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   19213篇
  免费   1300篇
  国内免费   98篇
耳鼻咽喉   157篇
儿科学   471篇
妇产科学   493篇
基础医学   2423篇
口腔科学   386篇
临床医学   1875篇
内科学   4325篇
皮肤病学   263篇
神经病学   2221篇
特种医学   818篇
外科学   2746篇
综合类   241篇
一般理论   9篇
预防医学   1361篇
眼科学   340篇
药学   1091篇
中国医学   47篇
肿瘤学   1344篇
  2023年   220篇
  2022年   322篇
  2021年   581篇
  2020年   448篇
  2019年   525篇
  2018年   608篇
  2017年   454篇
  2016年   557篇
  2015年   558篇
  2014年   778篇
  2013年   995篇
  2012年   1587篇
  2011年   1570篇
  2010年   817篇
  2009年   706篇
  2008年   1255篇
  2007年   1202篇
  2006年   1082篇
  2005年   1083篇
  2004年   963篇
  2003年   854篇
  2002年   756篇
  2001年   226篇
  2000年   190篇
  1999年   224篇
  1998年   186篇
  1997年   111篇
  1996年   123篇
  1995年   105篇
  1994年   80篇
  1993年   81篇
  1992年   138篇
  1991年   118篇
  1990年   83篇
  1989年   100篇
  1988年   82篇
  1987年   70篇
  1986年   68篇
  1985年   79篇
  1984年   53篇
  1983年   51篇
  1982年   38篇
  1981年   40篇
  1979年   32篇
  1978年   27篇
  1977年   34篇
  1975年   31篇
  1972年   28篇
  1971年   34篇
  1968年   27篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
83.
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   
84.
The objective of this study was to assess the validity and observed effect size of a new instrument, the Optimality Index-United States (OI-US), for use in perinatal clinical research. Using a large, hospital-based, midwifery service clinical database that included complete obstetric data for 3425 women, we examined discriminant validity and the effects of two different scoring methods used with the OI-US. Discriminant validity was confirmed by comparing OI scores for women who remained low risk and did not require physician involvement in their care (OI score mean = 84%; standard deviation [SD] = 8%) compared to those whose condition changed to require physician involvement in their care (mean = 71%; SD = 10%; P < .001). Two methods of scoring the OI-US were compared, finding no significant difference and suggesting that the types of data available and the research question can drive this decision. Finally, effect size was calculated by two methods: Cohen's d (-1.4) and the effect size correlation (r = -0.548), the latter of which corresponds to a d of -1.3, both resulting in a similarly large effect size estimation. The OI-US is a new instrument that shows promise for use in perinatal clinical research, particularly when assessing more subtle clinical differences in outcomes between study groups.  相似文献   
85.
Our objective was to address the gap in knowledge about the extent to which perinatal mental health and risk behaviors are associated with childhood and adult experiences of abuse that arises because of barriers to screening and disclosure about past and current abuse. Survey data from an ongoing study of the effects of posttraumatic stress on childbearing were used to describe four groups of nulliparous women: those with no abuse history, adult abuse only, childhood abuse only, and abuse that occurred during both periods. The rates of abuse history disclosure were higher in the research context than in the clinical settings. Mental health morbidity and risk behaviors occurred in a dose-response pattern with cumulative abuse exposure. Rates of current posttraumatic stress disorder ranged from 4.1% among those never abused to 11.4% (adult only), 16.0% (childhood only), and 39.2% (both periods). Women abused during both periods also were more likely to be using tobacco (21.5%) and drugs (16.5%) during pregnancy. We conclude that mental health and behavioral risk sequelae affect a significant portion of both childhood and adult abuse survivors in prenatal care. The integration into the maternity setting of existing evidence-based interventions for the mental health and behavioral sequelae of abuse is needed.  相似文献   
86.
87.
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   
88.
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   
89.
90.
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