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   444篇
  免费   69篇
  国内免费   79篇
  2024年   3篇
  2023年   13篇
  2022年   28篇
  2021年   24篇
  2020年   16篇
  2019年   34篇
  2018年   36篇
  2017年   25篇
  2016年   29篇
  2015年   52篇
  2014年   46篇
  2013年   49篇
  2012年   39篇
  2011年   33篇
  2010年   28篇
  2009年   25篇
  2008年   28篇
  2007年   17篇
  2006年   17篇
  2005年   8篇
  2004年   8篇
  2003年   5篇
  2002年   6篇
  1999年   5篇
  1998年   2篇
  1997年   4篇
  1995年   1篇
  1994年   1篇
  1993年   1篇
  1992年   2篇
  1990年   1篇
  1989年   2篇
  1983年   1篇
  1982年   1篇
  1981年   2篇
排序方式: 共有592条查询结果,搜索用时 15 毫秒
1.
乙肝前S2(HBVPreS2)肽段由55个氨基酸组成,其N端肽段含Th和B细胞抗原决定簇。我们将化学合成的PreS2epitope(120-145)基因与HBcAg基因不同位点进行融合,融合基因在大肠杆菌中获得表达,并对融合蛋白进行了纯化。经ELISA和Western-blot实验表明,融合蛋白具有PreS2和HBcAg两者的抗原性。此外,研究还表明,强启动子能使表达水平有一定提高。  相似文献   
2.
Fire is a crucial event regulating the structure and functioning of many ecosystems. Yet few studies have focused on how fire affects taxonomic and functional diversities of soil microbial communities, along with changes in plant communities and soil carbon (C) and nitrogen (N) dynamics. Here, we analyze these effects in a grassland ecosystem 9 months after an experimental fire at the Jasper Ridge Global Change Experiment site in California, USA. Fire altered soil microbial communities considerably, with community assembly process analysis showing that environmental selection pressure was higher in burned sites. However, a small subset of highly connected taxa was able to withstand the disturbance. In addition, fire decreased the relative abundances of most functional genes associated with C degradation and N cycling, implicating a slowdown of microbial processes linked to soil C and N dynamics. In contrast, fire stimulated above‐ and belowground plant growth, likely enhancing plant–microbe competition for soil inorganic N, which was reduced by a factor of about 2. To synthesize those findings, we performed structural equation modeling, which showed that plants but not microbial communities were responsible for significantly higher soil respiration rates in burned sites. Together, our results demonstrate that fire ‘reboots’ the grassland ecosystem by differentially regulating plant and soil microbial communities, leading to significant changes in soil C and N dynamics.  相似文献   
3.
4.
HEPIS是一个新基因,关于HEPIS的表达和功能尚不十分清楚.本研究首先构建了HEPIS的表达载体pEGFP-C3-HEPIS,采用双荧光素酶报告实验检测了 HEPIS对Wnt、CRE、NF-KB和HRE信号通路的作用,随后采用RNA原位杂交(RISH)检测了 HEPIS在12种不同器官(乳腺,结肠,食道,肾,肝,肺,卵巢,胰腺,前列腺,直肠,胃和宫颈)的癌组织和正常组织的表达差异,并且检测了 HEPIS在40例直肠腺癌和直肠正常组织的表达.研究表明,在293T细胞转染pEGFP-C3-HEPIS后,无论是转录水平还是翻译水平,HEPIS均显著增加,且HEPIS可以显著抑制Wnt、CRE和NF-KB 3条信号通路,对NF-κB信号通路的抑制最为显著.RNA原位杂交实验证实HEPIS在12个器官的癌组织和正常组织中表达存在明显的表达差异.采用GEPIA对HEPIS在直肠癌及正常组织的表达差异进行了分析,结果表明HEPIS在正常直肠组织高表达,进一步采用RISH分析了 HEPIS在40例直肠癌和癌旁组织的表达差异,分析表明HEPIS在正常直肠组织的表达显著高于癌组织(P<0.01),与GEPIA分析结果一致,说明HEPIS可能是直肠癌的一个潜在抑癌基因.  相似文献   
5.

Background

Although the Newcastle disease virus (NDV) inactivated vaccines and attenuated live vaccines have been used to prevent and control Newcastle disease (ND) for years, there are some disadvantages. Recently, newly developed DNA vaccines have the potential to overcome these disadvantages. The low delivery efficiency, however, hindered the application of DNA vaccines for ND in practice.

Methodology/Principal Findings

The eukaryotic expression plasmid pVAX1-F (o) DNA that expressed the F gene of NDV encapsulated in PLGA nanoparticles (pFNDV-PLGA-NPs) were prepared by a double emulsion-solvent evaporation method and optimal preparation conditions of the pFNDV-PLGA-NPs were determined. Under the optimal conditions, the pFNDV-PLGA-NPs were produced in good morphology and had high stability with a mean diameter of 433.5±7.5 nm, with encapsulation efficiency of 91.8±0.3% and a Zeta potential of +2.7 mV. Release assay in vitro showed that the fusion gene plasmid DNA could be sustainably released from the pFNDV-PLGA-NPs up to 93.14% of the total amount. Cell transfection test indicated that the vaccine expressed and maintained its bioactivity. Immunization results showed that better immune responses of SPF chickens immunized with the pFNDV-PLGA-NPs were induced compared to the chickens immunized with the DNA vaccine alone. In addition, the safety of mucosal immunity delivery system of the pFNDV-PLGA-NPs was also tested in an in vitro cytotoxicity assay.

