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   25033篇
  免费   2184篇
  国内免费   2310篇
  29527篇
  2024年   45篇
  2023年   218篇
  2022年   481篇
  2021年   755篇
  2020年   650篇
  2019年   752篇
  2018年   770篇
  2017年   656篇
  2016年   885篇
  2015年   1456篇
  2014年   1657篇
  2013年   1826篇
  2012年   2313篇
  2011年   1990篇
  2010年   1420篇
  2009年   1282篇
  2008年   1598篇
  2007年   1457篇
  2006年   1373篇
  2005年   1269篇
  2004年   1176篇
  2003年   1044篇
  2002年   881篇
  2001年   576篇
  2000年   484篇
  1999年   443篇
  1998年   297篇
  1997年   224篇
  1996年   201篇
  1995年   181篇
  1994年   156篇
  1993年   116篇
  1992年   141篇
  1991年   112篇
  1990年   94篇
  1989年   90篇
  1988年   61篇
  1987年   73篇
  1986年   55篇
  1985年   29篇
  1984年   20篇
  1983年   37篇
  1982年   16篇
  1981年   17篇
  1979年   17篇
  1978年   14篇
  1977年   13篇
  1976年   13篇
  1972年   12篇
  1970年   14篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
103.
In inflamed joints of rheumatoid arthritis, PGE(2) is highly expressed, and IL-10 and IL-6 are also abundant. PGE(2) is a well-known activator of the cAMP signaling pathway, and there is functional cross-talk between cAMP signaling and the Jak-STAT signaling pathway. In this study, we evaluated the modulating effect of PGE(2) on STAT signaling and its biological function induced by IL-10 and IL-6, and elucidated its mechanism in THP-1 cells. STAT phosphorylation was determined by Western blot, and gene expression was analyzed using real-time PCR. Pretreatment with PGE(2) significantly augmented IL-10-induced STAT3 and STAT1 phosphorylation, as well as suppressors of cytokine signaling 3 (SOCS3) and IL-1R antagonist gene expression. In contrast, PGE(2) suppressed IL-6-induced phosphorylation of STAT3 and STAT1. These PGE(2)-induced modulating effects were largely reversed by actinomycin D. Pretreatment with dibutyryl cAMP augmented IL-10-induced, but did not change IL-6-induced STAT3 phosphorylation. Misoprostol, an EP2/3/4 agonist, and butaprost, an EP2 agonist, augmented IL-10-induced STAT3 phosphorylation and SOCS3 gene expression, but sulprostone, an EP1/3 agonist, had no effect. H89, a protein kinase A inhibitor, and LY294002, a PI3K inhibitor, diminished PGE(2)-mediated augmentation of IL-10-induced STAT3 phosphorylation. In this study, we found that PGE(2) selectively regulates cytokine signaling via increased intracellular cAMP levels and de novo gene expression, and these modulating effects may be mediated through EP2 or EP4 receptors. PGE(2) may modulate immune responses by alteration of cytokine signaling in THP-1 cells.  相似文献   
104.
Echinoderm microtubule-associated protein (EMAP)-like (EML) family proteins are microtubule-associated proteins that have a conserved hydrophobic EMAP-like protein (HELP) domain and multiple WD40 domains. In this study, we examined the role of EML4, which is a member of the EML family, in cell division. Time-lapse microscopy analysis demonstrated that EML4 depletion induced chromosome misalignment during metaphase and delayed anaphase initiation. Further analysis by immunofluorescence showed that EML4 was required for the organization of the mitotic spindle and for the proper attachment of kinetochores to microtubules. We searched for EML4-associating proteins by mass spectrometry analysis and found that the nuclear distribution gene C (NUDC) protein, which is a critical factor for the progression of mitosis, was associated with EML4. This interaction was mediated by the WD40 repeat of EML4 and by the C-terminus of NUDC. In the absence of EML4, NUDC was no longer able to localize to the mitotic spindle, whereas NUDC was dispensable for EML4 localization. Our results show that EML4 is critical for the loading of NUDC onto the mitotic spindle for mitotic progression.  相似文献   
105.
106.
