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   6009篇
  免费   535篇
  国内免费   1121篇
  7665篇
  2024年   20篇
  2023年   101篇
  2022年   236篇
  2021年   335篇
  2020年   223篇
  2019年   319篇
  2018年   268篇
  2017年   196篇
  2016年   287篇
  2015年   438篇
  2014年   523篇
  2013年   505篇
  2012年   644篇
  2011年   565篇
  2010年   361篇
  2009年   323篇
  2008年   388篇
  2007年   328篇
  2006年   268篇
  2005年   264篇
  2004年   193篇
  2003年   176篇
  2002年   148篇
  2001年   94篇
  2000年   66篇
  1999年   65篇
  1998年   50篇
  1997年   36篇
  1996年   36篇
  1995年   25篇
  1994年   36篇
  1993年   25篇
  1992年   28篇
  1991年   22篇
  1990年   20篇
  1989年   8篇
  1988年   6篇
  1987年   6篇
  1986年   6篇
  1985年   7篇
  1984年   3篇
  1983年   4篇
  1980年   1篇
  1979年   1篇
  1978年   1篇
  1969年   2篇
  1968年   3篇
  1966年   2篇
  1961年   1篇
  1960年   1篇
排序方式: 共有7665条查询结果,搜索用时 15 毫秒
101.
Congenital generalized hypertrichosis terminalis (CGHT) is a rare condition characterized by universal excessive growth of pigmented terminal hairs and often accompanied with gingival hyperplasia. In the present study, we describe three Han Chinese families with autosomal-dominant CGHT and a sporadic case with extreme CGHT and gingival hyperplasia. We first did a genome-wide linkage scan in a large four-generation family. Our parametric multipoint linkage analysis revealed a genetic locus for CGHT on chromosome 17q24.2-q24.3. Further two-point linkage and haplotyping with microsatellite markers from the same chromosome region confirmed the genetic mapping and showed in all the families a microdeletion within the critical region that was present in all affected individuals but not in unaffected family members. We then carried out copy-number analysis with the Affymetrix Genome-Wide Human SNP Array 6.0 and detected genomic microdeletions of different sizes and with different breakpoints in the three families. We validated these microdeletions by real-time quantitative PCR and confirmed their perfect cosegregation with the disease phenotype in the three families. In the sporadic case, however, we found a de novo microduplication. Two-color interphase FISH analysis demonstrated that the duplication was inverted. These copy-number variations (CNVs) shared a common genomic region in which CNV is not reported in the public database and was not detected in our 434 unrelated Han Chinese normal controls. Thus, pathogenic copy-number mutations on 17q24.2-q24.3 are responsible for CGHT with or without gingival hyperplasia. Our work identifies CGHT as a genomic disorder.  相似文献   
102.
103.
LeETR1反义基因对番茄的遗传转化   总被引:15,自引:0,他引:15  
从番茄果实中提取总RNA,根据GeneBank中LeETR1序列,设计合成特异性引物,利用RT-PCR及技术克隆了LeETR1基因3’端非编码区313bp的cDNA,经酶切图谱和序列分析鉴定无误后,反向插入到植物表达载体pPZP11A中,构建了表达LeETR1反义RNA的双元载体。经农杆菌途径转化番茄品种B1后,通过PCR检测从抗卡那霉素再生植株中筛选到13株阳性植株,Southern blot杂交确证反义基因已经整合到番茄染色体中。对果实乙烯释放的测定结果表明,转基因番茄乙烯释放高峰的出现比对照果实推迟10天,番茄红素的合成受到显抑制,果实不能形成正常的红色。推测LeETR1和番茄的成熟有着密切的关系。  相似文献   
104.
原子力显微镜(AFM)的发明为微纳尺度下高分辨率探测天然状态生物样本的物理特性提供了强大工具,是对传统生化特性检测方法的有力补充.近年来,多参数成像模式AFM的出现使得人们不仅可以获取生物样本表面形貌特征,还能同时获取生物样本多种力学特性图(如杨氏模量、黏附力、形变等),为研究生物结构、力学特性及其生理功能之间的关联提供了新的技术手段.多参数成像AFM的生物医学应用研究为细胞/分子生理活动及相关疾病内在机理带来了大量新的认识.本文结合作者在AFM细胞探测方面的研究工作,介绍了多参数成像AFM工作原理,总结了多参数成像AFM在细胞及分子力学特性探测方面的研究进展,并对其存在的问题进行了讨论和展望.  相似文献   
105.
目的:探讨利伐沙班用于急性肺栓塞的抗凝效果及对血清脑钠肽(Brain natriuretic peptide,BNP)、肌钙蛋白I (Troponin I,TnI)、D-二聚体(D-Dimer,D-D)、同型半胱氨酸(homocysteine,Hcy)水平的影响。方法:选择2014年2月至2017年12月在我院进行治疗的(高)中危组急性肺栓塞患者106例,并将其随机分为观察组和对照组。对照组皮下注射低分子肝素钙搭配华法林治疗,观察组予以利伐沙班治疗,观察和比较两组患者的临床疗效、治疗前后血清BNP、TnI、D-D、Hcy水平的变化及不良反应的发生情况。结果:治疗后,观察组患者总有效率为94.37%,显著高于对照组(42.10%,P0.05);观察组患者血清BNP、TnI、D-D、Hcy及肺动脉收缩压水平均显著低于对照组(P0.05),而动脉收缩压、动脉血氧分压水平较对照组水平显著升高(P0.05)。结论:利伐沙班应用于治疗急性肺栓塞的抗凝效果显著优于低分子肝素钙搭配华法林治疗,其可有效降低患者血清BNP、TnI、D-D、Hcy水平以及肺动脉收缩压。  相似文献   
106.
