全文获取类型
收费全文 | 550616篇 |
免费 | 9522篇 |
国内免费 | 2956篇 |
专业分类
电工技术 | 9721篇 |
技术理论 | 5篇 |
综合类 | 3603篇 |
化学工业 | 83283篇 |
金属工艺 | 22124篇 |
机械仪表 | 16761篇 |
建筑科学 | 14540篇 |
矿业工程 | 2681篇 |
能源动力 | 12984篇 |
轻工业 | 52606篇 |
水利工程 | 5854篇 |
石油天然气 | 7952篇 |
武器工业 | 248篇 |
无线电 | 64277篇 |
一般工业技术 | 102369篇 |
冶金工业 | 89858篇 |
原子能技术 | 8510篇 |
自动化技术 | 65718篇 |
出版年
2021年 | 4172篇 |
2020年 | 2952篇 |
2019年 | 3620篇 |
2018年 | 19378篇 |
2017年 | 18252篇 |
2016年 | 15642篇 |
2015年 | 5296篇 |
2014年 | 7884篇 |
2013年 | 21881篇 |
2012年 | 16284篇 |
2011年 | 27134篇 |
2010年 | 22154篇 |
2009年 | 20983篇 |
2008年 | 23220篇 |
2007年 | 24207篇 |
2006年 | 15425篇 |
2005年 | 14667篇 |
2004年 | 13637篇 |
2003年 | 13222篇 |
2002年 | 12220篇 |
2001年 | 12178篇 |
2000年 | 11286篇 |
1999年 | 11621篇 |
1998年 | 26784篇 |
1997年 | 19209篇 |
1996年 | 14671篇 |
1995年 | 11105篇 |
1994年 | 9983篇 |
1993年 | 9719篇 |
1992年 | 7256篇 |
1991年 | 6900篇 |
1990年 | 6815篇 |
1989年 | 6567篇 |
1988年 | 6212篇 |
1987年 | 5160篇 |
1986年 | 5082篇 |
1985年 | 6056篇 |
1984年 | 5659篇 |
1983年 | 5205篇 |
1982年 | 4666篇 |
1981年 | 4905篇 |
1980年 | 4491篇 |
1979年 | 4565篇 |
1978年 | 4331篇 |
1977年 | 4725篇 |
1976年 | 6086篇 |
1975年 | 3775篇 |
1974年 | 3562篇 |
1973年 | 3641篇 |
1972年 | 2986篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
991.
Abstract— During constant amplitude loading, two different types of crack systems have been reported In the high cycle fatigue (HCF) region, cracks nucleate on a small number of maxium shear strain amplitude planes One of these cracks becomes a dominant crack and leads to failure of the specimen In the low cycle fatigue (LCF) region, equally developed microcracks are observed over the entire gage section and grow during the majority of the life. The failure is due to a linking in which the microcracks join up during the last few cycles of the fatigue life.
To investigate the interaction of these two types of crack systems in biaxial fatigue, experiments were performed on thin-wall tubular specimens in tension, torsion and combined tension-torsion loading The test program included step loading and block loading in which two equivalent strain amplitudes were employed. One of the equivalent strain amplitudes is in the HCF region and the other was in the LCF region
Fatigue lives were predicted from constant amplitude damage curves when a single crack system dominated the fatigue process Two competitive crack systems were sometimes developed on the maximum shear strain amplitude planes in a single specimen under block loading This resulted in a conservative prediction of the fatigue life. 相似文献
To investigate the interaction of these two types of crack systems in biaxial fatigue, experiments were performed on thin-wall tubular specimens in tension, torsion and combined tension-torsion loading The test program included step loading and block loading in which two equivalent strain amplitudes were employed. One of the equivalent strain amplitudes is in the HCF region and the other was in the LCF region
Fatigue lives were predicted from constant amplitude damage curves when a single crack system dominated the fatigue process Two competitive crack systems were sometimes developed on the maximum shear strain amplitude planes in a single specimen under block loading This resulted in a conservative prediction of the fatigue life. 相似文献
992.
993.