克隆鸭乙型肝炎病毒DNA双体体内转染的研究   总被引:1,自引:0,他引:1  
用一种含头尾相连DHBVDNA双体的质粒体内转染2日龄芙蓉鸭,大多数鸭(86%)产生了短暂病毒血症。血清DHBs/preSAg和DHBVDNA于转染后第9天出现,第12~14天达峰值,第28天时多数转阴;少数鸭的病毒血症可持续50天以上。转染鸭肝组织中也检测到复制中间型DHBVDNA的存在。用转染鸭病毒血症期的血清作磷钨酸负染电镜观察,找到了完整的DHBV病毒颗粒,并且用此血清腹腔注射1日龄鸭,60%的鸭被感染成功,证明体内转染后有生物活性的DHBV病毒颗粒的产生。该研究方法的建立.对于研究DHBV变异株.DHBV基因结构与功能的关系等,均有一定理论意义及应用价值。  相似文献   
107.
IL-35 subunit EBI3 is up-regulated in pulmonary fibrosis tissues. In this study, we investigated the pathological role of EBI3 in pulmonary fibrosis and dissected the underlying molecular mechanism. Bleomycin-induced pulmonary fibrosis mouse model was established, and samples were performed gene expression analyses through RNAseq, qRT-PCR and Western blot. Wild type and EBI3 knockout mice were exposed to bleomycin to investigate the pathological role of IL-35, via lung function and gene expression analyses. Primary lung epithelial cells were used to dissect the regulatory mechanism of EBI3 on STAT1/STAT4 and STAT3. IL-35 was elevated in both human and mouse with pulmonary fibrosis. EBI3 knockdown aggravated the symptoms of pulmonary fibrosis in mice. EBI3 deficiency enhanced the expressions of fibrotic and extracellular matrix-associated genes. Mechanistically, IL-35 activated STAT1 and STAT4, which in turn suppressed DNA enrichment of STAT3 and inhibited the fibrosis process. IL-35 might be one of the potential therapeutic targets for bleomycin-induced pulmonary fibrosis.  相似文献   
108.
Entry of human immunodeficiency virus type 1 (HIV-1) virion into host cells involves three major steps, each being a potential target for the development of entry inhibitors: gp120 binding to CD4, gp120-CD4 complex interacting with a coreceptor, and gp41 refolding to form a six-helix bundle. Using a D-amino acid decapeptide combinatorial library, we identified peptide dC13 as having potent HIV-1 fusion inhibitory activity, and effectively inhibiting infection by several laboratory-adapted and primary HIV-1 strains. While dC13 did not block binding of gp120 to CD4, nor disrupt the gp41 six-helix bundle formation, it effectively blocked the binding of an anti-CXCR4 monoclonal antibody and chemokine SDF-1alpha to CXCR4-expressing cells. However, because R5-using primary viruses were also neutralized, the antiviral activity of dC13 implies additional mode(s) of action. These results suggest that dC13 is a useful HIV-1 coreceptor antagonist for CXCR4 and, due to its biostability and simplicity, may be of value for developing a new class of HIV-1 entry inhibitors.  相似文献   
109.
中国全新世人群颞下颌关节尺寸的时代变化   总被引:1,自引:0,他引:1  
本文通过对中国北方地区新石器时代(54例)、青铜铁器时代(189例) 和近代(92例) 成年男性颞下颌关节的多项测量项目的对比、分析, 对中国全新世人群颞下颌关节测量性状的变异问题进行了研究。结果显示近7000年来颞下颌关节的不同部位在全新世不同阶段有不同的变化特点。髁突、冠突在全新世厚度变薄, 髁突的变薄主要在新石器-青铜铁器时代, 冠突的变薄主要在青铜铁器-近代。髁突面积在全新世也在缩小, 在新石器-青铜铁器时代缩小的幅度更大。髁突顶缘弧度的变平、下颌窝的变浅主要发生在新石器-青铜铁器时代。髁突面积/下颌窝面积, 其变化主要发生在青铜铁器时代。这些变化可能与生活环境、食物结构改变、下颌骨与头骨不同的演化速率等有关。  相似文献   
110.
本文对内蒙古清水河县姑姑庵墓地出土的13例汉代的颅骨(男性6例, 女性7例)进行了体质人类学的研究, 该组颅骨在种族特征上可归入现代亚洲蒙古人种中的东亚人种范围。在若干古代和现代对比组中,姑姑庵汉代居民的体质特征与将军沟组、近代华北组最为接近,很可能是来自中原地区的移民或是当地早期中原移民的后裔。  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