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   2427篇
  免费   123篇
  国内免费   81篇
耳鼻咽喉   46篇
儿科学   102篇
妇产科学   39篇
基础医学   263篇
口腔科学   30篇
临床医学   253篇
内科学   627篇
皮肤病学   33篇
神经病学   137篇
特种医学   337篇
外科学   304篇
综合类   29篇
预防医学   101篇
眼科学   40篇
药学   140篇
中国医学   1篇
肿瘤学   149篇
  2022年   17篇
  2021年   36篇
  2020年   21篇
  2019年   30篇
  2018年   43篇
  2017年   21篇
  2016年   40篇
  2015年   48篇
  2014年   65篇
  2013年   67篇
  2012年   120篇
  2011年   90篇
  2010年   72篇
  2009年   78篇
  2008年   95篇
  2007年   136篇
  2006年   64篇
  2005年   92篇
  2004年   65篇
  2003年   64篇
  2002年   90篇
  2001年   70篇
  2000年   65篇
  1999年   68篇
  1998年   82篇
  1997年   82篇
  1996年   66篇
  1995年   69篇
  1994年   46篇
  1993年   41篇
  1992年   45篇
  1991年   49篇
  1990年   33篇
  1989年   54篇
  1988年   49篇
  1987年   37篇
  1986年   38篇
  1985年   51篇
  1984年   31篇
  1983年   29篇
  1982年   28篇
  1981年   17篇
  1980年   27篇
  1977年   20篇
  1976年   23篇
  1975年   13篇
  1972年   18篇
  1971年   19篇
  1970年   15篇
  1966年   15篇
排序方式: 共有2631条查询结果,搜索用时 0 毫秒
11.
12.
The effects of co-culture of human spermatozoa with human immortalized endometrial cells - epithelial or stromal - on sperm movement characteristics, including hyperactivation, were studied using computer- assisted sperm analysis (CASA). Epithelial and stromal cell types could be separated following 8-10 days of culture of endometrial cells originating from human biopsies. Both cell types were immortalized by the SV 40 large T antigen. Co-incubation of sperm with epithelial and stromal monolayers enhanced the rate of hyperactivation: 24.9% (P <0.05) and 17.8% (P = 0.05) versus 9.5% as control, respectively, whereas the majority of motility parameters remained unchanged. Conditioned media had no effect upon sperm parameters, including hyperactivation. Co-incubation with either monolayer was able to maintain sperm motility over a longer period than incubation in control medium alone. In four patients whose spermatozoa did not exhibit hyperactivation, co-incubation with epithelial cells, but not conditioned medium, allowed normal rates of hyperactivation (range: 6.9- 15.6%).   相似文献   
13.
A simplified method for R banding of human oocyte chromosomes   总被引:1,自引:1,他引:1  
A simple and reliable R banding technique was developed forkaryotyping mature human oocytes. The banding quality obtainedis sufficient for the diagnosis of specific aneuploidies andthe discrimination between whole chromosomes and separated chromatids.The ability to karyotype human oocytes accurately will facilitatestudy of the aetiology of chromosomal abnormalities in humanconcepti.  相似文献   
14.
15.
The aim of this study was to compare the efficacy of pure follicle stimulating hormone (FSH) with that of FSH/human menopausal gonadotrophin (HMG) combination in downregulated cycles. A total of 357 patients was evaluated retrospectively. Sixty percent of patients in the FSH group and 55% in the FSH/HMG group were new; the others were repeat patients. Ovulation was suppressed with leuprolide acetate in all patients, followed by either FSH (n = 218) or FSH/HMG (n = 119). There was no difference in patients' age, infertility factors, number of ampoules used, length of stimulation, oestradiol levels on day of human chorionic gonadotrophin (HCG) administration, number of oocytes recovered or the number of embryos transferred. Also, nuclear maturity at aspiration and fertilization rates were not different between the two groups. FSH stimulation resulted in a significantly higher percentage of mature oocytes that showed the typical 'mature' morphological characteristics (P < 0.0001). The clinical pregnancy rates per transfer were 40 and 28% in patients stimulated with pure FSH and FSH/HMG respectively (P < 0.05). The significantly higher number of immature oocytes matured in vitro in the FSH/HMG group (P = 0.001) suggests a possible effect on in-vitro maturation, due to luteinizing hormone present in HMG. The difference in mature oocyte quality may be an important determinant in the higher pregnancy rates for the FSH- stimulated patients.   相似文献   
16.
