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   426861篇
  免费   4246篇
  国内免费   1192篇
电工技术   6465篇
综合类   2568篇
化学工业   63116篇
金属工艺   20941篇
机械仪表   13984篇
建筑科学   9596篇
矿业工程   3502篇
能源动力   8627篇
轻工业   28205篇
水利工程   5908篇
石油天然气   11709篇
武器工业   20篇
无线电   44622篇
一般工业技术   88267篇
冶金工业   64268篇
原子能技术   10824篇
自动化技术   49677篇
  2021年   2969篇
  2019年   2939篇
  2018年   19185篇
  2017年   18274篇
  2016年   15374篇
  2015年   3847篇
  2014年   5825篇
  2013年   14715篇
  2012年   11783篇
  2011年   20728篇
  2010年   17418篇
  2009年   15949篇
  2008年   17329篇
  2007年   18236篇
  2006年   9274篇
  2005年   9650篇
  2004年   9236篇
  2003年   9041篇
  2002年   8078篇
  2001年   7773篇
  2000年   7685篇
  1999年   7586篇
  1998年   17633篇
  1997年   12709篇
  1996年   9786篇
  1995年   7227篇
  1994年   6537篇
  1993年   6470篇
  1992年   5155篇
  1991年   5101篇
  1990年   4963篇
  1989年   4944篇
  1988年   4819篇
  1987年   4288篇
  1986年   4217篇
  1985年   4664篇
  1984年   4374篇
  1983年   4139篇
  1982年   3797篇
  1981年   4082篇
  1980年   3825篇
  1979年   4057篇
  1978年   4196篇
  1977年   4429篇
  1976年   5872篇
  1975年   3748篇
  1974年   3704篇
  1973年   3799篇
  1972年   3303篇
  1971年   2968篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Announcement     
Samples of nine different fruits grown in Oyo State of Nigeria were obtained from different market locations within Ibadan Municipality and analysed for their vitamin C content. Sweet orange was found to contain the highest amount of vitamin C (56·0 mg100 g edible portion) whilst sweet banana variety II contained the lowest amount (9·4 mg100 g edible portion). Lime, grapefruit, pawpaw and ‘agbalumo’ were found to contain considerable amounts of vitamin C, having 46·5, 47·0, 43·2 and 48·0 mg100 g respectively. Consumption of these fruits would thus meet the nutritional requirement for vitamin C in this part of Nigeria. It is also recommended that sweet orange, agbalumo, grapefruit, lime and pawpaw, found to contain considerable amounts of vitamin C, should be processed either at home or factory level to make them available to the people all year round.  相似文献   
72.
73.
74.
75.
76.
Existing duality principles in structural optimisation are briefly reviewed and then they are extended to structures with segment-wise constant cross-sections. All theories are discussed in the particular context of optimal plastic beam design with symmetric convex specific cost functions and are confirmed by independent calculations on illustrative examples. It is shown that the optimal solution is always associated with a displacement field in which the mean absolute curvature value for each segment equals the subgradient of the specific cost function, with respect to the maximum absolute moment value for that segment. Moreover, the dual problem consists of the maximisation of the difference of two terms: the first one is the integral of the product of load and deflection (external work), and the second is the sum of products of segment lengths and the mean complementary cost values (taken with respect to the mean absolute curvature for that segment). Finally, some tentative proposals for a class of non-convex optimisation problems are presented. For special cases, the proposed general statements reduce to theorems by Heyman, Foulkes and Hemp.  相似文献   
77.
78.
Translated from Atomnaya Énergiya, Vol. 67, No. 2, pp. 111–113, August, 1989.  相似文献   
79.
This study empirically examined the organisational learning effects of the nonfinancial performance information provided by management accounting information systems (MAISs) under advanced manufacturing technology (AMT). In this study, a target costing system and the frequent and quick reporting of information were considered the facilitators of learning. First, we examined the relationships between AMT level and the amount of nonfinancial performance information produced by MAISs. The empirical results showed that there are significant positive relationships between the level of AMT and nonfinancial performance information. With a systems approach, we also proved the impact of the relationships among AMT levels, nonfinancial performance information and learning facilitators on the organisational performance of a firm. The results of our research suggest that under a high level of AMT, for the provision of information to result in an increase of performance through organisational learning, a target costing system must be introduced and a large amount of information should be provided frequently and quickly. The results of this study also showed that although AMT level may be low, fairly well-arranged facilitators and a moderately large amount of information may be necessary for the improvement of performance. In conclusion, effective organisational learning depends on the provision of relevant information as well as efficient learning support mechanisms.  相似文献   
80.
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