全文获取类型
收费全文 | 353412篇 |
免费 | 30601篇 |
国内免费 | 18671篇 |
专业分类
电工技术 | 21765篇 |
技术理论 | 60篇 |
综合类 | 46069篇 |
化学工业 | 44330篇 |
金属工艺 | 16763篇 |
机械仪表 | 22898篇 |
建筑科学 | 49257篇 |
矿业工程 | 16963篇 |
能源动力 | 13922篇 |
轻工业 | 16879篇 |
水利工程 | 16292篇 |
石油天然气 | 13799篇 |
武器工业 | 3496篇 |
无线电 | 21327篇 |
一般工业技术 | 33218篇 |
冶金工业 | 20765篇 |
原子能技术 | 3949篇 |
自动化技术 | 40932篇 |
出版年
2024年 | 991篇 |
2023年 | 3680篇 |
2022年 | 7009篇 |
2021年 | 8617篇 |
2020年 | 8893篇 |
2019年 | 7686篇 |
2018年 | 7173篇 |
2017年 | 8694篇 |
2016年 | 10163篇 |
2015年 | 11390篇 |
2014年 | 19637篇 |
2013年 | 18842篇 |
2012年 | 23683篇 |
2011年 | 25712篇 |
2010年 | 20134篇 |
2009年 | 21051篇 |
2008年 | 19640篇 |
2007年 | 25097篇 |
2006年 | 23491篇 |
2005年 | 20599篇 |
2004年 | 17367篇 |
2003年 | 15591篇 |
2002年 | 12882篇 |
2001年 | 10716篇 |
2000年 | 9110篇 |
1999年 | 7418篇 |
1998年 | 5737篇 |
1997年 | 5055篇 |
1996年 | 4591篇 |
1995年 | 3884篇 |
1994年 | 3409篇 |
1993年 | 2560篇 |
1992年 | 2276篇 |
1991年 | 1658篇 |
1990年 | 1499篇 |
1989年 | 1286篇 |
1988年 | 1014篇 |
1987年 | 700篇 |
1986年 | 528篇 |
1985年 | 425篇 |
1984年 | 427篇 |
1983年 | 294篇 |
1982年 | 264篇 |
1981年 | 204篇 |
1980年 | 178篇 |
1979年 | 143篇 |
1978年 | 77篇 |
1977年 | 87篇 |
1959年 | 85篇 |
1955年 | 75篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
82.
The heat transfer and flow characteristics of MWCNT-R141b nanorefrigerant with different mass fractions have been studied through experiments. Experimental results were compared with existing correlations. A two-step method was used to prepare the nanorefrigerants. Span-80 was used as surfactant with an average particle diameter of 20 nm. Transmittance method was used to evaluate the stability of nanorefrigerants. Results showed that the stability of MWCNT-R141b nanorefrigerant, which is the added dispersant, was good during the experiments. The 0.3 wt% MWCNT-R141b nanorefrigerants had optimal heat transfer enhancement effects compared with pure refrigerants. The maximum Nusselt number increased by 40%. The specific pressure drop of nanorefrigerant increased as the Reynolds number (Re) increased, and the specific pressure drop of the pure refrigerant was minimum, which is similar to R141b. 相似文献
83.
《Journal of the European Ceramic Society》2020,40(13):4562-4571
Discrete Element Method (DEM) has been used for numerical investigation of sintering-induced structural deformations occurring in inverse opal photonic structures. The influence of the initial arrangement of template particles on the stability of highly porous inverse opal α-Al2O3 structures has been analyzed. The material transport, densification, as well as formation of defects and cracks have been compared for various case studies. Three different stages of defects formation have been distinguished starting with local defects ending with intrapore cracks. The results show that the packing of the template particles defined during the template self-assembly process play a crucial role in the later structural deformation upon thermal exposure. The simulation results are in very good agreement with experimental data obtained from SEM images and previous studies by ptychographic X-ray tomography. 相似文献
84.
85.
In this research, we propose a novel framework referred to as collective game behavior decomposition where complex collective behavior is assumed to be generated by aggregation of several groups of agents following different strategies and complexity emerges from collaboration and competition of individuals. The strategy of an agent is modeled by certain simple game theory models with limited information. Genetic algorithms are used to obtain the optimal collective behavior decomposition based on history data. The trained model can be used for collective behavior prediction. For modeling individual behavior, two simple games, the minority game and mixed game are investigated in experiments on the real-world stock prices and foreign-exchange rate. Experimental results are presented to show the effectiveness of the new proposed model. 相似文献
86.
