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   9015篇
  免费   121篇
  国内免费   9篇
电工技术   98篇
综合类   2篇
化学工业   1010篇
金属工艺   101篇
机械仪表   301篇
建筑科学   216篇
矿业工程   28篇
能源动力   129篇
轻工业   873篇
水利工程   107篇
石油天然气   15篇
无线电   863篇
一般工业技术   1023篇
冶金工业   3522篇
原子能技术   108篇
自动化技术   749篇
  2021年   68篇
  2020年   51篇
  2019年   61篇
  2018年   60篇
  2017年   82篇
  2016年   65篇
  2015年   47篇
  2014年   104篇
  2013年   315篇
  2012年   160篇
  2011年   238篇
  2010年   211篇
  2009年   231篇
  2008年   260篇
  2007年   240篇
  2006年   245篇
  2005年   218篇
  2004年   178篇
  2003年   198篇
  2002年   200篇
  2001年   163篇
  2000年   162篇
  1999年   205篇
  1998年   858篇
  1997年   533篇
  1996年   457篇
  1995年   315篇
  1994年   283篇
  1993年   276篇
  1992年   115篇
  1991年   131篇
  1990年   149篇
  1989年   138篇
  1988年   140篇
  1987年   143篇
  1986年   111篇
  1985年   131篇
  1984年   95篇
  1983年   101篇
  1982年   69篇
  1981年   91篇
  1980年   75篇
  1979年   79篇
  1978年   73篇
  1977年   134篇
  1976年   232篇
  1975年   76篇
  1974年   71篇
  1973年   64篇
  1972年   54篇
排序方式: 共有9145条查询结果,搜索用时 15 毫秒
61.
Neuropathological examinations were carried out at necropsy on 274 cases of intrauterine death or neonatal death at or before three days after birth. Fifty six (20.4%) subjects had evidence of prenatal ischaemic brain damage. On review of the maternal case notes to ascertain antenatal clinical associations there was an increased incidence of intrauterine growth retardation, either based on birth weight for gestational age (odds ratio (OR) 2.0; 95% confidence interval (CI) 1.1 to 3.7) or diagnosed antenatally (OR 2.7; 95% CI 1.3 to 5.6). Oligohydramnios was also more common (OR 2.9; 95% CI 1.2 to 7.0). The association of intrauterine growth retardation and white matter damage remained after excluding fetuses with a major congenital anomaly (OR 2.4; 95% CI 1.1 to 5.1). The findings suggest that chronic intrauterine hypoxia may be associated with damage to cerebral white matter among fetuses and infants who die. The relation between ischaemic white matter damage and cerebral palsy among survivors remains speculative.  相似文献   
62.
Infants seem sensitive to hidden objects in habituation tasks at 3.5 months but fail to retrieve hidden objects until 8 months. The authors first consider principle-based accounts of these successes and failures, in which early successes imply knowledge of principles and failures are attributed to ancillary deficits. One account is that infants younger than 8 months have the object permanence principle but lack means-ends abilities. To test this, 7-month-olds were trained on means-ends behaviors and were tested on retrieval of visible and occluded toys. Means-ends demands were the same, yet infants made more toy-guided retrievals in the visible case. The authors offer an adaptive process account in which knowledge is graded and embedded in specific behavioral processes. Simulation models that learn gradually to represent occluded objects show how this approach can account for success and failure in object permanence tasks without assuming principles and ancillary deficits.  相似文献   
63.
Human peripheral blood monocytes were examined for migration across an endothelial cell monolayer in an in vitro vessel wall construct. Few monocytes invaded in the absence of a chemotactic gradient, despite significant adhesion to the endothelial monolayer. However, the addition of zymosan-activated human plasma to the lower compartment, to create a chemotactic gradient across the vessel wall, resulted in significantly enhanced monocyte migration. Pretreatment of the monocytes with monoclonal antibodies to thrombospondin (TSP) dramatically inhibited monocyte diapedesis into the vessel wall. The same treatment inhibited monocyte adhesion to endothelial cells in two-dimensional monolayer cultures as well as in vessel wall constructs (no chemotactic gradient). Of interest, however, the monoclonal antibodies had no inhibitory effect on monocyte migration into collagen gels devoid of endothelial cells in response to the same chemotactic gradient, suggesting the importance of TSP in monocyte-endothelial cell interactions. Monoclonal antibodies to fibronectin and normal mouse immunoglobulin G did not inhibit migration in this model of a vessel wall. Furthermore, monoclonal antibodies to TSP showed no inhibition of human peripheral blood neutrophil migration. Previous studies have shown that monocytes synthesize TSP and express this moiety on their surface. The present data suggest that monocytes may utilize TSP to interact with endothelial cells lining the vessel wall during diapedesis.  相似文献   
64.
The associations between stressful life events and smoking have been established among adolescents in the United States. However, whether these relationships are similar in adolescents from other non-Western cultures is unknown. Understanding these relationships in adolescents may help to provide opportunities to reduce the smoking rates in those cultures by providing positive coping methods that do not include smoking. In this longitudinal study, the associations between nine stressful life events scales and smoking behaviors were examined in a sample of Chinese adolescents. Six of these scales, positive school-related, negative school-related, positive family-related, positive peer-related, negative peer-related, and negative health-related had significantly different means among females and males. Among males, positive school-related stress was a protective factor for smoking susceptibility. Among females, positive school-related stress was a protective factor and negative school-related stress was a risk factor for lifetime smoking, and negative family-related stress was a risk factor for smoking susceptibility. Findings indicate that smoking among male adolescents in China may not be the result of stress; however, in females stress may contribute to the decision to smoke. Future directions are discussed.  相似文献   
65.
66.
67.
68.
69.
70.
POINT: AOP Will See Widespread Adoption Adrian Colyer, Rob Harrop, Rod Johnson, and Alexandre Vasseur AOP offers both the short--and long-term return on investment needed to ensure its widespread adoption. COUNTERPOINT: AOP Has Yet to Prove Its Value Danio Beuche and Cédric Beust Where is the proof that nonhierarchical modularization into aspects makes systems development cheaper or better?  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