Conclusions/Significance

The pFNDV-PLGA-NPs could induce stronger cellular, humoral, and mucosal immune responses and reached the sustained release effect. These results laid a foundation for further development of vaccines and drugs in PLGA nanoparticles.  相似文献   
6.
Infectious laryngotracheitis (ILT) is an acute respiratory disease caused by infectious laryngotracheitis virus (ILTV). The complete genome sequences of five attenuated ILTV vaccine strains and six virulent ILTV strains as well as two Australian ILTV field strains have been published in Australia and the USA so far. To provide the complete genome sequence information of ILTVs from different geographic regions, the whole genome of ILTV LJS09 isolated in China was sequenced. The genome of ILTV LJS09 was 153,201 bp in length, and contained 79 ORFs. Most of the ORFs had high sequence identity with homologous ORFs of reference strains. There was a large fragment deletion within the noncoding region of unique long region (UL) of ILTV LJS09 compared with SA2 and A20 strains. Though the origin binding protein of ILTV LJS09 existed, there was no AT-rich region in strain LJS09. Alignments of the amino acid sequences revealed seven mutations at amino acids 71 (Arg → Lys), 116 (Ala → Val), 207 (Thr → Ile) and 644 (Thr → Ile) on glycoprotein B, 155 (Phe → Ser) and 376 (Arg → His) on glycoprotein D and 8 (Gln→Pro) on glycoprotein L of ILTV LJS09 compared to those of virulent strain (USDA) as ILTV LJS09 did not grow on chicken embryo fibroblasts, suggesting the role of the key seven amino acids in determination of the cell tropism of ILTV LJS09. This is the first complete genome sequence of the virulent strain of ILTV in Asia using the conventional PCR method, which will help to facilitate the future molecular biological research of ILTVs.  相似文献   
7.
The primary objective of this 3 years study was to determine the prevalence of porcine pathogens of the lungs of swine in swine farms in southern China. A total of 5,420 samples were collected from 200 swine farms. The bacterium that was most commonly isolated was Streptococcus suis, with 10.24 % of the samples being positive, 114 lungs (2.1 %) were positive for pseudorabies virus and 263 (4.85 %) were positive for classical swine fever virus; much lower than positive for PRRSV (15.1 %, p = 0.023) and PCV2 (13.8 %, p = 0.038). lungs that were positive for PRRSV and/or PCV-2 have significantly increased odds of being positive for any of the S. suis (9.79 vs. 0.44 %, p = 0.003).  相似文献   
8.
Chlorophyll is an important photosynthetic pigment in the process of photosynthesis in plants and photosynthetic bacteria. Genes involved in chlorophyll biosynthesis in Arabidopsis and photosynthetic bacteria have been well documented. In rice, however, these genes have not been fully annotated. In this paper, a yellow-green leaf gene, yellow green leaf3 (ygl3) was cloned and analyzed. ygl3 encodes magnesium chelation ChlD (D) subunit, a key enzyme for chlorophyll synthesis, resulting in a yellow-green leaf phenotype in all growth stages in rice. Expression content of ygl3 is highest in the leaf blades, followed by the leaf sheaths, while there is virtually no expression of the gene in the stems and seeds. The sub-cellular structure and protein content of the photosynthetic system of the ygl3 mutant were revealed by transmission electron microscopy, BN-PAGE, and western blotting. The results show that the mutation of the ygl3 gene indirectly leads to a decrease in the protein content of the photosynthetic system and severely obstructs the formation of granum thylakoids.  相似文献   
9.
10.
Manganese (Mn) is an essential trace element, while excessive expose may induce neurotoxicity. Recently, lncRNAs have been extensively studied and it has been confirmed that lncRNAs participate in neural functions and aberrantly expressed lncRNAs are involved in neurological diseases. However, the pathological effects of lncRNAs on Mn-induced neurotoxicity remain unclear. In this study, the expression profiles of lncRNAs and messenger RNAs (mRNAs) were identified in Mn-treated hippocampal neurons and control neurons via microarray. Bioinformatic methods and intersection analysis were also employed. Results indicated that 566, 1161, and 1474 lncRNAs meanwhile 1848, 3228, and 4022 mRNAs were aberrantly expressed in low, intermediate, and high Mn-exposed groups compared with the control group, respectively. Go analysis determined that differentially expressed mRNAs were targeted to biological processes, cellular components, and molecular functions. Pathway analysis indicated that these mRNAs were enriched in insulin secretion, cell cycle, and DNA replication. Intersection analysis denominated that 135 lncRNAs and 373 mRNAs were consistently up-regulated while 150 lncRNAs and 560 mRNAs were consistently down-regulated. Meanwhile, lncRNA BC079195 was significantly up-regulated while lncRNAs uc.229- and BC089928 were significantly down-regulated in three comparison groups. The relative expression levels of 3 lncRNAs and 4 mRNAs were validated through qRT-PCR. To the best of our knowledge, this study is the first to identify the expression patterns of lncRNAs and mRNAs in hippocampal neurons of Sprague–Dawley rats. The results may provide evidence on underlying mechanisms of Mn-induced neurotoxicity, and aberrantly expressed lncRNAs/mRNAs may be useful in further investigations to detect early symptoms of Mn-induced neuropsychiatric disorders in the central nervous system.  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