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   480篇
  免费   9篇
  国内免费   8篇
系统科学   7篇
丛书文集   10篇
教育与普及   1篇
理论与方法论   2篇
现状及发展   84篇
研究方法   24篇
综合类   368篇
自然研究   1篇
  2022年   3篇
  2021年   8篇
  2020年   5篇
  2019年   4篇
  2017年   9篇
  2016年   6篇
  2015年   10篇
  2014年   20篇
  2013年   20篇
  2012年   26篇
  2011年   25篇
  2010年   9篇
  2009年   17篇
  2008年   19篇
  2007年   24篇
  2006年   27篇
  2005年   15篇
  2004年   20篇
  2003年   23篇
  2002年   18篇
  2001年   21篇
  2000年   14篇
  1999年   19篇
  1998年   7篇
  1997年   15篇
  1996年   11篇
  1995年   5篇
  1994年   4篇
  1993年   4篇
  1992年   4篇
  1991年   3篇
  1990年   6篇
  1989年   4篇
  1988年   4篇
  1987年   6篇
  1986年   4篇
  1985年   2篇
  1981年   2篇
  1980年   6篇
  1979年   8篇
  1978年   4篇
  1977年   3篇
  1976年   5篇
  1975年   3篇
  1974年   4篇
  1973年   4篇
  1971年   2篇
  1970年   2篇
  1969年   3篇
  1967年   3篇
排序方式: 共有497条查询结果,搜索用时 9 毫秒
401.
In this paper,the physique of the Hong Kong Correc-tional Services recruits were identified and reported.Kinanthropometry has been applied in the study of Olympic athletes and researchers concluded that specificsports were correlated with a specific type of physique.Athletes involved in the same sports have a similar phys-ique as well as body shape.Gold medal winners could beidentified by their specific type of body shape.And ath-letes in different sport have different and specific bodyshape.Hence,by applying kinanthropometry study,people in different occupations could be identified by their specific body shape and physique.The finalisedbody shape can be used as reference in the vetting stan-dards.The somatotyping and anthropometric input canbe used to improve the uniform sizing system.  相似文献   
402.
Sachs,Kozyrev和Grinber,指出平面图。有Hamliton圈的一个必要条件是∑sum fromi=3(i-2)φ_i=∑sumfromi=3(i- 2)φ'_i=n-2,其中φ_i和φ'_i分别为Hamilton 圈内、外度为i的面数.本文探讨面的度相等的平面图的面数,面并成顶点在边界上的连通区域与 Hamilton 圈.  相似文献   
403.
The three isoforms of the adaptor protein Shc play diverse roles in cell signalling. For example, the observation of p46 Shc in the nuclei of hepatocellular carcinoma cells suggests a function quite distinct from the better characterised cytoplasmic role. Ligands responsible for the transport of various Shc isoforms into organelles such as the nucleus have yet to be reported. To identify such ligands a far western approach was used to determine the p52 Shc interactome. The Ran-GTPase nuclear transport protein was identified and found to bind to p52 Shc in vitro with low micromolar affinity. Co-immunoprecipitation, pull down and fluorescence lifetime imaging microscopy experiments in stable cells confirmed cellular interaction and nuclear localisation. The nuclear transport factor protein NTF2, which functions in cohort with Ran, was shown to form a complex with both RAN and Shc, suggesting a mechanism for Shc entry into the nucleus as part of a tertiary complex. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Received 20 October 2008; received after revision 04 December 2008; accepted 15 December 2008  相似文献   
404.
Gastric cancer is a heterogeneous disease with multiple environmental etiologies and alternative pathways of carcinogenesis. Beyond mutations in TP53, alterations in other genes or pathways account for only small subsets of the disease. We performed exome sequencing of 22 gastric cancer samples and identified previously unreported mutated genes and pathway alterations; in particular, we found genes involved in chromatin modification to be commonly mutated. A downstream validation study confirmed frequent inactivating mutations or protein deficiency of ARID1A, which encodes a member of the SWI-SNF chromatin remodeling family, in 83% of gastric cancers with microsatellite instability (MSI), 73% of those with Epstein-Barr virus (EBV) infection and 11% of those that were not infected with EBV and microsatellite stable (MSS). The mutation spectrum for ARID1A differs between molecular subtypes of gastric cancer, and mutation prevalence is negatively associated with mutations in TP53. Clinically, ARID1A alterations were associated with better prognosis in a stage-independent manner. These results reveal the genomic landscape, and highlight the importance of chromatin remodeling, in the molecular taxonomy of gastric cancer.  相似文献   
405.
