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   3062篇
  免费   55篇
  国内免费   1篇
电工技术   2篇
化学工业   57篇
金属工艺   2篇
机械仪表   3篇
矿业工程   1篇
能源动力   2篇
轻工业   5篇
水利工程   1篇
无线电   37篇
一般工业技术   219篇
冶金工业   2787篇
原子能技术   1篇
自动化技术   1篇
  2023年   6篇
  2022年   8篇
  2021年   3篇
  2020年   23篇
  2019年   15篇
  2018年   14篇
  2017年   26篇
  2016年   13篇
  2015年   12篇
  2014年   7篇
  2013年   13篇
  2012年   30篇
  2011年   33篇
  2010年   17篇
  2009年   8篇
  2008年   19篇
  2007年   17篇
  2006年   15篇
  2005年   11篇
  2004年   8篇
  2003年   5篇
  2002年   2篇
  2001年   3篇
  2000年   5篇
  1999年   87篇
  1998年   915篇
  1997年   492篇
  1996年   333篇
  1995年   184篇
  1994年   139篇
  1993年   148篇
  1992年   18篇
  1991年   43篇
  1990年   32篇
  1989年   33篇
  1988年   33篇
  1987年   44篇
  1986年   36篇
  1985年   20篇
  1984年   1篇
  1983年   3篇
  1982年   10篇
  1981年   16篇
  1980年   20篇
  1979年   1篇
  1978年   2篇
  1977年   56篇
  1976年   133篇
  1975年   5篇
  1955年   1篇
排序方式: 共有3118条查询结果,搜索用时 234 毫秒
121.
122.
Oral health week     
This article reports on the Oral Health Week held in December 1994 and focuses on an initiative by the BDA which organised dentists and volunteers from Age Concern in a project to look at oral health for the elderly. It examines the aims and the results of the week and draws some useful conclusions on improving the outcome if a project such as this were attempted again.  相似文献   
123.
124.
The evidence for and against the prophylactic use of anticonvulsants and antibiotics in head injury is reviewed. There is a lack of blinded placebo-controlled trials in this area. On balance there is no compelling evidence to support the use of either anticonvulsant or antibiotic prophylaxis in head injury, with the possible exception of antibiotic prophylaxis in compound depressed skull fractures and penetrating brain injuries.  相似文献   
125.
126.
OBJECTIVE: We assessed the feasibility of contrast-enhanced color Doppler, power Doppler, and spectral duplex sonography for visualization and quantification of flow through transjugular intrahepatic portosystemic shunts (TIPS) in patients in whom the baseline sonographic evaluation was unsatisfactory. SUBJECTS AND METHODS: Thirty-three patients underwent color Doppler, power Doppler, and spectral duplex sonography after TIPS insertion or before TIPS revision (mean time interval +/- SD, 1 +/- 1 day). All sonograms were obtained before and after patients received echo-enhancing contrast material. Sonography was evaluated with regard to presence or absence of flow in the mid portion, portal segment, and hepatic segment of the shunt. The maximal peak velocity was measured in the mid portion of the shunt. For identifying and quantifying stenoses, the percentage of luminal diameter reduction was calculated at the tightest part of the shunt. Shunt angiography and measurements of portosystemic pressure gradients were independently evaluated and compared with the sonographic findings. RESULTS: Flow visualization on unenhanced color Doppler sonography was significantly improved through the use of power Doppler sonography and contrast-enhanced color Doppler and power Doppler sonography (p < .01). Between contrast-enhanced power Doppler and contrast-enhanced color Doppler sonography, a significant difference was found in the portal and hepatic segments (p < .05). All shunt stenoses (n = 8) and occlusions (n = 3) were revealed by power Doppler sonography, whereas color Doppler sonography failed to reveal six of eight stenoses. Compared with unenhanced sonography, the quality of spectral duplex sonography was improved in eight patients after contrast enhancement (p < .05). Maximal peak velocity ranged from 54 to 252 cm/sec (mean +/- SD, 132.7 +/- 52.1 cm/sec) in normal shunts and from 24.5 to 70.0 cm/sec (mean +/- SD, 45.0 +/- 18.9 cm/sec) in stenosed shunts. No correlation was found between maximal peak velocity and portosystemic pressure gradients (r = .28). CONCLUSION: Unenhanced power Doppler and contrast-enhanced color and power Doppler sonography can be helpful in the assessment of TIPS status in patients who previously underwent unsatisfactory sonography. These techniques may allow anatomic evaluation and quantification of shunt stenosis in most patients. Contrast enhancement may also considerably improve the quality of spectral duplex sonography.  相似文献   
127.
A pilot-study was carried out on ten Dutch goat farms to see whether there is a relationship between farm management factors and the occurrence of toxoplasmosis. Questionnaires were used to collect information about farm management factors and blood samples were taken to determine the prevalence of toxoplasmosis on these farms. The mean prevalence was 47% (range 5-90%). The presence of kittens on a farm was a risk factor for a higher prevalence of toxoplasmosis.  相似文献   
128.
129.
Altering the scintillation crystal configuration of a fixed-detector CT scanner increased the spatial resolution from 6.25 to 10 line pairs per centimeter. Sector scans of th orbit with this modified scanner showed the ophthalmic artery and superior ophthalmic vein and their branches and the intraorbital branches of the third, fifth, and sixth nerves, apparently seen with CT for the first time.  相似文献   
130.
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