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   1750篇
  免费   102篇
  国内免费   6篇
  1858篇
  2024年   3篇
  2023年   28篇
  2022年   61篇
  2021年   70篇
  2020年   74篇
  2019年   105篇
  2018年   89篇
  2017年   73篇
  2016年   79篇
  2015年   92篇
  2014年   115篇
  2013年   163篇
  2012年   122篇
  2011年   129篇
  2010年   65篇
  2009年   69篇
  2008年   61篇
  2007年   56篇
  2006年   46篇
  2005年   42篇
  2004年   41篇
  2003年   29篇
  2002年   25篇
  2001年   4篇
  2000年   12篇
  1999年   11篇
  1998年   6篇
  1997年   3篇
  1996年   3篇
  1995年   10篇
  1994年   7篇
  1993年   4篇
  1992年   9篇
  1991年   15篇
  1990年   15篇
  1989年   13篇
  1988年   23篇
  1987年   15篇
  1986年   5篇
  1985年   9篇
  1984年   14篇
  1983年   6篇
  1982年   5篇
  1981年   3篇
  1980年   4篇
  1979年   7篇
  1978年   4篇
  1975年   4篇
  1957年   1篇
  1956年   2篇
排序方式: 共有1858条查询结果,搜索用时 15 毫秒
991.
MicroRNAs control the genes involved in hematopoietic stem cell (HSCs) survival, proliferation and differentiation. The over-expression of miR-146 and miR-150 has been reported during differentiation of HSCs into T-lymphoid lineage. Therefore, in this study we evaluated the effect of their over-expression on CD133+ cells differentiation to T cells. miR-146a and miR-150 were separately and jointly transduced to human cord blood derived CD133+ cells (>97 % purity). We used qRT-PCR to assess the expression of CD2, CD3ε, CD4, CD8, CD25, T cell receptor alpha (TCR-α) and Ikaros genes in differentiated cells 4 and 8 days after transduction of the miRNAs. Following the over-expression of miR-146a, significant up-regulation of CD2, CD4, CD25 and Ikaros genes were observed (P < 0.01). On the other hand, over-expression of miR-150 caused an increase in the expression of Ikaros, CD4, CD25 and TCR-α. To evaluate the combinatorial effect of miR-146a and miR-150, transduction of both miRNAs was concurrently performed which led to increase in the expression of Ikaros, CD4 and CD3 genes. In conclusion, it seems that the effect of miR-150 and miR-146a on the promotion of T cell differentiation is time-dependant. Moreover, miRNAs could be used either as substitutes or complements of the conventional differentiation protocols for higher efficiency.  相似文献   
992.

Background

The present study was conducted to investigate the possible outcome of interaction between endothelial nitric oxide (NOS3) G894T and cholesteryl ester transfer TaqIB variants on the risk of coronary artery disease (CAD) and type 2 diabetes mellitus (T2DM). The sample included a total of 207 CAD patients (102 CAD patients with T2DM and 105 CAD patients without T2DM). There were also 101 patients with T2DM and 92 age- and sex-matched healthy individuals as controls. All study participants were from Western Iran. The sample was genotyped by polymerase chain reaction-restriction fragment length polymorphism.

Results

The presence of NOS3 T allele was not associated with the risk of CAD or T2DM, and the CETP B1 allele was only significantly associated with the increased risk of CAD in total CAD patients (odds ratio (OR)?=?5.1, p?=?0.019). However, the concomitant presence of both CETP B1 and NOS3 T alleles significantly increased the risk of CAD in total CAD patients (OR?=?18.1, p?<?0.001), in CAD patients without T2DM (OR?=?27.1, p?=?0.03), and in CAD patients with T2DM (OR?=?13.5, p?=?0.002). Also, the presence of both alleles increased the risk of T2DM (OR?=?12, p?=?0.004).

