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   41522篇
  免费   396篇
  国内免费   306篇
安全科学   1194篇
废物处理   1974篇
环保管理   5625篇
综合类   6627篇
基础理论   10933篇
环境理论   13篇
污染及防治   9856篇
评价与监测   2835篇
社会与环境   2940篇
灾害及防治   227篇
  2022年   316篇
  2021年   377篇
  2020年   230篇
  2019年   293篇
  2018年   922篇
  2017年   905篇
  2016年   1162篇
  2015年   673篇
  2014年   1009篇
  2013年   3053篇
  2012年   1379篇
  2011年   2159篇
  2010年   1623篇
  2009年   1731篇
  2008年   2110篇
  2007年   2234篇
  2006年   1503篇
  2005年   1360篇
  2004年   1306篇
  2003年   1325篇
  2002年   1276篇
  2001年   1404篇
  2000年   994篇
  1999年   636篇
  1998年   457篇
  1997年   461篇
  1996年   480篇
  1995年   567篇
  1994年   504篇
  1993年   435篇
  1992年   458篇
  1991年   467篇
  1990年   415篇
  1989年   415篇
  1988年   399篇
  1987年   336篇
  1986年   308篇
  1985年   322篇
  1984年   376篇
  1983年   358篇
  1982年   366篇
  1981年   297篇
  1980年   245篇
  1979年   274篇
  1978年   235篇
  1977年   202篇
  1975年   212篇
  1974年   213篇
  1973年   222篇
  1972年   192篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
We present a case of ultrasonographic prenatal diagnosis at 24 weeks of femur—fibula—ulna (FFU) complex. To our knowledge, this is the first report of an early prenatal diagnosis of FFU.  相似文献   
82.
83.
Observations of air temperature changes in a steppe marmot burrow were performed from late July to mid-October. Until early September, temperature in the burrow remained relatively constant, but then it began to decrease rapidly. This occurred after air temperature above the ground became equal to the temperature in the burrow. Supposedly, it is in this particular period that marmots begin to plug the entrance to the burrow with earth, thus reducing heat exchange between the increasingly cold aboveground air and the air in the burrow.  相似文献   
84.
In the periods of summer and autumn bloom of the Stephanodiscus hantzschii Crun. in recreational water bodies, studies on the vertical distribution of chlorophyll a, its contents per unit biomass, efficiency in using photosynthetically active radiation (EPhAR), and assimilative activity of microalgae were performed. The results confirmed the existence of two ecophysiological forms of St. hantzschii and provided evidence that both forms are typically autotrophic and can efficiently use low-intensity PhAR for photosynthesis.  相似文献   
85.
86.
87.
Benthic organisms can significantly alter the physical properties of marine sediments, but it has hitherto been difficult to assess and quantify the effects of bioturbation. In situ geophysical techniques offer new methods for measuring these effects: measurement of acoustic shear-wave velocity and electrical resistivity allows nondestructive assessment of the properties of the grain framework and pore-fluid matrix, respectively, of the seabed sediment. The influence of burrowing invertebrates on the structural properties of sandy sediments at intertidal locations on the coast of Wales (UK) was investigated during the periol 1986–1987 using these techniques. Three species (Arenicola marina, Corophium arenarium and Lanice conchilega) were selected on the basis of their contrasting styles of burrow construction. All three species produced measurable and significant, although different, changes in bed properties. They modified shear-wave propagation through the bed by changing bed rigidity: while A. marina and C. arenarium decreased rigidity by creating open burrows, L. conchilega increased rigidity by building shell-lined tubes. All produced a decrease in electrical resistivity by altering porosity and/or tortuosity, which implies an increase in permeability; these changes were attributable not only to the presence of the burrows but also to modification of the between-burrow sediment texture and bed properties.  相似文献   
88.
89.
90.
New experimental data on biological productivity of plant communities in oligotrophic and mesotrophic bogs of the middle taiga subzone over the past five years are presented. The relationship between net primary production and the stock of live phytomass is estimated. The stock of necromass in oligotrophic bog ecosystems increases from west to east, while the stock of live phytomass and net primary production decrease.  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