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   3059篇
  免费   4篇
电工技术   3篇
化学工业   13篇
金属工艺   6篇
机械仪表   1篇
建筑科学   9篇
矿业工程   6篇
能源动力   6篇
轻工业   220篇
石油天然气   2篇
无线电   36篇
一般工业技术   26篇
冶金工业   2725篇
原子能技术   1篇
自动化技术   9篇
  2019年   3篇
  2017年   3篇
  2016年   2篇
  2015年   2篇
  2014年   10篇
  2013年   14篇
  2012年   2篇
  2011年   6篇
  2010年   5篇
  2009年   6篇
  2008年   16篇
  2007年   16篇
  2006年   9篇
  2005年   14篇
  2004年   18篇
  2003年   16篇
  2002年   25篇
  2001年   9篇
  2000年   29篇
  1999年   114篇
  1998年   845篇
  1997年   489篇
  1996年   297篇
  1995年   154篇
  1994年   147篇
  1993年   184篇
  1992年   22篇
  1991年   35篇
  1990年   48篇
  1989年   45篇
  1988年   42篇
  1987年   34篇
  1986年   27篇
  1985年   25篇
  1984年   3篇
  1983年   6篇
  1982年   8篇
  1981年   15篇
  1980年   34篇
  1979年   4篇
  1978年   4篇
  1977年   72篇
  1976年   184篇
  1975年   5篇
  1974年   4篇
  1970年   2篇
  1968年   2篇
  1964年   1篇
  1961年   1篇
  1955年   2篇
排序方式: 共有3063条查询结果,搜索用时 15 毫秒
21.
22.
Increased detection thresholds for pure tones were observed in a large cohort of children exposed to lead environmentally while smaller studies in lead-exposed workers have reported conflicting results on assessments of auditory function. Pure tone detection thresholds were determined in a group of monkeys (Macaca fascicularis) dosed with 2 mg/kg/day of lead from birth through testing at 13 years of age. Blood lead concentrations were stable at about 30 micrograms/dl until monkeys were 10-11 years of age at which time they increased to between 50 and 70 micrograms/dl. Five age- and rearing-matched monkeys served as controls. Detection thresholds were determined at six frequencies between 0.125 and 31.5 kHz. Ear phones were fit over both ears, and thresholds were determined for each ear separately. The monkey signaled detection of the tone by breaking contact with a stainless steel bar. Three lead-exposed monkeys exhibited normal pure tone detection functions. Three monkeys had thresholds outside of the control range at some frequencies; there was a tendency for higher frequencies to be differentially more affected. These findings are consistent with reports of elevated pure tone thresholds in humans exposed to lead developmentally, although the effect is smaller than might have been predicted given the concurrent blood lead concentrations of these monkeys.  相似文献   
23.
SKOR, a K+ channel identified in Arabidopsis, displays the typical hydrophobic core of the Shaker channel superfamily, a cyclic nucleotide-binding domain, and an ankyrin domain. Expression in Xenopus oocytes identified SKOR as the first member of the Shaker family in plants to be endowed with outwardly rectifying properties. SKOR expression is localized in root stelar tissues. A knockout mutant shows both lower shoot K+ content and lower xylem sap K+ concentration, indicating that SKOR is involved in K+ release into the xylem sap toward the shoots. SKOR expression is strongly inhibited by the stress phytohormone abscisic acid, supporting the hypothesis that control of K+ translocation toward the shoots is part of the plant response to water stress.  相似文献   
24.
p53 mutations, a tumor suppressor gene located on chromosome 17p, are the most common genetic alterations found in human cancers. Although the p53 expression or mutation has been investigated in a variety of cancers there have been very few studies in extrahepatic bile duct cancers. In this study, we investigated the immunohistochemical expression of p53 in formalin fixed paraffin embedded archival specimens of 36 extrahepatic bile duct cancers in which p53 expression was found in eighteen (50%) cases. There was no significant difference in age, gender, size of tumor, histologic grade, extent of tumor involvement, lymph node metastasis and tumor resectability according to p53 immunoreactivity. Comparison of survival duration according to p53 expression showed no significant difference. In conclusion, we reported 50 percent of p53 expression in extrahepatic bile duct cancers by immunohistochemical staining and we found no prognostic significance of p53 expression in dinicopathologic parameters.  相似文献   
25.
BACKGROUND: Aneurysmal degeneration of a carotid reconstruction was not recognized until the patient, who was known to have recurrent carotid artery stenosis, had a thromboembolic stroke. This sequelae of carotid endarterectomy is a serious complication, associated with a high morbidity and mortality rate. This review was conducted to establish the risk of transient ischemic attack and stroke for patients found to have recurrent carotid stenosis associated with aneurysmal degeneration of the carotid artery after endarterectomy. METHODS: A case is reported, and 100 literature references of aneurysmal degeneration of the carotid artery after endarterectomy were reviewed. RESULTS: False aneurysm from anastomotic disruption was the most common presentation identified in the cases reviewed. Nineteen of the patients had a significant neurologic event; however, three (50%) of six patients with aneurysm and recurrent carotid artery stenosis had a transient ischemic attack or stroke. CONCLUSIONS: The incidence of neurologic symptoms is markedly increased when recurrent carotid artery stenosis is associated with carotid aneurysm. During postoperative surveillance after endarterectomy, the identification of recurrent carotid artery stenosis requires evaluation for aneurysmal degeneration of the carotid artery with duplex scanning. These patients are at significant risk for transient ischemic attack and stroke. This rare complication merits operative repair.  相似文献   
26.
27.
28.
29.
30.
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