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   88918篇
  免费   7557篇
  国内免费   49篇
  2022年   546篇
  2021年   1152篇
  2020年   699篇
  2019年   885篇
  2018年   1106篇
  2017年   1023篇
  2016年   1740篇
  2015年   2899篇
  2014年   3255篇
  2013年   4468篇
  2012年   5460篇
  2011年   5613篇
  2010年   3696篇
  2009年   3343篇
  2008年   4945篇
  2007年   5091篇
  2006年   4819篇
  2005年   4762篇
  2004年   4873篇
  2003年   4414篇
  2002年   4367篇
  2001年   1005篇
  2000年   693篇
  1999年   1018篇
  1998年   1344篇
  1997年   967篇
  1996年   895篇
  1995年   849篇
  1994年   822篇
  1993年   783篇
  1992年   714篇
  1991年   664篇
  1990年   649篇
  1989年   671篇
  1988年   595篇
  1987年   578篇
  1986年   511篇
  1985年   664篇
  1984年   810篇
  1983年   709篇
  1982年   851篇
  1981年   884篇
  1980年   803篇
  1979年   548篇
  1978年   607篇
  1977年   570篇
  1976年   573篇
  1975年   439篇
  1974年   543篇
  1973年   507篇
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
151.
A new species,Acanthocephaloides cyrusi, is described from the fishesSolea bleekeri andPomadasys commersoni from Lake St. Lucia, Natal, South Africa. It is distinguished from the other species in the genus by the more marked sexual dimorphism in length, the arrangement of hooks, the proboscis with the longest hooks at the anterior-most extremity and the greater size of the proboscis hooks and body spines. An acanthella, which may represent this species, was found in the tanaidApseudes digitalis.  相似文献   
152.
The acute onset of vertigo, nystagmus and postural instability, without brain-stem signs, is commonly attributed to a disorder of the labyrinth, the vestibular, sensory end organ. Identical symptoms can occur, however, with discrete infarctions or hemorrhages involving the central vestibulocerebellum. Whereas acute labyrinthine disorders are usually benign and self-limited, vascular injuries of the cerebellum may produce swelling, compression of the brain stem and acute hydrocephalus one to four days after the onset of symptoms. Therefore it is important to accurately distinguish between labyrinthine and vestibulocerebellar disorders with the neurologic examination. Acute labyrinthine disease causes unidirectional nystagmus with past-pointing and falling in the opposite direction of the nystagmus, environmental vertigo in the same direction and suppression of the nystagmus with visual fixation. Disorders of the vestibulocerebellum do not produce this consistent pattern of findings.  相似文献   
153.
Catalytic activities of lingual lipase were investigated by enzyme histochemistry in post-mortem tongues from male rats. Sections of fresh-frozen or formalin-calcium fixed tissue were incubated with naphthol-AS-nonanoate and α-naphthyl acetate substrate mixtures. The effects of pH level, sodium taurocholate activator and E600 inhibitor were also examined. The use of cryostat sections of tissues fixed in formalin-calcium and of nonanoate substrate within the range of pH 4.4–6.4, were optimal for localizing maximum reaction product, captured by Fast Blue BB, in acini and demilunes of the posterior deep and superficial lingual glands respectively. The reaction product corresponded with the distribution of secretory granules and failed to develop when taurocholate was omitted from the incubation medium. Similarly localized E600-resistant reaction product occurred with the acetate substrate and hexazotized New Fuchsin at pH 7.4, in the absence of taurocholate. Lipase and conventional esterase activities appear to be superimposed in posterior lingual glands of rat. The ability of their acini and demilunes to hydrolyse nonanoate substrate at an acidic pH optimum, when activated by sodium taurocholate, seems attributable to lipase destined for secretion into saliva – hence convenient for routine histochemical identification of the enzyme.  相似文献   
154.
Rheumatic fever     
  相似文献   
155.
156.
157.
158.
Homozygous typing cells (HTC) were primed, using responding and stimulating lymphocytes of the same HLA-D groups. These intra-HLA-D group primings showed strong specific responses. Restimulation by HLA-D heterozygous and homozygous cell panels showed no correlation between the restimulating determinant and HLA-D. On the other hand, an unrelated individual, not carrying Dw4 and primed to Dw4 HTC, is restimulated by three of four Dw4-HTC. Thus, one non-HLA-D-associated restimulating determinant and another HLA-D-associated determinant could be identified. The differences among the four Dw4 HTC recognized in secondary MLC could reflect either recognition of separate gene products or recognition of separate determinants on the same gene product.  相似文献   
159.
160.
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