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   1692篇
  免费   12篇
  国内免费   1篇
电工技术   8篇
综合类   1篇
化学工业   106篇
金属工艺   3篇
机械仪表   6篇
建筑科学   11篇
能源动力   6篇
轻工业   36篇
水利工程   11篇
石油天然气   6篇
武器工业   1篇
无线电   16篇
一般工业技术   52篇
冶金工业   1359篇
自动化技术   83篇
  2023年   2篇
  2022年   4篇
  2021年   5篇
  2020年   2篇
  2019年   7篇
  2018年   9篇
  2017年   8篇
  2016年   5篇
  2015年   2篇
  2014年   13篇
  2013年   19篇
  2012年   13篇
  2011年   21篇
  2010年   15篇
  2009年   12篇
  2008年   13篇
  2007年   19篇
  2006年   10篇
  2005年   28篇
  2004年   44篇
  2003年   11篇
  2002年   12篇
  2001年   10篇
  2000年   11篇
  1999年   49篇
  1998年   443篇
  1997年   282篇
  1996年   173篇
  1995年   78篇
  1994年   70篇
  1993年   93篇
  1992年   11篇
  1991年   17篇
  1990年   15篇
  1989年   9篇
  1988年   9篇
  1987年   12篇
  1986年   15篇
  1985年   17篇
  1984年   2篇
  1983年   5篇
  1982年   6篇
  1981年   8篇
  1980年   10篇
  1978年   2篇
  1977年   16篇
  1976年   59篇
  1968年   2篇
  1966年   2篇
  1955年   2篇
排序方式: 共有1705条查询结果,搜索用时 12 毫秒
61.
62.
Cerebral palsy has an incidence of approximately 1/500 births, although this varies between different ethnic groups. Genetic forms of the disease account for approximately 1%-2% of cases in most countries but contribute a larger proportion in populations with extensive inbreeding. We have clinically characterized consanguineous families with multiple children affected by symmetrical spastic cerebral palsy, to locate recessive genes responsible for this condition. The eight families studied were identified from databases of patients in different regions of the United Kingdom. After ascertainment and clinical assessment, we performed a genomewide search for linkage, using 290 polymorphic DNA markers. In three families, a region of homozygosity at chromosome 2q24-q25 was identified between the markers D2S124 and D2S148. The largest family gave a maximum LOD score of 3.0, by multipoint analysis (HOMOZ). The maximum combined multipoint LOD score for the three families was 5.75. The minimum region of homozygosity is approximately 5 cM between the markers D2S124 and D2S2284. We have shown that a proportion of autosomal recessive symmetrical spastic cerebral palsy maps to chromosome 2q24-25. The identification of genes involved in the etiology of cerebral palsy may lead to improved management of this clinically intractable condition.  相似文献   
63.
Drivers' choice of speed is an important aspect of everyday risk-taking behavior because it has been shown to be one of the most important predictors of road accident involvement. This research developed, validated, and applied a measure of drivers' speed choice that combined a high degree of experimental control with external and ecological validity. In Study 1, a video-simulation measure of drivers' speed choice was developed and found to relate specifically to speed-related accident involvement among, implying a degree of external validity. In Study 2, the measure was used to investigate the effect of auditory feedback on drivers' speed choice. It was found that increasing the level of internal car noise decreased drivers' preferred speeds. Further analyses indicated that this was likely due to perceptual effects on speed estimation. Results are discussed in terms of road safety and the ability of video-based measures to facilitate experimental control over tasks involving complex ecological stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
64.
65.
BACKGROUND: Right lower quadrant abdominal pain may pose a diagnostic problem in patients with cystic fibrosis. Abdominal ultrasound examination, used commonly in the diagnostic work-up, may reveal abnormalities of the appendix. However, interpretation of such findings is problematic, because the appearance of the gastrointestinal system during routine examination has not been documented in patients with cystic fibrosis. The purpose of this study was to investigate the findings during routine abdominal ultrasound scans in our cohort of patients with cystic fibrosis and in control subjects. METHODS: Abdominal ultrasound scans were performed prospectively during routine clinic visits in a cohort of patients with cystic fibrosis. RESULTS: Fifty patients aged 10+/-6 years, (range, 0.5-28 years) were examined; 45 had pancreatic insufficiency. Four patients (3 with pancreatic insufficiency) reported right lower quadrant pain at the time of the scan. According to standard ultrasound criteria, the appearance of the appendix was abnormal in 8 patients (16%), 6 had a mucoid appendix, and 2 had a pathologically thickened appendiceal wall. Only 1 of these 8 patients mentioned abdominal pain at the time of the study. Other incidental findings included gallstones (3 patients), intussusception (2 patients), and pancreatic cyst (1 patient). CONCLUSIONS: Abnormalities can be observed during routine abdominal ultrasonographic studies in cystic fibrosis. These findings may not be associated with abdominal pain; their clinical relevance needs further investigation.  相似文献   
66.
The management of hypertrophic cardiomyopathy   总被引:1,自引:0,他引:1  
  相似文献   
67.
68.
69.
70.
Predictions of P. R. Killeen's (1994) mathematical principles of reinforcement were tested for responding on ratio reinforcement schedules. The type of response key, the number of sessions per condition, and first vs. second half of a session had negligible effects on responding. Longer reinforcer durations and larger grain types engendered more responding, affecting primarily the parameter alpha (specific activation). Key pecking was faster than treadle pressing, affecting primarily the parameter delta (response time). Longer intertrial intervals led to higher overall response rates and shorter postreinforcement pauses and higher running rates, and ruled out some competing explanations. The treadle data required a distinction between the energetic requirements and rate-limiting properties of extended responses. The theory was extended to predict pause durations and run rates on ratio schedules.  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