全文获取类型
收费全文 | 412篇 |
免费 | 13篇 |
国内免费 | 12篇 |
专业分类
教育 | 297篇 |
科学研究 | 100篇 |
体育 | 23篇 |
综合类 | 12篇 |
文化理论 | 1篇 |
信息传播 | 4篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 15篇 |
2020年 | 13篇 |
2019年 | 10篇 |
2018年 | 4篇 |
2017年 | 2篇 |
2016年 | 4篇 |
2015年 | 3篇 |
2014年 | 30篇 |
2013年 | 18篇 |
2012年 | 20篇 |
2011年 | 31篇 |
2010年 | 23篇 |
2009年 | 25篇 |
2008年 | 30篇 |
2007年 | 29篇 |
2006年 | 35篇 |
2005年 | 35篇 |
2004年 | 22篇 |
2003年 | 19篇 |
2002年 | 13篇 |
2001年 | 14篇 |
2000年 | 9篇 |
1999年 | 4篇 |
1998年 | 5篇 |
1997年 | 6篇 |
1996年 | 7篇 |
1995年 | 3篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1989年 | 3篇 |
排序方式: 共有437条查询结果,搜索用时 15 毫秒
71.
Sridhar Mishra Devanshi B. Dubey Krachi Agarwal Deval B. Dubey Shweta Verma Nida Shabbir Rashmi Kushwaha D Himanshu Reddy Uma Shankar Singh Wahid Ali 《Indian journal of clinical biochemistry : IJCB》2023,38(2):172
Lymphocyte dysregulation in coronavirus disease-19 (COVID-19) is a major contributing factor linked to disease severity and mortality. Apoptosis results in the accumulation of cell-free DNA (cfDNA) in circulation. COVID-19 has a heterogeneous clinical course. The role of cfDNA levels was studied to assess the severity and outcome of COVID-19 patients and correlated with other laboratory parameters. The current case series included 100 patients with mild COVID-19 (MCOV-19) and 106 patients with severe COVID-19 (SCOV-19). Plasma cfDNA levels were quantified using SYBR green quantitative real-time PCR through amplification of the β-actin gene. CfDNA level was significantly higher in SCOV-19 at 706.7 ng/ml (522.6–1258) as compared to MCOV-19 at 219.8 ng/ml (167.7–299.6). The cfDNA levels were significantly higher in non-survivor than in survivors (p = 0.0001). CfDNA showed a significant correlation with NLR, ferritin, LDH, procalcitonin, and IL-6. The diagnostic sensitivity and specificity of cfDNA in the discrimination of SCOV-19 from MCOV-19 were 90.57% & 80%, respectively. CfDNA showed a sensitivity of 94.74% in the differentiation of non-survivors from survivors. CfDNA levels showed a significant positive correlation with other laboratory and inflammatory markers of COVID-19. CfDNA levels, NLR, and other parameters may be used to stratify and monitor COVID-19 patients and predict mortality. CfDNA may be used to predict COVID-19 severity with higher diagnostic sensitivity. 相似文献
72.
73.
Adilson Marques Élvio Rubio Gouveira Miguel Peralta João Martins Joed Venturini Duarte Henriques-Neto 《Journal of sports sciences》2020,38(14):1690-1697
ABSTRACT This study aimed to systematically review the association between cardiorespiratory fitness and telomere length (TL). Studies were identified from searches in Cochrane Central, PubMed, Scopus, Sportdiscus, and Web of Science databases through July 2019. Eligibility criteria included: cross-sectional, prospective, and experimental study design; outcomes included TL; results expressed the relationship between cardiorespiratory fitness and TL; studies published in English, Portuguese, or Spanish. A total of 20 articles met the inclusion criteria. Sixteen studies (80%) reported a significant relationship between cardiorespiratory fitness, or training load, and TL. Better cardiorespiratory fitness or a large cardiorespiratory training load are associated with an increase in TL. Although, TL was related to regular moderate-to-vigorous aerobic exercise and cardiorespiratory fitness in older healthy humans, it was not related to cardiorespiratory fitness among young subjects. There seems to be a positive and significant relationship between cardiorespiratory fitness and TL, mainly among middle age and older people, which emphasizes the importance of cardiorespiratory fitness for healthy ageing. Therefore, endurance exercise and better cardiorespiratory fitness may regulate the TL in middle age and older adults, slowing the cellular ageing process. 相似文献
74.
