全文获取类型
收费全文 | 26289篇 |
免费 | 2332篇 |
国内免费 | 658篇 |
专业分类
电工技术 | 942篇 |
技术理论 | 1篇 |
综合类 | 1226篇 |
化学工业 | 5506篇 |
金属工艺 | 1092篇 |
机械仪表 | 1402篇 |
建筑科学 | 1145篇 |
矿业工程 | 320篇 |
能源动力 | 856篇 |
轻工业 | 3431篇 |
水利工程 | 315篇 |
石油天然气 | 488篇 |
武器工业 | 95篇 |
无线电 | 3084篇 |
一般工业技术 | 4094篇 |
冶金工业 | 2017篇 |
原子能技术 | 264篇 |
自动化技术 | 3001篇 |
出版年
2024年 | 73篇 |
2023年 | 320篇 |
2022年 | 701篇 |
2021年 | 1026篇 |
2020年 | 767篇 |
2019年 | 700篇 |
2018年 | 793篇 |
2017年 | 924篇 |
2016年 | 908篇 |
2015年 | 1143篇 |
2014年 | 1514篇 |
2013年 | 1993篇 |
2012年 | 1992篇 |
2011年 | 2241篇 |
2010年 | 1786篇 |
2009年 | 1763篇 |
2008年 | 1654篇 |
2007年 | 1378篇 |
2006年 | 1111篇 |
2005年 | 787篇 |
2004年 | 612篇 |
2003年 | 509篇 |
2002年 | 430篇 |
2001年 | 323篇 |
2000年 | 300篇 |
1999年 | 296篇 |
1998年 | 551篇 |
1997年 | 408篇 |
1996年 | 259篇 |
1995年 | 210篇 |
1994年 | 200篇 |
1993年 | 192篇 |
1992年 | 135篇 |
1991年 | 117篇 |
1990年 | 108篇 |
1989年 | 109篇 |
1988年 | 74篇 |
1987年 | 67篇 |
1986年 | 64篇 |
1985年 | 81篇 |
1984年 | 75篇 |
1983年 | 49篇 |
1982年 | 45篇 |
1981年 | 47篇 |
1980年 | 47篇 |
1979年 | 39篇 |
1977年 | 55篇 |
1976年 | 83篇 |
1975年 | 41篇 |
1973年 | 33篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
A simple amplitude shift keying (ASK) optical link is demonstrated by using a low-cost self-pulsating laser diode and an envelope detector for a low-cost broadband local area network. A link sensitivity of -22 dBm was achieved at 200 Mbit/s. Because the self-pulsation frequency can be tuned by the bias current, frequency division multiplexing can be simply implemented for multiuser applications 相似文献
102.
103.
Core–shell type nanoparticles of poly(L ‐lactide)/poly(ethylene glycol) (LE) diblock copolymer were prepared by a dialysis technique. Their size was confirmed as 40–70 nm using photon correlation spectroscopy. The 1H‐NMR analysis confirmed the formation of core–shell type nanoparticles and drug loading. The particle size, drug loading, and drug release rate of the LE nanoparticles were slightly changed by the initial solvents that were used. The drug release behavior of LE core–shell type nanoparticles showed an initial burst during the first 12 h and then a sustained release until 100 h. The degradation behavior of LE block copolymer nanoparticles was divided into three phases: the initial rapid degradation phase, the stationary phase, and the rapid degradation phase until complete degradation. It was suggested that lidocaine release kinetics were predominantly governed by the diffusion mechanism in the initial burst phase and after that by both of the diffusion and degradation mechanisms. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2625–2634, 2002 相似文献
104.
