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   4907篇
  免费   449篇
  国内免费   366篇
  5722篇
  2024年   21篇
  2023年   89篇
  2022年   163篇
  2021年   258篇
  2020年   179篇
  2019年   257篇
  2018年   223篇
  2017年   140篇
  2016年   244篇
  2015年   358篇
  2014年   352篇
  2013年   368篇
  2012年   441篇
  2011年   367篇
  2010年   266篇
  2009年   231篇
  2008年   263篇
  2007年   233篇
  2006年   196篇
  2005年   140篇
  2004年   128篇
  2003年   130篇
  2002年   100篇
  2001年   90篇
  2000年   59篇
  1999年   74篇
  1998年   43篇
  1997年   35篇
  1996年   41篇
  1995年   28篇
  1994年   28篇
  1993年   31篇
  1992年   33篇
  1991年   27篇
  1990年   23篇
  1989年   11篇
  1988年   16篇
  1987年   7篇
  1986年   7篇
  1985年   11篇
  1984年   4篇
  1983年   2篇
  1982年   2篇
  1981年   2篇
  1976年   1篇
排序方式: 共有5722条查询结果,搜索用时 0 毫秒
11.
12.
Three previously undescribed diterpenoids, helioscopnoids A–C, and eight known compounds were isolated from the whole plants of Euphorbia helioscopia. Their structures were established by extensive analysis of spectra and data comparison with previous literatures. Among them, compound 4 was identified as 24,24-dimethoxy-25,26,27-trinoreuphan-3β-ol with revised configurations of C-13, C-14, and C-17 (13R*, 14R*, 17R*). Cytotoxicity assays revealed that all compounds exhibited varying levels of cytotoxicity against H1975 cells, with compound 9 displaying the most potent activity, as indicated by cell viability rates of 18.13 % and 20.76 % at concentrations of 20 μM and 5 μM, respectively. This study expands the understanding of E. helioscopia terpenoids’ structural diversity and biological activities, contributing to the exploration of potential therapeutic applications.  相似文献   
13.
14.
15.
Highlights:
1. A replication-competent recombinant VSV with RABV-G protein replacement was generated.
2. Single dose of VSV-RABVG immunization induce potent antigen-specific humoral immune response, especially the virus neutralizing antibodies.
3. Mice intranasally immunized with single dose of VSV-RABVG were 100% protected upon RABV challenge.  相似文献   
16.
Xiong R  Wu J  Zhou Y  Zhou X 《Journal of virology》2008,82(24):12304-12311
Rice stripe virus (RSV) is the type member of the genus Tenuivirus. RSV has four single-stranded RNAs and causes severe disease in rice fields in different parts of China. To date, no reports have described how RSV spreads within host plants or the viral and/or host factor(s) required for tenuivirus movement. We investigated functions of six RSV-encoded proteins using trans-complementation experiments and biolistic bombardment. We demonstrate that NSvc4, encoded by RSV RNA4, supports the intercellular trafficking of a movement-deficient Potato virus X in Nicotiana benthamiana leaves. We also determined that upon biolistic bombardment or agroinfiltration, NSvc4:enhanced green fluorescent protein (eGFP) fusion proteins localize predominantly near or within the walls of onion and tobacco epidermal cells. In addition, the NSvc4:eGFP fusion protein can move from initially bombarded cells to neighboring cells in Nicotiana benthamiana leaves. Immunocytochemistry using tissue sections from RSV-infected rice leaves and an RSV NSvc4-specific antibody showed that the NSvc4 protein accumulated in walls of RSV-infected leaf cells. Gel retardation assays revealed that the NSvc4 protein interacts with single-stranded RNA in vitro, a common feature of many reported plant viral movement proteins (MPs). RSV NSvc4 failed to interact with the RSV nucleocapsid protein using yeast two-hybrid assays. Taken together, our data indicate that RSV NSvc4 is likely an MP of the virus. This is the first report describing a tenuivirus MP.  相似文献   
17.
心肌组织工程的研究现状   总被引:3,自引:0,他引:3  
心肌组织工程的目的是通过在体外构建思想的心肌组织工程,用于替代和修复病损的心肌组织,从心肌组织工程的细胞来源,细胞培养基,细胞接种,细胞支架,生物反应器5个方面介绍心肌组织工程的研究现状。  相似文献   
18.
Self-assembly reaction of Cd(ClO4)2 · 6H2O with Norfloxacin (H-Norf) affords a novel 2D rectangular grid framework [Cd(Norf)(ClO4)(H2O)] (1) with strong blue luminescent emission (λem=425 nm), while Norf acts as a tetradentate bridging linker to connect three Cd centers and ClO4 − completes Cd center octahedron coordination geometry. The compound 1 has crystallographic data of triclinic, space group , a=9.4577(1) Å, b=9.5012(2) Å, c=12.2805(1) Å, V=3624.4(3) Å3, Z=2.  相似文献   
19.
Cytokines produced by immune-activated testicular interstitial macrophages (TIMs) may play a fundamental role in the local control mechanisms of testosterone biosynthesis in Leydig cells. We investigated whether in vivo immune-activation of TIMs can modulate Leydig cell steroidogenesis. To immune activate TIMs in vivo, mice were injected intraperitoneally (i.p.) with lipopolysaccharide (LPS, 6 mg/kg). TIMs and Leydig cells were purified for RNA analysis. LPS treatment resulted in a 47-fold increase in interleukin-1β (IL-1β) mRNA in TIMs. P450c17 mRNA levels in the Leydig cells from the same animals, decreased to less than 10% compared to control. The effect of LPS on IL-1β and P450c17 mRNA levels was reversible on both TIMs and Leydig cells, respectively. To determine if the effect of LPS on P450c17 was mediated by a possible decrease in pituitary LH secretion, mice were co-injected with LPS and hCG. Treatment with hCG did not change the effect observed with LPS alone, in TIMs or in Leydig cells. In vitro, LPS treatment of TIMs resulted in marked induction of IL-1β mRNA expression. In parallel, in vitro treatment of Leydig cells with recombinant IL-1 resulted in a dose-dependent inhibition of P450c17 mRNA expression and testosterone production. These data demonstrate that LPS treatment, in vivo and in vitro, induced IL-1 gene expression in TIMs, and that IL-1 inhibits P450c17 mRNA in vitro. Therefore, we suggest that immune-activation of TIMs might have caused the observed inhibition of P450c17 gene expression in Leydig cells in vivo.  相似文献   
20.
本实验研究0.05% MES对野生型拟南芥生长的影响。结果表明,含有MES的培养基pH变化较小,其培养10 d的拟南芥幼苗干重、鲜重、叶绿素含量和含水量均高于对照组,而叶片PAL和POD活性却低于对照组,说明MES通过影响培养基的pH变化促进拟南芥生长。  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