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   3107篇
  免费   129篇
  国内免费   12篇
耳鼻咽喉   136篇
儿科学   65篇
妇产科学   29篇
基础医学   371篇
口腔科学   43篇
临床医学   185篇
内科学   686篇
皮肤病学   173篇
神经病学   243篇
特种医学   260篇
外科学   333篇
综合类   22篇
现状与发展   1篇
预防医学   111篇
眼科学   44篇
药学   262篇
中国医学   40篇
肿瘤学   244篇
  2022年   29篇
  2021年   61篇
  2020年   20篇
  2019年   28篇
  2018年   47篇
  2017年   39篇
  2016年   43篇
  2015年   57篇
  2014年   60篇
  2013年   71篇
  2012年   124篇
  2011年   122篇
  2010年   78篇
  2009年   73篇
  2008年   110篇
  2007年   103篇
  2006年   138篇
  2005年   128篇
  2004年   121篇
  2003年   134篇
  2002年   137篇
  2001年   127篇
  2000年   149篇
  1999年   136篇
  1998年   55篇
  1997年   39篇
  1996年   36篇
  1995年   31篇
  1994年   16篇
  1993年   18篇
  1992年   79篇
  1991年   89篇
  1990年   70篇
  1989年   73篇
  1988年   66篇
  1987年   67篇
  1986年   71篇
  1985年   68篇
  1984年   38篇
  1983年   37篇
  1981年   13篇
  1980年   12篇
  1979年   28篇
  1975年   15篇
  1972年   13篇
  1971年   24篇
  1970年   12篇
  1969年   16篇
  1967年   18篇
  1966年   16篇
排序方式: 共有3248条查询结果,搜索用时 15 毫秒
71.
NADH dehydrogenase subunit-2 237 leucine/methionine (ND2-237 Leu/Met) polymorphism is associated with longevity in the Japanese population, and the ND2-237Met genotype may exert antiatherogenic effects. To investigate whether ND2-237 Leu/Met polymorphism is associated with risk of hypertension, we conducted a cross-sectional study of 398 Japanese male subjects. The frequency of hypertension was significantly higher in ND2-237Leu genotypic men than in ND2-237Met genotypic men. On analysis of covariance, the interaction between ND2-237 Leu/Met polymorphism and habitual drinking was significantly associated with both systolic blood pressure and diastolic blood pressure. Multiple logistic regression analysis revealed that the ND2-237Met genotype, particularly in younger subjects (age <60 years), had a lower odds ratio for hypertension than the ND2-237Leu genotype. Moreover, the association of ND2-237 Leu/Met polymorphism with hypertension may depend on the frequency of alcohol consumption. The odds ratio for hypertension was significantly higher in daily drinkers with ND2-237Leu when compared with non- or ex-drinkers with ND2-237Leu. However, the association between the ND2-237Met genotype and hypertension may not depend on the frequency of alcohol consumption. The present results suggest that ND2-237 Leu/Met polymorphism is associated with hypertension and that modification of hypertension risk is dependent on alcohol consumption in middle-aged Japanese men.  相似文献   
72.
73.
74.

Background

Although the clinicopathologic features and prognosis of Borrmann type advanced gastric cancer has been well characterized, those of advanced gastric cancer simulating early gastric cancer (AGC simulating EGC) still remains unclear.

Methods

We reviewed 1985 gastric cancer patients who had undergone gastrectomy at our hospital to determine the clinicopathologic characteristics, susceptible sites for lymph node metastasis, and prognosis of AGC simulating EGC in comparison with Borrmann type advanced gastric cancer.

Results

Among 102 patients with AGC simulating EGC, 100 patients (98%) had tumors with depressed type appearance. The frequencies of serosal invasion, lymph node metastasis, lymphatic vessel invasion, blood vessel invasion, and liver metastasis were significantly lower in AGC simulating EGC than in Borrmann type tumors. The prognosis of AGC simulating EGC was significantly better than that of the Borrmann type tumors. Multivariate analysis indicated that the gross appearance was an independent prognostic factor. In patients with AGC simulating EGC which invaded to the the muscularis propria (MP), most lymph node metastasis was restricted with the perigastric lymph nodes (1st-titer lymph nodes) and lymph node metastasis to 2nd-titer lymph nodes was only observed at station 8a.

