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   26541篇
  免费   1428篇
  国内免费   69篇
耳鼻咽喉   372篇
儿科学   2041篇
妇产科学   612篇
基础医学   3000篇
口腔科学   464篇
临床医学   1448篇
内科学   5286篇
皮肤病学   992篇
神经病学   1163篇
特种医学   979篇
外科学   3947篇
综合类   926篇
一般理论   12篇
预防医学   1302篇
眼科学   1304篇
药学   2175篇
中国医学   141篇
肿瘤学   1874篇
  2023年   129篇
  2022年   314篇
  2021年   756篇
  2020年   430篇
  2019年   506篇
  2018年   719篇
  2017年   483篇
  2016年   683篇
  2015年   614篇
  2014年   953篇
  2013年   1113篇
  2012年   1580篇
  2011年   1679篇
  2010年   915篇
  2009年   748篇
  2008年   1296篇
  2007年   1362篇
  2006年   1172篇
  2005年   1104篇
  2004年   1008篇
  2003年   929篇
  2002年   834篇
  2001年   741篇
  2000年   696篇
  1999年   609篇
  1998年   260篇
  1997年   188篇
  1996年   152篇
  1995年   139篇
  1993年   131篇
  1992年   359篇
  1991年   392篇
  1990年   345篇
  1989年   360篇
  1988年   312篇
  1987年   279篇
  1986年   269篇
  1985年   286篇
  1984年   226篇
  1983年   183篇
  1982年   124篇
  1979年   243篇
  1978年   160篇
  1977年   151篇
  1976年   136篇
  1975年   164篇
  1974年   154篇
  1973年   177篇
  1972年   139篇
  1971年   122篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.

Objective

The aim of this work was to evaluate the hypothesis that the distribution of circulating immune cell subsets, or their activation state, is significantly different between peripartum cardiomyopathy (PPCM) and healthy postpartum (HP) women.

Background

PPCM is a major cause of maternal morbidity and mortality, and an immune-mediated etiology has been hypothesized. Cellular immunity, altered in pregnancy and the peripartum period, has been proposed to play a role in PPCM pathogenesis.

Methods

The Investigation of Pregnancy-Associated Cardiomyopathy (IPAC) study enrolled 100 women presenting with a left ventricular ejection fraction of <0.45 within 2 months of delivery. Peripheral T-cell subsets, natural killer (NK) cells, and cellular activation markers were assessed by flow cytometry in PPCM women early (<6 wk), 2 months, and 6 months postpartum and compared with those of HP women and women with non–pregnancy-associated recent-onset cardiomyopathy (ROCM).

Results

Entry NK cell levels (CD3–CD56+CD16+; reported as % of CD3– cells) were significantly (P?<?.0003) reduced in PPCM (6.6?±?4.9% of CD3– cells) compared to HP (11.9?±?5%). Of T-cell subtypes, CD3+CD4–CD8–CD38+ cells differed significantly (P?<?.004) between PPCM (24.5?±?12.5% of CD3+CD4–CD8– cells) and HP (12.5?±?6.4%). PPCM patients demonstrated a rapid recovery of NK and CD3+CD4–CD8–CD38+ cell levels. However, black women had a delayed recovery of NK cells. A similar reduction of NK cells was observed in women with ROCM.

