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   4765篇
  免费   490篇
  国内免费   464篇
  5719篇
  2024年   12篇
  2023年   58篇
  2022年   130篇
  2021年   205篇
  2020年   162篇
  2019年   239篇
  2018年   198篇
  2017年   176篇
  2016年   200篇
  2015年   294篇
  2014年   313篇
  2013年   344篇
  2012年   379篇
  2011年   350篇
  2010年   245篇
  2009年   213篇
  2008年   241篇
  2007年   217篇
  2006年   186篇
  2005年   171篇
  2004年   185篇
  2003年   203篇
  2002年   231篇
  2001年   138篇
  2000年   116篇
  1999年   93篇
  1998年   83篇
  1997年   58篇
  1996年   36篇
  1995年   33篇
  1994年   25篇
  1993年   16篇
  1992年   15篇
  1991年   26篇
  1990年   20篇
  1989年   23篇
  1988年   9篇
  1987年   11篇
  1986年   12篇
  1985年   8篇
  1984年   9篇
  1983年   5篇
  1982年   5篇
  1981年   3篇
  1979年   5篇
  1973年   4篇
  1966年   2篇
  1959年   1篇
  1948年   1篇
  1947年   1篇
排序方式: 共有5719条查询结果,搜索用时 15 毫秒
91.
92.
陈威  杨颖增  陈锋  周文冠  舒凯 《植物学报》1983,54(6):779-785
植物因其固着生长的方式, 已经进化出各类特殊的机制来适应多变的外界环境。为提高自身的存活率, 植物进化出一类胁迫记忆机制, 以适应环境和保护自己。表观遗传修饰不仅能调控植物的正常生长发育, 而且参与植物对各种非生物或生物胁迫的响应。近年的研究表明, 表观遗传修饰在植物胁迫记忆调控中也发挥重要作用。例如, DNA甲基化、组蛋白甲基化及乙酰化等表观遗传修饰参与并维持特定的胁迫记忆。该文主要对表观遗传修饰介导的植物胁迫记忆最新进展进行综述, 并展望未来的重点和热点研究方向。  相似文献   
93.
The dipeptidyl peptidase 4 inhibitor vildagliptin (VLD), a widely used anti‐diabetic drug, exerts favourable effects on vascular endothelium in diabetes. We determined for the first time the improving effects of VLD on mitochondrial dysfunction in diabetic mice and human umbilical vein endothelial cells (HUVECs) cultured under hyperglycaemic conditions, and further explored the mechanism behind the anti‐diabetic activity. Mitochondrial ROS (mtROS) production was detected by fluorescent microscope and flow cytometry. Mitochondrial DNA damage and ATP synthesis were analysed by real time PCR and ATPlite assay, respectively. Mitochondrial network stained with MitoTracker Red to identify mitochondrial fragmentation was visualized under confocal microscopy. The expression levels of dynamin‐related proteins (Drp1 and Fis1) were determined by immunoblotting. We found that VLD significantly reduced mtROS production and mitochondrial DNA damage, but enhanced ATP synthesis in endothelium under diabetic conditions. Moreover, VLD reduced the expression of Drp1 and Fis1, blocked Drp1 translocation into mitochondria, and blunted mitochondrial fragmentation induced by hyperglycaemia. As a result, mitochondrial dysfunction was alleviated and mitochondrial morphology was restored by VLD. Additionally, VLD promoted the phosphorylation of AMPK and its target acetyl‐CoA carboxylase in the setting of high glucose, and AMPK activation led to a decreased expression and activation of Drp1. In conclusion, VLD improves endothelial mitochondrial dysfunction in diabetes, possibly through inhibiting Drp1‐mediated mitochondrial fission in an AMPK‐dependent manner.  相似文献   
94.
Autophagy is an evolutionarily conserved process for catabolizing damaged proteins and organelles in a lysosome-dependent manner. Dysregulation of autophagy may cause various diseases, such as cancer and neurodegeneration. However, the relevance of autophagy to diseases remains controversial because of the limited availability of chemical modulators. Herein, the authors developed a fluorescence-based assay for measuring activity of the autophagy protease, autophagin-1(Atg4B). The assay employs a novel reporter substrate of Atg4B composed of a natural substrate (LC3B) fused to an assayable enzyme (PLA(2)) that becomes active upon cleavage by this cysteine protease. A high-throughput screening (HTS) assay was validated with excellent Z' factor (>0.7), remaining robust for more than 5 h and suitable for screening of large chemical libraries. The HTS assay was validated by performing pilot screens with 2 small collections of compounds enriched in bioactive molecules (n = 1280 for Lopac? and 2000 for Spectrum? library), yielding confirmed hit rates of 0.23% and 0.70%, respectively. As counterscreens, PLA(2) and caspase-3 assays were employed to eliminate nonspecific inhibitors. In conclusion, the LC3B-PLA(2) reporter assay provides a platform for compound library screening for identification and characterization of Atg4B-specific inhibitors that may be useful as tools for interrogating the role of autophagy in disease models.  相似文献   
95.
