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   507篇
  免费   28篇
  国内免费   9篇
  2022年   3篇
  2020年   3篇
  2018年   3篇
  2017年   8篇
  2015年   8篇
  2014年   7篇
  2013年   11篇
  2012年   10篇
  2011年   13篇
  2010年   15篇
  2009年   19篇
  2008年   26篇
  2007年   19篇
  2006年   19篇
  2005年   9篇
  2004年   15篇
  2003年   10篇
  2002年   7篇
  2001年   16篇
  2000年   10篇
  1999年   14篇
  1998年   6篇
  1997年   6篇
  1996年   12篇
  1995年   3篇
  1994年   4篇
  1992年   7篇
  1991年   3篇
  1990年   10篇
  1989年   5篇
  1988年   6篇
  1986年   4篇
  1985年   3篇
  1983年   5篇
  1980年   4篇
  1979年   7篇
  1978年   8篇
  1974年   5篇
  1972年   3篇
  1959年   7篇
  1958年   23篇
  1957年   26篇
  1956年   26篇
  1955年   22篇
  1954年   22篇
  1953年   13篇
  1952年   13篇
  1951年   10篇
  1950年   9篇
  1912年   2篇
排序方式: 共有544条查询结果,搜索用时 15 毫秒
91.
We used partial sequences of mitochondrial 16S and cytochrome oxidase I genes to perform a phylogenetic study of collared frogs (Anura: Aromobatidae: Mannophryne ), a genus endemic to Venezuela and the islands of Trinidad and Tobago. We analysed 1.2 kb from 13 of the 15 described species of Mannophryne . Maximum parsimony, maximum likelihood and Bayesian analyses support the monophyly of Mannophryne . Mannophryne consists of three deeply differentiated clades that split from each other in a relatively short period of time. The diversification of Mannophryne occurred well before the glacial-interglacial periods of the Quaternary. Our data support the taxonomic validity of M. olmonae , a species endemic to Tobago Island. Mannophryne olmonae is more closely related to the continental species Mannophryne riveroi than to the Trinidad island endemic Mannophryne trinitatis . As in most tropical clades of frogs, molecular evidence indicates that species richness in Mannophryne is largely underestimated and, consequently, current priorities for conservation are inadequate.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 97 , 185–199.  相似文献   
92.
A multivariate morphometric study of Daniellia, an endemic genus of tropical and subtropical Africa, indicates that nine species may be recognized: D. alsteeniana, D. klainei, D. oblonga, D. ogea, D. oliveri, D. pilosa, D. pynaertii, D. soyauxii and D. thurifera. In our study we found that some characters, not previously studied in detail, were significant in species delimitation: petiole indumentum, petiole width, number and position of glands on the lower surface of the leaflets and presence or absence of glands at the insertion of each pair of leaflets. The rare and scattered material of D. pilosa and D. soyauxii made their classification uncertain, although some qualitative characters support their differentiation. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 159 , 268–279.  相似文献   
93.
Behçet's disease is a complex vasculitis of unknown etiology. Abundant neutrophils suggest the involvement of innate immunity. Cytokines are skewed to the T-helper-1 pattern. Few sterile organs are easily accessible for analysis in Behçet's disease. Cañete and coworkers identify inflamed joints as a feasible model and suggest the involvement of innate immunity in Behçet's disease.  相似文献   
94.
Mounting evidence is merging to affirm the effectiveness of bacterial lipopolysaccharides (LPS) as biological control agents, inducers of innate immunity, and to stimulate/potentiate the development of defense responses in plants through protein phosphorylation-mediated signal perception/transduction responses. In vivo labeling of protein phosphorylation events during signal transduction indicated the rapid phosphorylation of several proteins. Substantial differences and de novo LPS-induced phosphorylation were also observed with two-dimensional analysis. In this study, qualitative and quantitative changes in phosphoproteins of Nicotiana tabacum suspension cells during elicitation by LPS from the Gram-negative bacteria, Burkholderia cepacia, were analyzed using two-dimensional electrophoresis in combination with a phosphoprotein-specific gel stain. Trypsin digested phosphoproteins were analyzed by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF/MS) and nano-electrospray-ionization liquid chromatography tandem mass spectrometry (nano-ESI-LC/MS/MS). A total of 27 phosphoproteins were identified from 23 excised gel spots. The identified phosphoproteins indicate that LPS(B.cep)-induced signal perception/transduction involves G-protein coupled receptor signaling, Ca(2+)/calmodulin-dependent signaling pathways, H(+)-ATPase regulation of intracellular pH, thioredoxin-mediated signaling and phosphorylation of 14-3-3 regulatory proteins. Other targets of LPS(B.cep)-responsive phosphorylation included NTP pool maintenance, heat shock proteins, protein biosynthesis and chaperones as well as cytoskeletal tubulin. The results add novel insights into the biochemical process of LPS perception and resulting signal transduction.  相似文献   
95.
