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   33682篇
  免费   2341篇
  国内免费   1036篇
耳鼻咽喉   356篇
儿科学   417篇
妇产科学   375篇
基础医学   5204篇
口腔科学   564篇
临床医学   3453篇
内科学   5460篇
皮肤病学   804篇
神经病学   2470篇
特种医学   1609篇
外国民族医学   5篇
外科学   3842篇
综合类   2501篇
现状与发展   7篇
一般理论   9篇
预防医学   1849篇
眼科学   856篇
药学   3472篇
  15篇
中国医学   1064篇
肿瘤学   2727篇
  2024年   60篇
  2023年   412篇
  2022年   1099篇
  2021年   1520篇
  2020年   863篇
  2019年   946篇
  2018年   1076篇
  2017年   856篇
  2016年   1101篇
  2015年   1534篇
  2014年   1847篇
  2013年   2005篇
  2012年   2893篇
  2011年   2963篇
  2010年   1727篇
  2009年   1441篇
  2008年   2030篇
  2007年   1900篇
  2006年   1704篇
  2005年   1609篇
  2004年   1266篇
  2003年   1073篇
  2002年   881篇
  2001年   704篇
  2000年   732篇
  1999年   581篇
  1998年   265篇
  1997年   222篇
  1996年   169篇
  1995年   161篇
  1994年   137篇
  1993年   103篇
  1992年   162篇
  1991年   171篇
  1990年   140篇
  1989年   106篇
  1988年   88篇
  1987年   80篇
  1986年   72篇
  1985年   48篇
  1984年   34篇
  1983年   37篇
  1982年   30篇
  1981年   21篇
  1980年   21篇
  1979年   31篇
  1978年   18篇
  1977年   16篇
  1976年   13篇
  1974年   17篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Ageing is characterized by the accumulation of chronic and irreversible oxidative damage, chronic inflammation and organ dysfunction. To attenuate these ageing‐related changes, various natural phytochemicals are often applied. Trans‐communic acid (TCA), an active component of brown pine leaf extract, has antimicrobial and cancer chemopreventive activity and inhibits ultraviolet B (UVB)‐induced MMP‐1 expression. To determine whether the phytochemical TCA could affect the lifespan of an ageing model, Caenorhabditis elegans prevent ageing‐related phenotypes of the skin. Caenorhabditis elegans (C. elegans) wild‐type N2 and mutant strains were used in this study to explore the lifespan extension effect of TCA and its mechanism. We estimated lipofuscin accumulation and melanin levels, which are closely associated with skin senescence. Moreover, we explored the mechanism of action associated with ageing attenuation. We performed oxidative stress resistance and thermotolerance assays in C. elegans and surface plasmon resonance analysis of TCA binding with the forkhead box‐O3a (FoxO3a) protein. TCA, which is the active component in Korean red pine (Pinus densiflora), attenuated ageing‐related changes in skin cells. TCA lowered lipofuscin accumulation in fibroblasts and decreased melanin levels in melanocytes. These protective effects were mediated by activation of the representative longevity gene FoxO3a, which was induced by direct binding with TCA. Interestingly, TCA extended the lifespan of C. elegans, although it did not affect stress resistance, oxidative stress or thermotolerance. These results strongly suggest that TCA prevents the senescent phenotype of model organisms and exhibits beneficial effects on ageing‐related skin phenotypes through direct FoxO3a activation.  相似文献   
992.
Gene alterations of p53 tumor suppressor gene such as point mutations, deletions or insertions occur in various human cancers. p53 protein overexpression was studied immunohistochemically in 80 gastric adenocarcinomas using an anti-human p53 antibody (Pab 1801) and the avidin-biotin-peroxidase technique. We have also analyzed allele loss of the human p53 gene in 54 cases of gastric adenocarcinoma using polymerase chain reaction and restriction fragment length polymorphism. p53 immunostaining was also demonstrated in 48 of 80 carcinomas (60%). Normal mucosa was always negative. No relation could be found between p53 immunostaining and the degree of differentiation. 21 of the 54 patients(39%) were informative for the p53 exon 4. In ten of these informative cases(47.6%), tumor DNAs showed allele loss when compared with nonmetastatic lymph node DNAs. Seven of the ten(70%) showed p53 immunoreactivity. These findings suggest that mutations of the p53 gene may play a role in the development of gastric adenocarcinoma and that allele loss of p53 frequently occurs in p53 immunoreactive gastric adenocarcinoma.  相似文献   
993.
BackgroundThe 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) is a metabolite of tobacco-specific lung carcinogen that can be found in both smokers and non-smokers. Particularly, NNAL levels of children with a history of exposure to second-hand smoke (SHS) are higher than those of adults. Thus, we aimed to investigate the association between SHS exposure and urine NNAL levels in Korean adolescents.MethodsThis cross-sectional study used data from the Korea National Health and Nutrition Examination Survey VII. Overall, 648 never-smoking adolescents (425 boys and 223 girls) aged 12 to 18 were included in this study. Logistic regression analyses identified the relationship between SHS exposure and elevated urine NNAL levels.ResultsThe mean urine NNAL levels of the no exposure and exposure group in boys were 1.39 and 2.26 ng/mL, respectively, whereas they were 1.01 and 2.45 ng/mL in girls, respectively (P < 0.001). Among the adolescents exposed to SHS, the confounder-adjusted odds ratio (95% confidence intervals) for elevated urine NNAL levels according to exposure area as overall, home, and public area were 2.68 (1.58–4.53), 31.02 (9.46–101.74), and 1.89 (1.12–3.17) in boys; and 6.50 (3.22–13.11), 20.09 (7.08–57.04), and 3.94 (1.98–7.77) in girls, respectively.ConclusionSHS exposure was significantly associated with elevated urine NNAL levels in Korean adolescents, particularly in female adolescents and in those with home exposure. These findings remind us of the need to protect adolescents from SHS.  相似文献   
994.
