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   1489篇
  免费   2篇
  国内免费   2篇
化学工业   12篇
金属工艺   1篇
机械仪表   1篇
建筑科学   2篇
能源动力   2篇
轻工业   1篇
无线电   1篇
一般工业技术   4篇
冶金工业   1464篇
原子能技术   1篇
自动化技术   4篇
  2023年   1篇
  2019年   1篇
  2015年   2篇
  2014年   2篇
  2013年   4篇
  2012年   1篇
  2011年   2篇
  2009年   2篇
  2008年   2篇
  2007年   1篇
  2005年   1篇
  2004年   3篇
  2003年   3篇
  2002年   2篇
  2000年   1篇
  1999年   43篇
  1998年   418篇
  1997年   267篇
  1996年   180篇
  1995年   91篇
  1994年   79篇
  1993年   94篇
  1992年   9篇
  1991年   22篇
  1990年   21篇
  1989年   10篇
  1988年   14篇
  1987年   10篇
  1986年   15篇
  1985年   18篇
  1983年   2篇
  1982年   7篇
  1981年   8篇
  1980年   14篇
  1979年   2篇
  1978年   3篇
  1977年   53篇
  1976年   82篇
  1975年   3篇
排序方式: 共有1493条查询结果,搜索用时 15 毫秒
61.
62.
63.
64.
65.
The effects of reactive oxygen species (ROS) on elastin molecules (tropoelastin) were studied in vitro. ROS generated by ultraviolet A and hematoporphyrin rapidly degraded tropoelastin within 5 min. Their degradative activity was inhibited by the addition of NaN3. Treatment of tropoelastin with copper sulfate/ascorbic acid resulted in degradation of tropoelastin producing fragments of molecular weight 45, 30 and 10 kDa within 30 min. The degradation of tropoelastin was partially blocked by the addition of mannitol. ROS induced by the xanthine/xanthine oxidase system also degraded tropoelastin within 6 h. The degradation was blocked by catalase but not by superoxide dismutase (SOD). ROS generated by copper-ascorbate seems to be unique in that it cleaves relatively specific sites of the tropoelastin molecule. Thus ROS may play a degradative role in elastin metabolism which may cause the elastolytic changes or the deposition of fragmented elastic fibers in photoaged skin or age-related elastolytic disorders.  相似文献   
66.
BACKGROUND: The transition of a fatty streak into an atherosclerotic plaque is characterized by the appearance of focal and diffuse regions of cell death. We have investigated the distribution of apoptotic cell death and apoptosis-related proteins in early and advanced atherosclerotic lesions. METHODS AND RESULTS: Human atherosclerotic plaques were studied by whole-mount carotid endarterectomy specimens (n=18). This approach allowed comparison of adaptive intimal thickenings, fatty streaks, and advanced atherosclerotic plaques of the same patient. The fatty streaks differed from adaptive intimal thickenings by the presence of BAX (P<0.01), a proapoptotic protein of the BCL-2 family. Both regions were composed mainly of smooth muscle cells (SMCs), and macrophage infiltration was low and not different. Apoptosis, as detected by DNA in situ end labeling (terminal deoxynucleotidyl transferase end labeling [TUNEL] and in situ nick translation) was not present in these regions. Apoptosis of SMCs and macrophages, however, was present in advanced atherosclerotic plaques that were present mainly in the carotid sinus. A dense infiltration of macrophages (5.8+/-3% surface area) was present in these advanced atherosclerotic plaques. Cytoplasmic remnants of apoptotic SMCs, enclosed by a cage of thickened basal lamina, were TUNEL negative and remained present in the plaques as matrix vesicles. CONCLUSIONS: We conclude that SMCs within human fatty streaks express BAX, which increases the susceptibility of these cells to undergo apoptosis. The localization of these susceptible SMCs in the deep layer of the fatty streaks could be important in our understanding of the transition of fatty streaks into atherosclerotic plaques, which are characterized by regions of cell death. Matrix vesicles are BAX-immunoreactive cytoplasmic remnants of fragmented SMCs that can calcify and may be considered the graves of SMCs that have died in the plaques.  相似文献   
67.
68.
OBJECTIVES: To assess the impact of the implementation of the Ottawa ankle rules on radiography requests in French hospitals during a 5-month intervention period and the impact of using posters alone to sustain the effect of the rules during a 5-month postintervention period. DESIGN: Multicenter randomized controlled trial preceded and followed by observational studies of radiological practices. SETTING: The emergency departments of 5 Paris university teaching hospitals of the Assistance Publique-H?pitaux de Paris. PATIENTS: A total of 2218, 1911, and 851 patients-all aged 18 years and older-who were seen for acute ankle or midfoot injuries in emergency departments during preintervention, intervention, and postintervention periods, respectively. INTERVENTION: Implementation of the Ottawa ankle rules by emergency department physicians in the intervention hospitals (using meetings, posters, pocket cards, and data forms). During the postintervention period, posters alone were used to sustain the intervention effect. MAIN OUTCOME MEASURE: Percentage of patients for whom radiography was requested. RESULTS: During the preintervention period, 98% and 98.5% of patients were referred for radiography in the intervention and control groups, respectively. During the intervention period, the mean proportions of patients referred for radiography by physicians was 78.9% in the intervention group and 99% in the control group (P=.03). Between preintervention and intervention periods, a relative reduction of 22.4% (95% confidence interval [CI], 19.8%-24.9%) in radiography requests was observed in the intervention group, while requests increased by 0.5% (95% CI, 0%-1.4%) in the control group. During the postintervention period, the proportion of radiography requests in the intervention hospitals was lower than the proportion observed in the preintervention period (83.1% vs 98%). CONCLUSIONS: Implementation of the Ottawa ankle rules significantly reduced radiography requests in French hospitals. Using a minimal postintervention implementation strategy, the effect of this intervention decreased but persisted after it was discontinued.  相似文献   
69.
The spleen is the most commonly injured organ in blunt abdominal trauma. There remains much controversy in the diagnosis and management of the injured spleen, with a recent trend toward nonoperative management. A 5-year period was reviewed at a rural, Level I trauma center to address issues of operative versus nonoperative management. During this time period, there were 136 patients identified as having trauma to the spleen. Most (95%) were the result of blunt trauma, and a majority of these were from motor vehicle accidents. Computed tomography was the most frequent method of diagnosis. Approximately half of the patients underwent immediate operative intervention. Of those initially observed, 10 patients (16%) eventually were operated on. Most of the cases were due to underestimation of the severity of the splenic injury, and most received blood transfusion. This experience suggests that observation for splenic trauma is appropriate in many cases, as long as the surgeon is certain the spleen is not actively bleeding and the patient will not require blood transfusion.  相似文献   
70.
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