Y. G. Wang H. Q. Ye K. H. Kuo X. J. Feng S. Z. Long G. L. Lao 《Journal of Materials Science》1991,26(23):6325-6330
The microstructures of unhydrated calcium aluminosulphate Ca4Al6SO16 and Ca3SrAl6SO16 have been studied by high-resolution electron microscopy (HREM). The results showed that twinning and twinned slabs could be introduced taking the [1 1 2] direction as the twin axis so that it seems to be coincident with the law of twinning formed in body-centred cubic structures. A previously reported superlattice with a repeat period twice that of the fundamental structure along the 〈1 1 0〉 direction has also been found in both matrix and twin variants. The close intergrowth of Ca3SrAl6SO16 and another phase, possibly Sr3Al2O6 existing as an inclusion between these two twin variants, was determined and clearly revealed by electron diffraction and HREM images. The coherent interphase boundaries and orientation relationship between them can also be deduced. 相似文献
994.
Waveband-switchable SOA ring laser constructed with a phase modulator loop mirror filter 总被引:1,自引:0,他引:1
M.P. Fok K.L. Lee C. Shu 《Photonics Technology Letters, IEEE》2005,17(7):1393-1395
An electrically tunable multiwavelength source has been developed using a birefringence-based optical comb filter in a semiconductor optical amplifier ring laser. The filter is constructed with an electrooptic phase modulator placed inside a fiber loop mirror. By controlling the birefringence of the modulator through the applied bias, the radio-frequency power, or the modulation frequency, we achieve a continuous shift of the spectral comb to access different interleaved wavebands. Electrical waveband switching has been successfully demonstrated for 21 wavelengths at 100-GHz grid spacing with an optical signal-to-noise ratio over 40 dB. 相似文献
995.
Widely tunable bottom-emitting vertical-cavity SOAs 总被引:1,自引:0,他引:1
Cole G.D. Bjorlin E.S. Wang C.S. MacDonald N.C. Bowers J.E. 《Photonics Technology Letters, IEEE》2005,17(12):2526-2528
We present bottom-emitting tunable vertical-cavity semiconductor optical amplifiers (VCSOAs) with an effective wavelength tuning range of >20 nm. These devices utilize a high reflectivity micromechanically tunable Bragg mirror as the back reflector. Compared with our first generation tunable VCSOAs, the bottom-emitting devices exhibit a two-fold increase in the effective tuning range as well as a five-fold reduction in the required tuning voltage. 相似文献
996.
JaeHyuk Shin Ozturk C. Sakamoto S.R. Chiu Y.J. Dagli N. 《Microwave Theory and Techniques》2005,53(2):636-643
A novel traveling-wave electrode utilizing capacitively loaded T-rail elements was developed for low-voltage high-speed substrate-removed GaAs/AlGaAs electrooptic modulators. Electrodes with varying dimensions were fabricated and characterized. Electrode phase velocity, characteristic impedance, loss coefficient, and capacitive loading were extracted from the measured s-parameters up to 40 GHz. Electrode was also simulated using a finite-element solver. The measured and calculated electrode capacitance values were found to be in excellent agreement, showing that the electrode can be precisely designed. Approaches were outlined to provide a group velocity-matched very high-speed modulator electrode suitable for a low drive-voltage substrate-removed GaAs/AlGaAs electro-optic modulator 相似文献
997.
998.
Several coats, such as gray cast iron, cast iron alloyed with nickel and copper, nickel-aluminum, Nichrome (nickel-chromium
alloy), bronze, etc., have been investigated. Corrosion resistance of coats in a medium based on drilling mud and sodium chloride
and sulfate solutions has been checked. Alloyed cast iron admixed with tin-based compounds showed the best results.
__________
Translated from Khimicheskoe i Neftegazovoe Mashinostroenie, No. 3, pp. 43–44, March, 2006. 相似文献
999.
1000.
Jon T. Carter Paul E. Krajewski Ravi Verma 《JOM Journal of the Minerals, Metals and Materials Society》2008,60(11):77-81
The hot blow forming of magnesium sheet offers significant opportunity for forming complex, lightweight parts for automotive
applications. This paper characterizes the elevated-temperature formability of AZ31 magnesium sheet materials and the effect
of processing conditions on the performance of these materials. In addition, magnesium sheet application development at General
Motors Corporation is reviewed. 相似文献