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   5679篇
  免费   493篇
  国内免费   27篇
耳鼻咽喉   74篇
儿科学   250篇
妇产科学   240篇
基础医学   856篇
口腔科学   179篇
临床医学   556篇
内科学   1106篇
皮肤病学   93篇
神经病学   387篇
特种医学   321篇
外国民族医学   1篇
外科学   777篇
综合类   103篇
一般理论   9篇
预防医学   405篇
眼科学   91篇
药学   395篇
中国医学   1篇
肿瘤学   355篇
  2021年   99篇
  2020年   58篇
  2019年   85篇
  2018年   105篇
  2017年   76篇
  2016年   87篇
  2015年   112篇
  2014年   156篇
  2013年   195篇
  2012年   282篇
  2011年   255篇
  2010年   190篇
  2009年   165篇
  2008年   226篇
  2007年   245篇
  2006年   236篇
  2005年   229篇
  2004年   196篇
  2003年   209篇
  2002年   204篇
  2001年   187篇
  2000年   182篇
  1999年   185篇
  1998年   86篇
  1997年   70篇
  1996年   87篇
  1995年   71篇
  1994年   63篇
  1993年   55篇
  1992年   94篇
  1991年   85篇
  1990年   100篇
  1989年   112篇
  1988年   100篇
  1987年   99篇
  1986年   111篇
  1985年   114篇
  1984年   79篇
  1983年   76篇
  1981年   46篇
  1980年   38篇
  1979年   62篇
  1978年   46篇
  1977年   45篇
  1975年   37篇
  1974年   65篇
  1973年   49篇
  1972年   44篇
  1967年   36篇
  1966年   43篇
排序方式: 共有6199条查询结果,搜索用时 15 毫秒
71.
Respiratory viruses in children admitted to hospital in Edinburgh 1972-1985   总被引:1,自引:0,他引:1  
The temporal incidence of respiratory viruses identified in children admitted to an Edinburgh hospital over a period of 14 years, 1972-1985, is described, Respiratory syncytial (RS) virus was identified most often, usually (but not in 1979 and 1985) with single peaks of activity in the winter months. Influenza virus infections were seen in the winter and spring but we failed to find evidence of interference between RS and influenza virus. Of the viruses studied, the parainfluenza viruses were the least predictable in their epidemiological behaviour. The results of this study are compared with those of others and the role of certain aspects of the weather is considered.  相似文献   
72.
Summary The prevalence of ESBL was determined among isolates of Escherichia coli (n = 571) and Klebsiella spp. (n = 196) collected during a 1-week study period in 8 university and 3 large regional laboratories all over the Netherlands. 18 isolates were positive for at least one of the screening tests used, i.e., VITEK-ESBL, E-test ESBL and MIC ratio of ceftazidime/ceftazidime-clavulanic acid, cefotaxime/cefotaxime-clavulanic acid. In 5 of these 18 putative ESBLs no betalactamase production was detectable. A TEM type was found in three E. coli and two Klebsiella spp. An SHV type was present in five Klebsiella spp. In one E. coli and one Klebsiella pneumoniae both enzymes were present. In one Klebsiella oxytoca neither of the two enzymes was present. Using PCR for both ESBL TEM and ESBL SHV, an SHV ESBL was found in one E. coli and four Klebsiella isolates. The mutations at position 238 and 240 were already described. In one E. coli isolate a TEM ESBL was found with three mutations, at position 21, 164 and 265. These mutations were already described in other ESBLs but not in this combination suggesting a new TEM ESBL. The overall prevalence of ESBL producing E. coli and Klebsiella spp. was less than 1% (6 out of 767). Received: December 14, 1998 · Accepted: September 19, 1999  相似文献   
73.
74.
Declining testicular function with age. Hormonal and clinical correlates   总被引:6,自引:0,他引:6  
Testicular endocrine function and androgen-dependent secondary sexual characteristics were assessed in 283 men 18 to 96 years of age. Mean serum total testosterone levels remained unchanged up to age 70 and declined thereafter. In 29 per cent of the men over 70 years of age total testosterone levels were below the lower limit of normal for young adults, In contrast, mean free or unbound testosterone levels declined after age 50 and were below the lower limit of normal for young adults in 40 per cent of the men over 70 years of age. Serum-luteinizing hormone and follicle-stimulating hormone levels showed a slight but steady rise after age 40 which became more abrupt after age 70. Serum gonadotropin levels were elevated in approximately 60 per cent of the men over 70 years of age.Mean testis length and volume were decreased in 78 per cent and 37 per cent, respectively, of the men over 60 years of age. Facial, pubic and axillary hair were also reduced in amount whereas the prostate was enlarged in 73 per cent of the elderly men. There appeared to be an inverse relationship in older men between testicular size and gonadotropin levels, and a direct relationship between testicular and prostatic sizes.It would appear that some degree of Leydig cell hypofunction commonly begins at around 45 to 50 years of age, becoming more pronounced after age 70. The concomitant elevation in serum gonadotropin levels at this time indicates that this is due to a primary decline in testicular function and is not secondary to pituitary hypofunction.  相似文献   
75.
Eubacterium lentum and phenotypically similar organisms synthesize a steroid 21-dehydroxylase which converts biliary tetrahydrodeoxycorticosterone to pregnanolone. Tetrahydrodeoxycorticosterone, in contrast to pregnanolone, is carcinogenic for hamster embryonic cells (HECT test). In patients with recently diagnosed, untreated sigmoidal or rectal cancer the fecal concentration of 21-dehydroxylating organisms is reduced by more than 99% as compared with age-matched controls. The lack of fecal 21-dehydroxylating organisms, therefore, is a potential marker for the disorder. The role of steroid 21-dehydroxylase in the pathogenesis of colorectal cancer is unknown.  相似文献   
76.
Fanconi anemia (FA) is a genetic disease characterized by bone marrow failure and cancer predisposition. Here we have identified Spanish Gypsies as the ethnic group with the world's highest prevalence of FA (carrier frequency of 1/64-1/70). DNA sequencing of the FANCA gene in 8 unrelated Spanish Gypsy FA families after retroviral subtyping revealed a homozygous FANCA mutation (295C>T) leading to FANCA truncation and FA pathway disruption. This mutation appeared specific for Spanish Gypsies as it is not found in other Gypsy patients with FA from Hungary, Germany, Slovakia, and Ireland. Haplotype analysis showed that Spanish Gypsy patients all share the same haplotype. Our data thus suggest that the high incidence of FA among Spanish Gypsies is due to an ancestral founder mutation in FANCA that originated in Spain less than 600 years ago. The high carrier frequency makes the Spanish Gypsies a population model to study FA heterozygote mutations in cancer.  相似文献   
77.
78.
79.
80.
Purpose

