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   310746篇
  免费   5502篇
  国内免费   1366篇
电工技术   5063篇
综合类   599篇
化学工业   46565篇
金属工艺   11753篇
机械仪表   9058篇
建筑科学   7535篇
矿业工程   1646篇
能源动力   7697篇
轻工业   26716篇
水利工程   3338篇
石油天然气   5948篇
武器工业   51篇
无线电   35496篇
一般工业技术   62427篇
冶金工业   58381篇
原子能技术   7616篇
自动化技术   27725篇
  2021年   2937篇
  2020年   2292篇
  2019年   2651篇
  2018年   4878篇
  2017年   4961篇
  2016年   5227篇
  2015年   3427篇
  2014年   5558篇
  2013年   14298篇
  2012年   9057篇
  2011年   11586篇
  2010年   8995篇
  2009年   10036篇
  2008年   10641篇
  2007年   10445篇
  2006年   8796篇
  2005年   8087篇
  2004年   7995篇
  2003年   7674篇
  2002年   7369篇
  2001年   7262篇
  2000年   6843篇
  1999年   7223篇
  1998年   18542篇
  1997年   12955篇
  1996年   9847篇
  1995年   7387篇
  1994年   6477篇
  1993年   6510篇
  1992年   4566篇
  1991年   4365篇
  1990年   4261篇
  1989年   4219篇
  1988年   3911篇
  1987年   3514篇
  1986年   3527篇
  1985年   3908篇
  1984年   3615篇
  1983年   3325篇
  1982年   3151篇
  1981年   3191篇
  1980年   3154篇
  1979年   2933篇
  1978年   2968篇
  1977年   3303篇
  1976年   4428篇
  1975年   2487篇
  1974年   2440篇
  1973年   2460篇
  1972年   2054篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
The Journal of Supercomputing - Deadlock-free dynamic network reconfiguration process is usually studied from the routing algorithm restrictions and resource reservation perspective. The dynamic...  相似文献   
152.
Microsystem Technologies -  相似文献   
153.
Programming and Computer Software - Modern computer systems often include specialized processors that are programmed in domain-specific languages. The compiler-in-the-loop technology, which assumes...  相似文献   
154.
155.
Hydrogen fuel is a promising alternative to fossil fuels because of its energy content, clean nature, and fuel efficiency. However, it is not readily available. Most current producion processes are very energy intensive and emit carbon dioxide. Therefore, this article reviews technological options for hydrogen production that are eco-friendly and generate clean hydrogen fuel. Biological methods, such different fermentation processes and photolysis are discussed together with the required substrates and the process efficiency.  相似文献   
156.
Linear friction welding of the Ti6Al4V alloy is studied. A new definition of the energy input rate is proposed, based on an integration over time of the in-plane force and velocity; a strong correlation with the upset rate is then found. The effective friction coefficient is estimated to be 0·5±0·1 for varying frequencies and amplitudes, with only a weak dependence on the processing conditions displayed. A model is proposed that accounts for both the conditioning and equilibrium stages of the process, which is shown to be in good agreement with the experimental data. The model is used to study the mechanism by which the flash is formed. A criterion is proposed by which the rippled nature of its morphology can be predicted.  相似文献   
157.
Journal of Computer and Systems Sciences International - The height of a building is a basic characteristic needed for analytical services. It can be used to evaluate the population and functional...  相似文献   
158.
Bottom pour ladles with stopper rod systems are commonly used in the metal casting industry. However, stopper rod bottom-pouring systems have not yet been developed for the lower thermal masses of alloys typically used in the investment casting industry. Large thermal masses used with bottom pour systems are typically limited for ladles larger than 700 kg and to certain alloys with higher fluidity and longer solidification time like cast iron, aluminum alloys etc. In this study, bottom pour ladle designs and low thermal mass refractory systems have been developed and evaluated in production investment foundry trials with 300 kg pouring ladle. The ladles system and pouring practices used will be described along with the results from the pouring trials for SS304 that represents typical alloys used in Investment casting industries. Optimization of the variables used in an experimentation using Genetic algorithm is also explained.  相似文献   
159.
The aim of the present contribution is to study the influence of the post-spinning heat - treatment of single TiO2/PVP precursor fibers on the properties and morphology of the final titanium-based microfibers. The post-spinning treatment conditions were: calcination in air at 450–600?°C and pyrolysis in argon at 1000–1700?°C. Calcination resulted in a production of anatase-rich and pure rutile fibers. The use of an alternative sintering method, the low-temperature plasma treatment, led to the crystallization of the composite Magnéli phases/polymer fibers. As a result of the same one precursor, pyrolysis at 1000?°C, the Carbon/TiO2 composite fibers were obtained. Rising the treatment temperature in inert atmosphere led to the formation of the titanium carbide fibers. The formation process and all the obtained products were characterized by differential scanning calorimetry accompanied with thermogravimetric analysis (DSC/TGA), scanning and transmission electron microscopy (SEM, TEM), X-ray diffraction (XRD), and image analysis techniques.  相似文献   
160.
Successful fabrication of glass-based hybrid nanocomposites (GHNCs) incorporating Ag, core-shell CdSe/CdS and CdSxSe1?x nanoparticles (NPs) is herein reported. Both metallic (Ag) and semiconductor (CdSe/CdS) NPs were pre-synthesized, suspended in colloids and added into the sol-gel reaction medium which was used to fabricate the GHNCs. During fabrication of the nanocomposites a fraction (20–60%) of core-shell CdSe/CdS NPs was alloyed into CdSxSe1?x (0.20 < x < 0.35) NPs without changing morphology. Modulation of in situ alloying is possible via the relative content of organics added into the sol-gel protocol. Within colloids Ag (core-shell CdSe/CdS) NPs presented average diameter and polydispersity index of 49.5 nm (4.2 nm) and 0.41 (0.21), respectively. On the other hand, the Ag (core-shell CdSe/CdS) NPs’ average diameter and polydispersity index assessed from the GHNCs were respectively 51.5 nm (4.1 nm) and 0.43 (0.25), revealing negligible aggregation of the nanophases within the glass template. The new GHNCs herein introduced presented two independent excitonic transitions associated to homogenously dispersed semiconductor NPs, peaking around 420 nm (core-shell CdSe/CdS) and 650 nm (CdSxSe1?x) and matching the plasmonic resonance (Ag NPs) in the 400–500 nm range. We envisage that the new GHNCs represent very promising candidates for superior light manipulation while illuminated with multiple laser beams in quantum interference-based devices.  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