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   6873篇
  免费   443篇
  国内免费   227篇
电工技术   221篇
综合类   277篇
化学工业   982篇
金属工艺   303篇
机械仪表   408篇
建筑科学   421篇
矿业工程   183篇
能源动力   115篇
轻工业   389篇
水利工程   93篇
石油天然气   513篇
武器工业   30篇
无线电   658篇
一般工业技术   742篇
冶金工业   1462篇
原子能技术   56篇
自动化技术   690篇
  2024年   19篇
  2023年   89篇
  2022年   164篇
  2021年   262篇
  2020年   191篇
  2019年   149篇
  2018年   170篇
  2017年   164篇
  2016年   160篇
  2015年   238篇
  2014年   254篇
  2013年   353篇
  2012年   328篇
  2011年   385篇
  2010年   320篇
  2009年   285篇
  2008年   363篇
  2007年   316篇
  2006年   306篇
  2005年   266篇
  2004年   149篇
  2003年   126篇
  2002年   128篇
  2001年   117篇
  2000年   144篇
  1999年   210篇
  1998年   489篇
  1997年   334篇
  1996年   218篇
  1995年   141篇
  1994年   146篇
  1993年   137篇
  1992年   65篇
  1991年   38篇
  1990年   38篇
  1989年   35篇
  1988年   28篇
  1987年   29篇
  1986年   17篇
  1985年   16篇
  1984年   4篇
  1983年   7篇
  1982年   4篇
  1981年   9篇
  1980年   16篇
  1978年   6篇
  1977年   26篇
  1976年   73篇
  1975年   3篇
  1971年   3篇
排序方式: 共有7543条查询结果,搜索用时 756 毫秒
21.
一种新型基于石英的热光型光开关   总被引:1,自引:0,他引:1  
一种采用基于石英的平面光波回路技术(PLC)制造的热光型光开关正越来越引起关注,它具有低耦合损耗、高稳定性及适于大规模集成等优点。首先描述了采用热光相移器构成马赫-曾德于涉仪(MZI)结构的热光型光开关,然后讨论2×2MZI热光型开关的工作原理及基本特性,最后介绍了由2×2MZI热光型开关单元构成的大规模光开关阵列以及一种采用悬梁式结构热光相移器的低功率消耗的光开关。  相似文献   
22.
Until now, taste was the only primary sensory modality for which the human central nervous system pathways were unknown. We report sensations evoked by stimulation at microampere current levels in the region of the human thalamic nucleus (ventralis caudalis parvocellularis internis) corresponding to the monkey taste relay nucleus. Stimulation in this region during awake neurosurgical procedures evoked special visceral/somatic (taste/pungent smell), general visceral (fullness of a hollow viscus), as well as painful and nonpainful general somatic sensations. General somatic or visceral sensation was evoked by stimulation at 80% of sites where special visceral/somatic sensation was evoked. These results suggest that primate taste relay mediates multiple sensations in addition to taste.  相似文献   
23.
24.
Massachusetts provides diphtheria-tetanus toxoid-pertussis (DTP) vaccine, and since 1980 has monitored pertussis with a statewide diagnostic service. The incidence of bacteriologically confirmed pertussis was 104.5 per 100,000 person-years in 1-month-old infants and declined progressively thereafter. Infants < 6 months old experienced disproportionate morbidity: 44% of bacteriologically confirmed pertussis, 64% of hospitalizations, and 71% of hospital days. Most children with pertussis had received < 3 DTP doses during childhood, whereas 87% of adolescents with pertussis had received > or = 4 doses. Serodiagnosis by single serum anti-pertussis toxin antibody ELISA increased the incidence of confirmed pertussis in persons 11-19 years old from 3.0 to 12.9 per 100,000 and in persons > or = 20 years old from 0.16 to 0.56 per 100,000. Bacteriologic methods underestimate pertussis incidence, but a single serum anti-pertussis toxin antibody ELISA is a practical method for population-based diagnosis in adolescents and adults.  相似文献   
25.
文章论述利用过期火药的一种新途径。在2号岩石铵梯炸药中加入粉碎的过期火药以代替部分梯恩梯,制成一种XH-Ⅰ型岩石铵梯炸药,适用于各种爆破工程。并具有较高的经济效益和社会效益。  相似文献   
26.
Immune sensorineural hearing loss is manifested in several systemic immune diseases. Although hearing loss has been previously documented in patients with Sj?gren's syndrome (SS), the effect of SS on hearing is unclear. This prospective study was designed to assess the presence of hearing loss in 14 patients with SS and, if sensorineural hearing loss was present, to determine if the hearing loss was immune-mediated. Patients were evaluated with basic audiologic tests as well as for cellular immune inner ear reactivity as measured by the lymphocyte transformation test (LTT). Three patients had evidence of sensorineural hearing loss. Two patients had a positive LTT without evidence of sensorineural hearing loss. This preliminary study suggests that SS may not directly cause sensorineural hearing loss, immuno-mediated or otherwise.  相似文献   
27.
28.
The charts of all patients with acute cholecystitis undergoing either laparoscopic or minilap cholecystectomy at the Chinle Comprehensive Health Care Facility between October 1, 1991, and August 15, 1993, were retrospectively reviewed. During that period, 54 patients underwent laparoscopic cholecystectomy and 45 patients had minilap procedures. The two groups had similar mean age, sex distribution, temperature, leukocyte count, gallbladder wall thickness, and duration of preoperative symptoms. While laparoscopic cholecystectomy took an average of 16 min longer to perform than minilap cholecystectomy, patients who had laparoscopic cholecystectomy had less blood loss, reduced postoperative narcotic needs, and shorter hospital stays.  相似文献   
29.
通过采用竖向预应力技术 ,解决了 60m高度处单片 8m高悬臂钢筋混凝土墙根部裂缝宽度超过规范限值的问题 ;采用将预应力钢绞线顶端锚固于墙高中段等结构和施工措施 ,控制墙体长细比不超过 3 0 ,减少了由于长细比过大对墙体承载力的不利影响  相似文献   
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