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   5001篇
  免费   449篇
  国内免费   40篇
耳鼻咽喉   31篇
儿科学   115篇
妇产科学   119篇
基础医学   572篇
口腔科学   84篇
临床医学   473篇
内科学   944篇
皮肤病学   59篇
神经病学   241篇
特种医学   280篇
外科学   715篇
综合类   255篇
预防医学   467篇
眼科学   185篇
药学   368篇
  1篇
中国医学   96篇
肿瘤学   485篇
  2023年   48篇
  2022年   57篇
  2021年   96篇
  2020年   67篇
  2019年   109篇
  2018年   103篇
  2017年   95篇
  2016年   91篇
  2015年   130篇
  2014年   158篇
  2013年   204篇
  2012年   289篇
  2011年   280篇
  2010年   196篇
  2009年   193篇
  2008年   287篇
  2007年   290篇
  2006年   250篇
  2005年   267篇
  2004年   217篇
  2003年   214篇
  2002年   170篇
  2001年   123篇
  2000年   126篇
  1999年   125篇
  1998年   84篇
  1997年   70篇
  1996年   66篇
  1995年   46篇
  1994年   51篇
  1993年   42篇
  1992年   95篇
  1991年   79篇
  1990年   71篇
  1989年   73篇
  1988年   81篇
  1987年   75篇
  1986年   66篇
  1985年   58篇
  1984年   30篇
  1983年   31篇
  1982年   44篇
  1981年   26篇
  1980年   22篇
  1979年   20篇
  1978年   21篇
  1977年   18篇
  1976年   26篇
  1975年   15篇
  1974年   13篇
排序方式: 共有5490条查询结果,搜索用时 15 毫秒
41.
42.
PURPOSE: To determine performance characteristics of transvaginal ultrasonography (US) and hysterosonography for diagnosing endometrial abnormality in asymptomatic postmenopausal women with breast cancer receiving tamoxifen. MATERIALS AND METHODS: The authors prospectively examined 138 women receiving tamoxifen by using transvaginal US, hysterosonography, and office hysteroscopy. The combined hysteroscopic-histopathologic diagnosis was the reference standard. Sensitivity, specificity, positive and negative predictive values, and likelihood ratios of transvaginal US and hysterosonography were calculated. RESULTS: All 138 women underwent transvaginal US; 104, successful hysterosonography; and 117, successful hysteroscopy. Uterine abnormality was present in 47 (40.2%) of 117 women: 45 with polyps and two with submucosal fibroids. Receiver operating characteristic curve analysis revealed 6 mm to be the optimal endometrial thickness cutoff for diagnosing endometrial abnormalities. When a thickness greater than 6 mm or a focal endometrial finding was considered abnormal, transvaginal US had a sensitivity of 85.1% and a specificity of 55.7%. In 92 women who completed transvaginal US, hysterosonography, and hysteroscopy, hysterosonography was more specific (79.2%; P =.008) but not significantly more sensitive (89.7%; P =.508) than transvaginal US. When women with abnormal transvaginal US findings were further examined with hysterosonography, the sequential combination of transvaginal US and hysterosonography was more specific (77.1%) than transvaginal US alone (P <.001), without a significant decrease in sensitivity (78.7%; P =.25). CONCLUSION: In asymptomatic postmenopausal women receiving tamoxifen, 6 mm is the optimal endometrial thickness cutoff for diagnosing endometrial abnormalities with transvaginal US. Further examination with hysterosonography can improve specificity by reducing the high false-positive rate of transvaginal US.  相似文献   
43.
To determine whether reactive oxygen molecules could directly and reversibly increase the transfer of albumin across an endothelial barrier, we measured albumin transfer across monolayers of endothelium cultured on micropore filters before and after exposure to xanthine and xanthine oxidase. Xanthine and xanthine oxidase increased endothelial albumin transfer in a dose-dependent fashion. Parallel phase contrast and fluorescence microscopy demonstrated retraction of adjacent cells from one another and disruption of the actin filaments. The oxidant- induced increases in albumin transfer and changes in cell shape were reversed by removing xanthine oxidase and then incubating the monolayers for 3 1/2 hours in tissue culture media enriched with fetal bovine serum. However, incubation in tissue culture media without serum resulted in progressive injury and cell death. Hence, the brief exposure to oxidants initiated a progressive injury process that was reversed by incubation in serum. Because intracellular and extracellular calcium are important determinants of cell shape, and because some oxidized membrane lipids act as calcium ionophores, we asked whether oxidants altered endothelial calcium homeostasis. Xanthine-xanthine oxidase increased release of 45Ca++ from preloaded cells. The calcium antagonist lanthanum chloride prevented xanthine- xanthine oxidase increases in endothelial albumin transfer and prevented the changes in cell shape; chelation of extracellular calcium inhibited lysis of endothelium by xanthine-xanthine oxidase; and the calcium ionophore A23187 increased endothelial albumin transfer and mimicked the oxidant-induced changes in cell shape. Lanthanum chloride inhibited these effects of A23187. These data suggest that oxygen radicals can reversibly increase endothelial permeability to macromolecules, that this is associated with reversible changes in endothelial cell shape and actin filaments, and that the changes in cell shape are related to oxidant-induced changes in endothelial calcium homeostasis.  相似文献   
44.
Overlapping recombinant clones that encompass the insulin-like growth factor (IGF) I and II genes have been isolated from a human genomic DNA library. Each gene is present once per haploid genome; the IGF-I gene spans greater than 35 kilobase pairs (kbp) and the IGF-II gene is at least 15 kbp. The exon-intron organization of these genes is similar, each having four exons, which is one more than the related insulin gene. Comparison of the restriction endonuclease cleavage maps of the IGF-II and insulin genes, including their flanking regions and hybridization with an IGF-II cDNA probe, revealed that they are adjacent to one another. The IGF-II and insulin genes have the same polarity and are separated by 12.6 kbp of intergenic DNA that includes a dispersed middle repetitive Alu sequence. The order of the genes is 5'-insulin-IGF-II-3'.  相似文献   
45.
46.
肝动脉栓塞化疗后肝内胆道并发症(附108例分析)   总被引:3,自引:0,他引:3  
目的 探讨肝动脉栓塞化疗引起肝脏胆道并发症的临床表现,病理改变,发病机理及预防治疗的方法。方法 观察1990年6月至1999年6月收治108例经过1~6次肝动态栓塞化疗患者治疗结果。结果 肝动脉栓塞化疗4次以上得35例,发现胆道病变6例,发生率为17.14%;化疗3次以下者73例,发生2例,为2.47%,显著低于前者。结论 发生机理可能主要是因为胆管的营养血管多次被栓塞而没有及时建立起有效的侧支循  相似文献   
47.
一氧化氮在胃癌进展中的作用   总被引:1,自引:0,他引:1  
目的探讨一氧化氮(NO)在胃癌发病过程中的作用。方法42例经胃镜活检、病理检查证实为胃癌,采用地高辛标记的诱导型一氧化氮合酶(iNOS)mRNA探针经原位杂交显示细胞内的iNOSmRNA的表达情况,并与癌周组织及浅表胃炎组织比较。结果在42例胃癌患者,iNOSmRNA信号强阳性(+++)11例,中度阳性(++)14例,低度阳性(+)13例,可疑阳性(±)3例,阴性(-)1例;在癌周组织多为(±)或(-);与浅表性胃炎相比,差异有高度显著性(P<0.01)。结论大多数胃癌患者的癌细胞内iNOSmRNA表达阳性,提示胃癌细胞自身能产生一氧化氮  相似文献   
48.
49.
The aim of the study was to investigate the feasibility of using digital subtraction in contrast-enhanced MR imaging of the brain to reduce the MR contrast dosage without jeopardizing patient care. Fifty-two patients with intracranial lesions, either intra-axial or extra-axial, detected by computerized tomography were selected for contrast-enhanced MR imaging with half-dose and full-dose of gadopentetate dimeglumine. The half-dose unsubtracted, full-dose unsubtracted, and half-dose subtracted MR images were visually assessed by counting the number of enhancing brain lesions in the images and quantitatively analyzed by computing their lesion contrast-to-background ratios (CBR). The visual conspicuity of the half-dose subtracted MR images was comparable to that of the full-dose unsubtracted MR images ( p>0.05), whereas the CBR of the half-dose subtracted images was approximately two to three times higher than that of the full-dose unsubtracted images. The half-dose subtracted T1-weighted spin-echo images might be able to replace the conventional standard-dose T1-weighted spin-echo images in MR imaging of the brain.  相似文献   
50.