Conclusions

Compared with HP control women, early postpartum PPCM women show significantly reduced NK cells, and higher CD3+CD4–CD8–CD38+ cells, which both normalize over time postpartum. The mechanistic role of NK cells and “double negative” (CD4–CD8–) T regulatory cells in PPCM requires further investigation.  相似文献   
992.
Adequate real time two dimensional echocardiograms were prospectively obtained before and immediately after graded treadmill exercise testing in 41 of 48 patients who underwent cardiac catheterization for suspected coronary artery disease. Findings were correlated with thallium perfusion scans performed 5 to 10 minutes and 3 hours after the same exercise test. Exercise-induced wall motion abnormalities were detected in 19 of 23 patients with significant coronary artery disease and no prior myocardial infarction as well as in all 5 patients with known previous infarction. Three patients with coronary artery disease experienced new isolated right ventricular asynergy with exercise that would have been missed if only the left ventricle had been evaluated. Exercise-induced thallium perfusion defects showed good correlation with exercise-induced asynergy as detected with echocardiography. Two dimensional echocardiography performed immediately after treadmill stress testing is a feasible and rewarding technique in the evaluation of patients suspected to have coronary artery disease.  相似文献   
993.
A 25-year-old housewife who presented with Mycoplasma pneumonia who developed acute respiratory distress syndrome (ARDS) and required assisted ventilation. During her hospital stay, she developed acute renal failure because of rhabdomyolysis and was put on haemodialysis. She also had difficulty in weaning from ventilator because of acute motor-sensory axonal neuropathy (AMSAN) variant of the Guillain-Barre syndrome. The patient was treated with antibiotics and corticosteroids. The patient recovered from both the complications gradually.  相似文献   
994.
995.
In a total of 56 children and adolescents with Turner's syndrome (41 with karyotype 45,X) basal serum levels of somatomedin bioactivity, Sm-C/IGF-I (RIA), IGF II (RIA), GH response to arginine and GHRH (GRF(1-29)NH2), and spontaneous GH secretion during 5.5 h of deep sleep were determined in a cross-sectional manner. GH responses to GRF and arginine as well as IGF-II levels were found to be in the normal range. Levels of somatomedin bioactivity were higher than normal before a bone age of 10 years, in the low-normal range thereafter, and below normal in some patients. Levels of Sm-C/IGF-I were found normal before and low-normal after a bone age of ten years. There was a trend towards increasing Sm-C/IGF-I levels with age. In contrast to the normal pattern, spontaneous sleep-related GH secretion was declining with age and did not show the puberty-associated rise. These findings suggest a normally functioning growth hormone-somatomedin axis in Turner's syndrome with alterations of its functioning level occurring secondarily as a result of absent gonadal activation. In single patients abnormally low growth hormone and/or somatomedin secretion may be present.  相似文献   
996.
BackgroundDiagnosis of genital tuberculosis (TB) as a cause of infertility still remains a diagnostic dilemma for clinicians, as no standard guidelines exist. The recently proposed best practices for genital TB diagnosis have not been evaluated yet in India.ObjectivesTo implement best practices to diagnose and treat likely genital TB as a cause of infertility.MethodsBetween April 2016 and June 2018, consenting women seen at a tertiary hospital infertility clinic were assessed by thorough TB related clinical history, ultrasonography, tuberculin skin test (TST), and ESR. Those with suspected genital TB underwent laparohysteroscopy. Clinical and laboratory characteristics were compared between likely (microbiologically confirmed or probable TB) and unlikely (possible and no genital TB) genital TB. Fertility outcome was assessed among women initiated on anti-TB treatment (ATT).ResultsOf 185 women seeking infertility care, likely genital TB was identified among 29 (15.7%) women, with 6 (21%) confirmed and 23 (79%) probable genital TB. Compared to unlikely genital TB cases, the likely genital TB group were found to have past history of TB (p < 0.001); positive TST (p = 0.002) and elevated ESR (p = 0.001). Among the likely genital TB group, all 6 confirmed genital TB were started on ATT and 2 (33.3%) conceived. Of 5 probable genital TB started on ATT, 3 (60%) conceived.ConclusionApproximately 1/6th of women seeking infertility care met the criteria for likely genital TB. Conception among over-half of treated probable genital TB cases provides preliminary evidence that best clinical practices can be utilized, but needs further confirmatory studies.  相似文献   
