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   12117篇
  免费   99篇
  国内免费   5篇
电工技术   30篇
化学工业   392篇
金属工艺   62篇
机械仪表   52篇
建筑科学   38篇
矿业工程   3篇
能源动力   74篇
轻工业   253篇
水利工程   8篇
石油天然气   16篇
无线电   195篇
一般工业技术   416篇
冶金工业   10417篇
原子能技术   13篇
自动化技术   252篇
  2023年   13篇
  2022年   27篇
  2021年   28篇
  2020年   33篇
  2019年   40篇
  2018年   60篇
  2017年   44篇
  2016年   50篇
  2015年   45篇
  2014年   69篇
  2013年   116篇
  2012年   120篇
  2011年   134篇
  2010年   114篇
  2009年   118篇
  2008年   109篇
  2007年   90篇
  2006年   92篇
  2005年   63篇
  2004年   67篇
  2003年   58篇
  2002年   49篇
  2001年   37篇
  2000年   30篇
  1999年   333篇
  1998年   3384篇
  1997年   1992篇
  1996年   1217篇
  1995年   703篇
  1994年   552篇
  1993年   649篇
  1992年   73篇
  1991年   139篇
  1990年   111篇
  1989年   135篇
  1988年   140篇
  1987年   107篇
  1986年   95篇
  1985年   67篇
  1984年   8篇
  1983年   15篇
  1982年   54篇
  1981年   52篇
  1980年   74篇
  1978年   24篇
  1977年   190篇
  1976年   465篇
  1975年   13篇
  1955年   8篇
  1954年   4篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
93.
94.
95.
Patients with ulcerative colitis are usually non- or ex-smokers in contrast to Crohn's disease where smoking is common. Abnormalities of quantity and quality of intestinal mucus have been postulated in the pathogenesis of these diseases. It is possible that smoking habit may exert its effects via changes in mucus in inflammatory bowel disease. We have therefore studied incorporation of N-acetylglucosamine into synthesized colonic mucin in explants from 85 controls with normal colonoscopic appearances and histology, including 27 smokers and 58 nonsmokers, 36 patients with ulcerative colitis and 19 with ileocolonic Crohn's disease over 24 h in tissue culture. Incorporation of N-acetylglucosamine into normal explants was 31.3 +/- (SD) 7.1 dpm/microgram biopsy protein, incorporation was increased in patients with active Crohn's disease (mean 41.2 +/- (SD) 10.4 dpm/microgram biopsy protein, p = 0.003), decreased in inactive ulcerative colitis (mean 24.1 +/- 7.8 dpm/microgram biopsy protein, p = 0.0006) but normal in active ulcerative colitis (mean 35.0 +/- 13.8 dpm/microgram biopsy protein, p = 0.44). No significant relationship was found between cigarette smoking habits and mucus synthesis in controls with normal mucosa (nonsmokers, n = 58, mean 31.0 +/- (SD) 7.52 dpm/microgram biopsy protein; smokers, n = 27, mean 31.8 +/- (SD) 6.1 dpm/microgram biopsy protein, p = 0.9). This study shows that mucus glycoprotein synthesis is reduced in inactive ulcerative colitis, rising to normal levels in active disease and that synthesis is increased in Crohn's disease. There is no effect of smoking on mucus synthesis by control biopsies suggesting that the differences seen in inflammatory bowel disease are not related to cigarette smoking.  相似文献   
96.
Concentrations of 11 trace elements were determined in 56 control and 98 Alzheimer's disease (AD) olfactory bulb, olfactory tract, olfactory trigone, piriform cortex and amygdala specimens by instrumental neutron activation analysis. Iron and zinc were significantly elevated and bromine was significantly depleted in olfactory regions of AD patients, compared with normal age-matched control subjects. Elevated iron could possibly play a role in neuronal degeneration in AD by enhancing reactive free radical formation.  相似文献   
97.
98.
99.
We investigated clinical efficacy of green tea extracts (polyphenon E; poly E and (-)-epigallocatechin-3-gallate [EGCG]) delivered in a form of ointment or capsule in patients with human papilloma virus (HPV) infected cervical lesions. Fifty-one patients with cervical lesions (chronic cervicitis, mild dysplasia, moderate dysplasia and severe dysplasia) were divided into four groups, as compared with 39 untreated patients as a control. Poly E ointment was applied locally to 27 patients twice a week. For oral delivery, a 200 mg of poly E or EGCG capsule was taken orally every day for eight to 12 weeks. In the study, 20 out of 27 patients (74%) under poly E ointment therapy showed a response. Six out of eight patients under poly E ointment plus poly E capsule therapy (75%) showed a response, and three out of six patients (50%) under poly E capsule therapy showed a response. Six out of 10 patients (60%) under EGCG capsule therapy showed a response. Overall, a 69% response rate (35/51) was noted for treatment with green tea extracts, as compared with a 10% response rate (4/39) in untreated controls (P<0.05). Thus, the data collected here demonstrated that green tea extracts in a form of ointment and capsule are effective for treating cervical lesions, suggesting that green tea extracts can be a potential therapy regimen for patients with HPV infected cervical lesions.  相似文献   
100.
BACKGROUND AND PURPOSE: Studies on risk factors for stroke have been less intensive than those for coronary disease. Only a few studies have addressed the question of the role of heredity in the occurrence of stroke. We analyzed whether a positive parental history of cardiovascular disease predicts the risk of stroke independently from other risk factors and whether the role of parental history varies by age and stroke subtypes. METHODS: This study was a prospective follow-up of 14371 middle-aged men and women. A positive parental history of cardiovascular disease was defined as either stroke or coronary disease before the age of 60 years. The end point of the follow-up was an incident case of stroke. Multivariate analyses were performed with the Cox proportional hazards model. RESULTS: The risk ratio of stroke after multifactorial adjustment (age, smoking, blood pressure, cholesterol, diabetes, and education) associated with a positive parental history of stroke was 1.89 (P = .004) in men and 1.80 (P = .007) in women. The association between parental history of stroke and the risk of stroke was stronger among subjects aged 25 to 49 years than among older subjects. Parental history of coronary disease was not associated with the risk of stroke in men, but in women it had a borderline significant association with the risk of ischemic stroke. CONCLUSIONS: A positive parental history of stroke predicted the risk of stroke independently from the other risk factors.  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