The aim of this study was to evaluate the utility of added DWI sequences as an adjunct to traditional MR imaging in the evaluation of abnormal placentation in patients with suspicion for placenta accreta spectrum abnormality or morbidly adherent placenta (MAP).

Materials and methods

The study was approved by local ethics committee. The subjects included pregnant women with prenatal MRI performed between July 2013 to July 2015. All imaging was performed on a Philips 1.5T MR scanner using pelvic phased-array coil. Only T2-weighted and diffusion-weighted imaging (DWI) series were compiled for review. Two randomized imaging sets were created: set 1 included T2-weighted series only (T2W); set 2 included T2W with DWI series together (T2W + DWI). Three radiologists, blinded to history and pathology, reviewed the imaging, with 2 weeks of time between the two image sets. Sensitivity, specificity, and overall accuracy for MAP were calculated and compared between T2W only and T2W + DWI reads. Associations between imaging findings and invasion on pathology were tested using the Chi-squared test. Confidence scores, inter-reader agreement, and systematic differences were documented.

Results

A total of 17 pregnant women were included in the study. 8 cases were pathologically diagnosed with MAP. There were no significant differences in the diagnostic accuracy between T2W and T2W + DWI in the diagnosis of MAP in terms of overall accuracy (62.7% for T2W vs. 68.6% for T2W + DWI, p = 0.68), sensitivity (70.8% for T2W vs. 95.8% for T2W + DWI, p = 0.12), and specificity (55.6% for T2W vs. 44.4% for T2W + DWI, p = 0.49). There was no significant difference in the diagnostic confidence between the review of T2W images alone and the T2W + DWI review (mean 7.3 ± 1.8 for T2W vs. 7.5 ± 1.8 for T2W + DWI, p = 0.37).

Conclusion

With the current imaging technique, addition of DWI sequence to the traditional T2W images cannot be shown to significantly increase the accuracy or reader confidence for diagnosis of placenta accreta spectrum abnormality. However, DWI does improve identification of abnormalities in the placental–myometrial interface.

  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