全文获取类型
收费全文 | 19327篇 |
免费 | 857篇 |
国内免费 | 139篇 |
专业分类
电工技术 | 325篇 |
综合类 | 32篇 |
化学工业 | 4252篇 |
金属工艺 | 599篇 |
机械仪表 | 643篇 |
建筑科学 | 371篇 |
矿业工程 | 47篇 |
能源动力 | 1379篇 |
轻工业 | 1188篇 |
水利工程 | 152篇 |
石油天然气 | 84篇 |
武器工业 | 1篇 |
无线电 | 2400篇 |
一般工业技术 | 4388篇 |
冶金工业 | 1456篇 |
原子能技术 | 175篇 |
自动化技术 | 2831篇 |
出版年
2024年 | 103篇 |
2023年 | 422篇 |
2022年 | 1009篇 |
2021年 | 1167篇 |
2020年 | 918篇 |
2019年 | 951篇 |
2018年 | 1241篇 |
2017年 | 971篇 |
2016年 | 946篇 |
2015年 | 608篇 |
2014年 | 852篇 |
2013年 | 1531篇 |
2012年 | 899篇 |
2011年 | 1081篇 |
2010年 | 864篇 |
2009年 | 822篇 |
2008年 | 726篇 |
2007年 | 582篇 |
2006年 | 478篇 |
2005年 | 372篇 |
2004年 | 277篇 |
2003年 | 248篇 |
2002年 | 194篇 |
2001年 | 179篇 |
2000年 | 173篇 |
1999年 | 170篇 |
1998年 | 293篇 |
1997年 | 244篇 |
1996年 | 221篇 |
1995年 | 172篇 |
1994年 | 158篇 |
1993年 | 153篇 |
1992年 | 103篇 |
1991年 | 130篇 |
1990年 | 101篇 |
1989年 | 96篇 |
1988年 | 79篇 |
1987年 | 90篇 |
1986年 | 76篇 |
1985年 | 88篇 |
1984年 | 75篇 |
1983年 | 72篇 |
1982年 | 61篇 |
1981年 | 70篇 |
1980年 | 48篇 |
1979年 | 32篇 |
1978年 | 27篇 |
1977年 | 26篇 |
1976年 | 35篇 |
1971年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
In wireless communications, both control information and payload (user-data) are concurrently transmitted and required to be successfully recovered. This paper focuses on block-level detection, which is applicable for detecting transmitted control information, particularly when this information is selected or chosen from a finite set of information that are known at both transmitting and receiving devices. Using an orthogonal frequency division multiplexing architecture, this paper investigates and evaluates the performance of a time-domain decision criterion in comparison with a form of Maximum Likelihood (ML) estimation method. Unlike the ML method, the proposed time-domain detection technique requires no channel estimation as it uses the correlation (in the time-domain) that exists between the received and the transmitted selective information as a means of detection. In comparison with the ML method, results show that the proposed method offers improved detection performance, particularly when the control information consists of at least 16. However, the implementation of the proposed method requires a slightly increased number of mathematical computations. 相似文献
962.
Sanjay Kumar Ankur Jain Hiroki Miyaoka Takayuki Ichikawa Yoshitsugu Kojima 《International Journal of Hydrogen Energy》2017,42(27):17178-17183
Bis(cyclopentadienyl) nickel II is one of the best precursors of nickel catalyst which remarkably improved the hydrogen absorption-desorption of Mg–MgH2 system. The X-ray photoelectron spectroscopy (XPS) and Furrier Transformed Infrared Spectroscopy (FTIR) analyses revealed that bis (cyclopentadienyl) nickel II decomposed into metallic nickel during ball milling with MgH2. The nickel thus formed has homogeneously doped over the Mg - MgH2 surface. The Ni-doped Mg-MgH2 have shown the excellent catalytic effect on hydrogen absorption-desorption. The catalyzed MgH2 could desorb hydrogen below 225 °C (Tonset) under Ar flow, and absorb hydrogen at 50 °C under 1.5 MPa H2 pressure. The hydrogen absorption-desorption temperatures are remarkably decreased as compared to the uncatalyzed Mg-MgH2 system under the identical experimental conditions. 相似文献
963.
Gaurav Kumar Pal S. Bharath Kumar P. Prabhasankar P. V. Suresh 《Sensing and Instrumentation for Food Quality and Safety》2017,11(3):939-947
Incorporating exogenous proteins into food products is a better practice for improving nutritional attributes of food commodities. In the search for a way to improve the product and nutritional quality of noodles, this study was aimed to evaluate the impact of the incorporation of poultry based ingredients egg yolk powder (EYP) and chicken mincemeat (CMM) in noodles at different levels (5, 10 and 15%, w/w). The incorporated noodles were subjected to evaluation of the cooking, texture, colour, sensory and microstructure properties. The results showed that the incorporation of poultry based food ingredient types and amount influence the nutritional content of noodles. Simultaneously, poultry based ingredients incorporated noodles showed the acceptable firmness and colour charatertistics. Scanning electron micrograph of the incorporated noodles showed the gelatinized starch granules enveloped by protein matrix, and also indicating a better structure as compared to the control. The sensory profile of incorporated noodles was showed significant (p?≤?0.05) high overall quality. The result of this study showed that 10% (w/w) EYP and 15% (w/w) CMM incorporated noodles showed a better overall noodles quality attributes (texture, colour, sensory and microstructure). The results also provide ideas about the inclusion of the appropriate levels of poultry based ingredients (EYP and CMM) with a better sensory and nutritional profile. Therefore, this study may be useful in the food industry for the production of poultry based ingredients noodles with enhanced quality characteristics. 相似文献
964.
