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   25789篇
  免费   2240篇
  国内免费   1034篇
电工技术   1262篇
技术理论   1篇
综合类   1348篇
化学工业   3371篇
金属工艺   1332篇
机械仪表   1459篇
建筑科学   1540篇
矿业工程   612篇
能源动力   535篇
轻工业   1833篇
水利工程   454篇
石油天然气   1135篇
武器工业   216篇
无线电   2278篇
一般工业技术   2402篇
冶金工业   6179篇
原子能技术   348篇
自动化技术   2758篇
  2024年   109篇
  2023年   384篇
  2022年   702篇
  2021年   963篇
  2020年   772篇
  2019年   663篇
  2018年   684篇
  2017年   779篇
  2016年   699篇
  2015年   1060篇
  2014年   1302篇
  2013年   1527篇
  2012年   1547篇
  2011年   1411篇
  2010年   1287篇
  2009年   1156篇
  2008年   1079篇
  2007年   1059篇
  2006年   1018篇
  2005年   814篇
  2004年   540篇
  2003年   472篇
  2002年   472篇
  2001年   406篇
  2000年   344篇
  1999年   445篇
  1998年   1761篇
  1997年   1056篇
  1996年   778篇
  1995年   492篇
  1994年   444篇
  1993年   420篇
  1992年   150篇
  1991年   165篇
  1990年   125篇
  1989年   135篇
  1988年   146篇
  1987年   122篇
  1986年   125篇
  1985年   75篇
  1984年   41篇
  1983年   44篇
  1982年   59篇
  1981年   65篇
  1980年   77篇
  1978年   56篇
  1977年   172篇
  1976年   385篇
  1975年   50篇
  1974年   34篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
132.
The purpose of this study was to examine whether exposure of rat pups to alcohol postnatally over a period of brain development similar to that of the human 3rd trimester results in a permanent loss of cells in the inferior olivary nucleus. It was hypothesized that a deficit of neurons in the inferior olive, the sole source of climbing fibers, may contribute to the cerebellar dysfunction observed following exposure to alcohol during development. Sprague-Dawley rat pups were artificially reared and administered alcohol over postnatal days 4-9. One artificially reared group received a daily alcohol dose of 4.5 g/kg, administered as a 10.2% solution in 2 of 12 daily feedings (10.2% group). This pattern of alcohol administration resulted in high peak blood alcohol concentrations with near total clearance. The other artificially reared group was fed a diet made isocaloric to the alcohol-containing diet (gastrostomy control group). Pups were allowed to grow to adulthood and killed on postnatal day 115. The total number of neurons in the inferior olivary nucleus was estimated using unbiased stereological methods. Exposure to alcohol resulted in a significant deficit in the number of neurons in the inferior olive at 115 days of age. The total number of neurons in the alcohol-exposed group was 40.12 +/- 8.7 x 10(3), compared with 53.37 +/- 3.7 x 10(3) in the artificially reared controls. These results indicate that there is a permanent deficit of neurons in the inferior olive after postnatal exposure to alcohol.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
133.
用数学方法建立气测井油气储层识别模式,以解决录井中实时软件在判别依据少的条件下,及时识别油气显示假异常的难题。该判别式经实用,正到率达90%。  相似文献   
134.
135.
介绍了双迭片弯曲压电陶瓷换能器的制作及边缘固定金属压电陶瓷双迭片弯曲振动,并利用有限元分析了换能器的谐振模式,采用激光多普勒干涉仪对换能器的谐振特性以及振动速度和位移分布进行了测量和分析,结果表明:换能器空载性能良好,通过有限元分析与先进测量手段的结合,能够对换能器器件的制作与分析进行指导。  相似文献   
136.
通过工程地质调查、室内围岩物化分析和力学试验 ,深入研究了围岩变形力学机制和破坏机理 .根据新奥法施工原理 ,采取了有针对性的综合治理措施 ,将围岩复杂的变形力学机制转化为单一的变形力学机制 ,使该工程得到了有效治理 .取得的技术经验推广应用于该矿井其它失稳破坏工程 ,均获得了圆满成功  相似文献   
137.
138.
139.
140.
Patients with chlamydial infections (Ct) attending the outpatient Venereal Disease Clinic of Copenhagen from July 1-November 30 1995 were asked to fill in a questionnaire focusing upon knowledge, attitude and behaviour related to sexually transmitted diseases (STDs) in order to strengthen the future prevention of Ct. The questionnaire was answered by 37 men and 35 women with a median age of 27 and 21 years and a median number of three and two sexual partners within the last six months, respectively. Half of the patients had previously had an STD, and 92% had been tested for HIV, of whom one homosexual man was known HIV-positive. Notification about exposure from a partner was the reason for attending for 24%. All but one were in favour of partner notification, but only 6% wanted provider referral. During last intercourse condoms had neither been used with a steady partner by 75% especially by the young and women, who thought themselves safe, nor with a casual partner by 52% especially among the young and men, mainly because of thoughtlessness or perception of low risk. Before the actual STD diagnosis only 49% were able to name one symptom and 35% one complication related to Ct. A majority (79%) stated, that fear of catching another Ct would lead to better protection, and 70% found that more information would have a preventive effect. Future Ct prevention programs in Denmark should include intensified chlamydial screening and partner notification together with centrally produced mass media information supplemented by individual counselling.  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