全文获取类型
收费全文 | 15098篇 |
免费 | 1345篇 |
国内免费 | 33篇 |
专业分类
电工技术 | 195篇 |
综合类 | 28篇 |
化学工业 | 3989篇 |
金属工艺 | 580篇 |
机械仪表 | 769篇 |
建筑科学 | 236篇 |
矿业工程 | 5篇 |
能源动力 | 673篇 |
轻工业 | 1340篇 |
水利工程 | 44篇 |
石油天然气 | 12篇 |
武器工业 | 2篇 |
无线电 | 2593篇 |
一般工业技术 | 3494篇 |
冶金工业 | 835篇 |
原子能技术 | 131篇 |
自动化技术 | 1550篇 |
出版年
2024年 | 15篇 |
2023年 | 194篇 |
2022年 | 286篇 |
2021年 | 486篇 |
2020年 | 350篇 |
2019年 | 398篇 |
2018年 | 522篇 |
2017年 | 540篇 |
2016年 | 640篇 |
2015年 | 566篇 |
2014年 | 770篇 |
2013年 | 1019篇 |
2012年 | 1121篇 |
2011年 | 1335篇 |
2010年 | 990篇 |
2009年 | 966篇 |
2008年 | 805篇 |
2007年 | 687篇 |
2006年 | 581篇 |
2005年 | 480篇 |
2004年 | 466篇 |
2003年 | 458篇 |
2002年 | 361篇 |
2001年 | 281篇 |
2000年 | 295篇 |
1999年 | 266篇 |
1998年 | 375篇 |
1997年 | 208篇 |
1996年 | 186篇 |
1995年 | 115篇 |
1994年 | 109篇 |
1993年 | 79篇 |
1992年 | 84篇 |
1991年 | 47篇 |
1990年 | 55篇 |
1989年 | 53篇 |
1988年 | 31篇 |
1987年 | 28篇 |
1986年 | 30篇 |
1985年 | 16篇 |
1984年 | 23篇 |
1983年 | 23篇 |
1981年 | 13篇 |
1980年 | 11篇 |
1978年 | 7篇 |
1977年 | 15篇 |
1976年 | 20篇 |
1974年 | 7篇 |
1971年 | 8篇 |
1970年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
Sung D. Kwon Sung J. Song Dong H. Bae Young Z. Lee 《Journal of Mechanical Science and Technology》2002,16(9):1084-1092
The frequency dependency of Rayleigh surface wave is investigated indirectly by measuring the angular dependency of the backward
radiation of the incident ultrasonic wave in two kinds of degraded specimens by scuffing or corrosion. Then, the frequency
dependency is compared with the residual stress distribution or the corrosion-fatigue characteristics for the scuffed or corroded
specimens, respectively. The width of the backward radiation profile increases with the increase of the variation in residual
stress distribution for the scuffed specimens. In the corroded specimens, the profile width decreases with the increase of
the effective aging layer thickness and is inversely proportional to the exponent, m, in the Paris’ law that can predict the
crack size increase due to fatigue. The result observed in this study demonstrates high potential of backward radiated ultrasound
as a tool for nondestructive evaluation of subsurface gradient of material degradation generated by scuffing or corrosion. 相似文献
12.
13.
The transmission mode of holographic polymer‐dispersed liquid crystals (HPDLCs) was developed an under electric field. It is reported that orientation of LC molecules under an electric field induces orientation of oligomer molecules giving rise to low off‐state diffraction and small grating shrinkage. Copyright © 2005 Society of Chemical Industry 相似文献
14.
Erv J. Kuhlmann Dick Y. Jung Richard P. Guptill Charles A. Dyke Hyung K. Zang 《Fuel》1985,64(11):1552-1557
The presence of hydroaromatic, hydrogen donor components in a coal-derived solvent is one of the more important factors in the successful operation of a non-catalytic coal liquefaction process. Various hydrogen donor species present in a hydrogenated creosote oil have been identified. Their rate of disappearance under conditions that are consistent with a short residence time coal liquefaction process has been used to rank the reactivities of the various hydrogen donors. 1,2,3,10b-Tetrahydrofluoranthene was found to be an exceptional donor while 4,5-dihydropyrene, the hexahydropyrenes and 9,10-dihydrophenanthrene were found to be quite active. Sym.-octahydrophenanthrene and 2a,3,4,5-tetrahydroacenaphthene exhibited moderate activity. Tetralin and the four methyltetralin isomers were found to be unreactive under the coal liquefaction conditions employed. 相似文献
15.
