全文获取类型
收费全文 | 433762篇 |
免费 | 44012篇 |
国内免费 | 19217篇 |
专业分类
电工技术 | 26405篇 |
技术理论 | 33篇 |
综合类 | 27978篇 |
化学工业 | 78844篇 |
金属工艺 | 23653篇 |
机械仪表 | 27100篇 |
建筑科学 | 34156篇 |
矿业工程 | 12941篇 |
能源动力 | 12112篇 |
轻工业 | 31947篇 |
水利工程 | 7981篇 |
石油天然气 | 24728篇 |
武器工业 | 3853篇 |
无线电 | 50486篇 |
一般工业技术 | 53878篇 |
冶金工业 | 19644篇 |
原子能技术 | 4331篇 |
自动化技术 | 56921篇 |
出版年
2024年 | 1731篇 |
2023年 | 6142篇 |
2022年 | 11053篇 |
2021年 | 15890篇 |
2020年 | 12997篇 |
2019年 | 12302篇 |
2018年 | 13492篇 |
2017年 | 15350篇 |
2016年 | 14324篇 |
2015年 | 19148篇 |
2014年 | 23106篇 |
2013年 | 27663篇 |
2012年 | 28136篇 |
2011年 | 29899篇 |
2010年 | 27279篇 |
2009年 | 26095篇 |
2008年 | 25292篇 |
2007年 | 24240篇 |
2006年 | 24457篇 |
2005年 | 21079篇 |
2004年 | 14813篇 |
2003年 | 13400篇 |
2002年 | 13537篇 |
2001年 | 11864篇 |
2000年 | 10809篇 |
1999年 | 10611篇 |
1998年 | 7801篇 |
1997年 | 6589篇 |
1996年 | 6121篇 |
1995年 | 5057篇 |
1994年 | 4188篇 |
1993年 | 2962篇 |
1992年 | 2416篇 |
1991年 | 1799篇 |
1990年 | 1336篇 |
1989年 | 1056篇 |
1988年 | 841篇 |
1987年 | 582篇 |
1986年 | 446篇 |
1985年 | 295篇 |
1984年 | 198篇 |
1983年 | 135篇 |
1982年 | 156篇 |
1981年 | 112篇 |
1980年 | 86篇 |
1979年 | 41篇 |
1978年 | 7篇 |
1973年 | 4篇 |
1959年 | 21篇 |
1951年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
61.
Ying Ding Chunqing Wang Yanhong Tian Binbin Zhang 《Metallurgical and Materials Transactions A》2006,37(12):1017-1025
in-situ transmission electron microscopy (TEM) tensile tests on as-cast and aged 63Sn37Pb solder alloys were conducted, and the fracture
behavior in nanometer scale ahead of the crack tip was inspected and discussed. Results show that the fracture was completed
by connecting the discontinuous cracks or voids. Dislocation behavior was concentrated along the grain boundaries for as-cast
samples, and displayed mainly as dislocation climb. The crack was intergranular dominated under the lower strain rate. While
remarkable mutual dislocation emission was detected in the aged solder. Transgranular cracks were dominant in the fractured
area, and they propagated by linking up with the nanometer scale cracks ahead of the crack tips under the effective promotion
of the inverse dislocation emission. At the same time, the partial interphase or intergranular cracks in the thinned area
were also found. Under this condition, a new critical stress intensity factor K
c
′ to define the mutual dislocation emission was proposed. 相似文献
62.
The dynamic response of highway bridges subjected to moving truckloads has been observed to be dependent on (1) dynamic characteristics of the bridge; (2) truck configuration, speed, and lane position on the bridge; and (3) road surface roughness profile of the bridge and its approach. Historically, truckloads were measured to determine the load spectra for girder bridges. However, truckload measurements are either made for a short period of time [for example, weigh-in-motion (WIM) data] or are statistically biased (for example, weigh stations) and cost prohibitive. The objective of this paper is to present results of a 3D computer-based model for the simulation of multiple trucks on girder bridges. The model is based on the grillage approach and is applied to four steel girder bridges tested under normal truck traffic. Actual truckload data collected using a discrete bridge WIM system are used in the model. The data include axle loads, truck gross weight, axle configuration, and statistical data on multiple presence (side by side or following). The results are presented as a function of the static and dynamic stresses in each girder and compared with code provisions for dynamic load factor. The study provides an alternate method for the development of live-load models for bridge design and evaluation. 相似文献
63.
