全文获取类型
收费全文 | 908404篇 |
免费 | 11998篇 |
国内免费 | 2105篇 |
专业分类
电工技术 | 16553篇 |
综合类 | 807篇 |
化学工业 | 139170篇 |
金属工艺 | 35289篇 |
机械仪表 | 27531篇 |
建筑科学 | 21568篇 |
矿业工程 | 5557篇 |
能源动力 | 23701篇 |
轻工业 | 75983篇 |
水利工程 | 10117篇 |
石油天然气 | 19114篇 |
武器工业 | 64篇 |
无线电 | 99565篇 |
一般工业技术 | 178863篇 |
冶金工业 | 171339篇 |
原子能技术 | 20007篇 |
自动化技术 | 77279篇 |
出版年
2021年 | 8342篇 |
2020年 | 6145篇 |
2019年 | 7875篇 |
2018年 | 13440篇 |
2017年 | 13475篇 |
2016年 | 14191篇 |
2015年 | 9374篇 |
2014年 | 15603篇 |
2013年 | 41497篇 |
2012年 | 24387篇 |
2011年 | 33422篇 |
2010年 | 26651篇 |
2009年 | 29744篇 |
2008年 | 30381篇 |
2007年 | 29987篇 |
2006年 | 26047篇 |
2005年 | 23764篇 |
2004年 | 22734篇 |
2003年 | 22391篇 |
2002年 | 21455篇 |
2001年 | 21138篇 |
2000年 | 19970篇 |
1999年 | 20561篇 |
1998年 | 51133篇 |
1997年 | 36432篇 |
1996年 | 28141篇 |
1995年 | 21283篇 |
1994年 | 18854篇 |
1993年 | 18475篇 |
1992年 | 13705篇 |
1991年 | 12985篇 |
1990年 | 12865篇 |
1989年 | 12454篇 |
1988年 | 11824篇 |
1987年 | 10628篇 |
1986年 | 10379篇 |
1985年 | 11682篇 |
1984年 | 10677篇 |
1983年 | 9909篇 |
1982年 | 9136篇 |
1981年 | 9274篇 |
1980年 | 8839篇 |
1979年 | 8781篇 |
1978年 | 8587篇 |
1977年 | 9908篇 |
1976年 | 12841篇 |
1975年 | 7582篇 |
1974年 | 7214篇 |
1973年 | 7369篇 |
1972年 | 6170篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
A.A. Kendoush 《Nuclear Engineering and Design》1989,110(3):349-360
The paper describes new experimental evidence on the effects of fast neutron irradiation on the nucleation of bubbles in superheated demineralized water during sudden depressurization. The experimental range covered strating pressures of (0.33–6.0) MPa. It was shown that fast neutron irradiation causes significant increases in the bubble formation for specified conditions of pressure, temperature and rate of blowdown. A mechanistic interpretation of the measurements based on a thermodynamic model was included, and comparison was made, in terms of void fraction, with the experimental results. 相似文献
993.
994.
The composition of the volatile oil of Mexican oregano (Lippia graveolens HBK) isolated by steam distillation was investigated by means of column chromatography, gas chromatography and mass spectrometry. A total of 33 components were identified including 22 hydrocarbons, 4 alcohols, 4 ethers, 2 phenols and 1 ketone. Of the 33 components observed in the present study 7 were identified in Mexican oregano for the first time. 相似文献
995.
J. Ben Mariem M. A. Hamdi 《International journal for numerical methods in engineering》1987,24(7):1251-1267
In order to study problems on fluid–structure interaction, we have used a mixed formulation which couples the classical functional of the structure with a new variational formulation by integral equations for the fluid. This formulation has the advantage over the finite element methods of avoiding the discretization of the fluid domain. Furthermore, unlike collocation methods, the explicit calculation of the Hadamard finite part of the singular integrals is avoided. This leads after discretization by boundary finite elements to a small and symmetrical algebraic system. Typical examples are presented that demonstrate the efficiency of this variational formulation by studying the sound transmission through a baffled plane structure and through a flexible panel backed by a rigid cavity. These include the calculation of the transmission loss factor and the determination of which modes dominate the noise transmission. Good agreement is obtained between numerical results and analytical results found in the literature. 相似文献
996.
997.
The evolution of RFID security 总被引:11,自引:0,他引:11
As RFID technology progresses, security and privacy threats also evolve. By examining RFID's history, we can learn from past mistakes, rediscover successful solutions, and inspire future research. 相似文献
998.
Imre T.G. Cronje W.A. van Wyk J.D. Ferreira J.A. 《Industry Applications, IEEE Transactions on》2002,38(6):1613-1621
This paper covers the experimental investigation and theoretical calculation of losses in a planar inductor under load. Finite-element software is used to perform the loss calculations. Thermally controlled experiments are performed for a range of frequencies to validate the corresponding finite-element method loss calculations. The thermal dependence of the loss mechanisms is also considered. 相似文献
999.
In this paper, the space-vector transformation used in machine vector control is applied to power system analysis. The proposed method is used to model electric machines, power electronic converters, transformers, and transmission lines and to analyze power sources and loads with different connections (delta and wye). This method can also be applied to analyze steady-state (or transient phenomena) and unbalanced sources, including harmonics. Models obtained with this method are as simple as those of the per-phase approach. With the space-vector transformation, instantaneous active and reactive power concepts can be generalized, and new power system control strategies can be developed when power electronic converters are used. Steady-state, transient behavior, and harmonic analyses examples and applications are presented to illustrate the performance and advantages of the proposed method. This method can be extended to unbalanced systems (e.g., unsymmetric faults) using instantaneous symmetrical components in polyphase balanced circuits. 相似文献
1000.
Thin films on aluminum-tungsten alloys were prepared by co-deposition of pure aluminum and pure tungsten, each sputtered by an independently controlled magnetron source, on glass and sapphire substrates. Completely amorphous films were obtained in the Al80W20-Al67W33 composition range. Passivity and corrosion behavior of amorphous Al-W alloys were investigated in 1 M deaerated hydrochloric acid solution using polarization and impedance spectroscopy measurements and have been correlated with the properties of pure alloy components. Tungsten and sputter-deposited Al-W thin films are inherently passive materials while aluminum undergoes pitting corrosion in hydrochloric acid solution. The passive film formed at the OCP on each alloy possesses excellent electric and dielectric properties comparable to those of the isolating film on tungsten. The absolute impedance increases with increasing tungsten content in the alloy. According to electrochemical polarization measurements, alloying Al with W in solid solution significantly enhances the material's resistance to pitting corrosion by shifting the breakdown potential above 2000 mV (Al67W33) and lowering the corrosion rate at the OCP by more than two orders of magnitude. The most likely mechanism explaining the passivity of amorphous Al-W alloys, the Solute Vacancy Interaction Model (SVIM), involves the formation of complexes between highly oxidized solute atoms (W+6) and mobile cation vacancies, which restrict the transport of Cl− through the oxide film and inhibit its breakdown in hydrochloric acid solution. The role that film stress relaxation effects and microscopic defects in amorphous Al-W films, of the some composition, and deposited on various substrates play in their corrosion resistance is discussed. 相似文献