Immunophilin, FK506-binding protein 12 (FK506BP), is a receptor protein for the immunosuppressive drug FK506 by the FK506BP/FK506 complex. However, the precise function of FK506BP in inflammatory diseases remains unclear. Therefore, we examined the protective effects of FK506BP on atopic dermatitis (AD) in tumor necrosis factor-α (TNF-α)/interferon-γ (IFN-γ)-induced HaCaT cells and 2,4-dinitrofluorobenzene-induced AD-like dermatitis in Nishiki-nezumi Cinnamon/Nagoya (NC/Nga) mice using a cell-permeable PEP-1-FK506BP. Transduced PEP-1-FK506BP significantly inhibited the expression of cytokines, as well as the activation of NF-κB and mitogen-activated protein kinase (MAPK) in TNF-α/IFN-γ-induced HaCaT cells. Furthermore, topical application of PEP-1-FK506BP to NC/Nga mice markedly inhibited AD-like dermatitis as determined by a histological examination and assessment of serum IgE levels, as well as cytokines and chemokines. These results indicate that PEP-1-FK506BP inhibits NF-κB and MAPK activation in cells and AD-like skin lesions by reducing the expression levels of cytokines and chemokines, thus suggesting that PEP-1-FK506BP may be a potential therapeutic agent for AD.  相似文献   
995.
996.
997.
998.
Immortalized GT1–7 neurons were used to characterize the effect of muscimol, a GABAA receptor agonist, to enhance pulsatile gonadotropin-releasing hormone (GnRH) release. GT1–7 neurons were grown on Cytodex-3 beads and placed in special superfusion microchambers. The cells were superfused at a rate of 6.2 ml·h−1 with Media 199 (pH 7.35) using a commercially available perfusion system. After a pre-muscimol period of 120 min, the cells were exposed for 5 min to 0.35, 1, 5 or 10 μM muscimol or 5 μM muscimol+20 μM of the GABAA receptor antagonist, bicuculline. Following removal of the muscimol (and bicuculline, in the case of the latter experiment), the superfusion was continued for another 115 min. Sample fractions were collected at 5 min intervals throughout the perfusion. Basal GnRH release from the GT1–7 neurons was pulsatile with an average interpulse interval of 45.4±0.5 min and an average pulse amplitude of 191.5±22.6 pg·min·ml−1. Our results also demonstrated that the GABAA receptor agonist, muscimol, enhances pulsatile GnRH release from GT1–7 neurons in culture. The response to muscimol was saturable and concentration-dependent with an EC50 of 0.47 μM. The effects of 5 μM muscimol to increase GnRH pulsatility were blocked by co-exposure to the GABAA receptor antagonist, bicuculline. The average GnRH interpulse intervals were 41.7±1.8 min, 32.5±2.9 min, 30.6±0.7 min and 25.5±0.4 min in the period following exposure to 0.35, 1, 5 and 10 μM of muscimol, respectively (post-muscimol period). GnRH pulse amplitude (mean-area for each pulse) was increased during exposure to muscimol but not during the pre- or post-muscimol periods. The GABAA receptor antagonist, bicuculline, itself had no effect on pulsatile GnRH release. These results are consistent with previously published reports suggesting that activation of the GABAA receptor stimulates hypothalamic GnRH release in embryonic and neonatal animals.  相似文献   
999.
目的:探讨垂体脓肿的临床特征和治疗。方法:回顾性分析14例垂体脓肿患者的临床表现、影像学特征、诊断和治疗,并结合文献进行分析。结果:14例患者中头痛13例,垂体功能低下6例,视力视野影响6例,多饮多尿3例,发热3例。MRI增强病灶均呈环状强化。11例经蝶手术治疗,3例经开颅手术。术后随访头痛缓解者10例,视力、视野改善者4例,尿崩者2例恢复正常,垂体功能低下者中4例恢复正常,3例开颅手术者中2例复发,再经蝶手术治愈。结论:应用常规CT和MR术前诊断垂体脓肿困难,对鞍区囊性病变应考虑到垂体脓肿的可能。及早手术、正确选择手术入路、围手术期合理应用抗生素和适当的对症治疗是治疗垂体脓肿的关键。  相似文献   
1000.
目的 研究脑梗死后遗症大鼠模型脑组织ATP、ADP及单胺类神经递质含量的变化。方法 建立脑梗死后遗症大鼠模型,用高效液相色谱(HPLC)法测定大鼠脑组织ATP、ADP及单胺类神经递质含量。结果 刺激组(SG)毛发相对黯淡无光、卷曲,精神萎靡,惊恐,消瘦,肢体无力,摄食减少,饮水减少,手术伤口愈合迟缓,符合中医脑梗死后遗症征候。正常组(NG)大鼠脑组织ATP、ADP含量显著高于SG组、术后不刺激组(SG)(P〈0.01),同时NSG组大鼠脑组织ATP、ADP含量显著高于SG组(P〈0.05)。SG组大鼠脑组织NE、DA和5-HT含量显著低于NG组(P〈0.01),NSG组(P〈0.05);NSG组大鼠脑组织DA含量显著低于NG组(P〈0.05)。结论 脑梗死后遗症大鼠由于能量代谢障碍而出现脑组织的ATP、ADP含量降低,并且伴有大脑释放单胺类递质增加及脑细胞内的单胺类递质含量减少,单胺类递质分泌增加又加重了脑组织的损伤,加剧ATP、ADP等能量物质代谢障碍,形成恶性循环。  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