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   709458篇
  免费   76823篇
  国内免费   323篇
  786604篇
  2018年   6169篇
  2016年   8259篇
  2015年   11414篇
  2014年   13259篇
  2013年   19482篇
  2012年   21279篇
  2011年   21678篇
  2010年   14764篇
  2009年   13393篇
  2008年   19190篇
  2007年   20136篇
  2006年   18819篇
  2005年   18111篇
  2004年   18146篇
  2003年   17540篇
  2002年   17258篇
  2001年   29109篇
  2000年   29117篇
  1999年   23543篇
  1998年   8698篇
  1997年   8962篇
  1996年   8544篇
  1995年   8211篇
  1994年   8033篇
  1993年   7951篇
  1992年   20537篇
  1991年   19846篇
  1990年   19822篇
  1989年   19350篇
  1988年   18207篇
  1987年   17191篇
  1986年   15975篇
  1985年   16545篇
  1984年   13623篇
  1983年   11835篇
  1982年   9253篇
  1981年   8222篇
  1980年   7795篇
  1979年   13319篇
  1978年   10291篇
  1977年   9613篇
  1976年   9065篇
  1975年   9801篇
  1974年   10777篇
  1973年   10692篇
  1972年   9834篇
  1971年   9052篇
  1970年   7719篇
  1969年   7670篇
  1968年   7017篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Data are presented which indicate a possible action of alpha-fetoprotein (AFP) on female germinal cells. The in vitro maturation of mature mice oocytes was significantly inhibited when mouse AFP replaced albumin in the culture medium. In addition, the degenerative aspect of oocytes cultured with AFP seemed to indicate that this me?otic inhibition was caused by a premature degeneration of oocytes rather than by a blockage at a specific stage of maturation. Thus AFP, perhaps through its ligands, may play a role in the reduction of germinal cells during fetal and immediate post-natal life rather than in the arrest of me?osis at the diplotene stage.  相似文献   
992.
993.
994.
995.
996.
Vetches (Vicia spp .) are important forage legumes in the MiddleEast and Mediterranean regions. Most vetches are highly susceptibleto the root holoparasites Orobanche aegyptiaca and O. crenata,suffering severe quality and yield losses. However, purple vetch(V. atropurpurea) has shown good resistance to Orobanche. Microscopicstudies were performed to reveal anatomical differences of host-parasiteinteractions between susceptible and resistant vetch. SusceptibleV. sativa‘Yovel’ and resistant V. atropupurea‘Popany’were grown in association with O. aegyptiaca seeds, on glassmicrofibre sheets in a polyethylene-bag system. Whole root observationsusing stereoscopic microscopy detected necrotic lesions surroundingthe attachments of Orobanche radicles on resistant vetch roots.Hand-cut sections examined under the light microscope revealedthat in both susceptible and resistant vetch genotypes the Orobancheseeds germinated, attached and penetrated the host root epidermisand cortex. A reddish-brown secretion was observed in the apoplastat the interface between the parasite haustorium and the hosttissues, including the cell walls of the resistant vetch xylemvessels. Fixed and embedded sections observed under the lightmicroscope showed that in the susceptible genotype the parasitehaustorium penetrated through the endodermis into the host vascularcylinder, successfully forming a continuum with host vascularvessels. However, in the resistant genotype, the parasite haustoriumwas blocked at the root endodermis layer. The blockage was coupledwith secretion of unidentified material, thus preventing theparasite from establishing. These findings indicate that mechanicaland possibly chemical barriers are responsible for the hostdefence mechanism(s) conferring resistance of V. atropurpureato O. aegyptiaca. Copyright 2000 Annals of Botany Company Broomrape, Vicia atropurpurea, Vicia sativa, parasitic plants, plant resistance, tissue sections.  相似文献   
997.
998.
999.
Craniofacial fibrous dysplasia, a skeletal disorder most often affecting the mandible or maxilla, can cause a variety of complications. Nasal obstruction secondary to this unusual disorder presents a diagnostic and therapeutic challenge. The nasal obstruction in this case is due to expansion of fibrous lesions in adjacent bones as well as direct involvement of the turbinates with fibrous dysplasia. We describe the surgical correction of nasal obstruction in this unique setting and present a brief update of this intriguing disorder.  相似文献   
1000.
In addition to the immunostimulating activity, bone marrow mediators, myelopeptides (MP) show the dose-dependent effect on the development of pain sensitivity in mice. When injected in nanogram amounts, MP induce hyperalgesia and 3-9 fold higher production of antibodies against SREC. When injected in milligram amounts, they exhibit hypoalgesic effect and no influence on antibody production. Immunostimulating effect in MP (mol, mass less than 1 KD, fraction 3) is accompanied with hypoalgesia. Bone marrow factors of mol. masses 40-150 KD (fraction 1) eluted at Sephadex G-25 gel-filtration before MP enhance the pain sensitivity tHreshold and show a potent immunodepressive effect. Thus the bone marrow factors are capable of exhibiting the opposite effects on the immune system in the pain control system that evidences the tight interrelation between these systems.  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