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   1335362篇
  免费   100213篇
  国内免费   4271篇
耳鼻咽喉   16797篇
儿科学   43586篇
妇产科学   36358篇
基础医学   197846篇
口腔科学   35902篇
临床医学   129552篇
内科学   258084篇
皮肤病学   26371篇
神经病学   111932篇
特种医学   48179篇
外国民族医学   366篇
外科学   184046篇
综合类   28772篇
现状与发展   1篇
一般理论   460篇
预防医学   114401篇
眼科学   28980篇
药学   98830篇
  6篇
中国医学   3167篇
肿瘤学   76210篇
  2021年   10918篇
  2019年   11637篇
  2018年   16320篇
  2017年   12291篇
  2016年   13248篇
  2015年   15203篇
  2014年   20803篇
  2013年   32057篇
  2012年   44250篇
  2011年   46895篇
  2010年   27081篇
  2009年   24926篇
  2008年   42724篇
  2007年   45065篇
  2006年   45172篇
  2005年   43594篇
  2004年   41570篇
  2003年   39506篇
  2002年   38305篇
  2001年   60847篇
  2000年   62517篇
  1999年   52279篇
  1998年   14582篇
  1997年   13278篇
  1996年   13119篇
  1995年   12457篇
  1994年   11626篇
  1993年   10922篇
  1992年   41569篇
  1991年   40760篇
  1990年   39446篇
  1989年   37340篇
  1988年   34581篇
  1987年   33693篇
  1986年   32152篇
  1985年   30640篇
  1984年   23035篇
  1983年   19590篇
  1982年   11753篇
  1979年   20805篇
  1978年   14814篇
  1977年   12064篇
  1976年   11878篇
  1975年   12110篇
  1974年   14800篇
  1973年   14472篇
  1972年   13356篇
  1971年   12418篇
  1970年   11488篇
  1969年   10411篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
OBJECTIVE: To estimate the gestational age ranges that result in optimal birth outcomes for each of four risk-defined groups. STUDY DESIGN: Retrospective cohort study of singleton late third-trimester deliveries at a large urban teaching hospital between July 1995 and September 2003. Low-risk, advanced maternal age, hypertensive and diabetic patients were identified and grouped. Rates, by day of gestation at delivery, of cesarean delivery, major maternal perineal trauma, low 5-min APGAR score and NICU admission were determined for each study group. RESULTS: Each study group had meaningful changes in rates of obstetric outcomes as a function of gestational age at delivery and these patterns differed from group to group. A unique optimal time of delivery (OTD) was estimated for each group. The low-risk group OTD was calculated to be 37 weeks 1 day to 41 weeks 0 day; the advanced maternal age group OTD was 38 weeks 5 days to 39 weeks 6 days; the hypertension group OTD was 39 weeks 2 days to 40 weeks 1 day; and the diabetes mellitus group OTD was 40 weeks 3 days to 41 weeks 1 day. CONCLUSIONS: The OTD varied based on obstetrical risk. Strategies to increase the proportion of deliveries that occur within the OTD for specific risk-defined groups could theoretically improve birth outcomes.  相似文献   
992.
993.
Activated macrophages are known to oxidatively metabolize L-arginine to nitric oxide and citrulline. We have recently shown that nitric oxide is a potent inhibitory molecule in the in vitro rat mixed-splenocyte culture, resulting in inhibition of proliferation and cytolytic T-cell induction. We undertook this study using the sponge matrix allograft model in the rat to determine whether nitric oxide plays a role in an in vivo allograft response. Our experiments showed that on day 6 after grafting, when cytolytic activity of allograft-infiltrating cells is first detected, allogeneic graft fluid contains higher levels of NO2-/NO3- (the stable endproducts of nitric oxide metabolism) than syngeneic graft fluid. Furthermore, evaluation of the supernatants of cultured graft-infiltrating cells revealed that allogeneic graft-infiltrating cells spontaneously produce higher amounts of nitric oxide than syngeneic graft-infiltrating cells. The nitric oxide production was inhibited in the presence of NG-monomethyl-L-arginine (NMA), the competitive inhibitor of nitric oxide production. Most of the nitric oxide production was observed in the adherent macrophage fraction of the allograft-infiltrating cells. When allograft-infiltrating cells were cultured in the presence of NMA, donor-specific cytolytic activity was observed, whereas allograft-infiltrating cells cultured in the absence of NMA showed no cytolytic activity. These data show that nitric oxide production may play an important regulatory role in the allograft response.  相似文献   
994.
New long-acting beta 2-adrenoceptor agonists, formoterol and salmeterol, may soon appear in several European countries for treatment of asthma. This review examines currently available information and compares the basic pharmacology and describes the clinical effects of these new drugs. The long duration of bronchodilation seen in clinical studies seems to be similar, whereas in isolated tissues there might be a difference in the binding characteristics to the beta 2-adrenoceptor. Long-acting beta 2-agonists could have an inhibitory effect on inflammatory events related to asthma, but the clinical relevance of these effects is not clear at present. Long-term studies up to one year with both new drugs have not shown any unexpected side-effects, and no tachyphylaxis to beta-adrenoceptor stimulation has been reported. Patients appear to strongly prefer the new drugs compared to the short-acting beta 2-agonists. The potential place for these drugs in the treatment of asthma is discussed and some pitfalls pointed out. It is likely that the long-acting beta 2-agonists will be beneficial to many asthmatic patients.  相似文献   
995.
996.
997.
Seventeen autistic children were matched for age, race, and sex with 17 nonautistic children, and group differences in social skills were assessed. Appropriate social skills and levels of inappropriate assertiveness/impulsiveness were assessed and evaluated using the Matson Evaluation of Social Skills with Youngsters (MESSY). Significant differences in both the appropriate and inappropriate social behaviors displayed by the two groups were found. The implications of these results are discussed.  相似文献   
998.
We report the two-dimensional and Doppler color flow mapping echocardiographic findings in a neonate with left circumflex coronary arteriovenous fistula to a left superior vena cava. Doppler color flow mapping, in concert with detailed imaging, was essential to identify this rare fistula and to prepare for therapeutic intervention at initial cardiac catheterization.  相似文献   
999.
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