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   1148篇
  免费   50篇
  国内免费   1篇
林业   67篇
农学   35篇
基础科学   7篇
  118篇
综合类   319篇
农作物   83篇
水产渔业   31篇
畜牧兽医   453篇
园艺   16篇
植物保护   70篇
  2022年   10篇
  2021年   9篇
  2020年   12篇
  2019年   18篇
  2018年   15篇
  2017年   16篇
  2016年   23篇
  2015年   23篇
  2014年   21篇
  2013年   34篇
  2012年   38篇
  2011年   40篇
  2010年   29篇
  2009年   15篇
  2008年   47篇
  2007年   39篇
  2006年   29篇
  2005年   35篇
  2004年   33篇
  2003年   34篇
  2002年   31篇
  2001年   21篇
  2000年   33篇
  1999年   19篇
  1998年   11篇
  1997年   12篇
  1992年   30篇
  1991年   21篇
  1990年   33篇
  1989年   25篇
  1988年   19篇
  1987年   12篇
  1986年   21篇
  1985年   17篇
  1984年   13篇
  1983年   16篇
  1982年   14篇
  1981年   9篇
  1979年   12篇
  1976年   11篇
  1975年   10篇
  1974年   12篇
  1973年   10篇
  1972年   9篇
  1971年   15篇
  1970年   19篇
  1969年   29篇
  1968年   38篇
  1967年   35篇
  1966年   21篇
排序方式: 共有1199条查询结果,搜索用时 15 毫秒
41.
42.
43.
44.
Summary Choong's (1963) data for isothermal sorption of water vapor by wood are used to compute pressures, chemical potentials, and entropies of water in the wood specimens of his nonisothermal mass equilibrium experiments. Entropies of both the bound water and water vapor were reasonably constant. A balance existed between thermal diffusion and mass diffusion, as indicated by gradients in temperature and chemical potential. This balance also is suggested by opposing gradients in spreading pressure and vapor pressure. Equal chemical potentials showed that the vapor and bound water were in equilibrium. The model proposed by Siau (1980) for nonisothermal diffusion is consistent with these results. Expressions are given for the two unknown parameters in this model: moisture conductivity and heat of transfer. The constant entropy of water vapor is used to show that the heat of transfer exceeds the activation energy for bound water diffusion by about 25 percent.The author wishes to thank Dr. Christen Skaar for his helpful comments during preparation of this paper for publication  相似文献   
45.
46.
47.
48.
49.
50.
1. Modern records of 165 species of wetland beetle (Haliplidae, Hygrobiidae, Noteridae, Dytiscidae, Gyrinidae, Georissidae, Hydrochidae, Helophoridae, Hydrophilidae, Hydraenidae, Scirtidae, Dryopidae, Elmidae, Chrysomelidae, Curculionidae) were assembled for analysis. 2. Two hundred and eighty nine modern lists of seven or more species of water beetle from sites in Ireland were subjected to multivariate analysis. 3. Ten assemblage types were identified using TWINSPAN. Habitats typical of these assemblages are: A. deep rivers; B. rivers with riffles; C. puddles; D. canals and lakes with rich vegetation; E. ponds and ditches; F. turloughs; G. natural, minerotrophic fens; H. base-flushed cutover bogs; I. peat bogs; J. montane flushes. The distribution of these types is discussed. 4. Ordination of site data by DECORANA indicated that the important environmental variables dictating water beetle assemblage type in Ireland were: flow; water permanence; exposure; type of substratum. Acidity could not be isolated as a determinant, except within the analysis of assemblage types conducted using TWINSPAN. DECORANA isolated one brackish site as an outlier but salinity was not otherwise a major factor, probably because few brackish sites were included in the analysis. 5. The number of modern records for each species was used to provide a provisional set of species-quality scores. A simple rationale was devised to weight these scores in favour of relict species and against elusive species, species with short-lived adults and species primarily associated with man-made habitats. 6. The average species-quality score per site and the number of species recorded were used to rank sites within each TWINSPAN end-group. The most diverse sites with the highest quality were some turloughs, rich fens and base-flushed peat cutting complexes. Some montane lakes and flushes with relatively few species had high species-quality scores.  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