全文获取类型
收费全文 | 28932篇 |
免费 | 2423篇 |
国内免费 | 1105篇 |
专业分类
电工技术 | 1555篇 |
技术理论 | 3篇 |
综合类 | 1615篇 |
化学工业 | 4862篇 |
金属工艺 | 1305篇 |
机械仪表 | 1472篇 |
建筑科学 | 2033篇 |
矿业工程 | 582篇 |
能源动力 | 866篇 |
轻工业 | 2077篇 |
水利工程 | 478篇 |
石油天然气 | 1355篇 |
武器工业 | 184篇 |
无线电 | 3684篇 |
一般工业技术 | 3988篇 |
冶金工业 | 2215篇 |
原子能技术 | 329篇 |
自动化技术 | 3857篇 |
出版年
2024年 | 93篇 |
2023年 | 458篇 |
2022年 | 780篇 |
2021年 | 1251篇 |
2020年 | 874篇 |
2019年 | 807篇 |
2018年 | 908篇 |
2017年 | 865篇 |
2016年 | 842篇 |
2015年 | 1057篇 |
2014年 | 1361篇 |
2013年 | 1594篇 |
2012年 | 1784篇 |
2011年 | 1962篇 |
2010年 | 1617篇 |
2009年 | 1562篇 |
2008年 | 1527篇 |
2007年 | 1405篇 |
2006年 | 1365篇 |
2005年 | 1165篇 |
2004年 | 836篇 |
2003年 | 786篇 |
2002年 | 745篇 |
2001年 | 624篇 |
2000年 | 629篇 |
1999年 | 662篇 |
1998年 | 916篇 |
1997年 | 714篇 |
1996年 | 608篇 |
1995年 | 461篇 |
1994年 | 374篇 |
1993年 | 317篇 |
1992年 | 225篇 |
1991年 | 164篇 |
1990年 | 164篇 |
1989年 | 179篇 |
1988年 | 107篇 |
1987年 | 70篇 |
1986年 | 67篇 |
1985年 | 62篇 |
1984年 | 49篇 |
1983年 | 45篇 |
1982年 | 51篇 |
1981年 | 33篇 |
1980年 | 37篇 |
1979年 | 24篇 |
1977年 | 43篇 |
1976年 | 64篇 |
1975年 | 16篇 |
1973年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 499 毫秒
61.
The ring shape is a good solution to the study of the magnetization processes of magnetic materials because demagnetizing fields are easily avoided. However, when small samples are investigated, the magnitude of the field applied is necessarily limited by the low number of primary winding turns, and by the cross section of the wire itself. The use of sequential-type techniques for high current supply allows this problem to be avoided. One-cycle power production from the 50 Hz AC-line voltage is a simple example of such techniques. An electronic device designed around a commercial integrated circuit is described. A full period of current of 20-ms duration is applied to the load with a magnitude ranging from 0 to 100 A. Magnetization parameters of soft polycrystalline ring ceramics approaching the saturation region are studied as an application. The fitness to measure such characteristic parameters as saturation magnetization and magnetic hardness is shown 相似文献
62.
63.
64.
65.
Enhanced light output in nitride-based light-emitting diodes by roughening the mesa sidewall 总被引:1,自引:0,他引:1
Chia-Feng Lin Zhong-Jie Yang Jing-Hui Zheng Jing-Jie Dai 《Photonics Technology Letters, IEEE》2005,17(10):2038-2040
In this letter, we will report on a nitride-based light emitting diode with a mesa sidewall roughening process that increases light output power. The fabricated GaN-based light-emitting diode (LED) wafers were first treated through a photoelectrochemical (PEC) process. The Ga/sub 2/O/sub 3/ layers then formed around the GaN : Si n-type mesa sidewalls and the bottoms mesa etching regions. Selective wet oxidation occurred at the mesa sidewall between the p- and the n-type GaN interface. The light output power of the PEC treated LED was seen to increase by about 82% which was caused by a reduced index reflectance of GaN-Ga/sub 2/O/sub 3/-air layers, by a rough Ga/sub 2/O/sub 3/ surface, by a microroughening of the GaN sidewall surface, and by a selective oxidation step profile of the mesa sidewall that increases the light-extraction efficiency from the mesa sidewall direction. Consequently, this wet PEC treated process is suitable for high powered nitride-based LEDs lighting applications. 相似文献
66.
