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   15609篇
  免费   954篇
  国内免费   88篇
耳鼻咽喉   101篇
儿科学   363篇
妇产科学   369篇
基础医学   1938篇
口腔科学   314篇
临床医学   1523篇
内科学   3587篇
皮肤病学   219篇
神经病学   1730篇
特种医学   689篇
外科学   2306篇
综合类   66篇
一般理论   6篇
预防医学   1091篇
眼科学   303篇
药学   891篇
中国医学   34篇
肿瘤学   1121篇
  2024年   22篇
  2023年   192篇
  2022年   285篇
  2021年   500篇
  2020年   382篇
  2019年   449篇
  2018年   527篇
  2017年   411篇
  2016年   498篇
  2015年   489篇
  2014年   666篇
  2013年   845篇
  2012年   1392篇
  2011年   1365篇
  2010年   713篇
  2009年   599篇
  2008年   1063篇
  2007年   1029篇
  2006年   896篇
  2005年   920篇
  2004年   796篇
  2003年   681篇
  2002年   624篇
  2001年   96篇
  2000年   82篇
  1999年   103篇
  1998年   135篇
  1997年   76篇
  1996年   89篇
  1995年   64篇
  1994年   50篇
  1993年   56篇
  1992年   61篇
  1991年   42篇
  1990年   35篇
  1989年   40篇
  1988年   35篇
  1987年   23篇
  1986年   27篇
  1985年   36篇
  1984年   21篇
  1983年   31篇
  1982年   14篇
  1981年   22篇
  1979年   12篇
  1972年   14篇
  1971年   19篇
  1970年   10篇
  1969年   10篇
  1968年   20篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
OBJECTIVEIn a large, multiethnic cohort of youths with obesity, we analyzed pathophysiological and genetic mechanisms underlying variations in plasma glucose responses to a 180 min oral glucose tolerance test (OGTT).RESEARCH DESIGN AND METHODSLatent class trajectory analysis was used to identify various glucose response profiles to a nine-point OGTT in 2,378 participants in the Yale Pathogenesis of Youth-Onset T2D study, of whom 1,190 had available TCF7L2 genotyping and 358 had multiple OGTTs over a 5 year follow-up. Insulin sensitivity, clearance, and β-cell function were estimated by glucose, insulin, and C-peptide modeling.RESULTSFour latent classes (1 to 4) were identified based on increasing areas under the curve for glucose. Participants in class 3 and 4 had the worst metabolic and genetic risk profiles, featuring impaired insulin sensitivity, clearance, and β-cell function. Model-predicted probability to be classified as class 1 and 4 increased across ages, while insulin sensitivity and clearance showed transient reductions and β-cell function progressively declined. Insulin sensitivity was the strongest determinant of class assignment at enrollment and of the longitudinal change from class 1 and 2 to higher classes. Transitions between classes 3 and 4 were explained only by changes in β-cell glucose sensitivity.CONCLUSIONSWe identified four glucose response classes in youths with obesity with different genetic risk profiles and progressive impairment in insulin kinetics and action. Insulin sensitivity was the main determinant in the transition between lower and higher glucose classes across ages. In contrast, transitions between the two worst glucose classes were driven only by β-cell glucose sensitivity.  相似文献   
52.
53.
54.
55.
This prospective study evaluated the efficacy of transvaginal ultrasonography combined with water-contrast in the rectum (RWC-TVS) in the diagnosis of rectal infiltration in 35 women with rectovaginal endometriosis; ultrasonographic findings were compared with surgery and histology. The sensitivity of RWC-TVS in identifying rectal infiltration reaching at least the muscular layer was 100%, the specificity was 85.7%, the positive predictive value was 91.3%, and the negative predictive value was 100%. In 4 of 5 (80.0%) nodules reaching the submucosa, the depth of infiltration was underestimated by RWC-TVS. The RWC-TVS reliably determined the largest diameter of the endometriotic nodules and was well tolerated by the patients.  相似文献   
56.
57.
Sodium pancratistatin 3,4- O-cyclic phosphate ( 2) is a novel water-soluble synthetic derivative of pancratistatin ( 1), a natural alkaloid constituent of Amaryllidaceae plants, that exhibits good cytostatic and antineoplastic activity but is highly insoluble. Unlike most other natural alkaloids it does not act by binding to tubulin, and its mechanism of action has yet to be fully elucidated. Here the efficacy of 2 in a human colon adenocarcinoma model, DLD-1, and some understanding of its mode of action are investigated. Agreeing with previous studies, low cytotoxicity in vitro was seen for 2 with IC 50's of 253 and 19.7 microM for 1 and 96 h exposures, respectively. However in vivo the compound caused statistically significant tumor growth delays ( p < 0.01) at its maximum tolerated dose, and significant vascular shutdown and tumor necrosis were observed. Like 1, the compound appeared to have an unconventional mechanism of action with no effect on microtubule structure, yet causing a G 2/M block, while it was seen to disrupt mitochondrial function. The mechanism of action of 1 and 2 appears to be similar. Thus compound 2, being considerably more soluble than 1, has good potential as an anticancer agent, and further investigation is warranted.  相似文献   
58.
OBJECTIVES: To estimate the combined screening performance of first and early second trimester prenatal serum markers for Down syndrome, in screening for the development of preeclampsia, and analyze the correlation among marker levels, week of onset, and severity of the disease. METHODS: A retrospective cohort study was carried out on 32 women with preeclampsia and 3044 controls. Serum samples from these pregnancies were assayed for pregnancy-associated plasma protein-A (PAPP-A), alpha-fetoprotein (AFP), unconjugated estriol (uE3), human chorionic gonadotrophin (hCG), and inhibin-A. A likelihood ratio and the odds of being affected given a positive result (OAPR) of various combinations of markers were calculated and receiver operating characteristic (ROC) curves analysis was performed. RESULTS: In the pregnancies that subsequently developed preeclampsia, first trimester PAPP-A concentration was significantly lower and concentrations of early second trimester inhibin-A and hCG significantly elevated. Levels of early second trimester uE3 and AFP were not significantly altered. We also found that inhibin-A correlates with both onset of the disease and the severity. CONCLUSION: Down syndrome biochemical markers levels are altered in those patients who subsequently developed preeclampsia and may be a useful screening test for preeclampsia. Inhibin-A is the most predictive marker and correlates with the severity of subsequent preeclampsia and inversely with the week of occurrence of preeclampsia.  相似文献   
59.
60.
Background Abdominal cystic formations in newborns are relatively common and often diagnostic suspicion arises in this regard even before birth as a result of ultrasound scans carried out during pregnancy. The aim of this study is to highlight the problems posed by the prenatal diagnosis of abdominal cysts in order to outline the most appropriate therapeutic approach in case of suspected ovarian cysts. Materials and methods Between January 2003 and January 2007, 57 women were enrolled in this study for a prenatal ultrasound (US) that revealed the presence of an echo-rare or echo-free area in the foetal abdomen. After birth all babies underwent blood tests and abdominal US scans in order to confirm or identify the nature of the cyst. If abdominal US could not show the nature of the cystic formation, magnetic resonance imaging with sedation was performed. When the radiological tests were not useful to identify the nature of the cysts and surgery was then necessary, surgical procedures were performed with laparoscopy. Results Ultrasounds were useful to identify the diameter of the cysts but not all their origins; also MRI confirmed the morphology and volume of the cysts, but could not give further details about their origin. Discussion Abdominal ultrasound and finally laparoscopy used to treat and remove the cysts were useful to monitor all simple abdominal cysts. MRI seemed not to be useful for the treatment of this condition, especially in the pediatric age when mild sedation is required.  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