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   260549篇
  免费   4658篇
  国内免费   1797篇
电工技术   5408篇
技术理论   5篇
综合类   1144篇
化学工业   41961篇
金属工艺   11026篇
机械仪表   7751篇
建筑科学   6619篇
矿业工程   1657篇
能源动力   5593篇
轻工业   25833篇
水利工程   2887篇
石油天然气   5954篇
武器工业   243篇
无线电   27801篇
一般工业技术   49245篇
冶金工业   47336篇
原子能技术   5628篇
自动化技术   20913篇
  2021年   2468篇
  2019年   2103篇
  2018年   3377篇
  2017年   3341篇
  2016年   3673篇
  2015年   2803篇
  2014年   4575篇
  2013年   11345篇
  2012年   7697篇
  2011年   10216篇
  2010年   8128篇
  2009年   8680篇
  2008年   9487篇
  2007年   9603篇
  2006年   8448篇
  2005年   7409篇
  2004年   6670篇
  2003年   6215篇
  2002年   6218篇
  2001年   6326篇
  2000年   5915篇
  1999年   5889篇
  1998年   12905篇
  1997年   9565篇
  1996年   7301篇
  1995年   5545篇
  1994年   5093篇
  1993年   4961篇
  1992年   3946篇
  1991年   3753篇
  1990年   3830篇
  1989年   3781篇
  1988年   3537篇
  1987年   3024篇
  1986年   3056篇
  1985年   3412篇
  1984年   3326篇
  1983年   3078篇
  1982年   2701篇
  1981年   2907篇
  1980年   2653篇
  1979年   2843篇
  1978年   2742篇
  1977年   2847篇
  1976年   3703篇
  1975年   2458篇
  1974年   2292篇
  1973年   2323篇
  1972年   1983篇
  1971年   1787篇
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
61.
Intended learning outcomes (ILOs) indicate what learners will be able to achieve after they are taught. Traditionally, ILOs are expressed as plain text or unstructured documents. What if all ILOs of a specific course of study can be conceptualized through a structured diagrammatic technique? It was hypothesized that learners can benefit from this conceptualization in learning, especially in self‐regulated learning. The aim of this study was to investigate whether the ILOs represented in unstructured or structured formats can facilitate learners to identify learning paths. The results revealed that the mean ratings of all learning paths were statistically significantly higher with structured ILOs.  相似文献   
62.
63.
64.
65.
66.
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   
67.
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   
68.
69.
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   
70.
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