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   1408篇
  免费   43篇
  国内免费   4篇
电工技术   27篇
综合类   1篇
化学工业   270篇
金属工艺   36篇
机械仪表   27篇
建筑科学   18篇
矿业工程   5篇
能源动力   56篇
轻工业   85篇
水利工程   10篇
石油天然气   1篇
无线电   182篇
一般工业技术   284篇
冶金工业   250篇
原子能技术   6篇
自动化技术   197篇
  2023年   10篇
  2022年   20篇
  2021年   46篇
  2020年   33篇
  2019年   29篇
  2018年   44篇
  2017年   38篇
  2016年   39篇
  2015年   29篇
  2014年   44篇
  2013年   96篇
  2012年   47篇
  2011年   61篇
  2010年   46篇
  2009年   53篇
  2008年   75篇
  2007年   59篇
  2006年   38篇
  2005年   46篇
  2004年   33篇
  2003年   23篇
  2002年   25篇
  2001年   15篇
  2000年   15篇
  1999年   20篇
  1998年   57篇
  1997年   41篇
  1996年   43篇
  1995年   27篇
  1994年   22篇
  1993年   26篇
  1992年   21篇
  1991年   20篇
  1990年   14篇
  1989年   14篇
  1988年   11篇
  1987年   12篇
  1986年   10篇
  1985年   7篇
  1984年   15篇
  1983年   19篇
  1982年   7篇
  1981年   8篇
  1979年   8篇
  1978年   9篇
  1977年   13篇
  1976年   14篇
  1974年   9篇
  1973年   8篇
  1972年   6篇
排序方式: 共有1455条查询结果,搜索用时 0 毫秒
991.
无论全球化如何发展,固有的文化认同仍然存在,这也对电器的个性化提出了更高的要求。随着城市化的不断发展,城市文化逐渐生根。我们开始以相同的方式生活、工作和游戏。对于电器营销人员来说,  相似文献   
992.
In this paper, we discuss the design of leakage tolerant wide-OR domino gates for deep submicron (DSM), bulk CMOS technologies. Technology scaling is resulting in a 3×-5× increase in transistor IOFF/μm per generation causing 15-30% degradation in the noise margin of high performance domino gates. We investigate several techniques that can improve the noise margin of domino logic gates and thereby ensure their reliable operation for sub-130 nm technologies. Our results indicate that, selective usage of dual VTH transistors shows acceptable energy-delay tradeoffs for the 90 nm technology. However, techniques like supply voltage (Vcc) reduction or using non-minimum Le transistors are required in order to ensure robust and low power operation of wide-OR domino designs for the 70 nm generation.  相似文献   
993.
Solid state bonding was carried out between commercially pure titanium and 304 stainless steel at 850 °C temperature for 30–150 min under uniaxial load in vacuum. The transition joints were characterized using optical and scanning electron microscopes and revealed the presence of reaction layers in the diffusion zone. The chemical composition of these reaction products was determined by energy dispersive spectroscopy and the presence of phase/phase mixtures σ, -Fe + χ, χ + λ, λ + FeTi + β-Ti and β-Ti were predicted. Their existence was also confirmed by X-ray diffraction technique. The concentration–penetration plots for Ti, Fe, Cr and Ni are obtained from electron probe microanalysis, which also exhibit concentration gaps in the profile indicating formation of intermetallics in the diffusion zone. The width of intermetallic phases attains its maximum for 90 min joining time, then drops and again rises for 150 min bonding time. The maximum bond strength of 76% of that of titanium was achieved for the assemblies processed for 90 min owing to better coalescence of the mating surfaces, though the volume fraction of intermetallics is high.  相似文献   
994.
The competition among wireless data service providers brings in an option for the unsatisfied customers to switch their providers, which is called churning. The implementation of Wireless Local Number Portability (WLNP) is expected to further increase the churn rate (the probability of users switching the provider). However, the existing resource management algorithms for wireless networks fail to fully capture the far-reaching impact of this unforeseen competitiveness. From this perspective, we first formulate noncooperative games between the service providers and the users. A user's decision to leave or join a provider is based on a finite set of strategies. A service provider can also construct its game strategy set so as to maximize their utility (revenue) considering the churn rate. Based on the game theoretic framework, we propose an integrated admission and rate control (ARC) framework for CDMA-based wireless data networks. The admission control is at the session (macro) level while the rate control is at the link layer packet (micro) level. Two admission control modes are considered - one-by-one mode and batch processing mode, in which multiple users are admitted at a time. We show that: 1) for the one-by-one mode, the Nash equilibrium using pure strategy can be established for both under-loaded and fully-loaded systems and 2) for batch processing mode, there is either an equilibrium in pure strategy or a dominant strategy exists for the service provider. Therefore, the providers have clearly defined admission criteria as outcome of the game. Users are categorized into multiple classes and offered differentiated services based on the price they pay and the service degradation they can tolerate. We show that the proposed ARC framework significantly increases the provider's revenue and also successfully offers differentiated QoS to the users.  相似文献   
995.
