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   14729篇
  免费   1346篇
  国内免费   1624篇
  17699篇
  2024年   61篇
  2023年   247篇
  2022年   542篇
  2021年   894篇
  2020年   630篇
  2019年   728篇
  2018年   697篇
  2017年   499篇
  2016年   668篇
  2015年   977篇
  2014年   1103篇
  2013年   1238篇
  2012年   1353篇
  2011年   1275篇
  2010年   750篇
  2009年   704篇
  2008年   770篇
  2007年   650篇
  2006年   639篇
  2005年   408篇
  2004年   408篇
  2003年   383篇
  2002年   327篇
  2001年   241篇
  2000年   196篇
  1999年   195篇
  1998年   162篇
  1997年   116篇
  1996年   106篇
  1995年   95篇
  1994年   73篇
  1993年   64篇
  1992年   84篇
  1991年   58篇
  1990年   52篇
  1989年   50篇
  1988年   41篇
  1987年   28篇
  1986年   22篇
  1985年   28篇
  1984年   19篇
  1983年   13篇
  1982年   17篇
  1981年   11篇
  1980年   8篇
  1979年   11篇
  1978年   10篇
  1977年   7篇
  1975年   11篇
  1973年   7篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
spindlin1, a novel human gene recently isolated by our laboratory, is highly homologous to mouse spindlin gene. In this study, we cloned cDNA full-length of this novel gene and send it to GenBank database as spindlin1 (Homo sapiens spindlin1) with Accession No. AF317228. In order to investigate the function of spindlin1, we studied further the subcellular localization of Spindlin1 protein and the effects of spindlin1 overexpression in NIH3T3 cells. The results showed that the fusion protein pEGFP-N1-spindlin1 was located in the nucleus and the C-terminal is correlated with nuclear localization of Spindlin1 protein. NIH3T3 cells which could stably express spindlin1 as a result of RT-PCR analysis compared with the control cells displayed a complete morphological change; made cell growth faster; and increased the percentage of cells in G2/M and S phase. Furthermore, overexpressed spindlin1 cells formed colonies in soft agar in vitro and formed tumors in nude mice. Our findings provide direct evidence that spindlin1 gene may contribute to tumorigenesis.  相似文献   
112.
趋磁细菌是一类可以沿磁场方向进行运动的微生物统称,在细胞内合成由生物膜包被、链状排列、纳米级、单磁畴的磁铁矿 (Fe3O4) 或胶黄铁矿 (Fe3S4) 的磁小体颗粒。趋磁细菌在自然界分布广泛且多样性丰富,不仅在水环境和沉积环境的铁、硫、碳、氮、磷等元素生物地球化学循环中发挥重要作用,而且在污染治理、疾病诊断和治疗等方面有较好的应用。趋磁细菌磁小体由生物膜包被并在细胞调控下合成,是一类新型的生物源磁性纳米材料。相比常规化学合成的磁性纳米颗粒,磁小体具有大小均一、生物相容性高、兼具化学修饰和基因工程修饰功能等特点,在磁性分离、固定化酶、食品检测、环境监测、医学诊断、磁共振成像、磁热疗和靶向治疗等方面具有广阔的应用前景。在介绍趋磁细菌多样性研究的基础上,综述了趋磁细菌和磁小体的制备、修饰及其应用的最新进展,并对未来的研究进行了展望。  相似文献   
113.
Protein phosphorylation is one of the most common post-translational modification processes that play an essential role in regulating protein functionality.The Helicoverpa armigera single nucleopolyhedrovirus (HearNPv) orf2-encoded nucleocapsid protein HA2 participates in orchestration of virus-induced actin polymerization through its WCA domain,in which phosphorylation status are supposed to be critical in respect to actin polymerization.In the present study,two putative phosphorylation sites (232Thr and 250Ser) and a highly conserved Serine (245Ser) on the WCA domain of HA2 were mutated,and their phenotypes were characterized by reintroducing the mutated HA2 into the HearNPV genome.Viral infectivity assays demonstrated that only the recombinant HearNPV bearing HA2 mutation at 245Ser can produce infectious virions,both 232Tbr and 250Ser mutations were lethal to the virus.However,actin polymerization assay demonstrated that all the three viruses bearing HA2 mutations were still capable of initiating actin polymerization in the host nucleus,which indicated the putative phosphorylation sites on HA2 may contribute to HearNPV replication through another unidentified pathway.  相似文献   
114.
蛇毒类凝血酶calobin在毕赤酵母中的表达   总被引:1,自引:0,他引:1  
蛇毒类凝血酶是临床上防治血栓栓塞性疾病的有效药物。参照朝鲜蝮蛇(Agkistrodon caliginosus,Korean Viper)类凝血酶calobin基因序列(GenBank AccessionNo.U32937.1),将人工合成的calobin基因克隆到酵母表达载体pPICZαA,于毕赤酵母中表达,得到了分子量约为32kD的重组calobin蛋白,经甲醇诱导培养,表达产物可获得3.5g/L的高表达量。重组蛋白经过阴离子交换柱Q-Sepharose Fast Flow和分子筛Sephacryl-S-100凝胶过滤层析等纯化步骤进行了初步纯化。纯化后的重组calobin可以在纤维蛋白原平板上形成水解圈,经SDS-PAGE实验显示,重组蛋白能水解纤维蛋白原的Aα链,产生一条约40kD左右的降解带。在实验中未能发现重组calobin对纤维蛋白原的凝固作用。  相似文献   
115.
microRNAs (miRNAs) play essential roles in cardiogenesis. The altered expression of miRNAs can result in cardiac malformations by inducing abnormalities in the behavior of cardiac cells. However, the role of miR-10a in the regulation of cardiomyocyte progenitor cells (CMPCs) remains undetermined. In the present study, we found that up- or down-regulation of miR-10a inhibited or promoted the proliferation of human CMPCs, respectively, without affecting their differentiation toward cardiomyocytes. miR-10a bound to GATA6 directly and reduced GATA6 expression. Over-expression of GATA6 greatly attenuated the miR-10a-mediated inhibitory effect on the proliferation of human CMPCs. Thus, our results indicate that miR-10a could effectively modulate the proliferation of human CMPCs by targeting GATA6. The finding provides novel insights into the potency of miR-10a during heart development.  相似文献   
116.
