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   1151篇
  免费   67篇
  2023年   9篇
  2022年   26篇
  2021年   45篇
  2020年   25篇
  2019年   27篇
  2018年   49篇
  2017年   43篇
  2016年   39篇
  2015年   81篇
  2014年   87篇
  2013年   101篇
  2012年   96篇
  2011年   113篇
  2010年   64篇
  2009年   31篇
  2008年   57篇
  2007年   58篇
  2006年   53篇
  2005年   42篇
  2004年   30篇
  2003年   23篇
  2002年   28篇
  2001年   6篇
  2000年   8篇
  1999年   8篇
  1998年   6篇
  1996年   4篇
  1995年   4篇
  1994年   4篇
  1993年   4篇
  1992年   2篇
  1990年   2篇
  1989年   2篇
  1988年   5篇
  1985年   2篇
  1984年   4篇
  1981年   2篇
  1980年   2篇
  1979年   2篇
  1978年   4篇
  1976年   2篇
  1972年   2篇
  1970年   2篇
  1968年   1篇
  1967年   2篇
  1966年   1篇
  1964年   1篇
  1941年   1篇
  1939年   1篇
  1905年   1篇
排序方式: 共有1218条查询结果,搜索用时 15 毫秒
91.
92.
93.
A new tortoise beetle species, Cyrtonota abrili, is described from the Antioquia and Caldas departments in Colombia. New faunistic data are provided for 87 species, including 16 new additions to the country’s fauna. A checklist of the known 238 species of tortoise beetles recorded from Colombia is given.  相似文献   
94.

Background

Tumor suppressor gene (TSG) inactivation plays a crucial role in carcinogenesis. FUS1, NPRL2/G21 and RASSF1A are TSGs from LUCA region at 3p21.3, a critical chromosomal region in lung cancer development. The aim of the study was to analyze and compare the expression levels of these 3 TSGs in NSCLC, as well as in macroscopically unchanged lung tissue surrounding the primary lesion, and to look for the possible epigenetic mechanism of TSG inactivation via gene promoter methylation.

Methods

Expression levels of 3 TSGs and 2 DNA methyltransferases, DNMT1 and DNMT3B, were assessed using real-time PCR method (qPCR) in 59 primary non-small cell lung tumors and the matched macroscopically unchanged lung tissue samples. Promoter methylation status of TSGs was analyzed using methylation-specific PCRs (MSP method) and Methylation Index (MI) value was calculated for each gene.

Results

The expression of all three TSGs were significantly different between NSCLC subtypes: RASSF1A and FUS1 expression levels were significantly lower in squamous cell carcinoma (SCC), and NPRL2/G21 in adenocarcinoma (AC). RASSF1A showed significantly lower expression in tumors vs macroscopically unchanged lung tissues. Methylation frequency was 38–76 %, depending on the gene. The highest MI value was found for RASSF1A (52 %) and the lowest for NPRL2/G21 (5 %). The simultaneous decreased expression and methylation of at least one RASSF1A allele was observed in 71 % tumor samples. Inverse correlation between gene expression and promoter methylation was found for FUS1 (rs = −0.41) in SCC subtype. Expression levels of DNMTs were significantly increased in 75–92 % NSCLCs and were significantly higher in tumors than in normal lung tissue. However, no correlation between mRNA expression levels of DNMTs and DNA methylation status of the studied TSGs was found.

Conclusions

The results indicate the potential role of the studied TSGs in the differentiation of NSCLC histopathological subtypes. The significant differences in RASSF1A expression levels between NSCLC and macroscopically unchanged lung tissue highlight its possible diagnostic role in lung cancer in situ recognition. High percentage of lung tumor samples with simultaneous RASSF1A decreased expression and gene promoter methylation indicates its epigenetic silencing. However, DNMT overexpression doesn’t seem to be a critical determinate of its promoter hypermethylation.  相似文献   
95.
96.
97.
Here we present first dinucleotide affinity resins for purification of proteins that specifically recognize the 5' end of mRNA. Constructed resins possess either a naturally occurring mono- or trimethylated cap or their analogues resistant towards enzymatic degradation, bearing a CH(2) bridge between β and γ position of the 5',5'-triphosphate chain. All cap analogues were attached to a polymer support (EAH-Sepharose) through the carboxylic group that had been generated by derivatization of the 2',3'-cis diol of the second nucleotide in the cap structure with levulinic acid.  相似文献   
98.
We have previously reported the power of combining a 5'-phosphoramidate ProTide, phosphate pro-drug, motif with a 6-methoxy purine pro-drug entity to generate highly potent anti-HCV agents, leading to agents in clinical trial. We herein extend this work with the disclosure that a variety of alternative 6-substituents are tolerated. Several compounds exceed the potency of the prior 6-methoxy leads, and in almost every case the ProTide is several orders of magnitude more potent than the parent nucleoside. We also demonstrate that these agents act as pro-drugs of 2'-C-methyl guanosine monophosphate. We have also reported the novel use of hepatocyte cell lysate as an ex vivo model for ProTide metabolism.  相似文献   
99.
The purpose of our study was to establish the frequency and distribution of the four most common BRCA1 mutations in Polish general population and in a series of breast cancer patients. Analysis of the population frequency of 5382insC (c.5266dupC), 300T >G (p.181T >G), 185delAG (c.68_69delAG) and 3819del5 (c.3700_3704del5) mutations of the BRCA1 gene were performed on a group of respectively 16,849, 13,462, 12,485 and 3923 anonymous samples collected at birth in seven Polish provinces. The patient group consisted of 1845 consecutive female breast cancer cases. The most frequent BRCA1 mutation in the general population was 5382insC found in 29 out of 16,849 samples (0.17%). 300T >G and 3819del5 mutations were found in respectively 11 of 13,462 (0.08%) and four of 3923 (0.1%) samples. The population prevalence for combined Polish founder 5382insC and 300T >G mutations was 0.25% (1/400). The frequencies of 5382insC and 300T >G carriers among consecutive breast cancer cases were, respectively, 1.9% (35/1845) and 1.2% (18/1486). Comparing these data with the population frequency, we calculated the relative risk of breast cancer for 5382insC mutation at OR = 17 and for 300T >G mutation at OR = 26. Our results, based on large population studies, show high frequencies of founder 5382insC and 300T >G BRCA1 mutations in Polish general population. Carriage of one of these mutations is connected with a very high relative risk of breast cancer.  相似文献   
100.
Japanese hop (Humulus japonicus Siebold & Zucc.) was karyotyped by chromosome measurements, fluorescence in situ hybridization with rDNA and telomeric probes, and C-banding/DAPI. The karyotype of this species consists of sex chromosomes (XX in female and XY1Y2 in male plants) and 14 autosomes difficult to distinguish by morphology. The chromosome complement also shows a rather monotonous terminal distribution of telomeric repeats, with the exception of a pair of autosomes possessing an additional cluster of telomeric sequences located within the shorter arm. Using C-banding/DAPI staining and 5S and 45S rDNA probes we constructed a fluorescent karyotype that can be used to distinguish all autosome pairs of this species except for the 2 largest autosome pairs, lacking rDNA signals and having similar size and DAPI-banding patterns. Sex chromosomes of H. japonicus display a unique banding pattern and different DAPI fluorescence intensity. The X chromosome possesses only one brightly stained AT-rich terminal segment, the Y1 has 2 such segments, and the Y2 is completely devoid of DAPI signal. After C-banding/DAPI, both Y chromosomes can be easily distinguished from the rest of the chromosome complement by the increased fluorescence of their arms. We discuss the utility of these methods for studying karyotype and sex chromosome evolution in hops.  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