全文获取类型
收费全文 | 1476899篇 |
免费 | 27433篇 |
国内免费 | 6947篇 |
专业分类
电工技术 | 34300篇 |
综合类 | 6370篇 |
化学工业 | 270774篇 |
金属工艺 | 63887篇 |
机械仪表 | 41326篇 |
建筑科学 | 46203篇 |
矿业工程 | 11416篇 |
能源动力 | 50599篇 |
轻工业 | 108521篇 |
水利工程 | 14844篇 |
石油天然气 | 37481篇 |
武器工业 | 134篇 |
无线电 | 196118篇 |
一般工业技术 | 279893篇 |
冶金工业 | 144778篇 |
原子能技术 | 33900篇 |
自动化技术 | 170735篇 |
出版年
2021年 | 15747篇 |
2020年 | 11956篇 |
2019年 | 14819篇 |
2018年 | 15243篇 |
2017年 | 14586篇 |
2016年 | 21246篇 |
2015年 | 17488篇 |
2014年 | 28934篇 |
2013年 | 88529篇 |
2012年 | 35115篇 |
2011年 | 47204篇 |
2010年 | 42385篇 |
2009年 | 50849篇 |
2008年 | 44103篇 |
2007年 | 41221篇 |
2006年 | 44501篇 |
2005年 | 39007篇 |
2004年 | 41189篇 |
2003年 | 41111篇 |
2002年 | 40216篇 |
2001年 | 36451篇 |
2000年 | 35112篇 |
1999年 | 33834篇 |
1998年 | 38413篇 |
1997年 | 35385篇 |
1996年 | 32884篇 |
1995年 | 29268篇 |
1994年 | 27745篇 |
1993年 | 27606篇 |
1992年 | 25945篇 |
1991年 | 22840篇 |
1990年 | 23257篇 |
1989年 | 22315篇 |
1988年 | 20857篇 |
1987年 | 19180篇 |
1986年 | 18487篇 |
1985年 | 21853篇 |
1984年 | 22193篇 |
1983年 | 20136篇 |
1982年 | 19171篇 |
1981年 | 19273篇 |
1980年 | 17860篇 |
1979年 | 18456篇 |
1978年 | 17674篇 |
1977年 | 17192篇 |
1976年 | 17770篇 |
1975年 | 15985篇 |
1974年 | 15486篇 |
1973年 | 15538篇 |
1972年 | 13003篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
Molino A. Vacca F. Masera G. Nguyen T.Q. 《Vision, Image and Signal Processing, IEE Proceedings -》2006,153(6):860-868
To efficiently compute the phase difference (PD) between two complex numbers, two novel approaches are described. The problem of fast PD computation is central in many applications. As a case study, the main focus is on the phase correlation technique that is used for motion estimation. Starting from the problem statement, the system requirements are dealt with showing how PD requires a remarkable amount of computational resources. Reduced complexity techniques are then proposed and specifically tailored to suit the application needs. Each solution is completely implemented both in 0.25 mum as well as 0.13 mum CMOS. The so-called LUT-ROT exhibits noteworthy figures in terms of area occupation, delay and power dissipation, saving nearly 50% in terms of area and power when compared to recent work on this subject 相似文献
952.
Stievano I.S. Maio I.A. Canavero F.G. Siviero C. 《Advanced Packaging, IEEE Transactions on》2006,29(1):31-38
This paper addresses the impact of device macromodels on the accuracy of signal integrity and performance predictions for critical digital interconnecting systems. It exploits nonlinear parametric models for both single-ended and differential devices, including the effects of power supply fluctuations and receiver bit detection. The analysis demonstrates that the use of well-designed macromodels dramatically speeds up the simulation as well it preserves timing accuracy even for long bit sequences. 相似文献
953.
A. Yu. Grinev E. N. Voronin 《Journal of Communications Technology and Electronics》2006,51(3):255-262
It is shown that two approaches can efficiently be applied to calculate impulse responses of antennas radiating superwideband signals. The simultaneous use of these approaches makes it possible to lucidly describe the operation of certain antennas and substantially simplify the calculations. The impulse responses of some short-video-pulse scanning array antennas and the shapes of radiated signals are calculated. 相似文献
954.
