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   84761篇
  免费   1020篇
  国内免费   409篇
电工技术   847篇
综合类   2317篇
化学工业   11573篇
金属工艺   4820篇
机械仪表   3052篇
建筑科学   2176篇
矿业工程   562篇
能源动力   1141篇
轻工业   3642篇
水利工程   1273篇
石油天然气   342篇
无线电   9374篇
一般工业技术   16445篇
冶金工业   2980篇
原子能技术   290篇
自动化技术   25356篇
  2021年   25篇
  2019年   14篇
  2018年   14460篇
  2017年   13385篇
  2016年   9974篇
  2015年   614篇
  2014年   248篇
  2013年   245篇
  2012年   3181篇
  2011年   9439篇
  2010年   8316篇
  2009年   5577篇
  2008年   6806篇
  2007年   7801篇
  2006年   164篇
  2005年   1236篇
  2004年   1144篇
  2003年   1197篇
  2002年   555篇
  2001年   121篇
  2000年   201篇
  1999年   92篇
  1998年   184篇
  1997年   116篇
  1996年   120篇
  1995年   40篇
  1994年   43篇
  1993年   47篇
  1992年   22篇
  1991年   32篇
  1990年   17篇
  1989年   22篇
  1988年   28篇
  1987年   12篇
  1985年   14篇
  1969年   27篇
  1968年   43篇
  1967年   33篇
  1966年   42篇
  1965年   45篇
  1963年   28篇
  1962年   22篇
  1961年   18篇
  1960年   30篇
  1959年   35篇
  1958年   37篇
  1957年   36篇
  1956年   34篇
  1955年   63篇
  1954年   68篇
排序方式: 共有10000条查询结果,搜索用时 30 毫秒
1.
Licorice is an herbal plant in the Leguminosae family, and its roots and rhizomes are used as sweeteners in food and confectionery products. Moreover, it has a distinct inflammatory activity. In the present study, a sample pre-treatment method to induce the deglycosylation of active metabolites in callus cultures of Glycyrrhiza inflata (GI) and Glycyrrhiza glabra (GG) was developed. The results of the method evaluation showed the biotransformation of ononin to formononetin, a rare flavonoid found in trace amounts in licorice. The magnitude of enhancement was 3- and 19-fold in the GI and GG samples, respectively. Moreover, the anti-inflammatory activity assay showed that the potency of the sample pre-treatment group was higher than that of the untreated group because it exerted an enhanced suppression of cyclo-oxygenase 2 (COX-2), interleukin-6 (IL-6) and inducible nitric oxide synthase (iNOS) gene expression. This is the first report on the anti-inflammatory activity of licorice callus, which has the potential to be utilised as a functional food for health promotion. These findings support the idea of using sample preparation to impart nutraceutical properties to plant products.  相似文献   
2.
Mobile software applications have to cope with a particular environment that involves small size, limited resources, high autonomy requirements, competitive business models and many other challenges. To provide development guidelines that respond to these needs, several practices have been introduced; however, it is not clear how these guidelines may contribute to solve the issues present in the mobile domain. Furthermore, the rapid evolution of the mobile ecosystem challenges many of the premises upon which the proposed practices were designed. In this paper, we present a survey of the literature on software assurance practices for mobile applications, with the objective of describing them and assessing their contribution and success. We identified, organized and reviewed a body of research that spans in three levels: software development processes, software product assurance practices, and software implementation practices. By carrying out this literature survey, we reviewed the different approaches that researchers on Software Engineering have provided to address the needs that raise in the mobile software development arena. Moreover, we review the evolution of these practices, identifying how the constant changes and modernization of the mobile execution environment has impacted the methods proposed in the literature. Finally, we introduced discussion on the application of these practices in a real productive setting, opening an area for further research that may determine if practitioners have followed the proposed assurance paradigms.  相似文献   
3.
This paper presents an integrated passive damping approach in hybrid metal-CFRP parts for structural applications. In this concept a viscoelastic material is embedded in the joint zone of the hybrid component. To examine the connection strength single-lap-joint specimens were produced and tested and the influence of the used material combinations, different surface structures, and different process parameters i.e. the moment of cross-linking were evaluated. Afterwards, the metal-CFRP hybrids were tested in quasi-static tests to assess their connection strength and failure behaviour. Dynamic cyclic tensile tests with step-wise increased loading conditions were performed to determine the specimens damping behaviour and to estimate their fatigue performance. Finally, these results are compared to a state of the art metal-CFRP hybrid with rivets connecting both materials.  相似文献   
4.
In this paper, we consider the classical finite mixture model, which is an effective tool for modeling lifetime distributions for random samples from heterogeneous populations. We discuss new results on stochastic comparison for two finite mixtures when each of them is drawn from one of the following semiparametric families, i.e., proportional hazards, accelerated lifetime and proportional reversed hazards.  相似文献   
5.
6.
7.
Variations of Incomplete Open Cubes is the major project by the twentieth-century conceptual artist Sol LeWitt. In this paper we interpret the enumerative component of the project as embeddings of graphs. This formulation permits use of an algorithm to check the completeness of the list of the structures produced by the artist. Our conclusion is that the artist found the correct number of structures (that is, 122), but that his list contains a mistake in the presentation of a pair of incomplete cubes, a discovery that appears not to have been noted before.  相似文献   
8.
9.
10.
Understanding semantic word shifts in scientific domains is essential for facilitating interdisciplinary communication. Using a data set of published papers in the field of information retrieval (IR), this paper studies the semantic shifts of words in IR based on mining per-word topic distribution over time. We propose that semantic word shifts not only occur over time, but also over topics. The shifts are examined from two perspectives, the topic-level and the context-level. According to the over-time word-topic distribution, stable words and unstable words are recognized. The diverging and converging trends in the unstable type reveal characteristics of the topic evolution process. The context-level shifts are further detected by similarities between word vectors. Our work associates semantic word shifts with the evolving of topics, which facilitates a better understanding of semantic word shifts from both topics and contexts.  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