AF Minnick MJ Roberts WB Young RM Kleinpell RJ Marcantonio 《Canadian Metallurgical Quarterly》1997,35(4):399-409
OBJECTIVES: Market forces make it essential to know what policies and actions influence patients' reports of hospital services. No studies have examined the role of patient characteristics, labor quality and staff characteristics, nonlabor resources, managerial practices, and employee attitudes within a single investigation. METHODS: The authors collected, simultaneously, data about labor, management and service processes, nonlabor resources, and employee attitudes on 117 nonintensive medical-surgical inpatient units in 17 hospitals selected from a pool of 69 institutions within a metropolitan area by a stratified random sample. Of the 2,595 patients who agreed to participate, 2,051 (79%) completed telephone interviews regarding their experiences with physical care, education, and pain management services within 26 days of hospital discharge. RESULTS: A significant amount of variation in patients' service reports was explained (adjusted R2 = 0.41 physical care, 0.35 pain management, 0.44 education). Although the predictors varied for each service report, patient characteristics, especially those related to personal resources, had a large explanatory role. A labor assignment pattern that could explain why earlier studies found labor quality and staff characteristics to have only a weak role in the prediction of patients' service reports was noted. CONCLUSIONS: The results related to patient characteristics may indicate opportunities to improve care by confronting service design strategies that erroneously rely on a homogeneous patient population. Measurement challenges identified by this study must be addressed to determine the role of labor quantity and staff characteristics. 相似文献
105.
Woodward S.L. Koren U. Miller B.I. Young M.G. Newkirk M.A. Burrus C.A. 《Photonics Technology Letters, IEEE》1992,4(12):1330-1332
A distributed Bragg reflector (DBR) laser tuned by resistive heating is presented. It has a tuning range greater than 10 nm with only a 33% reduction in output power and a 10% increase in linewidth. Its behavior is easily modeled, agreeing well with simple theory 相似文献
106.
GaN buffer and main layers were grown by the conventional hydride vapor phase epitaxy technique using GaCl3 consecutively. The deposited buffer layers were investigated by atomic force microscopy and X-ray analysis. To examine the behavior of the buffer layers at main layer growth temperature, heat treatment was conducted at 900°C. Based on the results of the buffer layer study, GaN thick films were grown at 1050°C. Optimum deposition conditions of buffer layer from the buffer and main layer studies generally coincided. On the φ scanning pattern, the GaN films grown on (0001) Al2 O3 were single-crystalline. Band-edge emission dominated photoluminescence was observed at room temperature. 相似文献
107.
108.
A microprocessor clock generator based on an analog phase-locked loop (PLL) is described for deskewing the internal logic control lock to an external system lock. This PLL is fully generated onto a 1.2-million-transistor microprocessor in 0.8-μm CMOS technology without the need for external components. It operates with a lock range from 5 to 110 MHz. The clock skew is less than 0.1 ns, with a peak-to-peak jitter of less than 0.3 ns for a 50-MHz system clock frequency 相似文献
109.
Young Nam Chun Jen-Shih Chang Alexander A. Berezin J. Mizeraczyk 《Dielectrics and Electrical Insulation, IEEE Transactions on》2007,14(1):119-124
Numerical modelling of the flow velocity fields for the near corona wire electrohydrodynamic (EHD) flow was conducted. Solutions of the steady, two-dimensional momentum equations have been computed for a wire-plate type electrostatic precipitator (ESP). The equations were solved in the conservative finite-difference form on a fine uniform rectilinear grid of sufficient resolution to accurately capture the momentum boundary layers. The numerical procedure for the differential equations was used by SIMPLEST algorithm. The CFD code coupled with Poisson's electric field, ion transport equations and the momentum equation with electric body force, was used for the numerical simulation with the Chen-Kim k-epsiv turbulent model. The numerical results show that EHD secondary flow was clearly visible in the downstream regions of the corona wire despite the low Reynolds number for the electrode (Re cw=12.4). Secondary flow vortices caused by the EHD increases with increasing discharge current or EHD number, hence pressure drop of ESP increases 相似文献
110.
本文分析了校园网上商店建设的背景,提出了建设校园网上商店的必要性。运用ASP.net技术,提出了校园网上商店的商业模式分析、体系结构、平台设计方案和实现方法。 相似文献