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   8109篇
  免费   683篇
  国内免费   297篇
耳鼻咽喉   44篇
儿科学   224篇
妇产科学   204篇
基础医学   1403篇
口腔科学   143篇
临床医学   501篇
内科学   943篇
皮肤病学   106篇
神经病学   234篇
特种医学   135篇
外国民族医学   3篇
外科学   1497篇
综合类   1175篇
现状与发展   1篇
预防医学   269篇
眼科学   63篇
药学   634篇
  1篇
中国医学   188篇
肿瘤学   1321篇
  2024年   14篇
  2023年   83篇
  2022年   151篇
  2021年   306篇
  2020年   280篇
  2019年   353篇
  2018年   298篇
  2017年   346篇
  2016年   282篇
  2015年   340篇
  2014年   477篇
  2013年   480篇
  2012年   372篇
  2011年   498篇
  2010年   451篇
  2009年   400篇
  2008年   387篇
  2007年   437篇
  2006年   396篇
  2005年   369篇
  2004年   370篇
  2003年   292篇
  2002年   243篇
  2001年   212篇
  2000年   186篇
  1999年   189篇
  1998年   133篇
  1997年   108篇
  1996年   89篇
  1995年   79篇
  1994年   52篇
  1993年   48篇
  1992年   30篇
  1991年   17篇
  1990年   24篇
  1989年   16篇
  1988年   27篇
  1987年   12篇
  1986年   12篇
  1985年   26篇
  1984年   32篇
  1983年   28篇
  1982年   31篇
  1981年   16篇
  1980年   24篇
  1979年   21篇
  1978年   13篇
  1977年   7篇
  1976年   8篇
  1975年   8篇
排序方式: 共有9089条查询结果,搜索用时 31 毫秒
21.
A single intramuscular injection of 2 mg estradiol valerate (EV) results in neuronal degeneration and β-endorphin depletion in the hypothalamic arcuate nucleus of adult female rats. We have hypothesized that peroxidase-positive astrocytes in this brain region oxidize estrogens and catecholestrogens to semiquinone radicals which mediate oxidative neuronal injury. In the present study, dietary administration of the potent antioxidant 21-aminosteroid, U-74389F, completely blocked EV-induced β-endorphin depletion in the hypothalami of adult female rats. Neither EV nor 21-aminosteroid treatment had any effect on hypothalamic concentrations of neuropeptide Y and Met-enkephalin, confirming that the estradiol lesion is fairly selective for the β-endorphin cell population. The present findings support the hypothesis that the toxic effect of estradiol on hypothalamic β-endorphin neurons is mediated by free radicals.  相似文献   
22.
p21对缺血-再灌注损伤后肾小管上皮细胞演变的影响   总被引:2,自引:0,他引:2  
目的 探讨p21对缺血-再灌注损伤(IRI)后肾小管上皮细胞演变的影响。方法 选择低龄(2个月龄)和高龄(12个月龄)p21(+/+)和p21(-/-)鼠,建立左肾IRI模型。于IRI后0、1、3、7d及1、3、6个月光镜下观察肾小管组织学变化,采用免疫组化法检测肾小管上皮细胞增殖细胞核抗原(PCNA)表达,组织化学染色观察肾小管上皮细胞衰老相关β-半乳糖苷酶(SA-β-gal)活力,末端脱氧核糖转移酶介导的生物素化脱氧尿嘧啶缺刻标记技术(TUNEL)检测肾小管上皮细胞凋亡。结果 IRI后0d,肾小管以坏死为主,高龄鼠比低龄鼠严重、p21(-/-)鼠比p21(+/+)鼠严重(P均〈0.05)。肾小管上皮细胞凋亡在IRI 1d后出现,7d达高峰,且高龄鼠比低龄鼠明显、p21(-/-)鼠比p21(+/+)鼠明显(P均d0.05)。低龄鼠IRI后1个月出现SA—β-gal染色阳性的肾小管上皮细胞,而对侧肾此时未见衰老细胞,3和6个月时衰老的肾小管上皮细胞显著增多,且p21(+/+)鼠比p21(-/-)鼠明显(P〈0.05);p21(+/+)高龄鼠IRI后0d双肾即可见大量的SA-β-gal染色阳性肾小管上皮细胞,且较p21(-/-)鼠显著增多(P〈O.05),但1d后,p21(+/+)和p21(-/-)鼠IRI肾衰老细胞均明显减少(P均〈0.05),1个月后又呈进行性增加,且p21(+/+)鼠始终比p21(-/-)鼠严重。高龄和低龄p21(+/+)鼠PCNA阳性染色细胞出现的几率差异无显著性(P〉0.05),但低龄鼠细胞增殖能力要强于高龄鼠;而p21(-/-)鼠的细胞增殖能力明显强于p21(+/+)鼠,低龄鼠更为显著(P均〈0.05)。对高龄鼠IRI后1d细胞衰老和凋亡进行相关分析显示,二者呈显著负相关Cp21(+/+)鼠:r=-0.82,P〈0.001,p21(-/-)鼠:r=-0.76,P〈0.0013。结论 ①IRI可促进正常肾小管上皮细胞衰老的进程;②已经进入衰老状态的肾小管上皮细胞在遭受IRI刺激后,更易走向死亡[坏死和(或)凋亡];③p21在IRI所致肾小管上皮细胞演变过程中发挥重要的调控作用。  相似文献   
23.
