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   384308篇
  免费   4007篇
  国内免费   1281篇
电工技术   6910篇
综合类   2517篇
化学工业   52866篇
金属工艺   18938篇
机械仪表   15505篇
建筑科学   9025篇
矿业工程   2077篇
能源动力   8779篇
轻工业   24769篇
水利工程   4055篇
石油天然气   4896篇
武器工业   15篇
无线电   47750篇
一般工业技术   79117篇
冶金工业   55352篇
原子能技术   6246篇
自动化技术   50779篇
  2021年   2205篇
  2020年   1597篇
  2019年   1952篇
  2018年   22524篇
  2017年   22158篇
  2016年   15696篇
  2015年   3196篇
  2014年   4246篇
  2013年   11725篇
  2012年   10957篇
  2011年   23397篇
  2010年   20387篇
  2009年   18436篇
  2008年   19418篇
  2007年   21890篇
  2006年   7540篇
  2005年   10762篇
  2004年   8878篇
  2003年   8847篇
  2002年   7012篇
  2001年   6653篇
  2000年   6222篇
  1999年   6459篇
  1998年   16534篇
  1997年   11436篇
  1996年   8845篇
  1995年   6624篇
  1994年   5939篇
  1993年   5880篇
  1992年   4156篇
  1991年   4066篇
  1990年   3863篇
  1989年   3654篇
  1988年   3570篇
  1987年   3018篇
  1986年   2943篇
  1985年   3206篇
  1984年   2927篇
  1983年   2828篇
  1982年   2638篇
  1981年   2542篇
  1980年   2462篇
  1979年   2305篇
  1978年   2110篇
  1977年   2604篇
  1976年   3562篇
  1975年   1764篇
  1974年   1729篇
  1973年   1665篇
  1972年   1466篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
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   
82.
83.
84.
85.
A technology for slag formation in the ladle–furnace unit is considered; the slag is based on the CaO–SiO2–MgO–Al2O3–B2O3 system. This technology permits both microalloying of the steel with boron (reduced from the oxide phase) and desulfurization of the steel. The resulting boron content in the steel is 0.001–0.008%; the sulfur content in low-alloy steel and pipe steel is low (0.004–0.010%); and the consumption of manganese ferroalloys is reduced to 0.5 kg/t for 08кп steel and 1.4 kg/t for 09Г2C steel. In addition, the proposed technology increases the strength of the rolled steel, without loss in its plasticity; and reduces the environmental impact thanks to the replacement of fluorspar by colemanite.  相似文献   
86.
Context and objective: The aim of this study was to develop, characterize and evaluate a mucoadhesive caplet resulting from a polymeric blend (polymeric caplet) for intravaginal anti-HIV-1 delivery.

Materials and methods: Poly(lactic-co-glycolic) acid, ethylcellulose, poly(vinylalcohol), polyacrylic acid and modified polyamide 6, 10 polymers were blended and compressed to a caplet-shaped device, with and without two model drugs 3′-azido-3′-deoxythymidine (AZT) and polystyrene sulfonate (PSS). Thermal analysis, infrared spectroscopy and microscopic analysis were carried out on the caplets employing temperature-modulated DSC (TMDSC), Fourier transform infra-red (FTIR) spectrometer and scanning electron microscope, respectively. In vitro and in vivo drug release analyses as well as the histopathological toxicity studies were carried out on the drug-loaded caplets. Furthermore, molecular mechanics (MM) simulations were carried out on the drug-loaded caplets to corroborate the experimental findings.

Results and discussion: There was a big deviation between the Tg of the polymeric caplet from the Tg's of the constituent polymers indicating a strong interaction between constituent polymers. FTIR spectroscopy confirmed the presence of specific ionic and non-ionic interactions within the caplet. A controlled near zero-order drug release was obtained for AZT (20 d) and PSS (28 d). In vivo results, i.e. the drug concentration in plasma ranged between 0.012–0.332?mg/mL and 0.009–0.256?mg/mL for AZT and PSS over 1–28 d.

Conclusion: The obtained results, which were corroborated by MM simulations, attested that the developed system has the potential for effective delivery of anti-HIV-agents.  相似文献   
87.
88.
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   
89.
90.
Powder Metallurgy and Metal Ceramics - The mechanisms of phase interactions in granular media were studied to elaborate the results obtained previously at the Nekrasov Iron and Steel Institute of...  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