In "Stationary distributions for the random waypoint mobility model" (TMC, Vol. 3, No, 1), Navidi and Camp find the stationary distribution of the random waypoint model, with or without pause on a rectangular area. In this short note, we show that, under the stationary regime, speed and location are independent. 相似文献
67.
O Bernard B Chachuat A Hélias B Le Dantec B Sialve J-P Steyer L Lardon P Neveu S Lambert J Gallop M Dixon P Ratini A Quintabà S Frattesi J M Lema E Roca G Ruiz J Rodriguez A Franco P Vanrolleghem U Zaher D J W De Pauw K De Neve K Lievens D Dochaine O Schoefs H Fibrianto R Farina V Alcaraz Gonzalez V Gonzalez Alvarez P Lemaire J A Martinez F Esandi O Duclaud J F Lavigne 《Water science and technology》2005,52(1-2):457-464
The TELEMAC project brings new methodologies from the Information and Science Technologies field to the world of water treatment. TELEMAC offers an advanced remote management system which adapts to most of the anaerobic wastewater treatment plants that do not benefit from a local expert in wastewater treatment. The TELEMAC system takes advantage of new sensors to better monitor the process dynamics and to run automatic controllers that stabilise the treatment plant, meet the depollution requirements and provide a biogas quality suitable for cogeneration. If the automatic system detects a failure which cannot be solved automatically or locally by a technician, then an expert from the TELEMAC Control Centre is contacted via the internet and manages the problem. 相似文献
68.
Christian Ligoure Michel Cloitre Christille Le Chatelier Fabrice Monti 《Polymer》2005,46(17):6402-6410
A remarkable correlation exists between the degree of expansion of polyurethane foams and the structure of the reacting premixes. Polyurethane foams obtained from reacting premixes containing microemulsions are highly expanded. The expansion rate is proportional to the volume fraction of microemulsion in the premix. The stability of premixes with and without microemulsion is completely different suggesting distinct creaming mechanisms. We apply this idea to synthesize polyurethane foams from microemulsions successfully. This approach can be used to rationalize the design of polyurethane formulations leading to highly expanded foams. 相似文献
69.
A high‐melt‐strength polypropylene (HMSPP) was prepared using a twin‐screw reactive extruder from a commercial isotactic polypropylene through two stages, first, maleic anhydride is grafted to polypropylene to obtain a maleic anhydride‐grafted polypropylene (PP‐g‐MA), and then the grafted polymer is reacted with epoxy to extend the branched chain. Fourier transformed infrared spectroscopy indicated that maleic anhydride was grafted on polypropylene and reacted with epoxy. Melt flow rate and sag resistance test showed that the melt strength of the HMSPP improved considerably. Differential scanning calorimetry test showed that the long chain branches (LCBs) act as a nucleating agent in the crystallization of the HMSPP, which leads to a high crystallization temperature and crystallinity. Furthermore, the LCB efficiency of the HMSPP can also be calculated by analyzing its rheological property. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers 相似文献
70.
N. Hémono J. Rocherullé M. Le Floch B. Bureau P. Bénard-Rocherullé 《Journal of Materials Science》2006,41(2):445-453
The glass forming region in the B2O3-Al2O3-Y2O3 composition diagram has been determined by a melting and quenching procedure at temperatures up to 1800°C. Different physical
characteristics (density, coefficient of thermal expansion, glass transition and crystallization peak temperatures) have been
determined for a 35B2O3-40Al2O3-25Y2O3 glass composition (in mol.%). By using a predictive model and some NMR structural data, different elastic moduli (Young's
modulus, bulk modulus, shear modulus and Poisson's ratio) have been calculated. The devitrification behaviour has also been
studied. Internal crystallization is the dominant mechanism and a new (Y, Al)BO3 ternary phase has been characterized by X-ray powder diffraction. The temperature and time nucleation dependence have been
determined from DTA experiments as well as the crystallization kinetics (i.e. the Avrami exponent and the activation energy
for crystal growth). 相似文献