全文获取类型
收费全文 | 262039篇 |
免费 | 4316篇 |
国内免费 | 1820篇 |
专业分类
电工技术 | 5442篇 |
技术理论 | 5篇 |
综合类 | 1164篇 |
化学工业 | 42235篇 |
金属工艺 | 11041篇 |
机械仪表 | 7762篇 |
建筑科学 | 6610篇 |
矿业工程 | 1660篇 |
能源动力 | 5619篇 |
轻工业 | 25844篇 |
水利工程 | 2892篇 |
石油天然气 | 5999篇 |
武器工业 | 243篇 |
无线电 | 27899篇 |
一般工业技术 | 49369篇 |
冶金工业 | 47699篇 |
原子能技术 | 5629篇 |
自动化技术 | 21063篇 |
出版年
2021年 | 2485篇 |
2019年 | 2135篇 |
2018年 | 3398篇 |
2017年 | 3376篇 |
2016年 | 3705篇 |
2015年 | 2810篇 |
2014年 | 4604篇 |
2013年 | 11385篇 |
2012年 | 7707篇 |
2011年 | 10232篇 |
2010年 | 8144篇 |
2009年 | 8693篇 |
2008年 | 9504篇 |
2007年 | 9630篇 |
2006年 | 8462篇 |
2005年 | 7419篇 |
2004年 | 6679篇 |
2003年 | 6226篇 |
2002年 | 6227篇 |
2001年 | 6337篇 |
2000年 | 5925篇 |
1999年 | 5900篇 |
1998年 | 13012篇 |
1997年 | 9617篇 |
1996年 | 7330篇 |
1995年 | 5563篇 |
1994年 | 5114篇 |
1993年 | 4981篇 |
1992年 | 3957篇 |
1991年 | 3766篇 |
1990年 | 3840篇 |
1989年 | 3793篇 |
1988年 | 3549篇 |
1987年 | 3040篇 |
1986年 | 3068篇 |
1985年 | 3423篇 |
1984年 | 3331篇 |
1983年 | 3088篇 |
1982年 | 2709篇 |
1981年 | 2927篇 |
1980年 | 2656篇 |
1979年 | 2849篇 |
1978年 | 2756篇 |
1977年 | 2863篇 |
1976年 | 3731篇 |
1975年 | 2467篇 |
1974年 | 2305篇 |
1973年 | 2327篇 |
1972年 | 1985篇 |
1971年 | 1788篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
Yang C.W. Fang Y.K. Lin C.S. Tsair Y.S. Chen S.M. Wang W.D. Wang M.F. Cheng J.Y. Chen C.H. Yao L.G. Chen S.C. Liang M.S. 《Electronics letters》2003,39(21):1499-1501
A novel technique to form high-K dielectric of HfSiON by doping base oxide with Hf and nitridation with NH/sub 3/, sequentially, is proposed. The HfSiON gate dielectric demonstrates excellent device performances such as only 10% degradation of saturation drain current and almost 45 times of magnitude reduction in gate leakage compared with conventional SiO/sub 2/ gate at the approximately same equivalent oxide thickness. Additionally, negligible flatband voltage shift is achieved with this technique. Time-dependent dielectric breakdown tests indicate that the lifetime of HfSiON is longer than 10 years at V/sub dd/=2 V. 相似文献
32.
Chou Y.C. Leung D. Lai R. Grundbacher R. Barsky M. Kan Q. Tsai R. Wojtowicz M. Eng D. Tran L. Block T. Liu P.H. Nishimoto M. Oki A. 《Electron Device Letters, IEEE》2003,24(6):378-380
The authors have investigated the reliability performance of G-band (183 GHz) monolithic microwave integrated circuit (MMIC) amplifiers fabricated using 0.07-/spl mu/m T-gate InGaAs-InAlAs-InP HEMTs with pseudomorphic In/sub 0.75/Ga/sub 0.25/As channel on 3-in wafers. Life test was performed at two temperatures (T/sub 1/ = 200 /spl deg/C and T/sub 2/ = 215 /spl deg/C), and the amplifiers were stressed at V/sub ds/ of 1 V and I/sub ds/ of 250 mA/mm in a N/sub 2/ ambient. The activation energy is as high as 1.7 eV, achieving a projected median-time-to-failure (MTTF) /spl ap/ 2 /spl times/ 10/sup 6/ h at a junction temperature of 125 /spl deg/C. MTTF was determined by 2-temperature constant current stress using /spl Delta/G/sub mp/ = -20% as the failure criteria. The difference of reliability performance between 0.07-/spl mu/m InGaAs-InAlAs-InP HEMT MMICs with pseudomorphic In/sub 0.75/Ga/sub 0.25/As channel and 0.1-/spl mu/m InGaAs-InAlAs-InP HEMT MMICs with In/sub 0.6/Ga/sub 0.4/As channel is also discussed. The achieved high-reliability result demonstrates a robust 0.07-/spl mu/m pseudomorphic InGaAs-InAlAs-InP HEMT MMICs production technology for G-band applications. 相似文献
33.
Stability analysis of the finite difference time domain scheme containing macromodels is presented. It is shown that for a stable macromodel, the stability of the combined scheme depends on the field interpolation at the macromodel boundary. The maximal allowable time step is shown to be much larger than for subgridding. 相似文献
34.
