全文获取类型
收费全文 | 853篇 |
免费 | 43篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 23篇 |
综合类 | 3篇 |
化学工业 | 236篇 |
金属工艺 | 16篇 |
机械仪表 | 22篇 |
建筑科学 | 11篇 |
矿业工程 | 4篇 |
能源动力 | 69篇 |
轻工业 | 39篇 |
水利工程 | 7篇 |
石油天然气 | 1篇 |
无线电 | 88篇 |
一般工业技术 | 211篇 |
冶金工业 | 73篇 |
原子能技术 | 9篇 |
自动化技术 | 91篇 |
出版年
2024年 | 7篇 |
2023年 | 12篇 |
2022年 | 27篇 |
2021年 | 55篇 |
2020年 | 55篇 |
2019年 | 58篇 |
2018年 | 41篇 |
2017年 | 45篇 |
2016年 | 45篇 |
2015年 | 34篇 |
2014年 | 37篇 |
2013年 | 58篇 |
2012年 | 47篇 |
2011年 | 58篇 |
2010年 | 42篇 |
2009年 | 41篇 |
2008年 | 33篇 |
2007年 | 18篇 |
2006年 | 28篇 |
2005年 | 12篇 |
2004年 | 20篇 |
2003年 | 11篇 |
2002年 | 10篇 |
2001年 | 4篇 |
2000年 | 6篇 |
1999年 | 4篇 |
1998年 | 9篇 |
1997年 | 6篇 |
1996年 | 10篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1993年 | 8篇 |
1992年 | 5篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1972年 | 1篇 |
排序方式: 共有903条查询结果,搜索用时 15 毫秒
41.
P. Dupriez A. Piper A. Malinowski J.K. Sahu M. Ibsen B.C. Thomsen Y. Jeong L.M.B. Hickey M.N. Zervas J. Nilsson D.J. Richardson 《Photonics Technology Letters, IEEE》2006,18(9):1013-1015
We demonstrate a pulsed ytterbium-doped fiber master-oscillator power amplifier source at 1060 nm producing over 300 W of average power in 20-ps pulses at 1-GHz repetition rate. The pulses generated by a gain-switched diode were compressed by a chirped fiber Bragg grating and amplified without any distortion with excellent spectral quality. This fiber master oscillator power amplifier system offers versatility and potential for further power scaling. 相似文献
42.
Polymer electrolyte fuel cells (PEFCs) employ membrane electrolytes for proton transport during the cell reaction. The membrane
forms a key component of the PEFC and its performance is controlled by several physical parameters, viz. water up-take, ion-exchange
capacity, proton conductivity and humidity. The article presents an overview on Nafion membranes highlighting their merits
and demerits with efforts on modified-Nafion membranes.
Energy security refers to various security measures that a given nation, or the global community as a whole, must carryout
to maintain an adequate energy supply 相似文献
43.
44.
Mrutyunjaya Sahu K.K. Khatua S.S. Mahapatra 《Flow Measurement and Instrumentation》2011,22(5):438-446
Most natural rivers and streams consist of two stage channels known as main channel and flood plains. Accurate prediction of discharge in compound open channels is extremely important from river engineering point of view. It helps the practitioners to provide essential information regarding flood mitigation, construction of hydraulic structures and prediction of sediment load so as to plan for effective preventive measures. Discharge determination models such as the single channel method (SCM), the divided channel method (DCM), the coherence method (COHM) and the exchange discharge method (EDM) are widely used; however, they are insufficient to predict discharge accurately. Therefore, an attempt has been made in this work to predict the total discharge in compound channels with an artificial neural network (ANN) and compare with the above models. The mean absolute percentage error with artificial neural networks is found to be consistently low as compared to other models. 相似文献
45.
A high piezoelectric transition temperature is indicated for present orthorhombic samples of lead meta-niobate (PbNb2O6) by the high value of the temperature (Tm) at which the real part (?′) of electrical permittivity peaks. It is 573 to 580°C. The imaginary component (?″) increases sharply at these temperatures. Cooling run after heating to 700°C gives changed values of ?′ and ?″ and Tm. Present work reports impedance spectroscopy (up to 700°C over 20 Hz to 5.5 MHz) and Differential Scanning Calorimetry or DSC on the pure orthorhombic phase, and, for the first time, on the pure rhombohedral phase. DSC shows an endothermic dip across Tm during heating and an exothermic peak during cooling for the orthorhombic sample only. 相似文献
46.