Objectives: The study was designed to assess the reliability of measurement of 24-hour urinary 17α-hydroxyprogesterone (17-OHP) by radio-immunoassay (RIA) as an alternative biochemical assessment for monitoring the treatment of congenital adrenal hyperplasia (CAH) due to 21 -hydroxylase deficiency (21 -OHD) and to assess the need for sample purification by column chromatography to improve assay specificity.
Methodology: Morning serum 17-OHP was measured using RIA and 24-hour urinary pregnanetriol using gas chromatography. Twenty-four-hour urinary 17-OHP was measured in samples from 17 prepubertal patients with CAH due to 21 -OHD, and 20 normal prepubertal children as controls. In 24 urine samples, RIA of 17-OHP was performed with and without column chromatography.
Results: There was a good correlation between 24-hour urinary 17-OHP and 24-hour urinary pregnanetriol (r = 0.962, P <0.01) and between 24-hour urinary 17-OHP and morning serum 17-OHP ( r = 0.955, P <0.01). There was no significant difference in the RIA of the urine samples with and without purification by column chromatography.
Conclusions: The measurement of 24-hour urinary 17-OHP is a reliable alternative for the biochemical monitoring of 21-OHD, and RIA specificity is unaffected by omission of column chromatography.  相似文献   
24.
陈书盘  耿沁 《肿瘤》1997,17(5):258-261
目的评价检测CYFRA21┐1对非小细胞肺癌的诊断价值。方法用ELISA法测定70例肺癌(LC)其中47例非小细胞肺癌(NSCLC),3例小细胞肺癌(SCLC)和20例未分型肺癌、64例肺部良性疾病患者及40例健康人血清CYFRA21┐1浓度。试验的诊断性能用相对操作特征(ROC)分析法估测之。结果测得全阈诊断准确率(OveralDiag┐nosticAccuracies)LC为0.75、NSCLC为0.76,SQC为0.83,ADE为0.67和SCLC为0.38。在相应于特异性为0.95的界定值3.47μg/L处,各型的灵敏度分别为SQC0.62,LC0.53,NSCLC0.51,ADE0.48和SCLC0.00。结论结果显示CYFRA21┐1是NSCLC较灵敏和特异的一个标志物。未观察到TNM各期间该标志物的平均水平有明显的差异;然而异常升高水平的患者的比例随病期的进展而显著增加,提示一系列检测CYFRA21┐1水平可能有助于监查NSCLC患者的疗效。  相似文献   
25.
26.
应用免疫且化的方法对59例肝细胞癌p21蛋白及增殖细胞核抗原的表达进行研究,并对两者在肝细胞癌中的表达关系进行比较。结果显示:p21在癌周肝组织的表达水平高于癌组织,在癌组织中的表达与肝细胞癌的分化程度有关,癌组织的分化降低,p21表达水平也随之降低p21的表达与PCNA的表达呈负相关关系(r=-0.327,P<0.01)。提示:p21的缺失表达可能促进PCNA合成的增加,对肝癌的发生发展起重要作用。  相似文献   
27.
An apparently balanced de novo reciprocal translocation t(5;21) (q13;q22) was demonstrated in a girl with acrobrachycephaly, ventriculomegaly, pulmonary stenosis and anal malformation. The possible relationships between her karyotype and malformations are discussed.  相似文献   
28.
