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   244122篇
  免费   2649篇
  国内免费   432篇
电工技术   4322篇
综合类   259篇
化学工业   39786篇
金属工艺   9411篇
机械仪表   7446篇
建筑科学   5609篇
矿业工程   1405篇
能源动力   5214篇
轻工业   25004篇
水利工程   2487篇
石油天然气   5111篇
武器工业   32篇
无线电   25214篇
一般工业技术   45098篇
冶金工业   46375篇
原子能技术   5973篇
自动化技术   18457篇
  2021年   2121篇
  2019年   2038篇
  2018年   3503篇
  2017年   3439篇
  2016年   3713篇
  2015年   2252篇
  2014年   3924篇
  2013年   10311篇
  2012年   6210篇
  2011年   8391篇
  2010年   6621篇
  2009年   7305篇
  2008年   7678篇
  2007年   7796篇
  2006年   6991篇
  2005年   6117篇
  2004年   5883篇
  2003年   5671篇
  2002年   5745篇
  2001年   5613篇
  2000年   5440篇
  1999年   5364篇
  1998年   12708篇
  1997年   8993篇
  1996年   6940篇
  1995年   5410篇
  1994年   4809篇
  1993年   4693篇
  1992年   3723篇
  1991年   3419篇
  1990年   3637篇
  1989年   3513篇
  1988年   3357篇
  1987年   2944篇
  1986年   2980篇
  1985年   3423篇
  1984年   3257篇
  1983年   2936篇
  1982年   2785篇
  1981年   2856篇
  1980年   2766篇
  1979年   2662篇
  1978年   2714篇
  1977年   2985篇
  1976年   3851篇
  1975年   2404篇
  1974年   2283篇
  1973年   2406篇
  1972年   1992篇
  1971年   1874篇
排序方式: 共有10000条查询结果,搜索用时 29 毫秒
991.
Conclusions The possibility of obtaining clinker from high-alumina cement by melting a mixture of lime and technical alumina in an electric-arc furnace at the Klyuchevsk Ferroalloy Plant has been shown.The high-alumina cement obtained from fused clinker is significantly better in its physicochemical properties than the cement produced on the basis of the lime-alumina slags from the ferroalloy industry.Translated from Ogneupory, No. 5, pp. 25–27, May, 1984.  相似文献   
992.
993.
Materials made from yttrium silicates were synthesized by the sol-gel method. The effect of the amount of yttrium oxide, which varied from 10 to 50% (molar content), and the water:alcoholate molar ratio was investigated. Structure formation and the character of crystallization of gels in heat treatment in the 650–1300°C range were investigated. __________ Translated from Steklo i Keramika, No. 1, pp. 3–6, January, 2007.  相似文献   
994.
The monoethylenic isomers of C18, C20 and C22 chain lengths of the depot fat of a nonhominid primate (cynomolgus monkeys,Macaca fascicularis), fed a partially hydrogenated herring oil (IV=76.0) for 30 months, were examined by 2 different approaches. The first isolation method involved preparative gas liquid chromatography and argentation thin layer chromatography (TLC). The second sequence involved a chain-length fractionation system based on the TLC of the methoxy-bromomercuri quence involved a chain-length fractionation system based on the TLC of the methoxy-bromomercuri adducts of the total methyl esters to isolate groups of acids of common degrees of unsaturation, and then high performance liquid chromatography on a reverse-phase column. In both cases, the monoethylenic isomer distribution was determined by ozonolysis in BF3/MeOH. Comparable results were obtained with the 2 methods. The second approach is recommended for small biological samples, especially for those containing a relatively high proportion of di- and other polyethylenic isomers which might interfere. Presented in part at the AOCS annual meeting, New Orleans, May 1981.  相似文献   
995.
Male rats were fed 100 nM dichlorodiphenyltrichloroethane-14C in oil by gastric tube. Recovery of dichlorodiphenyltrichloroethane-14C in thoracic duct lymph was 60% in 12 hr. Lymph dichlorodiphenyltrichloroethane-14C (97%) occurred in lipoproteins of d<1.006, designated chylomicrons. Mechanical separation of chylomicron triglyceride core (labeled with triglyceride-3H) from chylomicron membrane (labeled with phospholipid-32P) showed that 97% dichlorodiphenyltrichloroethane-14C was present in triglyceride core. To investigate possible association of plasma clearance of the two core lipids, rats were pulse injected with chylomicrons, doubly labeled with triglyceride-3H and dichlorodiphenyltrichloroethane-14C. The decay of dichlorodiphenyltrichloroethane-14C in sequential serum samples was rapid (T1/2=2 min) and was independent of triglyceride-3H decay. In tissues removed 14 min after injection of chylomicrons, 30% administered dichlorodiphenyltrichloroethane-14C was found in liver but only 1% in adipose tissue. In hepatectomized (eviscerated) rats, the decay of serum dichlorodiphenyltrichloroethane-14C (T1/2=10 min) was also independent of and more rapid than triglyceride-3H decay. With sucrose density gradients, it was shown that chylomicron dichlorodiphenyltrichloroethane-14C transferred to higher density serum proteins in vitro and in vivo and to bovine albumin in vitro. Thus, dichlorodiphenyltrichloroethane was transported from intestine largely in the triglyderide phase of chylomicrons; disappearance of chylomicron-dichlorodiphenyltrichloroethane from the systemic circulation was rapid and partly independent of the presence of the liver and of triglyceride hydrolysis; some dichlorodiphenyltrichloroethane was transported from serum chylomicrons to albumin or other plasma proteins before tissue uptake.  相似文献   
996.
997.
A study of the effect of long-term alcohol consumption on the liver of well-nourished rats is described. Rats fed for 16 weeks on a semipurified diet supplemented with high levels of vitamins and lipotropic factors and alcohol corresponding to 35% of the total caloric intake developed marked fatty changes of the liver. Mild fatty changes were observed in pair-fed controls receiving as isoenergetic equivalent of sucrose instead of alcohol. Intracellular hyaline bodies, corresponding ultrastructurally to giant mitochondria were abundantly found in the hepatocytes of alcoholic rats, while in the controls they were not seen. Te findings in this investigation are postulated to provide further evidence that the long-term intake of alcohol exerts a direct causative role in the pathogenesis of liver damage.  相似文献   
998.
Apparatus has been developed for studying the development of crystallinity and orientation during the melt spinning of synthetic fibers. Tension in the fiber and temperature, diameter, and x-ray diffraction patterns are measured as a function of distance from the spinneret for a running monofilament. Measurements are presented for linear polyethylene over a range of spinning variables together with other investigations carried out on the final as-spun fibers. These data indicate that the development of crystallinity in polyethylene is controlled by a balance between increased crystallization kinetics caused by the stress in the fiber and a tendency for increased supercooling with change in any spinning variable that increases cooling rates in the fiber. The type of crystalline orientation observed, its development during the spinning process, and the changes observed with changes in spinning conditions suggest a model for the as-spun fiber structure in which varying amounts of row nucleation and twisting of lamellar, folded-chain crystal overgrowths occur depending on the spinning conditions. As-spun fiber birefringence was shown to depend primarily on the crystalline orientation. Mechanical properties correlated well with c-axis crystalline orientation function and spinline stress.  相似文献   
999.
1000.
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