全文获取类型
收费全文 | 232653篇 |
免费 | 14578篇 |
国内免费 | 5981篇 |
专业分类
电工技术 | 9191篇 |
技术理论 | 14篇 |
综合类 | 8829篇 |
化学工业 | 41624篇 |
金属工艺 | 10703篇 |
机械仪表 | 14098篇 |
建筑科学 | 13751篇 |
矿业工程 | 3984篇 |
能源动力 | 7561篇 |
轻工业 | 15442篇 |
水利工程 | 2700篇 |
石油天然气 | 7881篇 |
武器工业 | 928篇 |
无线电 | 32507篇 |
一般工业技术 | 35714篇 |
冶金工业 | 15915篇 |
原子能技术 | 2696篇 |
自动化技术 | 29674篇 |
出版年
2024年 | 651篇 |
2023年 | 3098篇 |
2022年 | 5214篇 |
2021年 | 7587篇 |
2020年 | 5668篇 |
2019年 | 5136篇 |
2018年 | 6114篇 |
2017年 | 6607篇 |
2016年 | 6595篇 |
2015年 | 7072篇 |
2014年 | 9754篇 |
2013年 | 13522篇 |
2012年 | 13839篇 |
2011年 | 15748篇 |
2010年 | 13153篇 |
2009年 | 13157篇 |
2008年 | 12714篇 |
2007年 | 11319篇 |
2006年 | 11245篇 |
2005年 | 9967篇 |
2004年 | 7577篇 |
2003年 | 6829篇 |
2002年 | 6247篇 |
2001年 | 5589篇 |
2000年 | 5471篇 |
1999年 | 5959篇 |
1998年 | 6699篇 |
1997年 | 5173篇 |
1996年 | 4580篇 |
1995年 | 3671篇 |
1994年 | 2959篇 |
1993年 | 2433篇 |
1992年 | 1861篇 |
1991年 | 1568篇 |
1990年 | 1323篇 |
1989年 | 1192篇 |
1988年 | 960篇 |
1987年 | 770篇 |
1986年 | 602篇 |
1985年 | 544篇 |
1984年 | 410篇 |
1983年 | 310篇 |
1982年 | 289篇 |
1981年 | 234篇 |
1980年 | 216篇 |
1979年 | 176篇 |
1978年 | 150篇 |
1977年 | 191篇 |
1976年 | 263篇 |
1975年 | 110篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Antoniades N. Boskovic A. Tomkos I. Madamopoulos N. Lee M. Roudas I. Pastel D. Sharma M. Yadlowsky M.J. 《Selected Areas in Communications, IEEE Journal on》2002,20(1):149-165
This paper demonstrates the use of computer simulation for topological design and performance engineering of transparent wavelength-division multiplexing metropolitan-area networks. Engineering of these networks involves the study of various transport-layer impairments such as amplifier noise, component ripple, chirp/dispersion, optical crosstalk, waveform distortion due to filter concatenation, fiber nonlinearities, and polarization effects. A computer simulation methodology composed of three main simulation steps is derived and implemented. This methodology obtains performance estimations by applying efficient wavelength-domain simulations on the entire network topology, followed by time-/frequency-domain simulations on selected paths of the network and finally Q-budgeting on an identified worst case path. The above technique provides an efficient tool for topological design and network performance engineering. Accurate simulation models are presented for each of the performance impairments, and the computer simulation methodology is used for the design and engineering of a number of actual metro network architectures 相似文献
92.
In this work, a quantitative analysis is applied to resolve the newly reported polarity-dependent charge-to-breakdown (Q/sub BD/) data from thick oxides of 6.8 nm down to ultrathin oxides of 1.9 nm. Three independent sets of Q/sub BD/ data, i.e., n/sup +/poly/NFET stressed under inversion and accumulation, and p/sup +/ poly/PFET under accumulation are carefully investigated. The Q/sub BD/ degradation observed for p-type anodes, either poly-Si or Si-substrate, can be nicely understood with the framework of maximum energy released by injected electrons. Thus, this work provides a universal and quantitative account for a variety of experimental observations in the time-to-breakdown (T/sub BD/) and Q/sub BD/ polarity-dependence of oxide breakdown. 相似文献
93.