A small handful of recent studies have addressed a phenomenon known as “phantom vibration syndrome”. This refers to when phone users perceive their device to vibrate, indicating that a call or text is incoming, when in fact the phone did not vibrate at all. Though these studies show that most users do not find phantom vibration hallucinations to be very bothersome, they also find that a large majority of users experience this phenomenon. This paper explores what the striking prevalence of phantom vibration syndrome means for our contemporary relationships with technology. I begin with a review of the theories purporting to explain these data, which largely rely on particular understandings of the brain. Next I develop an alternative theory of phantom vibration syndrome based on insights from the philosophical tradition of phenomenology. This account considers the ways users develop bodily and perceptual habits regarding how the phone is understood and used. By critically contrasting these different theories, we can refine our questions about what the high prevalence of phantom vibration syndrome implies about our contemporary technological situation. 相似文献
87.
Fundamental Evaluation of Power Supply and Rectifiers for Wireless Power Transfer Using Magnetic Resonant Coupling
下载免费PDF全文
![点击此处可从《Electrical Engineering in Japan》网站下载免费的PDF全文](/ch/ext_images/free.gif)
This paper provides a fundamental analysis of a power supply and rectifiers for wireless power transfer using magnetic resonant coupling (MRC). MRC enables efficient wireless power transfer over middle‐range transfer distances. MRC for wireless power transfer should operate at a high frequency in the industry science medical band, such as 13.56 MHz, because the size of the transfer device decreases at higher transfer frequencies. Therefore, the output frequency of the power supply on the transmitting side should be 13.56 MHz. In addition, the rectifier on the receiving side is operated at a high frequency. This paper focuses on the reflected power in the power supply and rectifiers. Thus, the parametric design method is clarified for the power supply, including a low‐pass filter to match the output, the impedance of the power supply with the characteristic impedance of the transmission line. In addition, the effects on the rectifiers of silicon carbide and gallium nitride diodes are confirmed by performing an experiment and a loss analysis. 相似文献
88.
In this work, TiO2 nanoparticles are surface modified by NH2-terminated organic moieties arised from 4,4′-methylene diphenyl diisocyanate (MDI). These nanoparticles are incorporated into ether-based segmented polyurethane (SPU) matrix. MDI is utilized as monomer together with poly(tetramethylene oxide) (PTMO) comonomer for preparing the final polymer as well. The NH2-functionalized TiO2 nanoparticles are covalently linked to the NCO terminals of the resulting SPU macromolecules during film preparation stage. Therefore, in addition to butylene glycol, these surface modified nanoparticles with enhanced organophilicity could play the role of the second chain extender of NCO-capped SPU macromolecules through formation of urea linkages. Optical and thermal behaviors of the transparent and flexible film (SPU/TiO2–MDI) is compared with those of unmodified TiO2 (SPU/TiO2) and TiO2-unloaded SPU films. Though the particle loading is only 5 wt.%, incorporation of TiO2 and TiO2–MDI nanoparticles into the SPU polymer enhances significantly the light absorption in UV region at 300–400 nm. SEM images of the prepared films clearly show a considerable decrease in particle aggregation for TiO2–MDI into SPU matrix compared to that of unmodified TiO2. TG analyses indicate a one-step decomposition pattern with onset temperatures of about 360 and 380 °C for neat SPU and SPU/TiO2–MDI, respectively. Moreover, DTA thermograms of both nanocomposites show obviously two exothermic phase transitions in the thermal range of 330–440 °C. 相似文献
89.
In this paper, the dynamic behaviors on the basis of simulation for high-purity heat integrated air separation column (HIASC) are studied. A nonlinear generic model control (GMC) scheme is proposed based on the nonlinear behavior analyses of a HIASC process, and an adaptive generic model control (AGMC) scheme is further presented to correct the model parameters online. Related internal model control (IMC) scheme and multi-loop PID (M-PID) scheme are also developed as the comparative base. The comparative researches are carried out among these linear and nonlinear control schemes in detail. The simulation research results show that the proposed AGMC schemes present advantages in both servo control and regulatory control for the high-purity HIASC. 相似文献
90.