This study provides a checklist of the Caesalpinioideae (Leguminosae) present in Equatorial Guinea, comprising 52 genera and 124 taxa. Seven species are known from Annobón, 33 from Bioko and 109 from Río Muni. The best represented genus is Senna with eight species. In addition, bibliographic references for Caesalpinioideae (Leguminosae) from Equatorial Guinea have been gathered and checked. Fourteen species are included based on literature records, because their distribution ranges suggest they may occur in Equatorial Guinea, 11 introduced species could be naturalized, and 45 taxa are recorded for the first time from the country. This represents an increase of over 35% in the floristic knowledge of Caesalpinioideae from Equatorial Guinea. A statistical summary is presented at the end of the checklist.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 151 , 541–562.  相似文献   
96.
97.
98.
本研究旨在探讨谷糠结合态多酚(bound phenol of inner shell,BPIS)发挥抗乳腺癌细胞活性的作用机制。首先采用细胞计数法检测BPIS对乳腺癌细胞以及正常乳腺细胞活性的影响;然后综合运用SEA、SIB以及GeneCards等数据库获得BPIS和乳腺癌的相关靶点,并分析活性成分与作用靶点的互作网络以及通路。本研究筛选得到BPIS抗乳腺癌相关靶点39个,主要涉及糖脂代谢和细胞自噬等生物过程以及MAPK、PI3K/AKT、FoxO等多条信号通,表明BPIS抗乳腺癌是多成分、多靶点、多通路协同作用的过程,而与细胞死亡相关的细胞自噬很可能在BPIS抑制乳腺癌过程中发挥主要作用。  相似文献   
99.
研究抗肿瘤药阿霉素对Wnt通路抑制因子FrpHE(frizzled-related protein)和DKK-1(Dickkopf-1)表达的作用.将抗肿瘤药阿霉素加入到人肝癌HepG2(HepG2,含野生型p53;Hep3B,p53缺失)、人大肠癌(Lovo,含野生型p53)和人神经胶质瘤细胞(U251,p53突变)细胞株中.以RT-PCR技术检测阿霉素对Wnt通路抑制因子FrpHE和DKK-1的表达调节作用,以流式细胞术检测在肿瘤细胞中Wnt通路的关键调节因子β-catenin的表达.在加入阿霉素24h后FrpHEmRNA表达水平在人肝癌细胞(HepG2,含野生型p53;Hep3B,p53缺失)中与对照组相比表达水平显著增加.在人大肠癌细胞(Lovo,含野生型p53)和人神经胶质瘤细胞(U251,p53突变型)细胞中,未见FrpHE mRNA表达.DKK-1mRNA表达水平在人肝癌细胞(HepG2,含野生型p53;Hep3B,p53缺失)、人大肠癌细胞(Lovo,含野生型p53)和人神经胶质瘤细胞(U251,p53突变型)中与对照组相比表达水平显著增加.β-catenin的阳性细胞百分比强度和平均荧光量强度与对照组相比,表达水平降低.提示化疗药阿霉素能明显诱导抑制剂FrpHEmRNA和DKK-1mRNA的表达.  相似文献   
100.
Phytoextraction has been reported as an economically and ecologically sound alternative for the remediation of metal-contaminated soils. Willow is a metal phytoextractor of interest because it allows to combine a gradual contaminant removal with production of biomass that can be valorized in different ways. In this work two willow clones growing on a metal-contaminated site were selected: ‘Belgisch Rood’ (BR) with a moderate metal extraction capacity and ‘Tora’ (TO) with a twice as high metal accumulation. All cultivable bacteria associated with both willow clones were isolated and identified using 16SrDNA ARDRA analysis followed by 16SrDNA sequencing. Further all isolated bacteria were investigated for characteristics that might promote plant growth (production of siderophores, organic acids and indol acetic acid) and for their metal resistance. The genotypic and phenotypic characterization of the isolated bacteria showed that the TO endophytic bacterial population is more diverse and contains a higher percentage of metal-resistant plant growth promoting bacteria than the endophytic population associated with BR. We hypothesize that the difference in the metal accumulation capacity between BR and TO clones might be at least partly related to differences in characteristics of their associated bacterial population.  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