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   5908篇
  免费   29篇
  国内免费   31篇
安全科学   143篇
废物处理   325篇
环保管理   494篇
综合类   866篇
基础理论   1426篇
环境理论   2篇
污染及防治   1496篇
评价与监测   464篇
社会与环境   724篇
灾害及防治   28篇
  2023年   50篇
  2022年   102篇
  2021年   76篇
  2020年   33篇
  2019年   50篇
  2018年   85篇
  2017年   102篇
  2016年   121篇
  2015年   79篇
  2014年   171篇
  2013年   474篇
  2012年   193篇
  2011年   260篇
  2010年   232篇
  2009年   234篇
  2008年   273篇
  2007年   270篇
  2006年   257篇
  2005年   230篇
  2004年   201篇
  2003年   222篇
  2002年   184篇
  2001年   258篇
  2000年   161篇
  1999年   104篇
  1998年   45篇
  1997年   61篇
  1996年   56篇
  1995年   61篇
  1994年   67篇
  1993年   59篇
  1992年   60篇
  1991年   62篇
  1990年   67篇
  1989年   53篇
  1988年   58篇
  1987年   56篇
  1986年   55篇
  1985年   41篇
  1984年   49篇
  1983年   48篇
  1982年   50篇
  1980年   32篇
  1979年   35篇
  1978年   29篇
  1977年   29篇
  1976年   29篇
  1974年   31篇
  1973年   31篇
  1972年   29篇
排序方式: 共有5968条查询结果,搜索用时 218 毫秒
81.
The objective of this work was to isolate cellulose nanocrystal (CNC) from oil palm fronds (Elaeis guineensis) and its subsequent characterization. Isolation involves sodium hydroxide/anthraquinone pulping with mechanical refining followed by total chlorine free bleaching (includes oxygen delignification, hydrogen peroxide oxidation and peracetic acid treatment) before acid hydrolysis. Bleaching significantly decreased kappa number and increased α-cellulose percentage of fibers as confirmed by Technical Association of the Pulp and Paper Industry standards. Transmission electron microscopy (TEM), X-ray diffraction, Fourier transform infrared spectroscopy and thermogravimetric analysis revealed that acid hydrolysis along with bleaching improved crystallinity index and thermal stability of the extracted nanocrystals. It was observed that CNC maintained its cellulose 1 polymorph despite hydrolysis treatment. Mean diameter as observed by TEM and average fiber aspect ratio of obtained CNC was 7.44 ± 0.17 nm and 16.53 ± 3.52, respectively making it suitable as a reinforcing material for nanocomposite.  相似文献   
82.
The structure of bumblebee communities has been studied in some ecosystems of Kunashir Island and Southern Sakhalin. The island taxocenes include five to eight bumblebee species. Bombus hypnorum is dominant in the majority of habitats. In geothermal areas near hot springs on Kunashir, the families of this species develop more rapidly than in areas without geothermal heating.  相似文献   
83.
Experiments have been performed to evaluate the impact of weak permanent horizontal magnetic field of about 400 A/m on seed formation in the main magnetic orientation types of radish, the north-south (NS) and west-east (WE) types. The results show that external magnetic field exposure retards plant progression through all stages of ontogeny but does not alter the ratio of NS and WE types. Under its effect, the numbers of pods and seeds and seed weight decrease in the NS-type but increase in the WS-type plants. Therefore, external magnetic field acts as an ecological factor that differentiates the responses of radish plants depending on the type of their magnetic orientation. Differences in the sensitivity of plants to magnetic field exposure are explained by specific features of their physiological status.  相似文献   
84.
The open collaborative philosophy employed in the success of open source (OS) software can be applied to hardware design. Specifically, the development of OS appropriate technologies (OSAT) can improve sustainable development efforts worldwide. Yet, widespread OSAT use is far from ubiquitous. Given that lack of communication, access to information and poor collaboration are among the largest barriers to a more effective OSAT dissemination, this paper explores opportunities to overcome such obstacles using four techniques: (1) collaborative online platforms, (2) crowd-sourcing, (3) the concept of knowledge commons, and (4) enabled educational institutions through service learning and applied research. The results are analyzed, and conclusions are drawn that outline paths to higher multiuser collaboration for OSAT deployment.  相似文献   
85.
It has been shown that the growth of technogenic dust pollution is accompanied by the accumulation of heavy metals in soil and plant phytomass, compared to the control, and that the morphometric and reproductive characteristics of Matricaria chamomila are most sensitive to the impact of these pollutants. The response of plants is manifested in increased variation in morphological characters, mobilization of compensatory protective biochemical mechanisms, and production of more viable seed progeny.  相似文献   
86.
87.
Microcalorimetric, gasometric, and nuclear magnetic resonance (NMR) methods have been used to evaluate heat production, gas exchange, and root membrane permeability in dandelion of different morphological forms from populations exposed to different levels of air pollution. The results show that these forms differ in the level of energy metabolism and that the form with a higher metabolic level (T. off. f. dahlstedtii) is more tolerant of air pollution with motor vehicle exhausts.  相似文献   
88.
Intrapopulation diversity and correlations of 30 volatile compounds in needles have been studied in Scots pine populations of southern Siberia. Significant differences between populations have been revealed in the correlation pattern of relative terpenoid contents in needle samples. Stable combinations of closely associated mono- and sesquiterpenes and specific features of the general pattern of correlations between relevant characters have been determined.  相似文献   
89.
Behavioral Ecology and Sociobiology - ᅟMales of fiddler crabs (genus: Uca) construct courtship structures using mud or sand to attract mate-searching females for underground mating. A sensory...  相似文献   
90.
Regional Environmental Change - Increased dieback and mortality of “dark needle conifer” (DNC) stands (composed of fir (Abies sibirica), Siberian pine (Pinus sibirica) and spruce (Picea...  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