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   257545篇
  免费   4328篇
  国内免费   3372篇
测绘学   6864篇
大气科学   19054篇
地球物理   53797篇
地质学   89062篇
海洋学   21375篇
天文学   56224篇
综合类   1001篇
自然地理   17868篇
  2021年   2250篇
  2020年   2593篇
  2019年   2854篇
  2018年   3419篇
  2017年   3109篇
  2016年   5662篇
  2015年   4204篇
  2014年   6908篇
  2013年   14219篇
  2012年   6467篇
  2011年   7747篇
  2010年   6786篇
  2009年   9445篇
  2008年   8237篇
  2007年   7694篇
  2006年   9634篇
  2005年   7676篇
  2004年   7603篇
  2003年   7100篇
  2002年   6712篇
  2001年   5995篇
  2000年   5941篇
  1999年   5206篇
  1998年   5221篇
  1997年   5026篇
  1996年   4677篇
  1995年   4413篇
  1994年   4103篇
  1993年   3853篇
  1992年   3629篇
  1991年   3587篇
  1990年   3761篇
  1989年   3507篇
  1988年   3296篇
  1987年   3845篇
  1986年   3405篇
  1985年   4219篇
  1984年   4729篇
  1983年   4406篇
  1982年   4308篇
  1981年   3923篇
  1980年   3632篇
  1979年   3503篇
  1978年   3481篇
  1977年   3279篇
  1976年   3040篇
  1975年   2955篇
  1974年   2913篇
  1973年   3081篇
  1972年   2022篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
The aim of this study is to assess the Iberian populations of Forsskaolea tenacissima L. according to its biogeographical interest, habitat, geographical range and conservation status. Results point out that they are restricted to gravel wadis of Tabernas Desert (SE Spain), are scarcely included in protected areas and represent historically isolated populations with relict behaviour. We also describe a new association, Senecioni-Forsskaoleetum tenacissimae. Conservation status of species is cause for concern and two conservation actions must be carried out. Firstly, protected areas should house Forsskaolea populations and secondly, phytosociological characterization of a community allows inventorying its habitat and directing conservation efforts to community level.  相似文献   
932.
933.
934.
A zoobenthos submodel is included in an ecosystem model. The new model is used to assess the role of zoobenthos in the phosphorus exchange at the water–bed interface, in particular, the phosphorus cycle in the water body ecosystem is described more accurately. The calculated zoobenthos distribution over the bed of a lake can be used in modeling the lake ichthyocenoses.  相似文献   
935.
— Brunei Darussalam experienced a severe haze episode between the beginning of February and the end of April 1998 due mainly to local peat and forest fires in Brunei and in neighbouring Sabah and Sarawak. The extensive research studies of the haze carried out in Brunei are outlined together with selected results. Particulate matter (PM10) was the only significant criteria pollutant and it exceeded WHO guidelines and accepted air quality standards on most days during the haze episode. Gaseous criteria pollutants (CO, SO2, NO2, O3) were generally well below WHO guidelines and at these concentrations they are expected to have no significant health or environmental effects. Measurements of volatile organic compounds (VOCs) revealed the presence of benzene, toluene, ethylbenzene, and xylenes (BTEX), aldehydes, phenol, and polynuclear aromatic hydrocarbons (PAHs). Personal exposure monitoring of PM10 revealed significant differences in exposure patterns between different individuals depending on the location, time and activity. Data on outpatient visits showed an increase for some illnesses (e.g., acute respiratory infection) during the months of haze. No significant impacts of haze on rainwater acidity or deposition were noted. Emission factors for some volatile compounds were determined in combustion experiments in which peat was burned at temperatures typical of smouldering.  相似文献   
936.
937.
938.
Relationships of mineralized microbiota with the content of polycyclic aromatic hydrocarbons in hydrothermal systems are considered. It has been established that the mineralized microbiota can serve as an indicator of hydrothermal hydrocarbon flows in present-day and ancient deposits.  相似文献   
939.
940.
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