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   242106篇
  免费   2485篇
  国内免费   1638篇
电工技术   4229篇
综合类   2466篇
化学工业   28226篇
金属工艺   15500篇
机械仪表   11675篇
建筑科学   5075篇
矿业工程   1433篇
能源动力   4573篇
轻工业   9893篇
水利工程   2675篇
石油天然气   2493篇
武器工业   15篇
无线电   30139篇
一般工业技术   53243篇
冶金工业   32766篇
原子能技术   2674篇
自动化技术   39154篇
  2022年   422篇
  2021年   718篇
  2020年   542篇
  2019年   691篇
  2018年   21417篇
  2017年   21076篇
  2016年   13998篇
  2015年   1951篇
  2014年   1778篇
  2013年   4899篇
  2012年   7578篇
  2011年   19508篇
  2010年   17452篇
  2009年   14948篇
  2008年   15615篇
  2007年   18512篇
  2006年   3864篇
  2005年   7944篇
  2004年   5962篇
  2003年   5516篇
  2002年   3710篇
  2001年   3121篇
  2000年   2972篇
  1999年   3141篇
  1998年   9487篇
  1997年   6182篇
  1996年   4808篇
  1995年   3181篇
  1994年   2822篇
  1993年   2757篇
  1992年   1653篇
  1991年   1639篇
  1990年   1518篇
  1989年   1323篇
  1988年   1180篇
  1987年   861篇
  1986年   886篇
  1985年   916篇
  1984年   803篇
  1983年   698篇
  1982年   699篇
  1981年   681篇
  1980年   567篇
  1979年   476篇
  1978年   414篇
  1977年   533篇
  1976年   958篇
  1975年   299篇
  1974年   276篇
  1973年   256篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Machine Learning - We propose a set of highly scalable algorithms for the combinatorial data analysis problem of seriating similarity matrices. Seriation consists of finding a permutation of data...  相似文献   
32.
Orduna-Malea  Enrique  Aytac  Selenay  Tran  Clara Y. 《Scientometrics》2019,121(1):433-450
Scientometrics - The purpose of this study is to ascertain the suitability of GS’s url-based method as a valid approximation of universities’ academic output measures, taking into...  相似文献   
33.
34.
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   
35.
36.
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   
37.
The consequences of high energy mechanical milling, microwave-assisted heating and rapid thermal cooling on magnetic ordering in polycrystalline CaCu3Ti4O12 cubic perovskite have been investigated by means of X-ray powder diffractometry (300?K), dc magnetization in field – cooled and zero – field cooled modes (H = 100?Oe and 1000?Oe, T?=?5–300?K) (MT curves) and MH loop characteristics (T?=?5?K and 300?K, Hmax = 70?kOe). The MT curves of unmilled and 16?h milled samples show pure antiferromagnetic and weak ferromagnetic ordering, respectively, 1?h and 6?h milled samples demonstrate the coexistence of both the phases while microwave-assisted and quenched samples exhibit classic antiferromagnetic transition and a low temperature paramagnetic–like contribution with different weights, well supported by the MH loop characteristics. The observed transformations in the magnetic ordering are attributed to the ball-milling induced stress which curtails hybridization of empty Ti-3d orbitals with Cu-3d and O-2p orbitals and secondary phase formation. Oxygen vacancies associated with bound magnetic polarons originate ferromagnetism in the milled samples while unpaired electrons inhabited at the empty sites are the cause of paramagnetic centers. The low-temperature Curie – tail in MT curve for quenched and microwave assisted samples is attributed to Ti3+ cations.  相似文献   
38.
39.
40.
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   
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