BACKGROUND AND PURPOSE.: Heme-proteins, besides causing renal tubular obstruction, maycontribute to rhabdomyolysis-induced renal injury through aheme-iron-mediated lipid peroxidation process. In the presentstudy, we compared the combined therapy of a lipid peroxidationinhibitor, 21-aminosteroid (21-AS) and fluid-alkaline-mannitol(FAM) diuresis with either of them alone to determine the efficacyof the combination therapy and to delineate the roles of lipidperoxidation and cast formation. METHODS AND RESULTS.: Employing Raman spectroscopy, we confirmed in vitro the abilityof 21-AS to inhibit iron-induced fatty acid peroxidation. 21-ASwas then administered to rats developing renal failure fromglycerol-induced rhabdomyolysis. Although 21-AS inhibited rhabdomyolysis-inducedplasma and renal lipid peroxidation, renal protection was incomplete.Administration of FAM to inhibit cast formation afforded a betterrenal protection. However, when these therapies were combinedto inhibit both lipid peroxidation and cast formation, therewas a synergistic renal functional protection. This was accompaniedby a maximum inhibition of renal and plasma lipid peroxidation,as well as, renal tubular necrosis and cast formation. Comparedto combination therapy, FAM therapy alone, despite identicalvolume, was accompanied by a higher tubular necrosis and castformation. CONCLUSIONS.: That combining a lipid peroxidation inhibitor with fluid-alkalinediuresis in rhabdomyolysis further lowers renal lipid peroxidation,tubular necrosis and cast formation and synergistically limitsrenal dysfunction (i) supports a role for lipid peroxidationin the pathophysiology of rhabdomyolysis ARF, (ii) underscoresthe role of intratubular heme retention, a cause for tubularobstruction as well a source for prodigious amount of iron,likely involved in the lipid peroxidation, and (iii) raisesthe possibility of interactions between non-oxidant and oxidantmechanisms.  相似文献   
29.
目的 探究miR-21靶向E2F1对三阴性乳腺癌细胞恶性生物学活性及裸鼠肿瘤抑制率的影响。方法将MDA-MB-231细胞分为5组,即MDA-MB-231组、miR-21 inhibitor组、miR-NC inhibitor组、siRNA-E2F1组和siRNA-NC组。检测细胞中miR-21表达(RT-PCR法);分别检测细胞增殖(MTT法)、侵袭(Transwell法)、迁移(划痕实验)和凋亡能力(流式细胞仪);检测细胞中E2F1蛋白表达;检测miR-21与E2F1的靶向关系(双荧光素酶实验报告)。结果MDA-MB-231细胞中miR-21表达明显高于MCF10A细胞(P<0.05);miR-21 inhibitor组细胞细胞中miR-21表达明显低于MDA-MB-231组(P<0.05)。与MDA-MB-231组相比,miR-21 inhibitor组细胞吸光度值、侵袭能力、迁移能力和细胞中E2F1蛋白表达均明显降低,细胞凋亡能力明显升高(P<0.05);MDA-MB-231组细胞吸光度值、侵袭、迁移、凋亡能力和细胞中E2F1蛋白表达与miR-NC inhibitor组相比差异无统计学意义(P>0.05)。预测软件显示E2F1的3′UTR端与miR-21有碱基互补结合点位。通过向MDA-MB-231细胞中转染野生型E2F1(E2F1-WT)时,miR-21组荧光素酶活性明显低于miR-NC组(P<0.05);miR-21组和miR-NC组突变体荧光素酶活性相比差异无统计学意义(P>0.05)。与siRNA-NC组相比,siRNA-E2F1组细胞增殖、侵袭、迁移和细胞中E2F1蛋白表达均明显降低,细胞凋亡能力明显增加(P<0.05)。与miR-NC inhibitor组裸鼠移植肿瘤第8天时相比,miR-21 inhibitor组裸鼠肿瘤体积明显降低,肿瘤抑制率为45.3%(P<0.05)。结论低表达miR-21可抑制三阴性乳腺癌细胞增殖、侵袭,促进凋亡,且抑制裸鼠移植瘤体积,其作用机制可能与抑制E2F1表达有关。  相似文献   
30.
The etiological role of human papillomavirus (HPV) in esophageal carcinoma (EC) in relation to p53, mdm2, p21(waf), c-erbB2 and the overall survival (OS) rate was investigated. Tumor and normal tissues from 50 EC were evaluated by polymerase chain reaction and InnoLiPA for HPV. Single strand conformation polymorphism/sequencing were used to detect p53 gene mutations. Immunohistochemistry was performed to determine p53, mdm2, p21(waf)and c-erbB2 expression. Human papillomavirus was detected in 54% of tumors and in 24% of normal tissues. p53, mdm2 and c-erbB2 overexpression was detected in 68%, 70% and 60% of tumors and in 14%, 16% and 10% of normal samples, whereas loss of p21(waf) was evident in 64% of tumors. p53 mutations were detected in 20% of cases. Exon 8 and 5 showed the highest mutation rate (40% each), followed by exons 6 and 7 (10% each). There was a significant correlation between HPV and p53, mdm2, c-erbB2 overexpression. The OS was significantly associated with overexpression of p53 and loss of p21(waf). Human papillomavirus infection is frequent in Egyptian EC. Both p53-dependent and p53-independent pathways seem to be involved in HPV-associated EC. mdm2 and c-erbB2 are possible targets for HPV in the p53-independent pathway. However, only advanced stage and aberrant expression of p53 and p21(waf) are independent prognostic markers.  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