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   17196篇
  免费   1423篇
  国内免费   7篇
  2024年   12篇
  2023年   118篇
  2022年   300篇
  2021年   537篇
  2020年   310篇
  2019年   400篇
  2018年   457篇
  2017年   354篇
  2016年   662篇
  2015年   1074篇
  2014年   1161篇
  2013年   1347篇
  2012年   1629篇
  2011年   1461篇
  2010年   931篇
  2009年   777篇
  2008年   1026篇
  2007年   997篇
  2006年   887篇
  2005年   810篇
  2004年   775篇
  2003年   619篇
  2002年   619篇
  2001年   107篇
  2000年   92篇
  1999年   111篇
  1998年   125篇
  1997年   96篇
  1996年   90篇
  1995年   65篇
  1994年   60篇
  1993年   49篇
  1992年   48篇
  1991年   38篇
  1990年   37篇
  1989年   49篇
  1988年   38篇
  1987年   26篇
  1986年   20篇
  1985年   28篇
  1984年   31篇
  1983年   22篇
  1982年   19篇
  1981年   19篇
  1980年   21篇
  1979年   19篇
  1978年   14篇
  1976年   17篇
  1974年   13篇
  1968年   11篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
In modern vertebrates upper and lower jaws are morphologically different. Both develop from the mandibular arch, which is colonized mostly by Hox-free neural crest cells. Here we show that simultaneous inactivation of the murine homeobox genes Dlx5 and Dlx6 results in the transformation of the lower jaw into an upper jaw and in symmetry of the snout. This is the first homeotic-like transformation found in this Hox-free region after gene inactivation. A suggestive parallel comes from the paleontological record, which shows that in primitive vertebrates both jaws are essentially mirror images of each other. Our finding supports the notion that Dlx genes are homeotic genes associated with morphological novelty in the vertebrate lineage.  相似文献   
942.
In Saccharomyces cerevisiae, OLE1 encodes a Δ9 fatty acid desaturase, an enzyme that plays a critical role in maintaining the correct ratio of saturated to monounsaturated fatty acids in the cell membrane. Previous studies have demonstrated that (i) OLE1 expression is repressed by unsaturated fatty acids (UFAs) and induced by low oxygen tension, (ii) a component of this regulation is mediated through the same low oxygen response element (LORE) in the OLE1 promoter, and (iii) Mga2p is involved in LORE-dependent hypoxic induction of OLE1. We now report that LORE-CYC1 basal promoter-lacZ fusion reporter assays demonstrate that UFAs repress the reporter expression under hypoxic conditions in a dose-dependent manner via LORE. Electrophoretic mobility shift assays show that UFAs repress the hypoxia-induced complex formation with LORE. Studies with a construct encoding a truncated form of Mga2p support the hypothesis that both hypoxia and UFA signals affect the processing of Mga2p and the UFA repression of OLE1 hypoxic induction is mediated through Mga2p. Data from Western blot assays provide evidence that under normoxic conditions, Mga2p processing produces approximately equimolar levels of the membrane-bound and processed forms and is unaffected by UFAs. Hypoxic induction of OLE1, however, is associated with increased processing of the protein, resulting in an approximately fivefold increase in the soluble active form that is counteracted by exposure of the cells to unsaturated fatty acids. Data from this study suggest that the Mga2p-LORE interaction plays an important role in OLE1 expression under both normoxic and hypoxic conditions.  相似文献   
943.
944.
Treatment with HIV-1 protease inhibitors (PI) is associated with a reduced incidence or regression of Kaposi sarcoma (KS). Here we show that systemic administration of the PIs indinavir or saquinavir to nude mice blocks the development and induces regression of angioproliferative KS-like lesions promoted by primary human KS cells, basic fibroblast growth factor (bFGF), or bFGF and vascular endothelial growth factor (VEGF) combined. These PIs also block bFGF or VEGF-induced angiogenesis in the chorioallantoic membrane assay with a potency similar to paclitaxel (Taxol). These effects are mediated by the inhibition of endothelial- and KS-cell invasion and of matrix metalloproteinase-2 proteolytic activation by PIs at concentrations present in plasma of treated individuals. As PIs also inhibit the in vivo growth and invasion of an angiogenic tumor-cell line, these data indicate that PIs are potent anti-angiogenic and anti-tumor molecules that might be used in treating non-HIV KS and in other HIV-associated tumors.  相似文献   
945.
946.
947.
948.
949.
The aim of this review is to summarize some of the main findings from our laboratory as well as from others concerning the biochemical, molecular, and functional properties of the alpha1b-adrenergic receptor. Experimental and computational mutagenesis of the alpha1b-adrenergic receptor have been instrumental in elucidating some of the molecular mechanisms underlying receptor activation and receptor coupling to Gq. The knockout mouse model lacking the alpha1b-adrenergic receptor has highlighted the potential implication of this receptor subtype in variety of functions including the regulation of blood pressure, glucose homeostasis, and the rewarding response to drugs of abuse.  相似文献   
950.
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