An adaptive quasi-Newton algorithm for eigensubspace estimation   总被引:1,自引:0,他引:1  
We derive and discuss a new adaptive quasi-Newton eigen-estimation algorithm and compare it with the RLS-type adaptive algorithms and the quasi-Newton algorithm proposed by Mathew et al. (1995) through experiments with stationary and nonstationary data.  相似文献   
996.
Senna (Cassia angustifolia) is widely used in Indian folk medicine for the prevention of various disorders. Herein, we have demonstrated that water extracted arabinogalactan protein (AGP) rich fraction possesses strong antioxidative activity. The AGP rich fraction was analyzed using chemical, chromatographic, and spectroscopic methods. Effect of water extracted polymers on bovine serum albumin spectrum was determined using excitation wavelength of 282 nm. The antioxidant capacity of this fraction was studied by ferric reducing antioxidant power (FRAP) and DPPH radical assays. This polymeric fraction, ≥88% of which gets precipitated with Yariv reagent, consisted mainly of (1→5)-/(1→3,5)-linked α-arabinosyl, (1→3)-/(1→3,6)-linked-galactosyl residues and terminal arabinofuranosyl residues. Its in vitro antioxidant capacity is comparable to that of standard antioxidants. Fluorescence quenching studies furnishes evidence for the interaction of the arabinogalactan protein with bovine serum albumin.  相似文献   
997.
NaA zeolite nanoparticles (seed crystals) of size 50–65 nm were synthesized using water-in-oil (w/o) type emulsions at a considerably low temperature of 65 ± 1°C in a short duration of 2 h. The emulsions were stabilized using non-ionic surfactants e.g. sorbitan monooleate (Span 80), sorbitan monolaurate (Span 20), polyoxyethylene(5)nonylphenylether with ethoxy numbers of 5 (Igepal CO-520) and polyoxyethylene sorbitan monooleate (Tween 80) of hydrophilic-lipophilic balance (HLB) values of 4.3, 8.6, 10 and 15 respectively. Among the surfactants, the intermediate HLB values of 8.6 (Span 20) and 10 (Igepal CO-520) were effective in synthesizing highly dispersible NaA nanoparticles of size 50–65 nm. The membrane prepared hydrothermally in multi-steps at 65 ± 1°C, using the Span 20-derived seed crystals deposited on porous support, showed the formation of high quality interlocked NaA coating. Single gas nitrogen (N2) permeation of the membrane exhibited a permeance value of 1.01 × 10−8 mol m−2 s−1 Pa−1 at ambient temperature (30°C).  相似文献   
998.
An integrated ΔE-E silicon detector telescope using silicon planar technology has been developed. The technology developed is based on standard integrated circuit technology and involves double sided wafer processing. The ΔE and E detectors have been realized in a PIN configuration with a common buried N+ layer. Detectors with ΔE thicknesses of 10, 15 and 25 μm, and E detector with thickness of 300 μm have been fabricated and tested with alpha particles using 238Pu-239Pu dual alpha source. The performance of the detector with ΔE detector of thickness 10 μm and E detector of thickness 300 μm has been studied for identification of charged particles using 12 MeV 7Li+ ion beam on carbon target. The results of these tests demonstrate that the integrated detector telescope clearly separates the charged particles, such as alpha particles, protons and 7Li. Due to good energy resolution of the E detector, discrete alpha groups corresponding to well known states of 15N populated during the reaction could be clearly identified.  相似文献   
999.
Image-based quality monitoring system of limestone ore grades   总被引:1,自引:0,他引:1  
In this study, an image analysis-based ore quality monitoring system was developed. The study was conducted at a limestone mine located in India. The samples were collected based on a stratified random sampling method, and images of these samples were taken in a simulated environment in a laboratory. The image preprocessing and segmentation were performed using different segmentation methods to extract morphological, colour and textural features. A total of 189 features was extracted during this study. Principal components analysis was conducted to reduce the feature vector for modeling purposes. Five principal components, which were extracted from the feature vectors, captured 95% of the total feature variance. A neural network model was used as a mapping function for ore grade prediction. The five principal components were used as input, and four grade attributes of limestone (CaO, Al2O3, Fe2O3 and SiO2) were used as output. The developed model was then used for day to day quality monitoring at 3 different face locations of the mine. Results revealed that this technique can be successfully used for ore grade monitoring at the mine level in a controlled environment.  相似文献   
1000.
Junctions of silver-copper oxide and silver-zinc oxide, respectively were prepared within the pores of diameters, 20 nm, in anodic aluminium oxide membranes. Voltage-current characteristics were measured over the temperature range 373–573 K which showed rectification behaviour. Using the standard equation the difference between the work functions of the metal and the semiconductor was calculated. This showed a variation with the temperature of measurement. This is explained as arising due to the effect of pressure generated as a result of thermal expansion of the metallic phases concerned between the electrodes. This is consistent with the theoretical prediction of Fermi level shifting of the semiconductor within the bandgap as a function of pressure. Dedicated to Prof. C N R Rao  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