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   430篇
  免费   32篇
  国内免费   1篇
  463篇
  2024年   2篇
  2023年   7篇
  2022年   19篇
  2021年   26篇
  2020年   21篇
  2019年   47篇
  2018年   36篇
  2017年   22篇
  2016年   27篇
  2015年   20篇
  2014年   33篇
  2013年   46篇
  2012年   39篇
  2011年   33篇
  2010年   18篇
  2009年   8篇
  2008年   13篇
  2007年   11篇
  2006年   10篇
  2005年   5篇
  2004年   6篇
  2003年   4篇
  2001年   3篇
  2000年   1篇
  1998年   3篇
  1997年   1篇
  1991年   1篇
  1953年   1篇
排序方式: 共有463条查询结果,搜索用时 15 毫秒
51.
Premature graying of hair with unclear etiology, which is known as premature canities, is a common cause of referrals to the dermatologists. We assessed the relationship between serum iron, copper, and zinc concentrations with premature canities. This study was conducted on patients under 20 years old suffering from premature canities, having a minimum of ten gray hair fibers, and referring to university hospitals of Isfahan (Iran). The results were compared with age–sex-matched controls. Demographic data and disease characteristics were recorded for two groups. We studied serum iron, copper, and zinc concentrations of 66 patients and 66 controls using atomic absorption and Ferrozine methods. The mean age of studied cases was 17.8 ± 2.0 years, and the mean age of the onset of canities was 15.5 ± 3.2 years with no significant difference between males and females (P > 0.05). Serum copper concentration was significantly lower in patients compared with controls (90.7 ± 37.4 vs. 105.3 ± 50.2 μg/dL, P = 0.048), but serum iron concentration was significantly lower in controls compared to patients (88.8 ± 39.5 vs. 108.3 ± 48.4 μg/dL, P = 0.008). Also, there was no significant difference between patients and controls in serum zinc concentration (114.8 ± 67.8 vs. 108.2 ± 49.9 μg/dL, P = 0.285). According to these results, among copper, zinc, and iron, a low serum copper concentration may play a role in premature graying of hairs in our society. Further studies are needed to find the underlying mechanism of this relationship.  相似文献   
52.
Faam B  Daneshpour MS  Azizi F  Salehi M  Hedayati M 《Gene》2012,498(1):116-119

Introduction

Thyroid peroxidase (TPO) gene variations are one cause of thyroid autoimmune diseases. The aim of this study was to examine the association between the T1936C, T2229C and A2257C polymorphisms of the TPO gene and Anti-TPO level.

Materials and methods

In this case–control study, 188 individuals (86 males and 102 females), aged 20–80 years, were randomly selected from among the Tehran Lipid and Glucose Study (TLGS) population. A2257C and T2229C SNPs were detected with RFLP by use of BsrI and Eco57I as the restriction enzymes respectively, while the T1936C SNP was determined with ARMS-PCR.

Results

In the presence of the C allele of T1936C, Anti-TPO level was significantly increased (CC: 238 ± 43.3, CT: 47.7 ± 15.9, TT: 74.1 ± 11.3 IU/L p = 0.002); however, this association was attenuated after adjustment for sex and age (p = 0.059). No significant difference, before and after adjustment, was found in Anti-TPO level in the presence of T2229C SNP (CC: 129.1 ± 24.5, CT: 43.5 ± 12.6, TT: 126.5 ± 13.8 IU/L p = 0.196). The association between A2257C and Anti-TPO level was only significant after adjustment for potential confounders (p = 0.007). The association between ATC and CTT haplotypes and Anti-TPO level was significant (p = 0.023, 0.021 respectively), the association between CTT and Anti-TPO concentration was also significant after adjustment for sex (p = 0.014).

