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   2422篇
  免费   157篇
  2023年   5篇
  2022年   24篇
  2021年   51篇
  2020年   30篇
  2019年   39篇
  2018年   57篇
  2017年   35篇
  2016年   78篇
  2015年   115篇
  2014年   104篇
  2013年   185篇
  2012年   216篇
  2011年   181篇
  2010年   101篇
  2009年   97篇
  2008年   156篇
  2007年   133篇
  2006年   135篇
  2005年   113篇
  2004年   124篇
  2003年   104篇
  2002年   99篇
  2001年   28篇
  2000年   17篇
  1999年   17篇
  1998年   29篇
  1997年   13篇
  1996年   21篇
  1995年   13篇
  1994年   21篇
  1993年   27篇
  1992年   18篇
  1991年   15篇
  1990年   26篇
  1989年   7篇
  1988年   13篇
  1987年   8篇
  1986年   8篇
  1985年   20篇
  1984年   8篇
  1983年   8篇
  1982年   8篇
  1981年   13篇
  1980年   8篇
  1979年   14篇
  1978年   8篇
  1975年   4篇
  1974年   7篇
  1973年   3篇
  1968年   3篇
排序方式: 共有2579条查询结果,搜索用时 31 毫秒
991.
The cellular and non-cellular components of fibrous septa formed at early and late stages in a sequential model of experimental hepatic fibrosis have been investigated using ultrastructural and immunocytochemical techniques. In the early septa, cells with intermediate features between lobular Ito cells and active fibroblasts were formed. These cells frequently displayed subplasmalemmal microfilaments (myofibroblast-like cells). Macrophages were also present. Scanty typical fibroblasts were present in the late septa. This cellular recruitment might be related to an extracellular glycoprotein-fibronectin-which is at present under investigation as a chemotactic factor for fibroblasts. Strong positivity for fibronectin in early septa and its sharp decrease in late septa seems to support this view. Fibroblasts and/or macrophages are the likely source of fibronectin synthesis.  相似文献   
992.
Two cases of coronary arteriovenous fistulae are reported. In the first case, the right coronary artery (RCA) drained into the right ventricular outflow tract, and the distal RCA filled through a branch of the left anterior descending coronary artery. In the second case, the RCA drained into the right atrium and filled through a branch of the left circumflex artery. The fistulae were closed with subcoronary mattress sutures that preserved the continuity of the native circulation.  相似文献   
993.
Binding of hepatocyte growth factor (HGF) to its receptor Met induces autophosphorylation and activation of the tyrosine kinase activity. In HGF-treated HepG2 cells, we studied: (i) the expression patterns of early(c-myc,c-jun,and c-fos) and delayed-early (ornithinedecarboxylase and c-met) response genes and (ii) thepossible involvement of protein kinase transducersin the control of the expression of c-metand of other genes eventually induced downstream. c-metand c-mycmRNAs peaked 1–2 h after HGF, while c-junandc-fosmRNAs slightly increased at 1 h. Ornithinedecarboxylase activity was induced earlier (4 h) thanthe mRNA (8–10 h). The transducers involved in HGF-triggered gene inductions were investigated using different protein kinase inhibitors: genistein for the receptor tyrosine kinase, herbimycin A for the nonreceptor tyrosine kinase (pp60c-src), wortmannin for phosphatidylinositol 3-kinase (PI3K) and H7 for protein kinase C (PKC). The similarity of responses to PKC inhibition led to suppose that c-mycand ornithinedecarboxylase mRNAs were induced sequentially along the same transduction pathway triggered by HGF. Ornithine decarboxylase activity seemed to be largely regulated by phosphorylation(s). The mRNA expression of c-junwas likely to undergo a negative regulation through a mechanism involving PI3K, while that ofc-metseemed to be almost independent from various protein kinases (PI3K, pp60c-src, and PKC).  相似文献   
994.
The sequence diversity of 45 Opa outer membrane proteins from Neisseria meningitidis, Neisseria gonorrhoeae, Neisseria sicca, and Neisseria flava indicates that horizontal genetic exchange of opa alleles has been rare between these species. A two-dimensional structural model containing four surface-exposed loops was constructed based on rules derived from porin crystal structure and on conservation of sequence homology within transmembrane β-strands. The minimal continuous epitopes recognized by 23 monoclonal antibodies were mapped to loops 2 and 3. Some of these epitopes are localized on the bacterial cell surface, in support of the model.  相似文献   
995.
Rab proteins are small molecular weight GTPases that control vesicular traffic in eucaryotic cells. A subset of Rab proteins, the Rab3 proteins are thought to play an important role in regulated exocytosis of vesicles. In transfected AtT-20 cells expressing wild-type Rab3D, we find that a fraction of the protein is associated with dense core granules. In the same cells, expression of a mutated isoform of Rab3D, Rab3D N135I, inhibits positioning of dense core granules near the plasma membrane, blocks regulated secretion of mature ACTH, and impairs association of Rab3A to membranes. Expression of Rab3D N135I does not change the levels of ACTH precursor or the efficiency with which the precursor is processed into ACTH hormone and packaged into dense core granules. We also find that cells expressing mutated Rab3D differentiate to the same extent as untransfected AtT-20 cells. We conclude that expression of Rab3D N135I specifically impairs late membrane trafficking events necessary for ACTH hormone secretion.  相似文献   
996.
The floc-forming ability of flocculent strains ofZygosaccharomyces bailii andZ fermentati, isolated from musts, was tested for susceptibility to proteinase and sugar treatments.Z. fermentati was found highly resistant to the proteolytic enzymes tested, whereasZ. baili was only trypsin-resistant.The inhibition of flocculation by sugars distinguished two types: inZ. fermentati flocculation was completely inhibited by mannose, inZ. bailli by various sugars.By SEM observation, the cell surface ofZygosaccharomyces revealed the presence of a column structure, resulting from fusion of vesicles present on the cell surface.  相似文献   
997.
998.
999.
We have studied the ability of hydrolases (acid phosphatase and glycosidases) from the aleurone layers of resting wheat grains to interact with Con A- and WGA-Sepharose as a way to examine their glycoprotein nature. Aliquots (6–85% depending on the enzyme) of all the enzymes interacted with Con A-Sepharose. The major part of α-mannosidase activity (85%) was present in this form. Aliquots (2–20% depending on the enzyme) of the following four enzymes, β-galactosidase, α-mannosidase, β-N-acetylglucosaminidase and acid phosphatase, interacted with WGA-Sepharose. All the enzymes were found in forms which were unable to interact with either lectin. No forms of hydrolases interacting with both lectins were found in the crude extract. The specific activities of most of the enzymes recovered from the lectin-Sepharose gels were greater than those measured in the crude extract. In particular, the highest specific activities were found for β-N-acetylglucosaminidase and β-galactosidase recovered from WGA-Sepharose. Different lectin-binding forms of hydrolases were compared with respect to pH optimum and stability under various conditions (heat and guanidine hydrochloride treatments). The lectin-binding pattern of the hydrolases released in the incubation medium by the aleurone layers was similar to that reported above for the enzymes extracted from these tissues, suggesting that none of the hydrolase forms found in the aleurone layers is selectively released during incubation of these tissues.  相似文献   
1000.
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