Through subtraction of tumor-specific CpG methylation, we identified receptor tyrosine kinase-like orphan receptor 2 (ROR2) as a candidate tumor suppressor gene (TSG). ROR2 is a specific receptor or co-receptor for WNT5A, involved in canonical and non-canonical WNT signaling, with its role in tumorigenesis controversial. We characterized its functions and related cell signaling in common carcinomas. ROR2 was frequently silenced by promoter CpG methylation in multiple carcinomas including nasopharyngeal, esophageal, gastric, colorectal, hepatocellular, lung, and breast cancers, while no direct correlation of ROR2 and WNT5A expression was observed. Ectopic expression of ROR2 resulted in tumor suppression independent of WNT5A status, through inhibiting tumor cell growth and inducing cell cycle arrest and apoptosis. ROR2 further suppressed epithelial-mesenchymal transition and tumor cell stemness through repressing β-catenin and AKT signaling, leading to further inhibition of tumor cell migration/invasion and increased chemo-sensitivity. Thus ROR2, as an epigenetically inactivated TSG, antagonizes both β-catenin and AKT signaling in multiple tumorigenesis. Its epigenetic silencing could be a potential tumor biomarker and therapeutic target for carcinomas.  相似文献   
406.
Influenza viruses account for significant morbidity worldwide. Inflammatory responses, including excessive generation of reactive oxygen and nitrogen species (RONS), mediate lung injury in severe influenza infections. However, the molecular basis of inflammation-induced lung damage is not fully understood. Here, we studied influenza H1N1 infected cells in vitro, as well as H1N1 infected mice, and we monitored molecular and cellular responses over the course of 2 weeks in vivo. We show that influenza induces DNA damage to both, when cells are directly exposed to virus in vitro (measured using the comet assay) and also when cells are exposed to virus in vivo (estimated via γH2AX foci). We show that DNA damage, as well as responses to DNA damage persist in vivo until long after virus has been cleared, at times when there are inflammation associated RONS (measured by xanthine oxidase activity and oxidative products). The frequency of lung epithelial and immune cells with increased γH2AX foci is elevated in vivo, especially for dividing cells (Ki-67-positive) exposed to oxidative stress during tissue regeneration. Additionally, we observed a significant increase in apoptotic cells as well as increased levels of DNA double strand break (DSB) repair proteins Ku70, Ku86 and Rad51 during the regenerative phase. In conclusion, results show that influenza induces DNA damage both in vitro and in vivo, and that DNA damage responses are activated, raising the possibility that DNA repair capacity may be a determining factor for tissue recovery and disease outcome.  相似文献   
407.
以AlN薄膜为压电层,采用体硅微细加工工艺制备背空腔型结构薄膜体声波谐振器.材料测试结果表明,在优化溅射工艺下沉积的AlN薄膜具有(002)择优取向及良好的柱状晶结构.扫描电镜表征结果证实所制得空腔背部平滑且各向异性较好.用网络分析仪测试可知,所制得的谐振器具有较好的频率特性:谐振频率为2.537 GHz,机电耦合系数3.75%,串、并联品质因数分别为101.8、79.7.  相似文献   
408.
一种改进的iTrace技术的研究   总被引:2,自引:0,他引:2  
张婵 《科学技术与工程》2007,7(12):3013-3016
针对现有ICMP反向追踪方法中iTrace信息标记的IP地址或相关信息,导致重构完整攻击路径需要过多的数据包,并且计算量大的问题,提出了在iTrace分组中重新编码的方案。该方案可在较短的时间内推算出主要攻击路径,显著减少路径重构时对数据包的需求量,从而可以使受害者更快捷地追踪到攻击源,为受害者尽快响应攻击、减少攻击带来的损失创造了条件。  相似文献   
409.
作者给出了Kuratowski十四集定理的又一个等价形式,并进一步证明了拓扑空间(X,τ)中的任意子集经过取内部和闭包两种运算至多可产生7个不同的集合(包含A本身)。  相似文献   
410.
Severe acute respiratory syndrome (SARS) is caused by infection of a previously undescribed coronavirus (CoV). L-SIGN, encoded by CLEC4M (also known as CD209L), is a SARS-CoV binding receptor that has polymorphism in its extracellular neck region encoded by the tandem repeat domain in exon 4. Our genetic risk association study shows that individuals homozygous for CLEC4M tandem repeats are less susceptible to SARS infection. L-SIGN is expressed in both non-SARS and SARS-CoV-infected lung. Compared with cells heterozygous for L-SIGN, cells homozygous for L-SIGN show higher binding capacity for SARS-CoV, higher proteasome-dependent viral degradation and a lower capacity for trans infection. Thus, homozygosity for L-SIGN plays a protective role during SARS infection.  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