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   17457篇
  免费   79篇
  国内免费   3篇
林业   3727篇
农学   1315篇
基础科学   143篇
  3088篇
综合类   761篇
农作物   2149篇
水产渔业   1948篇
畜牧兽医   1364篇
园艺   1129篇
植物保护   1915篇
  2024年   4篇
  2023年   17篇
  2022年   15篇
  2021年   37篇
  2020年   47篇
  2019年   61篇
  2018年   2770篇
  2017年   2736篇
  2016年   1229篇
  2015年   97篇
  2014年   61篇
  2013年   73篇
  2012年   876篇
  2011年   2211篇
  2010年   2143篇
  2009年   1288篇
  2008年   1398篇
  2007年   1649篇
  2006年   96篇
  2005年   146篇
  2004年   151篇
  2003年   185篇
  2002年   100篇
  2001年   8篇
  2000年   44篇
  1999年   4篇
  1998年   4篇
  1997年   4篇
  1996年   4篇
  1995年   2篇
  1994年   2篇
  1993年   14篇
  1992年   8篇
  1990年   4篇
  1989年   7篇
  1988年   11篇
  1987年   2篇
  1986年   2篇
  1981年   2篇
  1979年   1篇
  1977年   5篇
  1975年   1篇
  1972年   2篇
  1971年   2篇
  1969年   2篇
  1968年   4篇
  1967年   1篇
  1948年   1篇
  1940年   1篇
  1930年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
Xyloglucan endotransglycosylase is an identified relaxation factor with functions of easing and extending of plant cell walls.Its activities are directly related to plant growth and elongation of organisms.Anthocephalus chinensis is a tall and fast growing evergreen tree species.We cloned the full cDNA sequence of AcEXT genes which is abundantly expressed in the cambium of A.chinensis.The sequence analysis of nucleotides and amino acids revealed the presence of a 1396 bp full cDNA sequence,including a 960 bp complete open reading frame(ORF) encoding a 320 amino acid protein.The deduced amino acid sequence of AcXET was homologous to the other known XET proteins and contained the conserved EIDFE catalytic site which was specific to all the XETs.Our data should serve as a foundation for further insight into AcXET gene molecular mechanisms during wood formation and cell wall engineering of woody plants.  相似文献   
972.

Introduction   

Wood quality is an important criterion in the selection of superior genotypes when breeding for solid wood.  相似文献   
973.

• Context   

Understanding biological processes in forests is necessary to orientate ecosystem management towards potential C sequestration. To achieve this, information is required about changes in forest biomass C pools, including the stem components (bark, sapwood and heartwood).  相似文献   
974.

Introduction   

Forest fuel management in the context of fire prevention generally induces heterogeneous spatial patterns of vegetation. However, the impact of the canopy structure on both wind flows and fire behavior is not well understood.  相似文献   
975.
976.

Introduction   

The great spatial and temporal heterogeneity of Mediterranean ecosystems can influence establishment success in woody species, whose natural regeneration occurs to a very small extent. In this work, the effect of the spatial pattern of environmental variables (light availability, soil moisture and herbaceous production) on seedling emergence, growth, survival and establishment success was examined by using a spatially explicit approach.  相似文献   
977.

Introduction  

As the major resources of Siberian larch planted in Finland will be at a harvestable age in the near future, knowledge concerning wood and fibre properties of cultivated larches is needed. The properties affect both the character of pulp and paper, as well as properties important in the structural usage.  相似文献   
978.

• Introduction   

For large trees without a continuous sequence of growth rings in their trunk, such as the African baobab (Adansonia digitata L.), the only accurate method for age determination is radiocarbon dating. As of today, this method was limited to dating samples collected from the remains of dead specimens.  相似文献   
979.

• Introduction   

Stem taper equations have been widely used for volume estimation to varied top diameter limits or for biomass calculations. However, their main drawback is that specific calibration is often necessary for each species or clone, and accounting for genetic and environmental effects is often a challenge.  相似文献   
980.

• Introduction   

Canopy gap dynamics in old-growth boreal forests is a result of tree mortality caused by insects, diseases, or meteorological phenomena. Canopy gaps improve the possibilities of natural regeneration, and concentrations of decomposed deadwood are often found in these natural openings, which provide specific habitats for many deadwood-dependent species and organisms.  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