BaMgAl10O17∶Eu2 (BAM) was prepared in the microemulsion system and its phase behavior was studied. There exists a small region in the reverse microemulsion system where the dispersed particles are of spherical form. In this way, BAM blue phosphor with good dispersion can be synthesized. The microemulsion phase diagrams of the pseudo-ternary system (Triton X-100/cosurfactant-oil-BAM brine) were first established intuitively by the dilution method. The microstructure of microemulsions was determined through eyeballing, conductance technique, and polar optical microscopy. Its phase behavior is affected by various factors, such as temperature (room temperature, 30, 40 ℃), oil, surfactants, and cosurfactants in microemulsions. According to the phase diagrams, the microemulsion system of Triton X-100/1-hexanol-hexane-BAM brine was chosen to prepare the precursor. The BAM phosphor can be obtained via sintering the precursor at a comparatively low temperature. The phosphors were characterized by XRD and vacuum ultraviolet (VUV) spectra. 相似文献
64.
Zhang Z.G. Chan S.C. Tsui K.M. 《Circuits and Systems II: Express Briefs, IEEE Transactions on》2008,55(6):576-580
This paper proposes a new Kalman-filter-based recursive frequency estimator for discrete-time multicomponent sinusoidal signals whose frequencies may be time-varying. The frequency estimator is based on the linear prediction approach and it employs the Kalman filter to track the linear prediction coefficients (LPCs) recursively. Frequencies of the sinusoids can then be computed using the estimated LPCs. Due to the coloredness of the linear prediction error, an iterative algorithm is employed to estimate the covariance matrix of the prediction error and the LPCs alternately in the Kalman filter in order to improve the tracking performance. Simulation results show that the proposed Kalman-filter-based iterative frequency estimator can achieve better tracking results than the conventional recursive least-squares-based estimators. 相似文献
65.
66.
Xue‐Bing Zhao Lei Wang De‐Hua Liu 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(6):950-956
Previous work has shown that the enzymatic hydrolysis of sugarcane bagasse could be greatly enhanced by peracetic acid (PAA) pretreatment. There are several factors affecting the enzymatic digestibility of the biomass, including lignin and hemicelluloses content, cellulose crystallinity, acetyl group content, accessible surface area and so on. The objective of this work is to analyze the mechanism of the enhancement of enzymatic digestibility caused by PAA pretreatment. Delignification resulted in an increase of the surface area and reduction of the irreversible absorption of cellulase, which helped to increase the enzymatic digestibility. The Fourier transform infrared (FTIR) spectrum showed that the absorption peaks of aromatic skeletal vibrations were weakened or disappeared after PAA pretreatment. However, the infrared crystallization index (N.O'KI) was increased. X‐ray diffraction (XRD) analysis indicated that the crystallinity of PAA‐treated samples was increased owing to the partial removal of amorphous lignin and hemicelluloses and probable physical change of cellulose. The effect of acetyl group content on enzymatic digestibility is negligible compared with the degree of delignification and crystallinity. The results indicate that enhancement of enzymatic digestibility of sugarcane bagasse by PAA pretreatment is achieved mainly by delignification and an increase in the surface area and exposure of cellulose fibers. Copyright © 2008 Society of Chemical Industry 相似文献
67.
Oxide films were deposited on different substrates by laser molecular beam epitaxy. Reflection high-energy electron diffraction was performed to in situ investigate the change of growth mode and the lattice relaxation during the growth. An asymmetrical phenomenon was found in the two kinds of strain states, compressive stress and tensile stress of heterostructures with different lattice mismatch. In the case of BaTiO3/SrTiO3 (2.2%), 2D layer-by-layer growth mode without lattice relaxation can be maintained for a longer period for BTO films on STO with compressive stress, comparing to STO films on BTO with tensile stress. When MgO films were deposited on SrTiO3 with a large mismatch of 7.8%, compressive stress leads to rapid lattice relaxation with a very thin wet layer, and 3D strained island were observed. As a comparison, SrTiO3 films on MgO with tensile stress were configured. No RHEED patterns can be observed duo to a large tensile stress. 相似文献
68.
2008年29届奥运会在北京举行,使得有关奥运的话题成为热门中的热门,与运动有关或无关的众多品牌、厂商对北京奥运年均寄予厚望,为赢取更大的收获和提升品牌知名度作最大的努力。其实早在几年前,国内外运动鞋品牌企业就已经大张旗鼓,在产品研发与广告宣传等多方面投入重金,为在这次北京奥运年带来的难得契机中处于市场制高点或明或隐地博杀着。 相似文献
69.
In this paper, a methodology is developed to use data acquisition derived from condition monitoring and standard diagnosis for rehabilitation purposes of transformers. The interpretation and understanding of the test data are obtained from international test standards to determine the current condition of transformers. In an attempt to ascertain monitoring priorities, the effective test methods are selected for transformer diagnosis. In particular, the standardization of diagnostic and analytical techniques are being improved that will enable field personnel to more easily use the test results and will reduce the need for interpretation by experts. In addition, the advanced method has the potential to reduce the time greatly and increase the accuracy of diagnostics. The important aim of the standardization is to develop the multiple diagnostic models that combine results from the different tests and give an overall assessment of reliability and maintenance for transformers. 相似文献
70.