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   303876篇
  免费   8025篇
  国内免费   3594篇
电工技术   7539篇
技术理论   7篇
综合类   3190篇
化学工业   49250篇
金属工艺   13591篇
机械仪表   10173篇
建筑科学   9010篇
矿业工程   2424篇
能源动力   6957篇
轻工业   28789篇
水利工程   3601篇
石油天然气   7523篇
武器工业   437篇
无线电   32649篇
一般工业技术   56865篇
冶金工业   50099篇
原子能技术   6097篇
自动化技术   27294篇
  2022年   2445篇
  2021年   3735篇
  2020年   2613篇
  2019年   3061篇
  2018年   5062篇
  2017年   5037篇
  2016年   5308篇
  2015年   4268篇
  2014年   6243篇
  2013年   13627篇
  2012年   9977篇
  2011年   12987篇
  2010年   10193篇
  2009年   10887篇
  2008年   11544篇
  2007年   11643篇
  2006年   10323篇
  2005年   10852篇
  2004年   9056篇
  2003年   8268篇
  2002年   7743篇
  2001年   7685篇
  2000年   6902篇
  1999年   6795篇
  1998年   13834篇
  1997年   10308篇
  1996年   8013篇
  1995年   6071篇
  1994年   5464篇
  1993年   5260篇
  1992年   4205篇
  1991年   3962篇
  1990年   3989篇
  1989年   3907篇
  1988年   3647篇
  1987年   3105篇
  1986年   3128篇
  1985年   3463篇
  1984年   3379篇
  1983年   3114篇
  1982年   2732篇
  1981年   2925篇
  1980年   2669篇
  1979年   2862篇
  1978年   2756篇
  1977年   2858篇
  1976年   3704篇
  1975年   2468篇
  1974年   2308篇
  1973年   2333篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
82.
83.
84.
85.
86.
Spinel LiSr0·1Cr0·1Mn1·8O4 was synthesised by high temperature solid state method in order to enhance the electrochemical performance. The LiSr0·1Cr0·1Mn1·8O4 (LSCMO) materials were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical tests. The XRD and SEM studies confirm that LSCMO had spinel crystal structure with a space group of Fd3m, and the particle of LSCMO shows irregular shape. The cyclic voltammetry data illustrated that the heavy current charge–discharge performance of LMO was improved by Sr2+ and Cr3+ doping. The galvanostatic charge–discharge of LSCMO cathode materials was measured at 1, 5, 10 and 20 C. The results indicated that LSCMO improved the capacity retention.  相似文献   
87.
Manente  F.  Pietrobon  L.  Ronchin  L.  Vavasori  A. 《Catalysis Letters》2021,151(12):3543-3549
Catalysis Letters - In this work we studied the reactivity of the Trifluoroacetic acid hydroxylamine system in the one step salt free synthesis of amides from ketones. A particular regards was paid...  相似文献   
88.
89.
Russian Journal of Nondestructive Testing - The possibility of approaching the problems of testing the regularities of elastoplastic deformation of 20GL steel by the method of analyzing the...  相似文献   
90.
Colostrum is essential for good neonate health; however, it is not known whether different calves absorb the nutrients from colostrum equally well. In this study, the absorption of protein, IgG, and γ-glutamyl transferase was compared in newborn dairy bull calves for 1 wk after feeding colostrum from different sources. Thirty-five Holstein-Friesian bull calves were randomly allocated into 3 groups and fed colostrum within 4 h after birth. Group A calves (n = 12) were bottle fed colostrum from their own dam for 3 d. Colostrum from these group A cows was also used as foster cow colostrum for the group B calves (n = 12), such that each group A and B calf pair received identical colostrum from each milking of the respective group A dam (10% of birth weight per day). The group C calves (n = 11) were fed 1 bottle (2 L) of pooled colostrum and transition milk (referred to as pooled colostrum), as was the standard practice on the dairy farm. The pooled colostrum was collected from the other dairy cows on the farm 0 to 4 d postpartum and stored at 4°C for less than 12 h. Blood was sampled from calves before the first feeding and at 1, 2, 3, and 7 d after birth. Levels of total solids, total protein, and IgG were higher in the dam colostrum than in the pooled colostrum. At birth, there were no differences between the calf groups for any measurements, and all calves had very low IgG levels. After receiving colostrum, the glucose, plasma γ-glutamyl transferase, serum total protein, and IgG concentrations increased significantly in all calves. There were no differences in any blood measurements at any time point between the pairs of group A and group B calves that received colostrum from the same cow except for the IgG concentration 2 d after birth. However, the group A calves had a higher total serum protein level and IgG concentration than the group C calves for all the time points after the first feeding. The group B calves had a higher IgG concentration than the group C calves on d 1, 2, and 7 after birth. Compared with groups A and B, there was no difference in the proportion of calves in group C that failed to have passive immunity transferred adequately based on the IgG threshold (<10 g/L). Thus, the calves receiving identical colostrum from the same cow had the same levels of IgG, and even the pooled colostrum provided sufficient transfer of IgG as the calves were fed within 4 h after birth.  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