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   2011篇
  免费   14篇
  国内免费   3篇
综合类   3篇
化学工业   17篇
金属工艺   3篇
机械仪表   3篇
建筑科学   5篇
矿业工程   1篇
能源动力   3篇
轻工业   6篇
水利工程   13篇
石油天然气   6篇
无线电   5篇
一般工业技术   20篇
冶金工业   1928篇
自动化技术   15篇
  2022年   1篇
  2021年   1篇
  2020年   2篇
  2018年   2篇
  2017年   1篇
  2016年   7篇
  2015年   6篇
  2014年   4篇
  2013年   5篇
  2012年   2篇
  2011年   3篇
  2010年   5篇
  2009年   4篇
  2008年   4篇
  2007年   3篇
  2006年   3篇
  2005年   5篇
  2004年   6篇
  2003年   9篇
  2002年   5篇
  2001年   2篇
  2000年   2篇
  1999年   57篇
  1998年   675篇
  1997年   299篇
  1996年   228篇
  1995年   115篇
  1994年   98篇
  1993年   120篇
  1992年   10篇
  1991年   23篇
  1990年   28篇
  1989年   32篇
  1988年   34篇
  1987年   27篇
  1986年   15篇
  1985年   14篇
  1984年   1篇
  1983年   3篇
  1982年   4篇
  1981年   13篇
  1980年   14篇
  1978年   1篇
  1977年   27篇
  1976年   104篇
  1973年   1篇
  1971年   1篇
  1956年   1篇
  1955年   1篇
排序方式: 共有2028条查询结果,搜索用时 15 毫秒
91.
92.
93.
94.
95.
96.
97.
OBJECTIVE: To estimate the prevalence of radiographically detectable hippocampal atrophy (HA) in a normal aging sample and to test whether such atrophy is associated with memory dysfunction. DESIGN: One hundred fifty-four medically healthy and cognitively normal elderly persons (aged 55 to 88 years) received magnetic resonance imaging and/or computed tomographic scans designed to identify HA. One hundred forty-five of these subjects also underwent psychometric tests of memory function. Multivariate analyses of variance were used to evaluate differences in memory performance between subjects with and without HA. SETTING: This study was conducted at a research clinic for the investigation of age-associated neuropsychological and neuroradiologic changes. PARTICIPANTS: Based on the following criteria, 154 subjects were consecutively selected from a larger group of elderly research volunteers participating in a study of normal aging: age of 55 years or greater; Global Deterioration Scale score of 2 or less; and Mini-Mental State examination score of 28 or greater. Subjects with evidence for significant medical, psychiatric, or neurologic disease were excluded. MAIN OUTCOME MEASURES: Outcome measurements included individual psychometric test scores and computed tomographic-magnetic resonance imaging hippocampal atrophy ratings. RESULTS: Nearly 33% of the subjects had radiographic evidence for HA. The prevalence of HA increased significantly with age and was more common in male than female subjects. After controlling for age, level of education, and vocabulary, subjects with HA were found to perform more poorly on tests of recent (secondary) verbal memory when compared with subjects without HA (P < .01). No significant differences were found for tests of immediate (primary) memory. CONCLUSION: We conclude that HA is a common accompaniment of normal aging and is associated with mild memory impairment. Additional research is needed to determine whether HA constitutes a significant risk for future dementia.  相似文献   
98.
99.
Composite metacarpophalangeal joint reconstruction using the toe proximal phalanx and the metacarpal head, with a capsular repair, is an option during free toe transfer procedures for absent fingers. Eleven composite metacarpophalangeal finger joint reconstructions were performed in four patients concurrent with combined second and third toe-to-hand transfer. The average follow-up period was 5 years. Postoperative assessment included range of motion, stability, radiographic changes, and pain. The average range of motion was 52 degrees, average ulnar stress deviation was 14 degrees. No patients complained of pain. Composite metacarpophalangeal joint reconstruction should be considered in free toe-to-hand procedures when metacarpal head articular cartilage is preserved.  相似文献   
100.
Recent data suggesting complex I dysfunction in Parkinson's disease (PD) arises from mitochondrial DNA (mtDNA) mutation does not conclusively answer whether the responsible genetic lesion is inherited (primary) or somatic (secondary). To address this question, we identified a family in which multiple members over three generations are affected with PD through exclusively maternal lines. Cytoplasmic hybrids (cybrids) were created for 15 family members over two generations by transferring each individual's mtDNA to mtDNA-depleted human neuroblastoma cells. Eight of the 15 cybrid lines contained mtDNA obtained from maternally descended family members and seven contained mtDNA from paternally descended family members. After 6 weeks of culture, cybrid cell lines were assayed for complex I activity and oxidative stress, and mitochondrial morphology was analyzed by electron microscopy. Compared with the cybrid lines containing mtDNA from paternal descendants, cybrid lines containing mtDNA from maternal descendants had lower complex I activity, increased reactive oxygen species production, increased radical scavenging enzyme activities, and more abnormal mitochondrial morphologic features. These findings were present in cybrid lines containing mtDNA from maternal descendants with PD as well as in currently asymptomatic young maternal descendants, and support a precedent for inherited mtDNA mutation in some persons with PD.  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