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   99224篇
  免费   1045篇
  国内免费   813篇
  2021年   113篇
  2020年   55篇
  2019年   59篇
  2018年   11899篇
  2017年   10719篇
  2016年   7555篇
  2015年   752篇
  2014年   471篇
  2013年   551篇
  2012年   4482篇
  2011年   13082篇
  2010年   12177篇
  2009年   8377篇
  2008年   9984篇
  2007年   11594篇
  2006年   509篇
  2005年   707篇
  2004年   1182篇
  2003年   1202篇
  2002年   961篇
  2001年   435篇
  2000年   367篇
  1999年   206篇
  1998年   88篇
  1997年   102篇
  1996年   96篇
  1995年   85篇
  1994年   72篇
  1993年   107篇
  1992年   154篇
  1991年   154篇
  1990年   129篇
  1989年   119篇
  1988年   134篇
  1987年   112篇
  1986年   102篇
  1985年   93篇
  1984年   97篇
  1983年   83篇
  1982年   80篇
  1981年   51篇
  1979年   77篇
  1978年   61篇
  1977年   68篇
  1976年   57篇
  1975年   88篇
  1974年   62篇
  1973年   61篇
  1972年   303篇
  1971年   331篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
201.

Background  

Plants trigger and tailor defense responses after perception of the oral secretions (OS) of attacking specialist lepidopteran larvae. Fatty acid-amino acid conjugates (FACs) in the OS of the Manduca sexta larvae are necessary and sufficient to elicit the herbivory-specific responses in Nicotiana attenuata, an annual wild tobacco species. How FACs are perceived and activate signal transduction mechanisms is unknown.  相似文献   
202.
The present study sought to determine which of the common Poaceae species in the study area contribute most to the Poaceae pollen season curve, and to determine the phenological behaviour of the species studied. The different floral phenophases in thirty-three Poaceae species common in and around the city of Córdoba (SW Iberian Peninsula) were checked periodically over the period 2004–2006. Results showed that longer phenological ranges were recorded in the coolest and wettest year, and shorter ranges in the warmest and driest year. Moreover, ranges varied as a function of altitude: populations in lower-lying areas flowered earlier than those at higher altitudes. The results, taken in conjunction with the findings of preliminary research into potential pollen production, showed that probably only four of the Poaceae species studied—Dactylis glomerata, Lolium rigidum, Trisetaria panicea and Vulpia geniculata—were major contributors to the Poaceae airborne pollen curve.  相似文献   
203.
204.
205.

Background  

The extended light-harvesting complex (LHC) protein superfamily is a centerpiece of eukaryotic photosynthesis, comprising the LHC family and several families involved in photoprotection, like the LHC-like and the photosystem II subunit S (PSBS). The evolution of this complex superfamily has long remained elusive, partially due to previously missing families.  相似文献   
206.
207.
208.
A male sterile line was isolated in marigold (Tagetes erecta L.) and cytological analysis determined this to be a novel genic male sterility trait (Tems). Through the use of amplified fragment length polymorphisms (AFLPs) and bulked segregant analysis (BSA), tightly linked markers of Tems were identified with a view towards a map-based cloning strategy. It was found that spontaneous homeotic conversion of floral organs was the underlying cause of the male sterility in this marigold line. Thus, petals of male sterile plants resembled sepal-like structures and the stamens were partially converted to styles, although without the full characteristics or function of the true style organs. We have constructed a fine marker-based map for the Tems gene. This is intended to provide a tool for marker assisted selection (MAS) strategies in hybrid breeding and map-based cloning strategies for the male sterility locus. We discuss the significance of this spontaneously derived genic male sterility trait relating to the homeotic conversion of floral organs in marigold.  相似文献   
209.
The role of CCN proteins in vivo is only just becoming understood. A prototypical member of the CCN family, CCN3 suppresses proliferation. In a study in press, Shimoyama and colleagues show that mice lacking CCN3 have a hyperproliferative response to vascular injury. These data, along with other recent observations, suggest that CCN3 may represent a novel therapy for hyperproliferative diseases.  相似文献   
210.
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