Chih-Wea Wang Chi-Feng Wu Jin-Fu Li Cheng-Wen Wu Tony Teng Kevin Chiu Hsiao-Ping Lin 《Journal of Electronic Testing》2002,18(6):637-647
In this paper we propose a novel built-in self-test (BIST) design for embedded SRAM cores. Our contribution includes a compact and efficient BIST circuit with diagnosis support and an automatic diagnostic system. The diagnosis module of our BIST circuit can capture the error syndromes as well as fault locations for the purposes of repair and fault/failure analysis. In addition, our design provides programmability for custom March algorithms with lower hardware cost. The combination of the on-line programming mode and diagnostic system dramatically reduces the effort in design debugging and yield enhancement. We have designed and implemented test chips with our BIST design. Experimental results show that the area overhead of the proposed BIST design is only 2.4% for a 128 KB SRAM, and 0.65% for a 2 MB one. 相似文献
94.
大颗粒尿素造粒工艺简介 总被引:4,自引:0,他引:4
介绍了大颗粒尿素造粒工艺,着重介绍了荷兰NSM公司的流化床造粒技术和法国K-T公司的流化床转鼓造粒(FDG)技术。 相似文献
95.
96.
97.
Mountfield K. Mitchell P. Lee J.-W. Demczyk B. Artman J. 《IEEE transactions on magnetics》1987,23(5):2037-2039
A sequence of Co78 Cr22 films, 500 nm in thickness, was prepared by deposition on glass in a modified Varian D.C. magnetron S-gun sputtering system. The substrate temperature during deposition, Ts , was fixed at various values with an upper limit of 300°C. Specimens were examined by VSM, TM, FMR and TEM. Ms rises significantly with increasing Ts , peaking at 200°C at 370 emu/cm3. The effective volume-averaged anisotropy drops for Ts >110°C from +1.6 KOe to progressively negative values (-4.3 KOe at 300°C). From FMR we find indications of the presence, in addition to the transition and bulk layers, of a highly negative anisotropy constituent (sim-11.5 KOe anisotropy field). This resonance appears at Ts values of 150°C and above. TEM plane and cross-section views taken on a Ts = 150°C specimen show islands composed of tilted columns within the bulk. For vertical recording, specimens prepared at Ts values between 50 and 100°C are recommended. On the other hand, for longitudinal recording applications, films prepared at Ts values above 250°C would seem to be appropriate. 相似文献
98.
The behavior of two series of concrete slabs exposed to sulfate-bearing soils was investigated by a numerical model called
STADIUM. In addition to the diffusion of ions and moisture, the model also accounts for the effects of dissolution/precipitation
reactions on the transport mechanisms. The simulations yielded by the model were compared to the actual degradation of the
slabs after 8 years of exposure. The microstructural alterations of concrete resulting from the penetration of magnesium,
chloride and sulfate ions were studied by backscatter mode scanning electron microscope observations and energy-dispersive
X-ray analyses. The comparison of both series of data indicates that the model can reliably predict the various features of
the microstructural alterations of concrete.
Editorial Note Laval University (Canada) is a RILEM Titular Member. Prof. J. Marchand was awarded the 2000 Robert L'Hermite Medal. He is Editor in Chief for Concrete Science and Engineering and Associate Editor for Materials and Structures. He participates in RILEM TC 186-ISA ‘Internal Sulfate attack’. 相似文献
Résumé Le comportement de deux séries de dalles sur sol en béton exposées à des sols chimiquement agressifs a été étudié à l'aide d'un code de calcul numérique appelé STADIUM. Ce modèle permet de décrire le transport couplé de l'eau et des ions dans des matériaux poreux non-saturés en prenant en considération l'influence des réactions chimiques. Les résultats des simultations de la dégradation du béton après huit ans d'exposition à des ions chlore, sulfate et magnésium. Les observations ont été réalisées par microscopie électronique à balayage. Des analyses par dispersion des rayons X ont également été effectuées. Les données démontrent clairement que le modèle perment de prédire avec précision le comportement du béton soumis à différents types d'agression chimique.
Editorial Note Laval University (Canada) is a RILEM Titular Member. Prof. J. Marchand was awarded the 2000 Robert L'Hermite Medal. He is Editor in Chief for Concrete Science and Engineering and Associate Editor for Materials and Structures. He participates in RILEM TC 186-ISA ‘Internal Sulfate attack’. 相似文献
99.
100.
The flow and heat transfer characteristics of a pair of embedded counter-rotating vortices are studied experimentally. In order to control the strength of longitudinal vortices, angle of attack of the vortex generators is varied from ±20° to ±45°, and the spacing between the vortex generators is 4 cm apart. The heat transfer measurements using thermo-chromatic liquid crystal are made to provide the local surface distributions of heat transfer coefficients. The following conclusions are obtained from the present experiment. For the common-flow-down cases, two maximum values in the local heat transfer distributions exist for the three angles of attack. With the common-flow-up cases, only one maximum value exists. The common-flow-down cases show better heat transfer characteristics than the common-flow-up cases. 相似文献