis, while remarkable differences were found in I. rotunda growing at the polluted and the clean site. Content of leaf carotenoids was largely reduced in I. rotunda growing at the polluted site, but increased in F. microcarpa and M. chinensis, compared with plants growing at the clean site. Plants growing at the clean site had a lower leaf N content than those growing at the polluted site. In addition, species with a higher resistance to pollution stress showed less difference in leaf N content than those sensitive species. CONCLUSION: Based on Fv/Fm measurements of the three woody species, I. rotunda showed the highest resistance to air pollutants from ceramic industries, followed by F. microcarpa. M. chinensis was the most sensitive species to air pollution, had lowest capacities to cope with the air pollution stress, which was consistent with visual injury symptoms observed in the crown profiles of plants at the polluted site. Fv/Fm, LAM, LA, leaf pigments and N content could be used alone or in combination to diagnose the extent of the physiological injury. The ratio of Fv/Fm, however, was the best and most effective parameter. RECOMMENDATION AND OUTLOOK: Tree species which have higher air-pollutant resistance, as diagnosed by such ecophysiological parameters, should be considered first and planted widely for urban afforestation or forest regeneration in areas where the forest was seriously degraded or forest health was markedly effected by the same kind of air pollutants.  相似文献   
408.
In sexually dimorphic ungulates, males generally spend less time foraging than females, possibly because of difference in body mass or because of the energetic requirements of lactation. The relationship between body size and foraging time has received little attention at the intra-specific level, because few studies have documented activity budgets for individuals of known size. Bighorn rams are a good model to explore how body mass affects foraging time, because they range in mass from 55 to 140 kg. We examined how the foraging time of bighorn rams varied according to individual characteristics. We observed rams in a marked population and constructed time budgets during the 3 months preceding the rut. We determined ram social rank based on agonistic encounters and collected fecal samples to count lungworm larvae. Time spent foraging was negatively correlated with body mass. After accounting for age differences, larger rams spent less time foraging and more time lying than smaller rams. Among rams aged 6–12 years, dominants spent less time feeding than subordinates, while fecal output of lungworm larvae was negatively correlated with foraging time for rams of all ages. Body mass accounts for much of the individual variation in foraging time, suggesting that sexual dimorphism is important in explaining differences in feeding time between males and females.Communicated by P. Heeb  相似文献   
409.
运用位移监控信息、土体平衡原理、护壁桩支撑设计原理指导深基坑支护适应基坑深度变大的难题,具有施工方便、经济、安全的、工期短等特点,为在闹市区深基坑支护施工提供了经验.图1,表1,参7.  相似文献   
410.
西洞庭湖自然保护区鸟类资源调查   总被引:3,自引:0,他引:3  
为更好地调查了解西洞庭湖自然保护区的鸟类资源,保护和维持生态平衡,2003—2005年我们对西洞庭湖自然保护区的鸟类资源进行了观察和动态监测,共观察到和鉴定出湿地鸟类217种,隶属于15目58科.本文具体地报道了2003—2005年的鸟类资源调查和动态监测结果,鸟类资源所面临的威胁及其保护措施.  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