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   260753篇
  免费   4663篇
  国内免费   1797篇
电工技术   5412篇
技术理论   5篇
综合类   1145篇
化学工业   42110篇
金属工艺   11013篇
机械仪表   7762篇
建筑科学   6610篇
矿业工程   1658篇
能源动力   5591篇
轻工业   25825篇
水利工程   2885篇
石油天然气   5954篇
武器工业   243篇
无线电   27856篇
一般工业技术   49255篇
冶金工业   47348篇
原子能技术   5618篇
自动化技术   20923篇
  2021年   2472篇
  2019年   2106篇
  2018年   3375篇
  2017年   3340篇
  2016年   3675篇
  2015年   2802篇
  2014年   4576篇
  2013年   11353篇
  2012年   7694篇
  2011年   10203篇
  2010年   8134篇
  2009年   8676篇
  2008年   9497篇
  2007年   9603篇
  2006年   8459篇
  2005年   7404篇
  2004年   6673篇
  2003年   6217篇
  2002年   6214篇
  2001年   6339篇
  2000年   5924篇
  1999年   5888篇
  1998年   12903篇
  1997年   9565篇
  1996年   7300篇
  1995年   5537篇
  1994年   5101篇
  1993年   4961篇
  1992年   3950篇
  1991年   3760篇
  1990年   3836篇
  1989年   3779篇
  1988年   3538篇
  1987年   3031篇
  1986年   3052篇
  1985年   3420篇
  1984年   3327篇
  1983年   3079篇
  1982年   2701篇
  1981年   2908篇
  1980年   2647篇
  1979年   2840篇
  1978年   2742篇
  1977年   2848篇
  1976年   3714篇
  1975年   2457篇
  1974年   2296篇
  1973年   2322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 32 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