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   268376篇
  免费   4437篇
  国内免费   3493篇
测绘学   7115篇
大气科学   19666篇
地球物理   56268篇
地质学   93779篇
海洋学   22320篇
天文学   57556篇
综合类   1060篇
自然地理   18542篇
  2021年   2297篇
  2020年   2673篇
  2019年   2906篇
  2018年   4537篇
  2017年   4163篇
  2016年   6300篇
  2015年   4311篇
  2014年   7036篇
  2013年   14387篇
  2012年   6922篇
  2011年   8703篇
  2010年   7713篇
  2009年   10309篇
  2008年   9101篇
  2007年   8760篇
  2006年   9811篇
  2005年   8026篇
  2004年   7878篇
  2003年   7376篇
  2002年   6900篇
  2001年   6127篇
  2000年   6063篇
  1999年   5257篇
  1998年   5286篇
  1997年   5086篇
  1996年   4715篇
  1995年   4460篇
  1994年   4151篇
  1993年   3891篇
  1992年   3665篇
  1991年   3619篇
  1990年   3784篇
  1989年   3539篇
  1988年   3318篇
  1987年   3871篇
  1986年   3448篇
  1985年   4261篇
  1984年   4763篇
  1983年   4447篇
  1982年   4339篇
  1981年   3941篇
  1980年   3667篇
  1979年   3523篇
  1978年   3500篇
  1977年   3299篇
  1976年   3071篇
  1975年   2978篇
  1974年   2935篇
  1973年   3100篇
  1972年   2035篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
921.
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   
922.
923.
924.
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   
925.
— 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   
926.
927.
928.
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   
929.
930.
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