17.
Purpose: As COVID-19 spreads globally and affects people''s health, there are concerns that the pandemic and control policies may have psychological effects on young people (age from 17 to 35 years). This psychological impact might vary in different countries, and thus we compared the prevalence of selfreported psychological distress, loneliness and posttraumatic stress symptoms (PTSS) among young people in the United Kingdom (UK) and China at the beginning of the COVID-19 pandemic. Methods: Data of this study came from two sources. One source was the first wave of COVID-19 study in Understanding Society, a special wave of the UK household longitudinal study, which provided the highquality, national-wide representative panel data. The sample comprised 1054 young people. The other source was an online survey on the mental health of 1003 young people from Shanghai, a highly developed area in China. The questionnaire included questions on the prevalence of common mental disorders (cut-off score ≥ 4), loneliness and potential PTSS (cut-off ≥ 33). Univariable analyses were conducted to test the differences in the self-reported prevalence of psychological distress and loneliness between the two groups. Multivariable logistic regression analyses were run to explore the predictors of psychological distress and loneliness among all the young people from England and Shanghai. Results: Among the samples with self-reported psychological distress, the UK sample accounted for 34.4% (n = 1054) and the Chinese sample accounted for 14.1% (n = 1003). The difference between the two groups was statistically significant (p < 0.001). Additionally, 57.1% of people in the UK and 46.7% in China reported that they sometimes or often felt lonely, of which the difference is statistically significant (p < 0.001). Regression analysis of the entire samples showed that nationality, gender, psychotherapy and loneliness were significant predictors of 12-item General Health Questionnaire scores, while the variables of age and living alone were not. Significant predictors of self-reported loneliness were the nationality, gender, age, living alone and psychotherapy. In China, 123 (12.3%) young people, 49 men (11.3%) and 74 women (13.0%), met the criteria of PTSS symptoms (cut-off scores ≥ 33). These scores were only collected in China. Conclusion: This evidence suggests that mental health and loneliness reported by young people were lower in China than that in the UK during the studied period. More research is needed to understand these differences. If the differential negative psychological impacts are confirmed, country-specific measures of prevention and intervention should be adopted to improve the mental health of young people under the ongoing impact of the pandemic.  相似文献   
18.
19.
20.
Midgut malrotation,the reliability of sonographic diagnosis   总被引:4,自引:0,他引:4  
We are unaware of any other anatomical study which deals with normal variations in the relationship between the superior mesenteric artery (SMA) and the superior mesenteric vein (SMV). In our investigation in the majority of cases, the SMV lies to the right of the SMA. It has been suggested that ultrasonographic demonstration of a left sided SMV, is characteristic of midgut malrotation so a prospective study was undertaken in order to try to correlate the position of the mesenteric vessels on Ultrasound with the radiological diagnosis of midgut malrotation on upper GI series. 427 children (95% infants) who were planned for upper GI investigation, have had color Doppler U.S. of the mesenteric vessels before the barium study. In 67 cases, the mesenteric vessels were obscured by intestinal gas. Among them, there were 2 cases of malrotation. Three different positions of the mesenteric vessels were found in the 360 remaining cases. 1) A left sided SMV was found in 4% of the cases, all had midgut malrotation on X-rays and at surgery. 2) A mesenteric vein anterior to the SMA was found in 5% of the cases, 28% had midgut malrotation. 3) A normal right sided SMV was found in 91% of the cases. However 3% of these had midgut malrotation. There are anatomical variations in the position of the mesenteric vessels and a normal relationship between SMA and SMV does not ecxclude the possibility of intestinal malrotation. Nevertheless, ultrasound remains a useful noninvasive screening technique for the diagnosis of midgut malrotation.Presented at the IPR meeting in Stockholm, May 1991. Selected for publication by an International Group of the ESPR  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