A Sahu 《Canadian Metallurgical Quarterly》1998,139(2):795-798
Leptin (OB protein) reduces food intake by acting at the hypothalamic level. The purpose of the present study was to identify potential targets of leptin signaling in the hypothalamus in ad-lib fed rats. Central administration of leptin (5 microg) for 3 days decreased food intake and body weight gain in association with a decrease in hypothalamic galanin (GAL), melanin-concentrating hormone (MCH), proopiomelanocortin (POMC) and neuropeptide Y (NPY) gene expression and with an increase in neurotensin (NT) gene expression. In pair-fed rats, NPY gene expression was increased and there was no change in either MCH, GAL, POMC or NT gene expression. This study identifies GAL, MCH, POMC and NT as non-NPY targets of leptin signaling and suggests that leptin's action on food intake and body weight is most likely mediated by inhibiting excitatory (e.g. NPY, MCH, GAL, POMC) and stimulating inhibitory (e.g., NT) signals in the feeding circuitry. 相似文献
47.
48.
The concurrent rain and air sampling was conducted for thirteen rain events between the last week of May and end of June 2001. Concentration of total PAHs varied from 84.25 to 777.49 ng/l whereas that in air was in the range of 4.05 to 34.42 ng/m(3). In rainwater the lower molecular weight PAHs (e.g. Phenanthrene, Fluoranthene and Pyrene) were found to be more prominent than the higher molecular weight compounds. The gas phase scavenging ratio (Wg) was found to increase with the molecular weight of the compound. The particle phase scavenging ratio (Wp) values for the more volatile PAHs were generally much higher than those for less volatile PAHs. The higher MW PAHs have Wg values equal to or larger than their Wp values. 相似文献
49.
P.P. Sahu Author Vitae 《Computers & Electrical Engineering》2007,33(2):127-132
This paper presents a design of a high-speed data recovery circuit for non return zero (NRZ) data transmission using delay-locked loop (DLL) with SAW filter. The jitter generation of the circuit is decreased by adjusting the loop gain in DLL whereas surface acoustic wave (SAW) filter with low centered frequency (fc) improves the jitter transfer function of DLL. It is seen that the circuit using SAW filter of fc = 1.24416 GHz and Q = 1000 provides the cut off frequency of about 600 kHz which is ∼10 times lower than that of conventional DLL circuit. 相似文献
50.
An Accurate, Low-Voltage, CMOS Switching Power Supply With Adaptive On-Time Pulse-Frequency Modulation (PFM) Control 总被引:1,自引:0,他引:1
Sahu B. Rincon-Mora G.A. 《IEEE transactions on circuits and systems. I, Regular papers》2007,54(2):312-321
Integrated switching power supplies with multimode control are gaining popularity in state-of-the-art portable applications like cellular phones, personal digital assistants (PDAs), etc., because of their ability to adapt to various loading conditions and therefore achieve high efficiency over a wide load-current range, which is critical for extended battery life. Constant-frequency, pulsewidth modulated (PWM) switching converters, for instance, have poor light-load efficiencies because of higher switching losses while pulse-frequency modulation (PFM) control in discontinuous-conduction mode (DCM) is more efficient at light loads because the switching frequency and associated switching losses are scaled down with load current. This paper presents the design and integrated circuit prototype results of an 83% power efficient 0.5-V 50-mA CMOS PFM buck (step-down) dc-dc converter with a novel adaptive on-time scheme that generates a 27-mV output ripple voltage from a 1.4- to 4.2-V input supply (battery-compatible range). The output ripple voltage variation and steady-state accuracy of the proposed supply was 5 mV (22-27 mV) and 0.6% whereas its constant on-time counterpart was 45 mV (10-55 mV) and 3.6%, respectively. The proposed control scheme provides an accurate power supply while achieving 2%-10% higher power efficiency than conventional fixed on-time schemes with little circuit complexity added, which is critical during light-loading conditions, where quiescent current plays a pivotal role in determining efficiency and battery-life performance 相似文献