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   780篇
  免费   6篇
  国内免费   18篇
安全科学   14篇
废物处理   8篇
环保管理   46篇
综合类   322篇
基础理论   195篇
环境理论   2篇
污染及防治   163篇
评价与监测   29篇
社会与环境   24篇
灾害及防治   1篇
  2018年   10篇
  2017年   13篇
  2016年   16篇
  2015年   17篇
  2014年   12篇
  2013年   35篇
  2012年   27篇
  2011年   33篇
  2010年   22篇
  2009年   26篇
  2008年   25篇
  2007年   27篇
  2006年   39篇
  2005年   25篇
  2004年   15篇
  2003年   21篇
  2002年   20篇
  2001年   12篇
  2000年   8篇
  1999年   27篇
  1998年   13篇
  1997年   11篇
  1996年   14篇
  1995年   7篇
  1994年   13篇
  1993年   8篇
  1991年   6篇
  1989年   7篇
  1988年   7篇
  1987年   9篇
  1985年   10篇
  1983年   8篇
  1970年   6篇
  1967年   8篇
  1966年   9篇
  1965年   10篇
  1964年   14篇
  1963年   10篇
  1962年   9篇
  1961年   8篇
  1960年   9篇
  1958年   7篇
  1957年   9篇
  1956年   7篇
  1955年   8篇
  1954年   11篇
  1953年   8篇
  1952年   5篇
  1939年   6篇
  1931年   5篇
排序方式: 共有804条查询结果,搜索用时 609 毫秒
521.
522.
523.
524.
District Swat is part of the high mountain Hindu-Kush Himalayan region of Pakistan. Documentation and analysis of land use change in this region is challenging due to very disparate accounts of the state of forest resources and limited accessible data. Such analysis is, however, important due to concerns over the degradation of forest land leading to deterioration of the protection of water catchments and exposure of highly erodible soils. Furthermore, the area is identified as hotspot for biodiversity loss. The aim of this paper is to identify geophysical and geographical factors related to land use change and model how these relationships vary across the district. For three selected zones across the elevation gradient of the district, we analyse land use change by studying land use maps for the years 1968, 1990 and 2007. In the high-altitude zone, the forest area decreased by 30.5 %, a third of which was caused by agricultural expansion. In the mid-elevation zone, agriculture expanded by 70.3 % and forests decreased by 49.7 %. In the lower altitudes, agriculture expansion was 129.9 % consuming 31.7 % of the forest area over the forty-year time period. Annual deforestation rates observed were 0.80, 1.28 and 1.86 % in high, mid and low altitudes, respectively. In the high-altitude ecosystems, accessibility (distance to nearest road and city) had no significant role in agriculture expansion; rather land use change appears significantly related to geophysical factors such as slope, aspect and altitude. In the low-elevation zone, accessibility was the factor showing the closest association with agriculture expansion and abandonment. The analysis illustrates that land use change processes vary quite considerably between different altitudinal and vegetation cover zones of the same district and that environmental constraints and stage of economic development provide important contextual information.  相似文献   
525.
Meister   总被引:2,自引:0,他引:2  
A mobile remote sensing system is presented for measuring the concentration of gaseous pollutants in ambient air and in directed effluent streams. MEISTER is based on Fourier-Transform-Infrared-Spectroscopy (FTIS), which is predestinated for a simultaneous analysis of a large number of atmospheric gases. The Kayser-Threde Double-Pendulum interferometer K300 and the Multicomponent Air Pollution Software (MAPS) of the Fraunhofer Institute of Atmospheric Environmental Research, which is based on radiative transfer modeling and least square fit procedures, enable a concentration determination under almost all meteorological conditions. CO, CO2, NO, N2O, CH4, H2O and HCl concentrations have been determined in good agreement with results from conventionalin situ sensors. NO2, SO2, NH3, HCHO and hydrocarbons have been successfully detected provided their concentrations were high enough.  相似文献   
526.
This article focuses on individual effects of the transformation from communist to capitalist structures in the system of occupational health and safety (OHS). Despite basic similarities among the communist nations the systems of OHS differed immensely. The political changes during transformation additionally contributed to varying opportunities for the development of OHS systems. Changes affecting the living and working conditions are significant and are demonstrated by the development of new work structures and work biographies. This is reflected in changed attitudes to demands and contents of work. No differences, however, were found between the employed and unemployed when asked about these issues. Conclusions for OHS in postcommunist states are drawn.  相似文献   
527.
This article deals with the special demands on occupational medicine due to the changes of work and of tasks at workplaces. Conclusions for research in occupational medicine are drawn from these processes. They are discussed on the basis on an analysis of literature from the years 1980–1998. Focus of future research in the field of occupational medicine is developed by taking international tendencies, the interdisciplinary setting of occupational medicine, and the close relations between science and practice into consideration.  相似文献   
528.
529.
530.
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