INTRODUCTION Genetic diversity is a major issue of conserva-tion biology recognized by the IUCN (Frankham etal., 2002). Within a population it reflects the evolu-tionary potential to adapt to novel environmentalchanges. Therefore, during the past few years, thegenetic diversity of many threatened mammals, birds,fish, insects and plants have been investigated(Frankham et al., 2002). As a direct and indirectconsequence of human actions, more and more spe-cies or populations are faci… 相似文献
75.
庞小峰 《商丘师范学院学报》1996,(Z1)
本文全面考虑了DNA的碱基对的相互作用、双链的整体振动效应和链内分子的集体激发等运动状态,应用在我们最近在蛋白质分子中建立的新理论与其它方法,研究了DNA分子的动力学特性,集体激发与孤立子运动.并应用此结果深入研究DNA的一些生物功能,如复制、转录等问题. 相似文献
76.
77.
Witas HW Jedrychowska-Dańska K Zawicki P 《Journal of Zhejiang University. Science. B》2007,8(7):512-514
The precise etiology and reasons for the increase in incidence of autoimmune disorders still remain unclear, and although both genetic and environmental factors have been proven to shape individual predisposition, it is not known which of the factors, if not both, is responsible for the boom observed during the last decades. In order to establish whether a higher frequency of autoimmune-predisposing alleles may explain this increase we took advantage of ancient DNA methodology to establish the genetic predisposition, conferred by cytotoxic T lymphocyte associated antigen-4 (CTLA4) +49A/G and human leukocyte antigens (HLA) DQBI^57, in population inhabiting Poland in the Middle Ages. After successful typing of 42 individuals from a 12th-14th's century archeological burial site, we found that frequencies of the predisposing alleles in the medieval population were higher than they are at present, suggesting thus that the recently observed incidence increase results most probably from factors of other than genetic nature. 相似文献
78.
Objective: To identify the mutations of iduronate-2-sulfatase (IDS) gene, to reveal its mutation features, and to establish a basis for genetic counseling and prenatal gene diagnosis of Hunter syndrome. Methods: Urine glycosaminoglycans (GAGs) assay, PCR and DNA sequencing were performed to detect mutation of IDS gene of the patient and his parents. Results: The result showed that the patient was: DS( ), HS( ), KS(-), CS(-), and that both of his parents were negative. A frame-shift deletion mutation (1062 del 16) was identified in exon 7 of the patient's IDS gene. His parents' genotypes were normal. Conclusion:The patient's mutation was not inherited by his parents but a novel one. The mutation probably altered the primary structure and tertiary structure of IDS enzyme protein remarkably and lowered the activity of IDS enzyme greatly. Therefore it is supposed to be the direct cause of the disorder. 相似文献
79.
Orathai Tangvarasittichai Watchiravut Jaiwang Surapon Tangvarasittichai 《Indian journal of clinical biochemistry : IJCB》2015,30(1):55-58
Increased levels of plasma DNA have frequently been noticed in the blood plasma of cancer patients. The possibility of using plasma DNA level as the indicator of tumor stage in breast cancer was investigated in plasma samples obtained from 100 breast cancer patients and 100 healthy women who were included as controls. Circulatory plasma free DNA was extracted from plasma samples and quantified by fluorometer. The median concentration of plasma DNA in the plasma samples from breast cancer patients classified by TNM staging system as stage I, II, III, IV and breast surgical patients were 0.5, 235, 422, 1,280 and 0.5 ng/ml, respectively. The level of plasma DNA in the stage II- IV group was significantly higher than those in the surgical group with breast cancer and control group (P value < 0.001). The plasma DNA concentration in stage II, III and IV of breast cancer were higher when compared with healthy group. These tumor size, TNM stage and metastasis were significantly correlated with plasma DNA. The cut point of 120 ng/ml was early screening and treatment follow up breast cancer. 相似文献
80.
马云彤 《西安文理学院学报》2010,13(1):44-47
拓扑异构酶Ⅰ在DNA翻译和转录过程中催化单链DNA的断裂和连接,从而松弛DNA超螺旋,促进复制与转录的进行.拓扑异构酶Ⅰ抑制剂能够阻断DNA链的再连接,结果导致TopⅠ断裂复合物的积累,抑制复制和转录,造成DNA损伤,从而激活DNA损伤检验点,抑制细胞生长和诱发凋亡。喜树碱是最早发现、也是最重要和最广泛使用的拓扑异构酶Ⅰ抑制剂.细胞周期中DNA损伤、修复和检验点应答的分子机制是目前生命科学研究热点,而喜树碱已成为进行相关研究的重要的药理学工具. 相似文献