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   4884篇
  免费   389篇
  国内免费   688篇
  2024年   11篇
  2023年   52篇
  2022年   184篇
  2021年   290篇
  2020年   218篇
  2019年   253篇
  2018年   238篇
  2017年   182篇
  2016年   257篇
  2015年   350篇
  2014年   461篇
  2013年   396篇
  2012年   535篇
  2011年   473篇
  2010年   316篇
  2009年   291篇
  2008年   314篇
  2007年   260篇
  2006年   174篇
  2005年   169篇
  2004年   115篇
  2003年   94篇
  2002年   62篇
  2001年   41篇
  2000年   34篇
  1999年   26篇
  1998年   8篇
  1997年   9篇
  1996年   7篇
  1995年   9篇
  1994年   6篇
  1993年   3篇
  1992年   12篇
  1991年   9篇
  1990年   9篇
  1989年   11篇
  1988年   5篇
  1987年   9篇
  1986年   13篇
  1985年   11篇
  1984年   5篇
  1983年   9篇
  1982年   3篇
  1980年   7篇
  1978年   4篇
  1974年   2篇
  1973年   3篇
  1972年   2篇
  1965年   1篇
  1956年   1篇
排序方式: 共有5961条查询结果,搜索用时 31 毫秒
111.
112.
Glycogen synthase kinase 3 (GSK-3) is a well-known conserved and ubiquitous protein kinase and playing a pivotal role in neurodevelopment, neurogenesis, learning/memory, and neuronal cell death. Dysfunction of GSK-3 had been seen in multiple neurodegenerative and psychiatric diseases. Bipolar disorder and schizophrenia are two common psychiatric diseases first occur in adolescence or young adulthood. They share similar risk genes as well as clinical symptoms, which make it is difficult to be discriminated from each other. Here, by using meta-analysis we reported that glycogen synthase kinase 3β promoter inactive mutant rs334558 may contribute to the development of schizophrenia not bipolar disorder. This might be used to distinguish these two diseases.  相似文献   
113.
114.
115.
The echinostome metacercariae encysted in Cipangopaludina sp. snails that were purchased from a market in Vientiane Municipality, Lao PDR, were identified as Echinostoma macrorchis (Digenea: Echinostomatidae) through recovery of adult flukes after experimental infection to rats and a cat. The metacercariae were round, 113-128 (121)×113-125 (120) µm, having a thick cyst wall, a head collar armed with collar spines, and excretory granules. The adult flukes recovered from the rats and cat at day 14 and 30 post-infection, respectively, were elongated, ventrally curved, and 3.9-6.3×0.7-1.1 mm in size. The head collar was distinct, bearing 43-45 collar spines with 5 angle spines on each side. Two testes were large (as the name implies), tandem, and slightly constricted at the middle, with irregular margins. Eggs were operculated, ovoid to elliptical, and 88-95×56-60 µm. In scanning electron microscopy, the head collar was prominent, with 43-45 collar spines. Scale-like tegumental spines were densely distributed on the ventral surface between the oral and ventral suckers. Sensory papillae were distributed mainly on the tegument around the 2 suckers. It is confirmed that E. macrorchis is distributed in Lao PDR using Cipangopaludina sp. snails as the second intermediate host.  相似文献   
116.
117.
The human gut microbiota is a complex system that is essential to the health of the host. Increasing evidence suggests that the gut microbiota may play an important role in the pathogenesis of colorectal cancer (CRC). In this study, we used pyrosequencing of the 16S rRNA gene V3 region to characterize the fecal microbiota of 19 patients with CRC and 20 healthy control subjects. The results revealed striking differences in fecal microbial population patterns between these two groups. Partial least-squares discriminant analysis showed that 17 phylotypes closely related to Bacteroides were enriched in the gut microbiota of CRC patients, whereas nine operational taxonomic units, represented by the butyrate-producing genera Faecalibacterium and Roseburia, were significantly less abundant. A positive correlation was observed between the abundance of Bacteroides species and CRC disease status (R?=?0.462, P?=?0.046?<?0.5). In addition, 16 genera were significantly more abundant in CRC samples than in controls, including potentially pathogenic Fusobacterium and Campylobacter species at genus level. The dysbiosis of fecal microbiota, characterized by the enrichment of potential pathogens and the decrease in butyrate-producing members, may therefore represent a specific microbial signature of CRC. A greater understanding of the dynamics of the fecal microbiota may assist in the development of novel fecal microbiome-related diagnostic tools for CRC.  相似文献   
118.
119.
Many insects possess symbiotic bacteria that affect the biology of the host. The level of the symbiont population in the host is a pivotal factor that modulates the biological outcome of the symbiotic association. Hence, the symbiont population should be maintained at a proper level by the host''s control mechanisms. Several mechanisms for controlling intracellular symbionts of insects have been reported, while mechanisms for controlling extracellular gut symbionts of insects are poorly understood. The bean bug Riptortus pedestris harbors a betaproteobacterial extracellular symbiont of the genus Burkholderia in the midgut symbiotic organ designated the M4 region. We found that the M4B region, which is directly connected to the M4 region, also harbors Burkholderia symbiont cells, but the symbionts therein are mostly dead. A series of experiments demonstrated that the M4B region exhibits antimicrobial activity, and the antimicrobial activity is specifically potent against the Burkholderia symbiont but not the cultured Burkholderia and other bacteria. The antimicrobial activity of the M4B region was detected in symbiotic host insects, reaching its highest point at the fifth instar, but not in aposymbiotic host insects, which suggests the possibility of symbiont-mediated induction of the antimicrobial activity. This antimicrobial activity was not associated with upregulation of antimicrobial peptides of the host. Based on these results, we propose that the M4B region is a specialized gut region of R. pedestris that plays a critical role in controlling the population of the Burkholderia gut symbiont. The molecular basis of the antimicrobial activity is of great interest and deserves future study.  相似文献   
120.
Class I fungal hydrophobins are small surface‐active proteins that self‐assemble to form amphipathic monolayers composed of amyloid‐like rodlets. The monolayers are extremely robust and can adsorb onto both hydrophobic and hydrophilic surfaces to reverse their wettability. This adherence is particularly strong for hydrophobic materials. In this report, we show that the class I hydrophobins EAS and HYD3 can self‐assemble to form a single‐molecule thick coating on a range of nanomaterials, including single‐walled carbon nanotubes (SWCNTs), graphene sheets, highly oriented pyrolytic graphite, and mica. Moreover, coating by class I hydrophobin results in a stable, dispersed preparation of SWCNTs in aqueous solutions. No cytotoxicity is detected when hydrophobin or hydrophobin‐coated SWCNTs are incubated with Caco‐2 cells in vitro. In addition, we are able to specifically introduce covalently linked chemical moieties to the hydrophilic side of the rodlet monolayer. Hence, class I hydrophobins provide a simple and effective strategy for controlling the surfaces of a range of materials at a molecular level and exhibit strong potential for biomedical applications. © 2012 Wiley Periodicals, Inc.  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