P Sharath Kumar 《Sadhana》2017,42(8):1309-1316
Multiple-load induction cooking applications are suitable used when multi-output inverters or multi-inverters are needed for multiple-load operation. Some common approaches and modifications are needed in inverter configuration for multiple-load application. This paper presents an inverter configuration with two loads by using pulse density modulation control technique. It allows the output power control of each load independently with constant switching frequency and constant duty ratio. The pulse density modulation control technique is obtained using phase on–off control between two legs of the inverter to reduce acoustic noise. The two-load three-leg inverter configuration provides reduction of the component count for extension of multiple loads. The control technique provides a wide range of output power control. In addition, it can achieve efficient and stable zero voltage switching operation in the whole load range. The proposed control scheme is simulated and experimentally verified with two-load inverter configuration. 相似文献
965.
Ashwani Kumar Tiwari Prasoon Kumar Singh Mukesh Kumar Mahato 《Mine Water and the Environment》2017,36(4):532-541
This study was carried out in the West Bokaro coalfield area of the Jharkhand state of India to assess water quality for drinking and domestic purposes. Thirty mine water samples were collected from opencast and underground mines, and concentrations of Al, As, Ba, Cr, Cu, Fe, Mn, Ni, Se, and Zn were determined using ICP-MS. Spatial distribution maps were prepared using GIS software so that the quality of the mine water could be easily understood. Metal concentrations were higher in the pre-monsoon season than in the post-monsoon season, irrespective of location, but there were more significant seasonal variations in the opencast mine water than in the underground mine water. The concentrations of Al, Ba, Fe, Mn, and Ni exceeded the desirable as well as the permissible drinking water limits in both seasons. The quality of the surface water as well as the groundwater in the region may be adversely affected by the high metal concentrations in this mine water. 相似文献
966.
Murugan Sumathy Subrata Kumar Datta 《Journal of Infrared, Millimeter and Terahertz Waves》2017,38(5):538-547
A single-section slow-wave structure for a W-band folded-waveguide traveling-wave tube with operating bandwidth of around 4% was designed for delivering the output power of 50 W at the operating voltage of 13.5 kV and operating beam current of 80 mA. The design was carried out using analytical formulations and 3D electromagnetic simulations. The beam-wave interaction analysis was carried out using large signal Lagrangian analysis and particle-in-cell simulation. The folded-waveguide slow-wave structure along with input-output couplers and RF windows were fabricated. Cold test measurements were carried out for dispersion characteristics of the slow-wave structure and voltage standing-wave ratio and insertion loss characteristics of the RF window. The measured cold circuit parameters show close agreement with the analysis. 相似文献
967.
Soma Maji Amir Raza Subhani Bijay Kumar Show Joydeep Maity 《Journal of Materials Engineering and Performance》2017,26(7):3058-3070
A systematic study has been carried out to ascertain the effect of cooling rate on structure and mechanical properties of eutectoid steel subjected to a novel incomplete austenitization-based cyclic heat treatment process up to 4 cycles. Each cycle consists of a short-duration holding (6 min) at 775 °C (above A1) followed by cooling at different rates (furnace cooling, forced air cooling and ice-brine quenching). Microstructure and properties are found to be strongly dependent on cooling rate. In pearlitic transformation regime, lamellar disintegration completes in 61 h and 48 min for cyclic furnace cooling. This leads to a spheroidized structure possessing a lower hardness and strength than that obtained in as-received annealed condition. On contrary, lamellar disintegration does not occur for cyclic forced air cooling with high air flow rate (78 m3 h?1). Rather, a novel microstructure consisting of submicroscopic cementite particles in a ‘interweaved pearlite’ matrix is developed after 4 cycles. This provides an enhancement in hardness (395 HV), yield strength (473 MPa) and UTS (830 MPa) along with retention of a reasonable ductility (%Elongation = 19) as compared to as-received annealed condition (hardness = 222 HV, YS = 358 MPa, UTS = 740 MPa, %Elongation = 21). 相似文献
968.
The objective of this research was to study the performance and emission characteristics of using waste plastic pyrolysis oil in diesel engine without any engine modification. The engine used in this study is a four-stroke single-cylinder naturally aspirated diesel engine (compression ignition). In the present work, the engine fuelled with blends of diesel fuel (DF) with plastic oil in the ratio of 90:10 (blend10%), 80:20 (blend20%), 70:30 (blend30%), and 50:50 (blend50%) are experimentally measured the efficiencies and emissions, analysed the performance, and compared results with that of DF. 相似文献
969.
In this investigation, biogas (BG) was used as an alternative fuel in a single-cylinder, four-stroke, air-cooled, direct injection (DI) diesel engine that was operated on a dual fuel mode. Biogas was produced from a non-edible seed de-oiled cake-pongamia pinnata (Karanja), which was collected from the biodiesel industries. The BG was inducted along with the air in suction of the engine at four different flow rates varying from 0.3?kg/h to 1.2?kg/h in steps of 0.3?kg/h. The investigation results revealed that BG inducted at a flow rate of 0.9?kg/h gives better combustion characteristics of engine behaviour than those of other flows throughout the engine operation. The ignition delay (ID) and combustion duration of the engine run by dual fuel operation at a BG flow rate of 0.9?kg/h were found to be longer by about 2 °CA and 2.9 °CA, respectively, in comparison with diesel at full load. The cylinder peak pressure was found to be overall higher by about 11?bar than that of diesel at full load. 相似文献
970.
Salleh Emee Marina Zuhailawati Hussain Ramakrishnan Sivakumar Dhindaw Brij Kumar 《Metallurgical and Materials Transactions A》2017,48(5):2519-2528
Metallurgical and Materials Transactions A - Magnesium (Mg) and its alloys have shown potential for use in the biomedical industry due to their excellent biological performance and biodegradability... 相似文献