全文获取类型
收费全文 | 445444篇 |
免费 | 8108篇 |
国内免费 | 2366篇 |
专业分类
电工技术 | 9120篇 |
技术理论 | 4篇 |
综合类 | 1902篇 |
化学工业 | 67807篇 |
金属工艺 | 15711篇 |
机械仪表 | 13492篇 |
建筑科学 | 13284篇 |
矿业工程 | 1627篇 |
能源动力 | 12256篇 |
轻工业 | 45931篇 |
水利工程 | 3745篇 |
石油天然气 | 2840篇 |
武器工业 | 159篇 |
无线电 | 60093篇 |
一般工业技术 | 81177篇 |
冶金工业 | 77432篇 |
原子能技术 | 5926篇 |
自动化技术 | 43412篇 |
出版年
2021年 | 3848篇 |
2020年 | 2714篇 |
2019年 | 3220篇 |
2018年 | 4717篇 |
2017年 | 4829篇 |
2016年 | 4974篇 |
2015年 | 4475篇 |
2014年 | 7101篇 |
2013年 | 21312篇 |
2012年 | 12120篇 |
2011年 | 16893篇 |
2010年 | 13028篇 |
2009年 | 14664篇 |
2008年 | 15752篇 |
2007年 | 15859篇 |
2006年 | 14241篇 |
2005年 | 13104篇 |
2004年 | 12573篇 |
2003年 | 12379篇 |
2002年 | 12216篇 |
2001年 | 12219篇 |
2000年 | 11031篇 |
1999年 | 11413篇 |
1998年 | 24883篇 |
1997年 | 18198篇 |
1996年 | 14418篇 |
1995年 | 11392篇 |
1994年 | 10117篇 |
1993年 | 9639篇 |
1992年 | 7323篇 |
1991年 | 6972篇 |
1990年 | 6578篇 |
1989年 | 6258篇 |
1988年 | 5998篇 |
1987年 | 5012篇 |
1986年 | 4948篇 |
1985年 | 6081篇 |
1984年 | 5693篇 |
1983年 | 4890篇 |
1982年 | 4550篇 |
1981年 | 4492篇 |
1980年 | 4269篇 |
1979年 | 4118篇 |
1978年 | 3819篇 |
1977年 | 4596篇 |
1976年 | 6160篇 |
1975年 | 3154篇 |
1974年 | 3033篇 |
1973年 | 2922篇 |
1972年 | 2336篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
121.
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
122.
123.
M. Riad Manaa Laurence E. Fried Evan J. Reed 《Journal of Computer-Aided Materials Design》2003,10(2):75-97
In this article, we review recent atomistic computational techniques to study the electronic structure aspects and chemistry
of energetic materials at high-pressure and/or high temperature. While several mechanisms have been proposed for the initial
events of energetic materials at high-pressure, we explore the validity of a proposed shear-induced local metallization via
molecular bond bending in the insensitive explosive TATB. We study the effect of high-stress (both uniform and uniaxial) on
the electronic energy band-gap and the first chemical event of a prototypical energetic material, that of nitromethane. We
also determine chemical reactions rate laws and decomposition mechanisms from a quantum-based molecular dynamics simulation
of HMX, a widely used explosive material, at conditions of high density and temperature similar to that encounter under detonation.
Finally, we review a new multi-scale computational tool recently developed to model the shock-induced chemistry of energetic
materials at the atomistic level, and report its applicability to shocked solid nitromethane.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
124.
125.
A new dual-quantisation sigma-delta modulator is proposed, which introduces an additional feedback path in the input of the second integrator. In this way, unlike other dual-quantisation architectures, larger signal-to-noise ratios can be obtained by means of aggressive noise-shaping, like in a conventional multibit modulator. The proposed modulator is also shown to be more robust against non-idealities than other dual-quantisation architectures. 相似文献
126.
Ming-Dou Ker Chyh-Yih Chang Yi-Shu Chang 《Components and Packaging Technologies, IEEE Transactions on》2004,27(3):445-451
This paper reports a real case of electrostatic discharge (ESD) improvement on a complementary metal oxide semiconductor integrated circuit (IC) product with multiple separated power pins. After ESD stresses, the internal damage have been found to locate at the interface circuit connecting between different circuit blocks with different power supplies. Some ESD designs have been implemented to rescue this IC product to meet the required ESD specification. By adding only an extra ESD clamp N-channel metal oxide semiconductor with a channel width of 10 /spl mu/m between the interface node and the ground line, the human-body-model (HBM) ESD level of this IC product can be improved from the original 0.5 to 3 kV. By connecting the separated vertical sync signal (VSS) power lines through the ESD conduction circuit to a common VSS ESD bus realized by the seal ring, the HBM ESD level of the enhanced version IC product with 12 separated power supplies pairs can be significantly improved from original 1 kV up to > 5 kV, without the noise coupling issue. 相似文献
127.
Low supply voltage high-performance CMOS current mirror with low input and output voltage requirements 总被引:1,自引:0,他引:1
Ramirez-Angulo J. Carvajal R.G. Torralba A. 《Circuits and Systems II: Express Briefs, IEEE Transactions on》2004,51(3):124-129
This paper presents a scheme for the efficient implementation of a low supply voltage continuous-time high-performance CMOS current mirror with low input and output voltage requirements. This circuit combines a shunt input feedback and a regulated cascode output stage to achieve low input resistance and very high output resistance. It can be used as a high-precision current mirror in analog and mixed signal circuits with a power supply close to a transistor's threshold voltage. The proposed current mirror has been simulated and a bandwidth of 40 MHz has been obtained. An experimental chip prototype has been sent for fabrication and has been experimentally verified, obtaining 0.15-V input-output voltage requirements, 100-/spl Omega/ input resistance, and more than 200-M/spl Omega/ (G/spl Omega/ ideally) output resistance with a 1.2-V supply in a standard CMOS technology. 相似文献
128.
A fundamental problem for regulatory networks is to understand the relation between form and function: to uncover the underlying design principles of the network. Circadian clocks present a particularly interesting instance, as recent work has shown that they have complex structures involving multiple interconnected feedback loops with both positive and negative feedback. While several authors have speculated on the reasons for this, a convincing explanation is still lacking.We analyse both the flexibility of clock networks and the relationships between various desirable properties such as robust entrainment, temperature compensation, and stability to environmental variations and parameter fluctuations. We use this to argue that the complexity provides the flexibility necessary to simultaneously attain multiple key properties of circadian clocks. As part of our analysis we show how to quantify the key evolutionary aims using infinitesimal response curves, a tool that we believe will be of general utility in the analysis of regulatory networks. Our results suggest that regulatory and signalling networks might be much less flexible and of lower dimension than their apparent complexity would suggest. 相似文献
129.
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
130.
Ching-Wen Tang Chi-Yang Chang 《Electronics letters》2002,38(15):801-803
A novel chip-type ceramic balun designed in the 2.4 GHz ISM band frequency is presented. A buried capacitor is included in the balun, so that the length of the coupled transmission lines can be reduced and can be designed very easily. A meander or spiral broadside coupled-line is adopted to realise the proposed LTCC multi-layer balun. The measured performances of phase and amplitude balance for this LTCC-MLC balun show a good match with computer simulation 相似文献