Conclusions

Our findings, for the first time, indicate that NOS3 T allele strongly interacts with CETP B1 allele to augment the risk of CAD and T2DM in the population of Western Iran.  相似文献   
993.
Hereditary neuropathy with liability to pressure palsies (HNPP) is an autosomal dominant disorder characterized by recurrent mononeuropathies. A 1.5-Mb deletion in chromosome 17p11.2-p12 has been associated with HNPP. Duplication of the same 1.5-Mb region is known to be associated with Charcot-Marie-Tooth disease type 1 (CMT1A), a more severe peripheral neuropathy characterized by symmetrically slowed nerve conduction velocity (NCV). The CMT1A duplication and HNPP deletion appear to be the reciprocal products of a recombination event involving a repeat element (CMT1A-REP) that flanks the 1.5-Mb region involved in the duplication/deletion. Patients from nine unrelated Italian families who were diagnosed with HNPP on the basis of clinical, electrophysiological, and histological evaluations were analyzed by molecular methods for DNA deletion on chromosome 17p. In all nine families, Southern analysis using a CMT1A-REP probe detected a reduced hybridization signal of a 6.0-kb EcoRI fragment mapping within the distal CMT1A-REP, indicating deletion of one copy of CMT1A-REP in these HNPP patients. Families were also typed with a polymorphic (CA)n repeat and with RFLPs corresponding to loci D17S122, D17S125, and D17S61, which all map within the deleted region. Lack of allelic transmission from affected parent to affected offspring was observed in four informative families, providing an independent indication for deletion. Furthermore, pulsed-field gel electrophoresis analysis of SacII-digested genomic DNA detected junction fragments specific to the 1.5-Mb HNPP deletion in seven of nine Italian families included in this study. These findings suggest that a 1.5-Mb deletion on 17p11.2-p12 is the most common mutation associated with HNPP.  相似文献   
994.
In this study, the effect of spraying mother plants with various levels of putrescine, spermidine, and cycocel (each at 0, 50, 500, and 5000 mg/l) were assessed on the frequency of haploid embryos produced from unfertilized ovaries and subsequent regeneration of derived embryos. Significantly higher haploid embryos were obtained when mother plants were sprayed with putrescine at 500 mg/l (5.2 embryos/fruit), spermidine at 50 mg/l (4.8 embryos/fruit), and cycocel at 50 mg/l (5.2 embryos/fruit) as compared to the control (without spraying, 3.2 embryos/fruit). However, embryogenesis induction was decreased drastically as the concentration of all the three compounds tested was increased and the lowest haploid embryos were observed when 5000 mg/l of spermidine (0.4 embryos/fruit) or cycocel (2.0 embryos/fruit) were applied. Only spermidine at 50 mg/l led to 100% regeneration into fully developed plantlets. The seed setting and size of fruits were also affected by polyamines and cycocel applications. Ploidy analysis using a flow cytometer indicated that all regenerated plantlets contain the gametic chromosome number (n?=?x?=?7) of parental plants and the results of chromosome counting also confirmed the haploid nature of regenerated plantlets. It can be concluded that the induction of haploid embryogenesis from unfertilized ovaries after pollination with irradiated pollen and subsequent conversion of derived embryos into the plantlets could be improved in Cucumis sativus L. by applying appropriate levels of putrescine, spermidine, and cycocel.  相似文献   
995.
Probiotics and Antimicrobial Proteins - Probiotics are living microorganisms that have favorable effects on human and animal health. The most usual types of microorganisms recruited as probiotics...  相似文献   
996.
The molecular analysis of metal hyperaccumulation in species such as Arabidopsis halleri offers the chance to gain insights into metal homeostasis and into the evolution of adaptation to extreme habitats. A prerequisite of metal hyperaccumulation is metal hypertolerance. Genetic analysis of a backcross population derived from Arabidopsis lyrata × A. halleri crosses revealed three quantitative trait loci for Cd hypertolerance. A candidate gene for Cdtol2 is AhCAX1, encoding a vacuolar Ca2+/H+ antiporter. We developed a method for the transformation of vegetatively propagated A. halleri plants and generated AhCAX1‐silenced lines. Upon Cd2+ exposure, several‐fold higher accumulation of reactive oxygen species (ROS) was detectable in roots of AhCAX1‐silenced plants. In accordance with the dependence of Cdtol2 on external Ca2+ concentration, this phenotype was exclusively observed in low Ca2+ conditions. The effects of external Ca2+ on Cd accumulation cannot explain the phenotype as they were not influenced by the genotype. Our data strongly support the hypothesis that higher expression of CAX1 in A. halleri relative to other Arabidopsis species represents a Cd hypertolerance factor. We propose a function of AhCAX1 in preventing a positive feedback loop of Cd‐elicited ROS production triggering further Ca2+‐dependent ROS accumulation.  相似文献   
997.
998.
999.
The synthesis of a series of novel 1-[(benzofuran-2-yl)phenylmethyl]-triazoles and -tetrazoles is described. The compounds were tested for human placental aromatase inhibition in vitro, using [1beta-3H]-androstenedione as the substrate for the aromatase enzyme, the percentage inhibition and IC50 data is included.  相似文献   
1000.
To determine the plasma lipid and lipoprotein profiles and their possible association with the type of β-thalassemia mutation we studied 103 major β-thalassemia patients including 71 children and 32 young adults compared to 102 healthy subjects consisted of 90 children and 12 young healthy adults. The plasma lipid and lipoprotein levels were measured by conventional methods. Considering all of the patients the levels of total cholesterol (TC), LDL-cholesterol (LDL-C), and HDL-cholesterol (HDL-C) were significantly lower compared to controls. However, the level of TG was significantly higher in cases than controls. Comparing thalassemic patients homozygous for a β0 type of mutation with those homozygous for a β+ type of mutation (IVSI.110 G:A) indicated that the levels of LDL-C, TC were significantly increased and TG concentration tended to be higher in the latter patients. In conclusion, our study indicates that hemolytic stress results in hypocholesterolemia in major β-thalassemia patients and the presence of more severe genotype in patients is correlated with more reduction in TG, TC, and LDL-C levels.  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