997.
One hundred forty-four serum samples from 52 patients with chronic hepatitis D virus infection were analyzed for hepatitis D virus RNA by dot-blot hybridization using hepatitis D virus cDNA probe labeled with 32P. The results were correlated with the presence of serum IgM anti-hepatitis D virus and hepatitis D antigen in liver biopsy specimens when available. Although there was a trend of positive correlation between serum hepatitis D virus RNA and IgM anti-hepatitis D virus, no statistical significance could be found. In the serum samples with hepatitis D virus RNA, 32% were found to be negative for IgM anti-hepatitis D virus. Therefore, in chronic hepatitis D virus, absence of IgM anti-hepatitis D virus does not rule out active viral infection, as suggested by previous studies. There was a strong correlation between serum hepatitis D virus RNA and hepatic hepatitis D virus antigen. These data indicate that detection of hepatitis D virus RNA in serum samples is a reliable noninvasive marker of active viral infection.  相似文献   
998.
Stringer SE  Nelson MS  Gupta P 《Blood》2003,101(6):2243-2245
We previously showed that heparan sulfate (HS) is required for in vitro cytokine + chemokine-mediated maintenance of primitive human hematopoietic progenitors. However, HS preparations are mixtures of polysaccharide chains of varying size, structure, and protein-binding abilities. Therefore, we examined whether the long-term culture-initiating cells (LTC-IC) supportive capability of HS is attributable to an oligosaccharide of defined length and protein-binding ability. Oligosaccharides of a wide range of sizes were prepared, and their capability to support human marrow LTC-IC maintenance in the presence of low-dose cytokines and a single chemokine, macrophage inflammatory protein-1alpha (MIP-1alpha), was examined. LTC-IC supportive capability of HS oligosaccharides correlated directly with size and MIP-1alpha binding ability. A specific MIP-1alpha-binding HS oligosaccharide preparation of M(r) 10 kDa that optimally supported LTC-IC maintenance was identified. This oligosaccharide had the structure required for MIP-1alpha binding, which we have recently described. The present study defines the minimum size and structural features of LTC-IC supportive HS.  相似文献   
999.
A case is presented of complete atrioventricular (A-V) block occurring after a 50 mg bolus injection of lidocaine. Base-line studies before administration of lidocaine showed evidence of trifascicular block manifested by complete right bundle branch block, left anterior hemiblock and a markedly prolonged H-V interval. Advanced A-V block and then complete A-V block distal to the His bundle developed after administration of lidocaine. Lidocaine should be used with caution in patients with trifascicular disease; if it is administered to such patients, insertion of a temporary pacemaker catheter should be considered.  相似文献   
1000.
Protein synthesis in reticulocytes and their lysates is regulated by heme. In heme deficiency a heme-regulated translational inhibitor (HRI) that blocks initiation of polypeptide chains is activated. HRI is a protein kinase (ATP: protein phosphotransferase, EC 2.7.1.37) that specifically phosphorylates the 38,000-dalton subunit of the Met-tRNA(f) (Met) binding factor (IF), which forms a ternary complex with Met-tRNA(f) (Met) and GTP, a finding that suggests that the inhibition by HRI involves the phosphorylation of IF.We have investigated the effect of HRI in the partial reactions of protein chain initiation in which the IF-promoted binding of Met-tRNA(f) (Met) to 40S ribosomal subunits is enhanced by another initiation factor [ternary complex dissociation factor (TDF)] and AUG. The results show that HRI at very low concentrations markedly inhibits the binding of Met-tRNA(f) (Met) to 40S subunits. The inhibitory effect of HRI requires ATP. Under these conditions HRI phosphorylates only the 38,000-dalton subunit of IF.The TDF preparations not only promote the binding of the ternary complex to 40S subunits but also promote the dissociation of the ternary complex in the presence of 5 mM Mg(2+) at 0 degrees . The preincubation of purified IF alone with low concentrations of HRI and ATP does not significantly affect its capacity to form the ternary complex; however, the TDF-promoted dissociation of the ternary complex is inhibited. The nonhydrolyzable analog adenosine 5'-[beta,gamma-imido]triphosphate does not substitute for ATP. These findings suggest that phosphorylation causes a conformational modification in IF, which results in inhibition of the interaction between the ternary complex and TDF that is required for the binding of the ternary complex to 40S subunits.  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