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   11371篇
  免费   913篇
  国内免费   762篇
  13046篇
  2024年   21篇
  2023年   212篇
  2022年   395篇
  2021年   635篇
  2020年   396篇
  2019年   514篇
  2018年   536篇
  2017年   341篇
  2016年   508篇
  2015年   714篇
  2014年   793篇
  2013年   916篇
  2012年   1070篇
  2011年   932篇
  2010年   572篇
  2009年   498篇
  2008年   534篇
  2007年   492篇
  2006年   427篇
  2005年   361篇
  2004年   303篇
  2003年   225篇
  2002年   187篇
  2001年   204篇
  2000年   170篇
  1999年   176篇
  1998年   104篇
  1997年   124篇
  1996年   106篇
  1995年   87篇
  1994年   93篇
  1993年   48篇
  1992年   74篇
  1991年   55篇
  1990年   44篇
  1989年   46篇
  1988年   38篇
  1987年   27篇
  1986年   19篇
  1985年   22篇
  1984年   12篇
  1983年   9篇
  1982年   2篇
  1981年   2篇
  1980年   1篇
  1979年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
Hypertension is an independent risk factor for the progression of chronic renal failure, and oxidative stress plays a critical role in hypertensive renal damage. Forkbox O1(FoxO1) signaling protects cells against oxidative stress and may be a useful target for treating oxidative stress-induced hypertension. Tongxinluo is a traditional Chinese medicine with cardioprotective and renoprotective functions. Therefore, this study aimed to determine the effects of Tongxinluo in hypertensive renal damage in spontaneously hypertensive rats(SHRs)and elucidate the possible involvement of oxidative stress and FoxO1 signaling in its molecular mechanisms. SHRs treated with Tongxinluo for 12 weeks showed a reduction in systolic blood pressure. In addition to increasing creatinine clearance, Tongxinluo decreased urinary albumin excretion, oxidative stress injury markers including malondialdehyde and protein carbonyls, and expression of nicotinamide adenine dinucleotide phosphate oxidase subunits and its activity in SHR kidneys. While decreasing phosphorylation of FoxO1, Tongxinluo also inhibited the phosphorylation of extracellular signal-regulated kinase1/2 and p38 and enhanced manganese superoxide dismutase and catalase activities in SHR kidneys. Furthermore, histology revealed attenuation of glomerulosclerosis and renal podocyte injury, while Tongxinluo decreased the expression of α-smooth muscle actin, extracellular matrixprotein, transforming growth factor β1 and small mothers against decapentaplegic homolog 3,and improved tubulointerstitial fibrosis in SHR kidneys. Finally, Tongxinluo inhibited inflammatory cell infiltration as well as expression of tumor necrosis factor-α and interleukin-6. In conclusion, Tongxinluo protected SHRs against hypertension-induced renal injury by exerting antioxidant, antifibrotic, and anti-inflammatory activities. Moreover, the underlying mechanisms of these effects may involve inhibition of oxidative stress and functional activation of FoxO1 signaling.  相似文献   
132.
Miniature chromosome maintenance 7 (MCM7) is an essential component of DNA replication licensing complex. Recent studies indicate that MCM7 is amplified and overexpressed in a variety of human malignancies. In this report, we show that MCM7 binds SF3B3. The binding motif is located in the N terminus (amino acids 221–248) of MCM7. Knockdown of MCM7 or SF3B3 significantly increased unspliced RNA of epidermal growth factor receptor, platelet-derived growth factor receptor, and c-Met. A dramatic drop of reporter gene expression of the oxytocin exon 1-intron-exon 2-EGFP construct was also identified in SF3B3 and MCM7 knockdown PC3 and DU145 cells. The MCM7 or SF3B3 depleted cell extract failed to splice reporter RNA in in vitro RNA splicing analyses. Knockdown of SF3B3 and MCM7 leads to an increase of cell death of both PC3 and DU145 cells. Such cell death induction is partially rescued by expressing spliced c-Met. To our knowledge, this is the first report suggesting that MCM7 is a critical RNA splicing factor, thus giving significant new insight into the oncogenic activity of this protein.  相似文献   
133.
134.
135.
报道了产自滇东南的中国兰科植物一新记录种--聚叶钗子股(Luisia appressifolia Averyanov)。研究发现,已往文献报道该种时,对其花部特征(如花颜色、萼片及花瓣形状、大小等)的描述仅依据腊叶标本,因标本严重失水导致描述信息不准或缺失。本文根据新鲜植株和花部材料对该种相关形态特征给予了补充。  相似文献   
136.
花颜色和花气味的量化研究方法   总被引:3,自引:0,他引:3  
花颜色和花气味是花部构成的重要内容。在已开展的传粉生态学研究中对二者的报道主要是描述性的,而其量化研究可以为揭示传粉机制提供有力的实验证据。本文主要介绍了花颜色的测量和标定方法,包括比色卡、分光色差仪和便携式光谱仪等;花气味的采集方法,包括动态顶空套袋-吸附采集法、吸附-溶剂洗脱法和固相微萃取法等;花气味的检测和分析方法,包括气相色谱-质谱联用仪分析和电子鼻型超速气相色谱仪分析等;以及昆虫行为学实验方法,包括气相色谱-昆虫触角电位联用技术、Y型嗅觉仪和飞行箱实验等。科研人员可以根据实验材料的特点和实验目的选择适合的量化研究方法。  相似文献   
137.
