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   2539393篇
  免费   198941篇
  国内免费   4616篇
耳鼻咽喉   36636篇
儿科学   79568篇
妇产科学   68111篇
基础医学   356016篇
口腔科学   73140篇
临床医学   229390篇
内科学   496301篇
皮肤病学   51863篇
神经病学   211064篇
特种医学   104682篇
外国民族医学   961篇
外科学   384839篇
综合类   57226篇
现状与发展   1篇
一般理论   980篇
预防医学   205266篇
眼科学   59066篇
药学   188701篇
  6篇
中国医学   4502篇
肿瘤学   134631篇
  2018年   27644篇
  2017年   22508篇
  2016年   23657篇
  2015年   27632篇
  2014年   37458篇
  2013年   54392篇
  2012年   77524篇
  2011年   76988篇
  2010年   44779篇
  2009年   44486篇
  2008年   71204篇
  2007年   76169篇
  2006年   77284篇
  2005年   82078篇
  2004年   80651篇
  2003年   74517篇
  2002年   69555篇
  2001年   115468篇
  2000年   118184篇
  1999年   102135篇
  1998年   28489篇
  1997年   25928篇
  1996年   25847篇
  1995年   25037篇
  1994年   23549篇
  1993年   21874篇
  1992年   83863篇
  1991年   81259篇
  1990年   78750篇
  1989年   75721篇
  1988年   70401篇
  1987年   69144篇
  1986年   65654篇
  1985年   62264篇
  1984年   46952篇
  1983年   39861篇
  1982年   23731篇
  1981年   20993篇
  1979年   44213篇
  1978年   30838篇
  1977年   25793篇
  1976年   24129篇
  1975年   26027篇
  1974年   32156篇
  1973年   30243篇
  1972年   28497篇
  1971年   26415篇
  1970年   24921篇
  1969年   23159篇
  1968年   21020篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
994.
OBJECTIVES: Most obstetric clinics have a program for the identification of small-for-gestational age (SGA) fetuses because of the increased risk of fetal complications that they present. We have a structured model for the identification and follow-up of SGA pregnancies. We aimed to determine whether the recognition of SGA antepartum improves fetal outcome. METHODS: All pregnancies at Malm? University Hospital from 1990 to 1998 (n = 26 968) were reviewed. SGA fetuses identified prior to delivery (n = 681) were compared with those not identified (n = 573). Also, all pregnancies with SGA fetuses were compared with those appropriate-for-gestational age (AGA) (n = 24 585). The risk of serious fetal complications (hypoxic encephalopathy grade 2 or 3, intracranial hemorrhage, Apgar score <4 at 5 min, neonatal convulsions, umbilical pH <7.0, cerebral palsy, mental retardation, stillbirth, intrapartum or infant death) was assessed with cross-tabulation and logistic regression analysis, adjusted for gestational age and degree of SGA. RESULTS: When compared with SGA fetuses identified before delivery (54%), SGA fetuses not identified before delivery were characterized by a four-fold increased risk of adverse fetal outcome (odds ratio, 4.1; 95% CI, 2.5-6.8). Similarly, compared with AGA fetuses, SGA fetuses were associated with a four-fold increased risk of serious fetal complications. CONCLUSIONS: A structured antenatal surveillance program for fetuses identified as SGA results in a lower risk of adverse fetal outcome, compared with cases of SGA fetuses not identified antepartum.  相似文献   
995.
996.