H. M. Park M. C. Sung 《International journal for numerical methods in engineering》2004,60(12):1949-1968
The Karhunen–Loève Galerkin procedure is employed to solve an inverse radiation problem of determining the time‐varying strength of a heat source, which mimics flames in a furnace, from temperature measurements in three‐dimensional participating media where radiation and conduction occur simultaneously. The inverse radiation problem is solved through the minimization of a performance function, which is expressed by the sum of square residuals between calculated and observed temperature, using a conjugate gradient method. Through the Karhunen–Loève Galerkin procedure, one can represent the system dynamics with a minimum degree of freedom, and consequently the amount of computation required in the solution of the inverse problem is reduced drastically when the present technique is adopted. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
16.
Design and practical implementation of multifrequency RF front ends using direct RF sampling 总被引:1,自引:0,他引:1
Psiaki M.L. Powell S.P. Hee Jung Kintner P.M. 《Microwave Theory and Techniques》2005,53(10):3082-3089
The use of direct RF sampling has been explored as a means of designing multifrequency RF front ends. Such front ends will be useful to multifrequency RF applications such as global navigation satellite system receivers that use global positioning system (GPS) L1, L2, and L5 signals and Galileo signals. The design of a practical multifrequency direct RF sampling front end is dependent on having an analog-to-digital converter whose input bandwidth accommodates the highest carrier frequency and whose maximum sampling frequency is more than twice the cumulative bandwidth about the multiple carrier signals. The principle of direct RF sampling is used to alias all frequency bands of interest onto portions of the Nyquist bandwidth that do not overlap. This paper presents a new algorithm that finds the minimum sampling frequency that avoids overlap. This design approach requires a multifrequency bandpass filter for the frequency bands of interest. A prototype front end has been designed, built, and tested. It receives a GPS coarse/acquisition code at the L1 frequency and GPS antispoofing precision code at both L1 and L2. Dual-frequency signals with received carrier-to-noise ratios in excess of 52 dB-Hz have been acquired and tracked using this system. 相似文献
17.
Injun Lee Taeseong Jung Junggi Kim Suho Ro Chulsu Kim Yeji Lee Youngmi Kim Juhyun Lee Misook Kang 《Journal of Industrial and Engineering Chemistry》2008,14(6):869-873
This study focuses on the relationship between photo-catalytic performance and optical property over Si-incorporated TiO2. The Si-incorporated TiO2 particles exhibited a pure structure of anatase having a particle size of less than 20 nm and surface area of more than 190 m2/g. The absorbance did not shift to a higher wavelength in spite of the incorporation of the Si ions, but the intensity of the photoluminescence (PL) curve was the smallest in the case of the 2.0 mol% Si-TiO2, which was related to the recombination between the excited electrons and holes. Based on these results, the photodecomposition of methyl orange in the liquid reaction was enhanced over the 2.0 mol% Si-incorporated TiO2 compared with that over pure TiO2: Methyl orange at 10.0 ppm was completely decomposed after 100 min when 1.0 g of the 2.0 mol% Si-incorporated TiO2 was used. 相似文献
18.
An experimental investigation was carried out to examine the tribological behavior of NAO (non-asbestos organic) type brake linings containing different volume ratios of graphite and antimony trisulfide (Sb2S3). A scale dynamometer was used for friction tests and particular emphases were given to the effect of applied pressure, sliding speed, and temperature on the coefficient of friction according to the relative amounts of the two solid lubricants. Results showed that the brake linings with both solid lubricants exhibited better friction stability and less speed sensitivity than the friction materials containing a single solid lubricant. In particular, the brake lining containing higher concentrations of graphite showed better fade resistance than others during high-temperature friction test. 相似文献
19.
ZnO thin film was deposited on various metal electrodes by reactive sputtering, and c-axis preferred orientation of the film has been studied. ZnO, which has high piezoelectricity, is promising for oscillators or filter devices such as surface acoustic wave (SAW) device, gas sensor, and film bulk acoustic resonator (FBAR). But, for the application of ZnO film for these devices, the film should be grown with c-axis normal to the electrode. In this study, Pt, Al, and Au were deposited on Si wafer, and the surface roughness and crystal structure of the ZnO film on the electrode were investigated using AFM, scanning electron microscopy (SEM), and X-ray diffraction (XRD). Columnar structures of ZnO films were grown with c-axis normal to all electrodes, and among them Pt electrode showed the highest preferred orientation of ZnO film. 相似文献
20.
Youngjean Jung Panayiotis Papadopoulos R. O. Ritchie 《International journal for numerical methods in engineering》2004,60(2):429-460
This work concerns the micromechanical constitutive modelling, algorithmic implementation and numerical simulation of polycrystalline superelastic alloys under multiaxial loading. The model is formulated in finite deformations and incorporates the effect of texture. The numerical implementation is based on the constrained minimization of the Helmholtz free energy with dissipation. Simulations are conducted for thin tubes of Nitinol under tension–torsion, as well as for a simplified model of a biomedical stent. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献