Prostate cancer (PCa) is a challenging issue for men's health worldwide due to its uncontrolled proliferation and high metastatic potential. Increasing evidence has supported plant extracts and natural plant derivatives as promising antitumor therapy with less toxic side effects. Yuanhuacine is an active component isolated from Daphne genkwa and can effectively suppress the tumorigenesis of several cancers. However, its role in PCa remains unclear. In this study, yuanhuacine dose-dependently inhibited the proliferation and induced apoptosis of PCa cells. Moreover, yuanhuacine also restrained the invasion and migration of PCa cells. Mechanically, yuanhuacine decreased the ubiquitination and degradation of p53 protein, and ultimately increased p53 levels, which was regulated by inhibiting the phosphorylation and total protein levels of mouse double minute 2 (MDM2). Moreover, elevation of MDM2 reversed the suppressive efficacy of yuanhuacine in PCa cell viability, invasion, and migration. The network pharmacologic and bioinformatics analysis confirmed that MDM2 might be a common target of D. genkwa and LINC00665. Furthermore, yuanhuacine inhibited LINC00665 expression. Upregulation of LINC00665 reversed yuanhuacine-mediated inhibition in MDM2 protein expression and suppressed p53 levels by enhancing its ubiquitination in yuanhuacine-treated cells. Importantly, the inhibitory effects of yuanhuacine on cell viability and metastatic potential were offset after LINC00665 elevation. Together, the current findings highlight that yuanhuacine may possess tumor-suppressive efficacy by inhibiting LINC00665-mediated MDM2/p53 ubiquitination signaling. Therefore, this study indicates that yuanhuacine may be a promising candidate for the treatment of PCa.  相似文献   
107.
旨在建立一种以agr基因为靶点,快速检测金黄色葡萄球菌的环介导等温扩增(LAMP)方法。针对金黄色葡萄球菌附属基因调控基因agr序列,设计了4条特异性引物;优化了LAMP体系中甜菜碱、dNTP浓度、长短引物比等因素;通过对14株不同金黄色葡萄球菌菌株和4株其他常见食品致病菌株进行检测,评估引物特异性。结果表明,在Mg2+浓度为2.4 mmol/L,dNTP浓度为0.8 mmol/L,甜菜碱浓度为0.1 mol/L,长短引物比为1:8,65 ℃反应50 min条件下扩增可达最佳效果。优化后的LAMP对14株金黄色葡萄球菌均表现为阳性,对4株非金黄色葡萄球菌菌株表现为阴性,证明引物具有特异性。本文首次利用agr基因作为靶基因片段,建立了一个简单、快速、特异性强的检测金黄色葡萄球菌的方法,在食品安全检测方面极具意义。  相似文献   
108.
Rhododendron maximum is an evergreen shrub native to the Appalachian Mountains of North America that has expanded in recent decades due to past disturbances and land management. The purpose of this study was to explore how bees and plants were affected by the experimental removal of R. maximum followed by a prescribed fire in one watershed compared to a neighboring reference watershed. Bees and plants were sampled for three years in both watersheds. Comparisons were based on the rarefaction and extrapolation sampling curves of Hill numbers as well as multivariate methods to assess effects on community composition. Bee richness, Shannon''s diversity, and Simpson''s diversity did not differ between watersheds in the year after removal but were all significantly higher in the removal watershed in year two, following the prescribed fire. Bee Shannon''s diversity and Simpson''s diversity, but not richness, remained significantly higher in the removal watershed in the third year. Similar but weaker patterns were observed for plants. Comparisons of community composition found significant differences for bees in the second and third year and significant differences for plants in all three years. For both groups, significant indicator taxa were mostly associated with the removal watershed. Because bees appeared to respond more strongly to the prescribed fire than to the removal of R. maximum and these benefits weakened considerably one year after the fire, clearing R. maximum does not appear to dramatically improve pollinator habitat in the southern Appalachians. This conclusion is underscored by the fact that about one quarter of the bee species in our study area were observed visiting R. maximum flowers. The creation of open areas with wildflowers may be a better way to benefit bees in this region judging from the high diversity of bees captured in the small roadside clearings in this study.  相似文献   
109.
TFP(10-100μmol/L)可引起裂殖酵母(Schizosaccharomyces pombe)胞外Ca2+内流,TFP浓度不同,促进Ca2+内流程度也不一样,50μmol/LTFP的促进作用最大。并且TFP浓度越大,Ca2+内流出现峰值也越早,10、20、50、100μmol/LTFP处理后,胞内总钙出现峰值时间分别为45、45、30、15分钟。胞外H+浓度也会对TFP引起的Ca2+内流产生不同影响,缓冲液的pH值为6.0时最有利于TFP引起胞内Ca2+含量增加,碱性条件下TFP的效果最不明显。由TFP引起的Ca2+内流增加要比单一地增加外钙浓度效果好得多,TFP在10μmol/L浓度的外钙条件下引起的胞内钙含量数值比1000μmol/L的外钙条件而无TFPT所引起的胞内钙含量还要高53.9%。缓冲液中加入0.8%的钙离子通道阻断剂LaC13或溶液中无葡萄糖的存在,TFP的促进作用消失,说明TFP促进Ca2+内流是通过钙离子通道来完成的并需要能量参与。  相似文献   
110.
用鲜花循环式动态顶空技术采集红厚壳鲜花的香气成分,TCT-GC-MS联用技术分析鉴定。4-羟基-2-丁酮,双烯酮,1、2-环氧-2-甲基丁烷,1、2-环氧-3-甲基丁烷,2-乙基戊烷,3-己醇,甲基环戊烷,2-丁醇等24个成分被检测出,占总离子流出峰面积的90.28%。并对结果进行了分析讨论。  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