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   95947篇
  免费   1402篇
  国内免费   467篇
电工技术   1013篇
综合类   2333篇
化学工业   13675篇
金属工艺   5122篇
机械仪表   3367篇
建筑科学   2372篇
矿业工程   630篇
能源动力   1825篇
轻工业   4752篇
水利工程   1420篇
石油天然气   425篇
无线电   10771篇
一般工业技术   18918篇
冶金工业   4119篇
原子能技术   444篇
自动化技术   26630篇
  2023年   196篇
  2022年   520篇
  2021年   539篇
  2020年   453篇
  2019年   431篇
  2018年   14833篇
  2017年   13721篇
  2016年   10365篇
  2015年   890篇
  2014年   701篇
  2013年   1108篇
  2012年   3632篇
  2011年   10026篇
  2010年   8757篇
  2009年   6040篇
  2008年   7206篇
  2007年   8124篇
  2006年   454篇
  2005年   1455篇
  2004年   1366篇
  2003年   1390篇
  2002年   714篇
  2001年   240篇
  2000年   329篇
  1999年   214篇
  1998年   407篇
  1997年   259篇
  1996年   297篇
  1995年   233篇
  1994年   198篇
  1993年   183篇
  1992年   158篇
  1991年   173篇
  1990年   117篇
  1989年   109篇
  1988年   139篇
  1987年   111篇
  1986年   89篇
  1985年   116篇
  1984年   96篇
  1983年   109篇
  1982年   100篇
  1981年   89篇
  1980年   78篇
  1979年   55篇
  1977年   57篇
  1976年   78篇
  1968年   51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 0 毫秒
1.
Wireless Personal Communications - This article presents a microstrip-fed octagonal shaped monopole antenna with dual band notched characteristics for UWB applications. Partial ground plane has...  相似文献   
2.
Wireless Personal Communications - The efficient management of resource sharing plays a crucial role in the cloud execution environment. The constraints such as heterogeneity and dynamic nature of...  相似文献   
3.
Wireless Personal Communications - Data security is currently become a serious concern in wireless communication system for both the users and providers. Without a secure medium, the data...  相似文献   
4.
Microsystem Technologies - The strategy for analysis of noise generated in the analog circuit is presented here. Further, methodology for optimization of noise to improve the performance of the...  相似文献   
5.
A flower‐shaped ultra‐wideband fractal antenna is presented. It comprises a fourth iterative flower‐shaped radiator, asymmetrical stub‐loaded feeding line, and coplanar quarter elliptical ground planes. A wide operating band of 12.12 GHz (4.58‐16.7 GHz) for S 11 ≤ ? 10 dB is achieved along with an overall antenna footprint of 15.7 × 11.4 mm2. In addition, other desirable characteristics, that is, omnidirectional radiation patterns, peak gain upto 5 dB, and fidelity factor more than 75% are achieved. A good agreement exists between the simulation and measured results. The obtained results illustrate that this antenna has wide operating range and compact dimensions than available structures.  相似文献   
6.
The separation of iron oxide from banded hematite jasper(BHJ) assaying 47.8% Fe, 25.6% Si O2 and 2.30%Al2O3 using selective magnetic coating was studied. Characterization studies of the low grade ore indicate that besides hematite and goethite,jasper, a microcrystalline form of quartzite, is the major impurity associated with this ore. Beneficiation by conventional magnetic separation technique could yield a magnetic concentrate containing 60.8% Fe with 51% Fe recovery. In order to enhance the recovery of the iron oxide minerals, fine magnetite, colloidal magnetite and oleate colloidal magnetite were used as the coating material. When subjected to magnetic separation, the coated ore produces an iron concentrate containing 60.2% Fe with an enhanced recovery of56%. The AFM studies indicate that the coagulation of hematite particles with the oleate colloidal magnetite facilitates the higher recovery of iron particles from the low grade BHJ iron ore under appropriate conditions.  相似文献   
7.
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   
8.
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   
9.
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   
10.
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