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   17454篇
  免费   1218篇
  国内免费   82篇
耳鼻咽喉   185篇
儿科学   395篇
妇产科学   291篇
基础医学   2368篇
口腔科学   354篇
临床医学   1357篇
内科学   4220篇
皮肤病学   534篇
神经病学   1348篇
特种医学   689篇
外科学   3167篇
综合类   280篇
一般理论   15篇
预防医学   1036篇
眼科学   480篇
药学   778篇
中国医学   43篇
肿瘤学   1214篇
  2023年   78篇
  2022年   165篇
  2021年   397篇
  2020年   239篇
  2019年   353篇
  2018年   387篇
  2017年   315篇
  2016年   383篇
  2015年   418篇
  2014年   600篇
  2013年   758篇
  2012年   1155篇
  2011年   1122篇
  2010年   678篇
  2009年   599篇
  2008年   1025篇
  2007年   1056篇
  2006年   1007篇
  2005年   1068篇
  2004年   994篇
  2003年   871篇
  2002年   895篇
  2001年   314篇
  2000年   292篇
  1999年   258篇
  1998年   180篇
  1997年   156篇
  1996年   136篇
  1995年   138篇
  1994年   127篇
  1993年   92篇
  1992年   120篇
  1991年   137篇
  1990年   114篇
  1989年   129篇
  1988年   145篇
  1987年   113篇
  1986年   110篇
  1985年   92篇
  1984年   94篇
  1983年   114篇
  1982年   135篇
  1981年   114篇
  1980年   93篇
  1979年   67篇
  1978年   68篇
  1977年   75篇
  1976年   49篇
  1975年   42篇
  1974年   50篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
1.
2.
3.

Objective

Arch obstruction after the Norwood procedure is common and contributes to mortality. We determined the prevalence, associated factors, and practice variability of arch reintervention and assessed whether arch reintervention is associated with mortality.

Methods

From 2005 to 2017, 593 neonates in the Congenital Heart Surgeons' Society Critical Left Heart Obstruction cohort underwent a Norwood procedure. Median follow-up was 3.7 years. Multivariable parametric models, including a modulated renewal analysis, were performed.

Results

Of the 593 neonates, 146 (25%) underwent 218 reinterventions for arch obstruction after the Norwood procedure: catheter-based (n = 168) or surgical (n = 50) at a median age of 4.3 months (quartile 1-quartile 3, 2.6-5.7). Interdigitation of the distal aortic anastomosis was protective against arch reintervention. Development of ≥ moderate tricuspid valve regurgitation and right ventricular dysfunction at any point was associated with arch reintervention. Nonsignificant variables for arch reintervention included shunt type and preoperative aortic measurements. Surgical arch reintervention was protective against arch reintervention, but transcatheter reintervention was associated with increased reintervention. Arch reintervention was not associated with increased mortality. There was wide institutional variation in incidence of arch reintervention (range, 0-40 reinterventions per 100 years patient follow-up) and in preintervention gradient (range, 0-64 mm Hg).

Conclusions

Interdigitation of the distal aortic anastomosis during the Norwood procedure decreased the risk of arch reintervention. Surgical arch reintervention is more definitive than transcatheter. Arch reintervention after the Norwood procedure is not associated with increased mortality. Serial surveillance for arch obstruction, integrated with changes in right ventricular function and tricuspid valve regurgitation, is recommended after the Norwood procedure to improve outcomes.  相似文献   
4.
5.
6.
Contraceptive use is an important strategy for the prevention of unwanted pregnancy and avoidance of induced abortion. Of all the contraception methods, emergency contraceptive (EC) offers the last chance to achieve this. However, few studies have documented the use of EC among young people in Ghana. This study explored knowledge and usage of EC as well as the factors associated with it among University of Cape Coast students. Data were obtained on the knowledge and usage of ECs among University of Cape Coast students in 2013. Logistic regression analysis was used to investigate the association between students’ socio-demographic characteristics and EC knowledge and use. More male students (72 %) than females (59 %) were sexually active. Fifty-seven percent of the respondents had ever heard of EC and 36 % had ever used EC. Although males were more likely to be sexually active, females were more likely to have knowledge of EC use compared to males. The study underscores the need to increase awareness regarding EC among University students in order to offer them the opportunity that EC provides if other forms of contraceptives are missed.  相似文献   
7.
8.
9.
10.
Most attempts to tissue-engineer cartilage have involved seeding of cultured cells into a biological or synthetic scaffold. We have developed a novel two-step culture approach that makes possible the in vitro formation of cartilaginous-like tissue by mature adult bovine chondrocytes without the aid of a synthetic matrix. The first step consists of culturing chondrocytes under conditions that maintain their rounded shape and their molecular phenotype as assessed by type II collagen and aggrecan production. This step was accomplished by culturing the isolated chondrocytes in alginate beads until the cells have reestablished a proteoglycan-rich cell-associated matrix (CM). The second step consists of culturing the cells with their CM, after recovery from the beads, on a tissue culture insert with a porous membrane. In this study, young adult bovine articular chondrocytes were cultured in alginate beads in the presence of 10% or 20% fetal bovine serum (FBS). After 7 days of culture, the alginate beads were dissolved by incubating the beads for 20 min in sodium citrate buffer, a calcium chelator. Following a brief centrifugation, the cells with their CM were recovered, resuspended in medium containing 10% or 20% FBS and seeded onto a tissue culture insert. After 1 week of culture on the insert, the individual cells with their CM progressively became incorporated into a mass of cartilaginous tissue. Culture with 20% FBS resulted in the best formation of tissues. These tissues, easily recovered from the insert, were then subjected to biochemical and histological analyses. The biochemical results showed that the chondrocytes remain phenotypically stable in the tissues. The de novo tissue has a relatively high ratio of PG/collagen. Histological examination of the tissue revealed it contained a cartilage-like matrix strongly stained with toluidine blue. This scaffold-free system appears ideal to study, in vitro, the development of transplantable cartilaginous tissue.  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