目的考察胡桃楸提取液对肿瘤细胞Hela、K562的抑制作用和相关机制。方法用MTT方法分析胡桃楸提取液对Hela、K562细胞增殖的影响。采用端粒酶PCR ELISA试剂盒分析胡桃楸提取液对Hela、K562细胞端粒酶的影响。结果 Hela细胞24、48和72 h的LD50分别为406.18μg/mL、319.48μg/mL和112.84μg/mL。K562细胞24 h LD50为154.50μg/mL。HLF细胞LD50为918.69μg/mL。胡桃楸提取液可抑制Hela细胞和K562细胞的端粒酶活性,而对HLF细胞端粒酶活性影响不大。结论胡桃楸提取液对Hela细胞、K562细胞有抑制作用,在低浓度下对HLF细胞杀伤不大。对肿瘤细胞抑制作用可能与抑制端粒酶活性相关。  相似文献   
96.
Inhibition of Trichoderma reesei cellulase by sugars and solvents   总被引:2,自引:0,他引:2  
Inhibition of Trichoderma reesei cellulase by sugars (glucose, delta-gluconolactone, and cellobiose) and solvents (ethanol, butanol, and acetone) was studied using cellulose azure. Glucose, cellobiose, ethanol, and butanol were noncompetitive inhibitors, delta-gluconolactone was a mixed inhibitor, and acetone was a noncompetitive activator. Converting cellobiose to glucose reduces the effective inhibitor binding constant by 6 times and converting cellobiose to ethanol reduces it by 16 times.  相似文献   
97.
Lawson MJ  Zhang L 《Gene》2008,407(1-2):54-62
SSRs (simple sequence repeats) have been shown to have a variety of effects on an organism. In this study, we compared SSRs in housekeeping and tissue-specific genes in human and mouse, in terms of SSR types and distributions in different regions including 5'-UTRs, introns, coding exons, 3'-UTRs, and upstream regions. Among all these regions, SSRs in the 5'-UTR show the most distinction between housekeeping genes and tissue-specific genes in both densities and repeat types. Specifically, SSR densities in 5'-UTRs in housekeeping genes are about 1.7 times higher than those in tissue-specific genes, in contrast to the 0.8-1.2 times differences between the two classes of genes in other regions. Tri-SSRs in 5'-UTRs of housekeeping genes are more GC rich than those of tissue-specific genes and CGG, the dominant type of tri-SSR in 5'-UTR, accounts for 74-79% of the tri-SSRs in housekeeping genes, as compared to 42-57% in tissue-specific genes. 75% of the tri-SSRs in the 5'-UTR of housekeeping genes have 4-5 repeat units, versus the 86-90% in tissue-specific genes. Taken together, our results suggest that SSRs may have an effect on gene expression and may play an important role in contributing to the different expression profiles between housekeeping and tissue-specific genes.  相似文献   
98.
通过农杆菌介导法,将含有油菜素内酯合成基因DET2的植物表达栽体pCAMBIA2301-DET2转入烟草,获得转基因烟草植株.用T1代转基因阳性株进行耐NaCl试验,结果显示,NaCl胁迫下转基因烟草、非转基因对照烟草的出苗率、幼苗鲜重、株高及根长均随NaCl浓度增加而下降.但在相同NaCl浓度下,转基因植株鲜重、株高及根长均明显高于非转基因对照烟草,并且转基因植株的丙二醛( MDA)含量低于非转基因植株,诱导蛋白基因P5CS表达高峰出现时间晚于非转基因植株.说明DET2的表达提高了烟草的耐NaCl能力.  相似文献   
99.
Summary Polyurethane foam cubes were employed as carriers to immobilize Rhizopus oryzae for L(+)-lactic acid production. The immobilizing capacity reached 450 g-fresh cell/l-cube. The production rate of L(+)-lactic acid could be threefold increased by using the immobilized R. oryzae. The immobilized cells could be steadily used in repetitive fermentations for more than 10 batches.  相似文献   
100.
A manner in which cells can communicate with each other is via secreted nanoparticles termed exosomes. These vesicles contain lipids, nucleic acids, and proteins, and are said to reflect the cell‐of‐origin. However, for the exosomal protein content, there is limited evidence in the literature to verify this statement. Here, proteomic assessment combined with pathway‐enrichment analysis is used to demonstrate that the protein cargo of exosomes reflects the epithelial/mesenchymal phenotype of secreting breast cancer cells. Given that epithelial‐mesenchymal plasticity is known to implicate various stages of cancer progression, the results suggest that breast cancer subtypes with distinct epithelial and mesenchymal phenotypes may be distinguished by directly assessing the protein content of exosomes. Additionally, the work is a substantial step toward verifying the statement that cell‐derived exosomes reflect the phenotype of the cells‐of‐origin.  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