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   19834篇
  免费   2230篇
  国内免费   1043篇
电工技术   1253篇
技术理论   1篇
综合类   1347篇
化学工业   3110篇
金属工艺   1333篇
机械仪表   1449篇
建筑科学   1534篇
矿业工程   611篇
能源动力   530篇
轻工业   1359篇
水利工程   454篇
石油天然气   1136篇
武器工业   216篇
无线电   2267篇
一般工业技术   2363篇
冶金工业   1049篇
原子能技术   347篇
自动化技术   2748篇
  2024年   104篇
  2023年   388篇
  2022年   707篇
  2021年   968篇
  2020年   773篇
  2019年   666篇
  2018年   689篇
  2017年   782篇
  2016年   699篇
  2015年   1061篇
  2014年   1303篇
  2013年   1452篇
  2012年   1549篇
  2011年   1408篇
  2010年   1286篇
  2009年   1154篇
  2008年   1078篇
  2007年   1060篇
  2006年   1015篇
  2005年   812篇
  2004年   534篇
  2003年   465篇
  2002年   470篇
  2001年   405篇
  2000年   339篇
  1999年   307篇
  1998年   242篇
  1997年   199篇
  1996年   199篇
  1995年   155篇
  1994年   132篇
  1993年   90篇
  1992年   92篇
  1991年   63篇
  1990年   52篇
  1989年   38篇
  1988年   42篇
  1987年   23篇
  1986年   34篇
  1985年   18篇
  1984年   16篇
  1983年   12篇
  1982年   13篇
  1981年   17篇
  1980年   10篇
  1979年   10篇
  1977年   10篇
  1976年   23篇
  1975年   10篇
  1974年   10篇
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
101.
油润滑下Al/MoSi2材料的摩擦学特性   总被引:1,自引:1,他引:0  
运用M-200型磨损试验机测定了油润滑下Al/MoSi2材料的摩擦磨损性能,采用SEM和X射线观察与分析了摩擦副表面的形貌和相组成,探讨了磨损机制。结果表明:采用20#机油润滑可有效地提高Al/MoSi2材料的摩察磨损综合性能;与干摩擦状态相比,其摩擦系统和磨损率分别下降了40%和60%;油润滑时,Al/MoSi2材料的磨损机制主要表现为疲劳点蚀和磨粒磨损。  相似文献   
102.
103.
本文通过实验并运用未确知数学的方法确定气体常数R,此法不仅给出R所在的区间,而且可根据可信度密度确定最可靠的R值  相似文献   
104.
Utilization of polyhydroxylated C60 (fullerenols) in a condensation reaction with diisocyanated oligo(tetramethylene oxide) led to the successful fabrication of elastomeric poly (urethane-ether) networks. These polymer networks exhibit interesting thermal behavior at low temperatures, improved tensile strength and elongation at ambient temperatures, and enhanced thermal mechanical stability at high temperatures, as compared with those of the parent linear polyurethane analogues; or with the conventional oligo (tetramethylene oxide)-derived polyurethane elastomers cross-linked by trihydroxylated reagents (1,I,1-trismethylol propane) or tetrahydroxylated reagents (pentaerythritol). The presence of a limited quantity of water molecules in the condensation reaction of fullerenols with diisocyanated prepolymers modified the physical properties of the resulting elastomeric products with a notable increase in tensile strength, modulus, and Ts over those of elasotmers prepared under anhydrous conditions. These water molecules contributed effectively to the increase of the number of cross-linking centers during the reaction.  相似文献   
105.
Protoporphyria is a genetic disorder in which patients may develop severe protoporphyrin-induced liver damage and require transplantation. Because unique problems occur in the perioperative period and because excess production of protoporphyrin by the bone marrow continues after liver transplantation, the efficacy of this procedure for protoporphyric liver disease is uncertain. We present follow-up of nine patients who underwent liver transplantation. Two patients died within 2 months of transplantation, one from complications of abdominal bleeding and the other from sepsis after bowel perforations. The remaining seven patients had follow-up at 14 months to 8 years after transplantation (mean, 3.8 years). Two of the seven had suffered skin burns from exposure to operating room lights, which healed without scarring. Three had axonal neuropathies in the postoperative period requiring prolonged mechanical ventilation, and motor defects persisted in two. Five patients had normal liver chemistries at follow-up (mean, 3.5 years), with liver biopsy results normal or showing mild portal triad abnormalities, but erythrocyte protoporphyrin levels remained significantly elevated (1,765 +/- 365 mcg/dL; normal, < 65). The other two patients, both of whom had rejection, cytomegalovirus infection, and biliary tract obstruction requiring endoscopic therapy, had a recurrence of protoporphyric liver disease as indicated by liver biopsy features. One died 5 years after transplantation from complications of the liver disease. The other was stable 3.3 years after transplantation and was being monitored for possible retransplantation. Thus, liver transplantation can be performed successfully in patients with protoporphyric liver disease, with intermediate survival rates comparable to the general transplant population. However, disease may recur in the graft, particularly if there are complications that cause cholestasis.  相似文献   
106.
摇臂参数设计方法   总被引:2,自引:0,他引:2  
建立了中小功率内燃机常用摇臂参数化设计模型。采用可变参数构成摇臂结构,并作结构的有限元网络,此后再进行有限元分析,计算出摇的质量、刚度、转动惯量 力。使摇臂的设计归结为几个主要参数的优选。实例分析表明,计算值和实测值基本相符,优选出的摇避设计优于原设计。  相似文献   
107.
The intratracheal instillation of xanthine-xanthine oxidase caused a marked decrease in dynamic respiratory compliance, indicating airway constriction. The constriction was significantly attenuated by fullerenol-1, but not by other agents or receptor antagonists.  相似文献   
108.
Previous analyses of the Wechsler Memory Scale-Revised (WMS-R; Wechsler, 1987) have reported one-, two-, and three-factor solutions and raised questions about the validity of the visual memory subtests. These various findings may stem in part from different methods of analysis, and from the study of different participant samples. To address these issues, we analysed data from the WMS-R and a spatial maze test administered to 154 participants with a history of alcohol dependence. Results from confirmatory factor analysis supported the interpretation of three factors underlying the WMS-R subtests and the spatial maze score in this sample, namely, attention-concentration, immediate memory, and delayed recall. This result held despite the inclusion of the maze score which is a well-validated measure of visuo-spatial memory.  相似文献   
109.
Commercial brewing trials with Zenith hops from the 1982 and 1983 crops have shown that these hops are suitable for producing both ales and lager beers.  相似文献   
110.
响洪甸抽水蓄能电站水下岩塞爆破施工要求高,技术新,难度大.由于施工准备充分,并进行了一系列材料及施工试验,工程进展顺利,排孔造孔、导洞药室开挖、药管与起爆体加工、装药与堵塞、网络施工、充水补气等工程施工质量符合设计要求,岩塞爆破准时成功起爆.  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