Yu L  Jiang BP  Luo D  Shen XC  Guo S  Duan JA  Tang YP 《Phytomedicine》2012,19(3-4):239-244
Chinese jujube (also known as Chinese date) is the fruit of Ziziphus jujuba Mill. (Rhamnaceae). As a famous folk medicine, it is used as antidote in traditional Chinese formula, Shi Zao Decoction, to relieve the drastic inflammatory irritant nature of Euphorbia species. The irritant activities may cause serious adverse effects in clinical practices. This study aimed to investigate the active components of Z. jujuba through the inhibitory effects on the inflammatory cells activated by Euphorbia kansui and prostratin, a phorbol ester isolated from Euphorbia fischeriana. Peritoneal macrophage of rat and splenic lymphocyte (splenocyte) of mouse were selected to evaluate these actions in vitro. Nitric oxide (NO) release of macrophage and the proliferation of splenocyte were examined through Griess method and MTT assay. TNF-α, as an important pro-inflammatory cytokines, was detected with enzyme-linked immunosorbent assay (ELISA) method. Six fractions extracted from Z. jujuba were evaluated and fraction F (triterpene acids fraction) was demonstrated to be the most active part, and then, 21 compounds isolated from Z. jujuba were tested at the concentrations range from 1 μg/ml to 100 μg/ml. The results show that 7 compounds of them are likely to be active compounds concerning to their pronounced inhibitory action on the activated inflammatory cells. These effects might be helpful to attenuate the irritant action of Euphorbiaceae plants and protect the gastrointestinal tissue from potent inflammatory injury, which should be beneficial to some diseases, like inflammatory bowel disease.  相似文献   
138.
IL-22-producing CD4+ T cells (IL-22+CD4+ T cells) and Th22 cells (IL-22+IL-17?IFN-γ?CD4+ T cells) represent newly discovered T-cell subsets, but their nature, regulation, and clinical relevance in gastric cancer (GC) are presently unknown. In our study, the frequency of IL-22+CD4+ T cells in tumor tissues from 76 GC patients was significantly higher than that in tumor-draining lymph nodes, non-tumor, and peritumoral tissues. Most intratumoral IL-22+CD4+ T cells co-expressed IL-17 and IFN-γ and showed a memory phenotype. Locally enriched IL-22+CD4+ T cells positively correlated with increased CD14+ monocytes and IL-6 and IL-23 detection ex vivo, and in vitro IL-6 and IL-23 induced the polarization of IL-22+CD4+ T cells in a dose-dependent manner and the polarized IL-22+CD4+ T cells co-expressed of IL-17 and IFN-γ. Moreover, IL-22+CD4+ T-cell subsets (IL-22+IL-17+CD4+, IL-22+IL-17?CD4+, IL-22+IFN-γ+CD4+, IL-22+IFN-γ?CD4+, and IL-22+IL-17+IFN-γ+CD4+ T cells), and Th22 cells were also increased in tumors. Furthermore, higher intratumoral IL-22+CD4+ T-cell percentage and Th22-cell percentage were found in patients with tumor-node-metastasis stage advanced and predicted reduced overall survival. In conclusion, our data indicate that IL-22+CD4+ T cells and Th22 cells are likely important in establishing the tumor microenvironment for GC; increased intratumoral IL-22+CD4+ T cells and Th22 cells are associated with tumor progression and predict poorer patient survival, suggesting that tumor-infiltrating IL-22+CD4+ T cells and Th22 cells may be suitable therapeutic targets in patients with GC.  相似文献   
139.
140.
Plant genomes encode diverse small RNA classes that function in distinct gene‐silencing pathways. To elucidate the intricate regulation of microRNAs (miRNAs) and endogenous small‐interfering RNAs (siRNAs) in response to chilling injury in tomato fruit, the deep sequencing and bioinformatic methods were combined to decipher the small RNAs landscape in the control and chilling‐injured groups. Except for the known miRNAs and ta‐siRNAs, 85 novel miRNAs and 5 ta‐siRNAs members belonging to 3 TAS families (TAS5, TAS9 and TAS10) were identified, 34 putative phased small RNAs and 740 cis/trans‐natural antisense small‐interfering RNAs (nat‐siRNAs) were also found in our results which enriched the tomato small RNAs repository. A large number of genes targeted by those miRNAs and siRNAs were predicted to be involved in the chilling injury responsive process and five of them were verified via degradome sequencing. Based on the above results, a regulatory model that comprehensively reveals the relationships between the small RNAs and their targets was set up. This work provides a foundation for further study of the regulation of miRNAs and siRNAs in the plant in response to chilling injury.  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