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   3053篇
  免费   236篇
  国内免费   14篇
耳鼻咽喉   31篇
儿科学   52篇
妇产科学   65篇
基础医学   456篇
口腔科学   27篇
临床医学   298篇
内科学   800篇
皮肤病学   107篇
神经病学   232篇
特种医学   107篇
外科学   485篇
综合类   40篇
一般理论   1篇
预防医学   132篇
眼科学   61篇
药学   174篇
中国医学   1篇
肿瘤学   234篇
  2023年   12篇
  2022年   27篇
  2021年   61篇
  2020年   42篇
  2019年   75篇
  2018年   75篇
  2017年   37篇
  2016年   70篇
  2015年   86篇
  2014年   129篇
  2013年   165篇
  2012年   240篇
  2011年   257篇
  2010年   125篇
  2009年   120篇
  2008年   210篇
  2007年   212篇
  2006年   171篇
  2005年   179篇
  2004年   187篇
  2003年   160篇
  2002年   121篇
  2001年   17篇
  2000年   16篇
  1999年   20篇
  1998年   37篇
  1997年   19篇
  1996年   23篇
  1995年   20篇
  1994年   20篇
  1993年   22篇
  1992年   14篇
  1991年   13篇
  1990年   12篇
  1989年   23篇
  1988年   24篇
  1987年   23篇
  1986年   8篇
  1985年   17篇
  1984年   9篇
  1983年   13篇
  1982年   12篇
  1981年   14篇
  1980年   11篇
  1978年   9篇
  1976年   10篇
  1975年   11篇
  1973年   7篇
  1968年   9篇
  1963年   8篇
排序方式: 共有3303条查询结果,搜索用时 21 毫秒
991.
992.
993.
994.
995.
The composition and activities of the faecal microbiota in twelve healthy subjects analysed in a single open study were monitored before (1-week baseline step), during (10 d supplementation step) and after (10 d follow-up step) the ingestion of a fermented milk containing Lactobacillus casei DN-114 001. Fluorescent in situ hybridisation with group-specific DNA probes, real-time PCR using L. paracasei group-specific primers and temporal temperature gradient gel electrophoresis (TTGE) using group-specific primers were carried out, together with bacterial enzyme activity and metabolite analyses to monitor the structure and activities of the faecal microbiota. L. casei DNA was detected in the faeces of all of the subjects by TTGE after 10 d supplementation. Its quantification by real-time PCR showed a 1000-fold increase during the test step compared with initial levels. No major modification in either the dominant members of the faecal microbiota or their activities was observed during the trial. In conclusion, the short-term consumption of a milk product containing L. casei DN-114 001 was accompanied by a high, transient increase in the quantity of this strain in the faeces of all of the subjects without markedly affecting biochemical or bacteriological factors.  相似文献   
996.
We previously identified constitutive Smad signaling in human melanoma cells despite resistance to transforming growth factor-beta (TGF-beta) control of cell proliferation. This led us to investigate the effect of inhibitory Smad7 overexpression on melanoma cell behavior. Using the highly metastatic cell line, 1205-Lu, we thus generated melanoma cell clones constitutively expressing Smad7, and their mock-transfected counterparts. Stable expression of Smad7 resulted in an inhibition of constitutive Smad2/3 phosphorylation, and in a reduced TGF-beta response of Smad3/Smad4-driven gene transactivation, as measured using transfected Smad3/4-specific reporter gene constructs. Smad7 overexpression, however, did not alter their proliferative capacity and resistance to TGF-beta-driven growth inhibition. On the other hand, expression of Smad7 efficiently reduced the capacity of human melanoma cells to invade Matrigel in Boyden migration chambers, while not affecting their motility and adhesion to collagen and laminin. Gelatin zymography identified reduced MMP-2 and MMP-9 secretion by Smad7-expressing melanoma cells as compared with their control counterparts. Smad7-expressing melanoma cells exhibited a dramatically reduced capacity to form colonies under anchorage-independent culture conditions, and, when injected subcutaneously into nude mice, were largely delayed in their ability to form tumors. These results suggest that TGF-beta production by melanoma cells not only affects the tumor environment but also directly contributes to tumor cell aggressiveness through autocrine activation of Smad signaling.  相似文献   
997.
998.
999.
The purpose of the study was to evaluate image quality (IQ) associated with vascular radiology and vascular surgery procedures in Belgium and to determine reference values for future image quality assessment. IQ was evaluated with the CD-DISC contrast-detail phantom. This circular PMMA phantom contains 225 holes with different diameter and depth, to quantify resolution and contrast. Images of the phantom were acquired for both fluoroscopy and subtraction images on 21 systems. Three observers evaluated the images by determining the threshold contrast visible for every diameter. This results in contrast-detail curves and image quality figures. We observed a large difference in IQ between the centres. No straightforward correlation could be found with radiation dose or other exposure settings. A comparison was made with the image quality evaluation of the systems performed with the TOR[18FG] phantom for fluoroscopy. There is no clear correlation observed between the results of the CD-DISC phantom and the TOR phantom. However, systems with very poor or very good image quality could be detected by both phantoms. An important result is that a 75th percentile reference contrast-detail curve could be proposed to separate the best centres from these with poorer quality. Some centres had also a significantly better image quality than others. Therefore, we introduced also a 25th percentile. Centres with IQ above this value are recommended to lower the dose and work with acceptable rather than excellent image quality. The CD-DISC phantom thus allows to guide the image quality setting.  相似文献   
1000.
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