The effect of spin splitting caused by structural asymmetry (Rashba’s contribution) and bulk asymmetry (Dresselhaus’s contribution) on the magnetoconductance of two-dimensional structures with high mobility of charge carriers is studied. The theory of weak localization with regard to both of the contributions is developed. The theory is valid in the entire region of classically low magnetic fields for arbitrary relations between the frequencies of spin precession and elastic collisions. The suppression of the correction for antilocalization is demonstrated in the case of equal contributions of structural anisotropy and bulk anisotropy to the spin splitting. The effect of the contribution, cubic in the wave vector, to the spin splitting on the quantum magnetoresistance is studied. 相似文献
35.
In self-organizing ad hoc networks, all the networking functions rely on the contribution of the participants. As a basic example, nodes have to forward packets for each other in order to enable multihop communication. In recent years, incentive mechanisms have been proposed to give nodes incentive to cooperate, especially in packet forwarding. However, the need for these mechanisms was not formally justified. In this paper, we address the problem of whether cooperation can exist without incentive mechanisms. We propose a model,based on game theory and graph theory to investigate equilibrium conditions of packet forwarding strategies. We prove theorems about the equilibrium conditions for both cooperative and noncooperative strategies. We perform simulations to estimate the probability that the conditions for a cooperative equilibrium hold in randomly generated network scenarios.. As the problem is involved, we deliberately restrict ourselves to a static configuration. We conclude that in static ad hoc networks where the relationships between the nodes are likely to be stab le-cooperation needs to be encouraged. 相似文献
36.
Peter V. Sushko Alexander L. ShlugerKatsuro Hayashi Masahiro HiranoHideo Hosono 《Thin solid films》2003,445(2):161-167
Recently it has been discovered that a nano-porous main group oxide 12CaO·7Al2O3 (C12A7) can be converted from a wide-gap insulator to a good transparent conductor. Using ab initio modelling we explain good conductivity of this material by very small barriers for hopping of localised electrons between neighbouring positive cages. We show that optical absorption of C12A7 in infrared region and at energies higher than 2.7 eV is due to inter-cage and intra-cage electron transitions, respectively. The proposed mechanisms can be useful in further search for conducting transparent media. 相似文献
37.
J. B. Quinn G. E. Schumacher L. W. Schultheis 《Journal of Failure Analysis and Prevention》2004,4(1):41-46
Several days after heart surgery, a patient discovered his upper right canine tooth had broken at the root. Such tooth damage,
recognized post-operatively, is usually assumed to be caused by blunt mechanical force from an instrument used by the anesthesiologist
during placement of a breathing tube at the start of surgery.
In this case, the patient had saved the crown portion of the broken tooth, and it was possible to examine the root fracture
characteristics. The curvature and direction of the crack path and natural tooth situation suggested that failure could be
described through a cantilever beam model. This was confirmed when a whole extracted sample tooth was embedded and broken
by a measured force in a manner consistent with the model. The resulting fracture surface matched that of the patient’s broken
canine tooth. However, the high load and force direction necessary to fracture the root was inconsistent with forces applied
during the anesthesia procedure. The failure analysis and further investigation indicated tooth clenching on the breathing
tube during recovery was the likely cause of fracture.
This paper presents an alternate explanation for intubation-related dental injury, demonstrates the practicality of fractographic
analysis of biological materials, and introduces a methodology for simulating in vitro tooth settings for mechanical testing. 相似文献
38.
L. A. Dombrovskii 《High Temperature》2003,41(6):819-824
Theoretical models of heat transfer by radiation through a vapor gap under conditions of film boiling of liquid are treated, namely, a general wave model for a gap of arbitrary thickness and an approximate model of geometrical optics. Calculations are performed of heat transfer by radiation under conditions of film boiling of water on hot surfaces of refractory metal and molten oxide. Practical recommendations are given to calculate the distribution of the power of absorbed radiation in a water layer. 相似文献
39.
40.
Demiguel S. Giraudet L. Joulaud L. Decobert J. Blache F. Coupe V. Jorge F. Pagnod-Rossiaux P. Boucherez E. Achouche M. Devaux F. 《Lightwave Technology, Journal of》2002,20(12):2004-2014
The design, fabrication, and performance of double-stage taper photodiodes (DSTPs) are reported. The objective of this work is to develop devices compatible with 40-Gb/s applications. Such devices require high efficiency, ultrawide band, high optical power handling capability, and compatibility with low-cost module fabrication. The integration of mode size converters improves both the coupling efficiency and the responsivity with a large fiber mode diameter. Responsivity of 0.6 A/W and 0.45 A/W are achieved with a 6-/spl mu/m fiber mode diameter and cleaved fiber, respectively, providing relaxed alignment tolerances (/spl plusmn/1.6 /spl mu/m and /spl plusmn/2 /spl mu/m, respectively), compatible with cost-effective packaging techniques. DSTPs also offer a wide bandwidth greater than 40 GHz and transverse-electric/transverse-magnetic polarization dependence lower than 0.2 dB. Furthermore, a DSTP saturation current as high as 11 mA results in optical power handling greater than +10 dBm and a high output voltage of 0.8 V. These capabilities allow the photodiode to drive the decision circuit without the need of a broad-band electrical amplifier. The DSTP devices presented here demonstrate higher responsivities with large fiber mode diameter and better optical power handling capabilities and are compared with classical side-illuminated photodiodes. 相似文献