Conclusion

The results of the present study confirmed the association between TPO gene polymorphisms and Anti-TPO level in the Tehranian population.  相似文献   
53.
Previously, an extracellular α-amylase (BKA) had been purified from the culture of Bacillus sp. KR8104. Subsequently, the crystal structure of the active enzyme revealed a 422 amino acids polypeptide. In this study, the bka was cloned into E. coli, which encoded a polypeptide of 659 amino acids including two additional fragments: one 44 residues N-terminal fragment and another 193 residues C-terminal fragment. In order to investigate the role of the C-terminal fragment, two constructs with and without this region [BKAΔ(N44) and BKAΔ(N44C193)] were designed and expressed in E. coli BL21. The optimum pH, thermal stability, and the end-products of starch hydrolysis were found to be similar in both constructs. The Km and V(max) values for BKAΔ(N44) were lower than BKAΔ(N44C193), using either starch or ethylidene-blocked 4-nitrophenylmaltoheptaoside as a substrate.  相似文献   
54.
We evaluated the effects of starvation and refeeding on digestive enzyme activities in juvenile roach, Rutilus rutilus caspicus. Fish were divided into four feeding groups (mean mass 1.68 ± 0.12 g). The control group was fed to satiation twice a day throughout the experiment with formulated diet (SFK). The other three groups were deprived of feed for 1(S1), 2(S2), and 3(S3) weeks, respectively, and then fed to satiation during the refeeding period. The results showed that trypsin specific activity was not affected significantly either by starvation or refeeding, in all experimental groups. Chymotrypsin specific activity did not change significantly in S1 fish during the experimental period. In S2 and S3 fish no significant changes were observed during the starvation period. Upon refeeding, the activity increased in S2 fish, while it decreased in S3 fish. Amylase specific activity decreased significantly during the starvation period in all experimental groups. Upon refeeding, the activity increased. Alkaline phosphatase specific activity did not change significantly during the experiment period in S3 fish, while it showed significant changes during the starvation and refeeding period in the S1 and S2 fish. Starvation also had a significant effect on the structure of the intestine.  相似文献   
55.
AH Beiki  S Saboor  M Ebrahimi 《PloS one》2012,7(9):e44164
Various methods have been used to identify cultivares of olive trees; herein we used different bioinformatics algorithms to propose new tools to classify 10 cultivares of olive based on RAPD and ISSR genetic markers datasets generated from PCR reactions. Five RAPD markers (OPA0a21, OPD16a, OP01a1, OPD16a1 and OPA0a8) and five ISSR markers (UBC841a4, UBC868a7, UBC841a14, U12BC807a and UBC810a13) selected as the most important markers by all attribute weighting models. K-Medoids unsupervised clustering run on SVM dataset was fully able to cluster each olive cultivar to the right classes. All trees (176) induced by decision tree models generated meaningful trees and UBC841a4 attribute clearly distinguished between foreign and domestic olive cultivars with 100% accuracy. Predictive machine learning algorithms (SVM and Naïve Bayes) were also able to predict the right class of olive cultivares with 100% accuracy. For the first time, our results showed data mining techniques can be effectively used to distinguish between plant cultivares and proposed machine learning based systems in this study can predict new olive cultivars with the best possible accuracy.  相似文献   
56.
An efficient method for producing doubled haploid plants of oilseed rape (Brassica napus L.) was established using in vitro colchicine treatment of haploid embryos. Haploid embryos in the cotyledonary stage were treated with one of four colchicine concentrations (125, 250, 500 and 1,000 mg/L); for one of three treatment durations (12, 24 and 36 h) at one of the two temperatures (8 and 25°C) and were compared to control embryos (without colchicine treatment). The number of chromosomes, seed recovery, size and density of leaf stomata, and pollen grain size from regenerated plants were determined. No doubled haploid plants were regenerated from control embryos; however, the doubled haploid plants were regenerated from colchicine-treated embryos. A high doubling efficiency, 64.29 and 66.66% of regenerated plants, was obtained from 250 mg/L colchicine treatment for 24 h and 500 mg/L colchicine treatment for 36 h, respectively, at 8°C. Following 500 mg/L colchicine treatment for 36 h, a few plants regenerated (9 plants). At the higher colchicine concentration (1,000 mg/L), no plant regenerated. These results indicate that the colchicine treatment of embryos derived from microspores can induce efficient chromosome doubling for the production of doubled haploid lines of oilseed rape.  相似文献   
57.
The assembly and constriction of an actomyosin contractile ring in cytokinesis is dependent on the activation of Rho at the equatorial cortex by a complex, here termed the cytokinesis initiation complex, between a microtubule-associated kinesin-like protein (KLP), a member of the RacGAP family, and the RhoGEF Pebble. Recently, the activity of the mammalian Polo kinase ortholog Plk1 has been implicated in the formation of this complex. We show here that Polo kinase interacts directly with the cytokinesis initiation complex by binding RacGAP50C. We find that a new domain of Polo kinase, termed the intermediate domain, interacts directly with RacGAP50C and that Polo kinase is essential for localization of the KLP-RacGAP centralspindlin complex to the cell equator and spindle midzone. In the absence of Polo kinase, RacGAP50C and Pav-KLP fail to localize normally, instead decorating microtubules along their length. Our results indicate that Polo kinase directly binds the conserved cytokinesis initiation complex and is required to trigger centralspindlin localization as a first step in cytokinesis.  相似文献   
58.
59.
60.
The production of recombinant proteins in the microbial host Escherichia coli often results in the formation of cytoplasmic protein inclusion bodies (IBs). Proteins forming IBs are often branded as difficult-to-express, neglecting that IBs can be an opportunity for their production. IBs are resistant to proteolytic degradation and contain up to 90% pure recombinant protein, which does not interfere with the host metabolism. This is especially advantageous for host-toxic proteins like antimicrobial peptides (AMPs). IBs can be easily isolated by cell disruption followed by filtration and/or centrifugation, but conventional techniques for the recovery of soluble proteins from IBs are laborious. New approaches therefore simplify protein recovery by optimizing the production process conditions, and often include mild resolubilization methods that either increase the yield after refolding or avoid the necessity of refolding all together. For the AMP production, the IB-based approach is ideal, because these peptides often have simple structures and are easy to refold. The intentional IB production of almost every protein can be achieved by fusing recombinant proteins to pull-down tags. This review discusses the techniques available for IB-based protein production before considering technical approaches for the isolation of IBs from E. coli lysates followed by efficient protein resolubilization which ideally omits further refolding. The techniques are evaluated in terms of their suitability for the process-scale production and downstream processing of recombinant proteins and are discussed for AMP production as an example.  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