为获得大孔树脂纯化岩高兰多酚的最佳工艺,以岩高兰的地上部分为原料,通过考察6种不同类型树脂(HPD-100、X-5、AB-8、D101、HPD-600、NKA-II)的含水率、吸附率和解吸率的大小,筛选出一种最适合纯化岩高兰多酚的树脂。在此基础上,选择对纯化工艺影响较大的4种因素(上样浓度、乙醇浓度、洗脱流速、洗脱体积),进行响应面法分析得到最佳工艺。结果表明:HPD-600型大孔树脂对岩高兰多酚的纯化效果最佳,其最优工艺参数为:上样浓度0.84 mg·mL-1;乙醇浓度62.15%;洗脱流速0.67 mL·min-1;洗脱体积2.71 BV。该条件下,岩高兰多酚的提取率为229.18 mg·g-1,岩高兰多酚的纯度由8.11%提高到22.56%,回收率为67.78%。本研究为岩高兰多酚的纯化工艺提供了新的技术路线,也可为岩高兰提取物的研究和应用提供参考。  相似文献   
117.
The microsporidian Nosema antheraeae is a pathogen that infects the Chinese oak silkworm, Antheraea pernyi. We sequenced the complete small subunit (SSU) rRNA gene and the internal transcribed spacer (ITS) of N. antheraeae, and compared the SSU rRNA sequences in other microsporidia. The results indicated that Nosema species, including N. antheraeae, formed two distinct clades, consistent with previous observations. Furthermore, N. antheraeae is clustered with N. bombycis with high bootstrap support. The organization of the rRNA gene of N. antheraeae is LSU-ITS1-SSU-ITS2-5S, also following a pattern similar to the Nosema type species, N. bombycis. Thus, N. antheraeae is a Nosema species and has a close relationship to N. bombycis.  相似文献   
118.
天麻AFLP分析技术体系的建立   总被引:4,自引:3,他引:4  
目的:建立一个适于天麻研究用的AFLP分析技术体系。方法:以11份天麻种质资源为试材,构建供试天麻的AFLP指纹图谱,同时对AFLP分析过程中DNA提取、酶切、连接、预扩增、引物筛选、选择性扩增、电泳和银染等多种因素进行分析。结果:AFLP分析体系要求DNA模板质量高,酶切连接可同时进行,37℃、9h效果较好,预扩增要求高质量DNA聚合酶,产物15倍稀释作为选择性扩增模板效果好,制胶前玻璃板的处理和银染时间的掌控对获得较好结果非常关键。P-GGA/M-GT引物构建的指纹图谱拥有可清晰辨认的扩增条带45条。结论:AFLP指纹技术具有稳定性高、重复性好等优点,可用于天麻DNA分析。  相似文献   
119.
目的:探讨猪肺表面活性物质(PPS)对海水淹溺肺损伤大鼠的治疗效果及量-效关系.方法:24只SD大鼠气管内注入海水观察120min,建立海水淹溺肺损伤模型后,随机等分为4个治疗组(n=6):生理盐水对照组,100mg/kgPPS组,150mg/kgPPS组和200mg/kgPPS组.分别监测4组大鼠给药后30min、60min、120min的BR和Pa02,120min后放血处死,计算大鼠存活率及支气管肺泡灌洗液(BALF)中TNF-α浓度和TP含量,取肺观察肺组织形态学改变.结果:各剂量PPS治疗组与对照组比较在治疗后各时间点的BR、TNF-α浓度和TP含量均有不同程度下降(P<0.05),Pa02及存活率上升(P<0.05),肺脏的病理形态学有明显改变.结论:单独应用PPS能明显减轻海水淹溺肺损伤.并且存在量-效关系.  相似文献   
120.
Alzheimer’s disease (AD) is the prevalent cause of dementia in the ageing world population. Apolipoprotein E4 (ApoE4) allele is the key genetic risk factor for AD, although the mechanisms linking ApoE4 with neurocognitive impairments and aberrant metabolism remains to be fully characterised. We discovered a significant increase in the ApoE4 content of serum exosomes in old healthy subjects and AD patients carrying ApoE4 allele as compared with healthy adults. Elevated exosomal ApoE4 demonstrated significant inverse correlation with serum level of thyroid hormones and cognitive function. We analysed effects of ApoE4-containing peripheral exosomes on neural cells and neurological outputs in aged or thyroidectomised young mice. Ageing-associated hypothyroidism as well as acute thyroidectomy augmented transport of liver-derived ApoE4 reach exosomes into the brain, where ApoE4 activated nucleotide-binding oligomerisation domain-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome by increasing cholesterol level in neural cells. This, in turn, affected cognition, locomotion and mood. Our study reveals pathological potential of exosomes-mediated relocation of ApoE4 from the periphery to the brain, this process can represent potential therapeutic target.Subject terms: Cognitive neuroscience, Alzheimer''s disease, Cellular neuroscience  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