Objective

Patients with postural tachycardia syndrome (POTS) often describe symptoms of fatigue, sleepiness, and lack of refreshing sleep. We aimed to provide further objective measures of sleep in patients with POTS.

Methods

POTS patients (n = 18) were selected based on autonomic testing and evaluation at our center. Controls (n = 16) of similar age, gender, and BMI were selected from new patients referred to the Stanford Sleep Disorders Clinic for any sleep-related complaint. All patients underwent polysomnography and completed several sleep questionnaires and a 2-week sleep diary.

Results

POTS patients and control subjects were of similar age (27 ± 10.2 vs. 29 ± 5.4 years, p = 0.92) and Body Mass Index (21 ± 3.8 vs. 24 ± 4.1, p = 0.14). The majority of subjects in both groups were females (72 % POTS vs. 81 % controls). POTS patients scored higher on subjective fatigue scales but not sleepiness scales. POTS patients scored in the normal range on the BDI and the “evening” category on the MEQ. Their sleep diaries were not different from controls. With the exception of mild OSA, slightly reduced %REM and prolonged REM latency, their PSG data were normal and no different from controls.

Conclusions

It is unlikely that the sleep-related complaints of POTS patients are the result of a primary sleep disorder unique to POTS. We propose that a combination of factors such as body fatigue, chronic pain, and other somatic symptoms common in POTS patients might be the underlying reason for sleep-related symptoms in POTS.
  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