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   112481篇
  免费   2309篇
  国内免费   517篇
电工技术   1151篇
综合类   2546篇
化学工业   16792篇
金属工艺   5395篇
机械仪表   3634篇
建筑科学   3191篇
矿业工程   656篇
能源动力   2092篇
轻工业   7685篇
水利工程   1495篇
石油天然气   493篇
武器工业   6篇
无线电   11452篇
一般工业技术   20333篇
冶金工业   9003篇
原子能技术   505篇
自动化技术   28878篇
  2023年   165篇
  2022年   548篇
  2021年   867篇
  2020年   560篇
  2019年   641篇
  2018年   14988篇
  2017年   14022篇
  2016年   10625篇
  2015年   1178篇
  2014年   1129篇
  2013年   1753篇
  2012年   4432篇
  2011年   10973篇
  2010年   9405篇
  2009年   6758篇
  2008年   7866篇
  2007年   8686篇
  2006年   958篇
  2005年   2077篇
  2004年   2047篇
  2003年   2007篇
  2002年   1357篇
  2001年   799篇
  2000年   733篇
  1999年   600篇
  1998年   2145篇
  1997年   1388篇
  1996年   990篇
  1995年   629篇
  1994年   503篇
  1993年   559篇
  1992年   239篇
  1991年   314篇
  1990年   235篇
  1989年   194篇
  1988年   220篇
  1987年   164篇
  1986年   170篇
  1985年   185篇
  1984年   133篇
  1983年   93篇
  1982年   119篇
  1981年   125篇
  1980年   121篇
  1979年   92篇
  1978年   81篇
  1977年   146篇
  1976年   234篇
  1975年   86篇
  1954年   70篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
23.
24.
Zhang  Xi  Wang  Xianhai  Zhao  Hongke  Ordóñez de Pablos  Patricia  Sun  Yongqiang  Xiong  Hui 《Scientometrics》2019,119(3):1311-1344
Scientometrics - Altmetrics indices are increasingly applied to measure scholarly influence in recent years because they can reflect the influence of research outputs more timely comparing with...  相似文献   
25.
Neat poly (lactic acid) (PLA) and PLA/cassava bagasse (CB) composites were used to produce seedling tubes by extrusion and injection molding. The tubes were buried in simulated soil, and their biodegradation was investigated by weight loss, scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). After 180 days, the composites' biodegradation was higher than neat PLA material, and the higher the CB content, the higher the biodegradation, which caused fissures and voids in the material. The biodegradation of PLA/CB composites increased the phosphorus content in the soil after 180 days. Composites of PLA with CB, an abundant agro-industrial residue in Brazil, are promising because they can reduce the environmental impact due to CB's proper destination, and the composites' costs and biodegradation are faster than pure PLA material. Both the faster biodegradation of the tube and the higher P content are advantageous for seedling tubes.  相似文献   
26.
This study investigates the preparation of polyetherimide (PEI) – LaNi5 composites films for hydrogen storage. Prior to the polymer addition, LaNi5 was ball-milled at different conditions (250, 350, and 450 RPM) and annealed at 500 °C for 1 h under vacuum. The composites were produced with BM-LaNi5-350 (PEI/LaNi5-350) and annealed BM-LaNi5-350 (PEI/LaNi5-350-TT). Membranes were successfully produced through solvent casting assisted by an ultrasonic bath. The particles dispersion and the film morphology did not change after hydrogenation cycles. In the H2 sorption experiments at 43 °C and 20 bar, the films stored H2 without incubation time; both samples reached a capacity of ~0.6 wt%. The H2 sorption kinetics of PEI/LaNi5-350 was comparable to that of BM-LaNi5-350, whereas PEI/LaNi5-350-TT presented significantly slower kinetics. LaNi5 oxidation was hindered by PEI, showing that it can be explored to improve metal hydrides air resistance. The results demonstrated that PEI films filled with LaNi5 are promising materials for hydrogen storage.  相似文献   
27.
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   
28.
29.
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   
30.
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   
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