Conclusion

AGC simulating EGC is less advanced in comparison with Borrmann type advanced gastric cancer. Based on the results of susceptible sites for lymph node metastasis in the current study, limited lymph node dissection could be indicated for AGC simulating EGC whose depth of invasion is MP.  相似文献   
75.
Odontology - There is no conclusive evidence regarding a causal relationship between periodontitis and atherosclerosis. In this study, we examined the microbiome in the oral cavity and atheromatous...  相似文献   
76.
77.

Objective:

The aims of this study are to propose a new set of Japanese diagnostic reference levels (DRLs) for 2014 and to study the impact of tube voltage and the type of reconstruction algorithm on patient doses. The volume CT dose index (CTDIvol) for adult and paediatric patients is assessed and compared with the results of a 2011 national survey and data from other countries.

Methods:

Scanning procedures for the head (non-helical and helical), chest and upper abdomen were examined for adults and 5-year-old children. A questionnaire concerning the following items was sent to 3000 facilities: tube voltage, use of reconstruction algorithms and displayed CTDIvol.

Results:

The mean CTDIvol values for paediatric examinations using voltages ranging from 80 to 100 kV were significantly lower than those for paediatric examinations using 120 kV. For adult examinations, the use of iterative reconstruction algorithms significantly reduced the mean CTDIvol values compared with the use of filtered back projection. Paediatric chest and abdominal scans showed slightly higher mean CTDIvol values in 2014 than in 2011. The proposed DRLs for adult head and abdominal scans were higher than those reported in other countries.

Conclusion:

The results imply that further optimization of CT examination protocols is required for adult head and abdominal scans as well as paediatric chest and abdominal scans.

Advances in knowledge:

Low-tube-voltage CT may be useful for reducing radiation doses in paediatric patients. The mean CTDIvol values for paediatric scans showed little difference that could be attributed to the choice of reconstruction algorithm.Since the introduction of CT in the 1970s, it has been established worldwide as one of the most important imaging modalities in diagnostic radiology. In the past decade, various dose-reduction techniques, such as tube current modulation1 and low tube voltage,2 have been shown to reduce radiation exposure. In particular, the use of an iterative reconstruction (IR) algorithm, in contrast to a filtered back projection (FBP) algorithm, has provided diagnostically acceptable images using low-radiation-dose CT.3,4Since estimates of the cancer risk attributable to the use of diagnostic X-rays have been reported,5,6 radiological technologists should aim to optimize scan parameters in order to avoid excessive radiation exposure. One powerful tool in this optimization applies the concept of diagnostic reference levels (DRLs). The DRLs of CT examinations are generally expressed in terms of the volume CT dose index (CTDIvol) or dose–length product. The DRL is used in medical imaging with ionizing radiation to indicate whether, in routine conditions, the patient dose from a specified procedure is unusually high or low; DRLs are usually reviewed at regular intervals and could be specific to a country or region.7 Surveys of DRLs for CT examination of adults811 and children12,13 have been reported in several countries.The current DRLs in Japan were established as target values by the Japan Association of Radiological Technologists in 2006. The DRLs refer to a set of medical exposure guidelines, although there are several issues with these guidelines.14 First, no more than two examinations (head and abdomen) are listed in DRLs, and they contain no information about the CT examination of children. Second, the DRL for abdomen examination employs a 30-cm phantom, whereas a 32-cm phantom is more commonly used worldwide. Therefore, a new set of Japanese DRLs has become an urgent necessity. In 2011, Asada et al15 reported mean CTDIvol values for the head (non-helical and helical), chest and upper abdomen of both adults and children, which were obtained using a nationally distributed questionnaire. The aims of this study are to propose a new set of Japanese DRLs for 2014 and to study the impact of tube voltage and the type of reconstruction algorithm on patient doses. The CTDIvol for both adults and children have been assessed and compared with both the results of the 2011 survey and data from other countries.  相似文献   
78.
79.
80.
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