OBJECTIVE: To describe the course and outcome of fetuses with absent or reversed end-diastolic (ARED) flow in the umbilical artery (UA) and to examine the influence of prematurity according to gestational age at delivery. METHODS: Sixty pregnancies complicated by ARED flow in the UA were monitored by repeat Doppler measurements of arterial and venous vessels, non-stress tests (cardiotocogram (CTG)) and maternal investigations, and were delivered between 24 and 34 weeks. Fetal outcome was investigated and compared to a control group of appropriate-for-gestational age (AGA) preterm neonates, matched for gestational age. Mortality, birth weight, Apgar scores, postnatal cord arterial pH and need for ventilation were all recorded, as were cases of respiratory distress syndrome, bronchopulmonary dysplasia, persistent ductus arteriosus, necrotizing enterocolitis, intraventricular hemorrhage, periventricular leukomalacia, abnormal neurological findings and those requiring surgical intervention. Additionally, the group of fetuses with ARED flow was divided into three subgroups of different degrees of prematurity (delivery between 24 + 0 and 28 + 6 weeks, delivery between 29 + 0 and 31 + 6 weeks, and delivery after 32 weeks) and compared according to the above parameters. RESULTS: Pre- or postnatal death occurred in 16 cases. Comparing the 44 (61%) that were born alive with the AGA neonates, significant differences were found in birth weight (P < 0.001), arterial pH value (P < 0.001), bronchopulmonary dysplasia (P = 0.002) and intestinal complications (P < 0.01). Prematurity-related complications were: need for ventilation (P = 0.001), respiratory distress syndrome (P < 0.0001), periventricular leukomalacia (P = 0.002) and pathological neurological testing (P = 0.005). CONCLUSIONS: Neonates displaying ARED flow before birth are growth restricted, acidemic at delivery and are at high risk of developing bronchopulmonary dysplasia and intestinal complications. While perinatal mortality seems to be related to abnormal fetal Doppler velocimetry, age at delivery has a significant impact on short-term morbidity. After 32 weeks, morbidity is low and delivery should be considered. It could be speculated from our data that prolongation of pregnancy with Doppler velocimetry monitoring could help to reduce morbidity, although prolongation remains limited in most cases.  相似文献   
997.
998.
999.
The purpose of this study was to provide, in a large number of patients, comprehensive Doppler echocardiographic assessment of normal St Jude Medical mitral valve prosthesis function using Doppler-derived hemodynamic variables, including the mitral valve prosthesis-to-left ventricular outflow tract time-velocity integral ratio and prosthesis performance index. The pressure half-time was less than 130 milliseconds in all patients, and all but one patient had either a peak early mitral diastolic velocity of 2 m/s or less or a mitral valve prosthesis-to-left ventricular outflow tract time-velocity integral ratio of less than 2.2. There was a significant (P < .001) negative correlation between the prosthesis performance index and prosthesis size. This negative correlation suggests that there is more efficient use of the in vitro geometric orifice area with smaller prostheses.  相似文献   
1000.
BACKGROUND: The index of myocardial performance (IMP) has been used as a prognostic systolic-diastolic index for patients with dilated cardiomyopathy and postmyocardial infarction. To date, systematic evaluation of the effect of heart rate and preload alteration on IMP has not been performed with normal or reduced left ventricular (LV) function. METHODS: We studied 14 mongrel dogs at baseline, after the induction of acute ischemic LV dysfunction, and with chronic LV dysfunction. Heart rate was altered by atrial pacing 10 and 20 beats above baseline, and volume loading was accomplished with 10 mL/kg of saline at a paced rate. Hemodynamics, and transmitral and transaortic pulsed Doppler, were obtained. RESULTS: With normal LV function, there were no changes in IMP with pacing. With acute LV dysfunction, IMP was also unchanged with pacing, although both LV ejection time (ET) (192 +/- 23 vs 208 +/- 25 milliseconds, P < .05) and isovolumic contraction time (58 +/- 25 vs 72 +/- 31 milliseconds, P < .05) declined. With chronic LV dysfunction, IMP was unchanged although LV ET declined (188 +/- 15 vs 204 +/- 18 milliseconds, P < .01). Volume loading did not alter the IMP with normal LV function although LV ET increased (208 +/- 25 vs 220 +/- 20 milliseconds, P < .001). With acute LV dysfunction, IMP decreased (0.66 +/- 0.11 vs 0.82 +/- 0.20, P < .05) because of a decrease in isovolumic relaxation time (63 +/- 33 vs 76 +/- 38 milliseconds, P < .05). With chronic LV dysfunction, IMP also declined with volume loading (0.59 +/- 0.29 vs 0.73 +/- 0.28, P < .01) because of an increase in LV ET (224 +/- 30 vs 198 +/- 22 milliseconds, P < .0001). CONCLUSION: Heart rate incrementation does not change IMP. However, volume loading reduces IMP primarily as a result of LV ET lengthening with chronic LV dysfunction. Further systematic evaluation of IMP is needed if this index is to be useful as a prognostic indicator.  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