We present PowerNap, an OS power management scheme, which can significantly improve the battery life of mobile devices. The key feature of PowerNap is the skipping of the periodic system timer ticks associated with the operating system. On an idle device, this modification increases the time between successive timer interrupts and enables us to put the processor/system into a more efficient low power state. This saves the energy consumed by workless timer interrupts and the excess energy consumed by the processor in less efficient low power states. PowerNap is tightly integrated with the kernel and is designed for optimal control of the latency and energy associated with transitioning in and out of the low power states. We describe an implementation of PowerNap and its impact on system software. Experiments with IBM's WatchPad verify the ability of PowerNap to extend battery life. An analytical model that quantifies the ability of the scheme to reduce power is also presented. The model is in good agreement with experimental results. We apply the model to small form-factor devices which use processors that have a PowerDown state. In such devices, PowerNap may extend battery life by more than 42 percent for small processor workloads and for background power levels below 10 mW. 相似文献
955.
Siu-Chung Wong Tse C.K. Orabi M. Ninomiya T. 《IEEE transactions on circuits and systems. I, Regular papers》2006,53(2):454-462
This paper describes the modeling of power-factor-correction converters under average-current-mode control, which are widely used in switch-mode power supply applications. The objective is to identify stability boundaries in terms of major circuit parameters for facilitating design of such converters. The approach employs a double averaging procedure, which first applies the usual averaging over the switching period and subsequently applies generalized averaging over the mains period. The resulting model, after two averaging steps and application of a harmonic balance procedure, is nonlinear and capable of describing the low-frequency nonlinear dynamics of the system. The parameter ranges within which stable operation is guaranteed can be accurately and easily found using this model. Experimental measurements are provided for verification of the analytical results. 相似文献
956.
This paper seeks to explore a method to accurately correct geometric distortions caused during the capture of three-dimensional (3-D) integral images. Such distortions are rotational and scaling errors which, if not corrected, will cause banding and moire effects on the replayed image. The method for calculating the angle of deviation in the 3-D Integral Images is based on Hough Transform. It allows detection of the angle necessary for correction of the rotational error. Experiments have been conducted on a number of 3-D integral image samples and it has been found that the proposed method produces results with accuracy of 0.05 deg 相似文献
957.
Observer-based estimators (OBE) were used for estimation of state variables and kinetic parameters in an anaerobic digestion (AD) process. A simplified first-order model with time-varying kinetic parameters was used to design an OBE for kinetic parameter estimation. This approach was validated on a laboratory-scale anaerobic reactor equipped with a multiwavelength fluorometer for on-line measurements of COD and VFA concentrations in the reactor effluent. The proposed estimators provide continuous adjustment of kinetic parameters and can be used for predictions of state variables between samples acquisition and during sensor failure. 相似文献
958.
959.
A. Yu. Pustynnikov V. G. Ryabov D. T. Kalimullin A. N. Nechaev Ya. A. Treskov 《Chemistry and Technology of Fuels and Oils》2006,42(3):188-191
Paving-and roofing-grade asphalts were obtained at LUKOIL-Permnefteorgsintez Ltd. by mixing peroxidized asphalt and a number
of high-boiling unoxidized petroleum products in certain ratios. The asphalts obtained have improved performance characteristics:
high plasticity and low brittleness temperature.
__________
Translated from Khimiya i Tekhnologiya Topliv i Masel, No. 2, pp. 26–28, May–June, 2006. 相似文献
960.
The NW‐SE trending Cantarell structure in the Gulf of Campeche hosts the largest oilfield in Mexico. The oil occurs predominantly in latest Cretaceous – earliest Tertiary breccias with subsidiary reserves in Upper Jurassic (Oxfordian and Kimmeridgian) and Lower Cretaceous oolitic and partially dolomitized limestones, dolomites and shaly limestones. Cantarell has been interpreted both as a fold‐and‐thrust zone and as a dextral transpressional structure. Analysis of structure contours at 100m intervals, on the tops of the Tertiary breccia and the Kimmeridgian (Upper Jurassic) dolomite, indicates that the structure is an upright cylindrical fold with gently plunging conical terminations; there is also a conical portion in the central part of the structure. The axes of the central, NW and SE cones are subvertical. This geometry indicates that the two fold terminations and the central cone are aprons rather than points, with the NW and central cone axes intersecting the cylindrical fold axis at the point where the geometry switches from conical to cylindrical. The apical angle (i.e. the angle between the fold and cone axes) varies as follows: (i) in the NW cone, it is ~70° in the breccia and ~76° in the Kimmeridgian dolomite; (ii) in the central cone, it is ~77° in the breccia and ~73° in the Kimmeridgian dolomite; and (iii) in the SE cone, it is ~64° in the breccia and ~57° in the Kimmeridgian dolomite. This indicates that whereas the fold opens with depth in the NW cone, it tightens with depth in the central and SE cones. Assuming a parallel fold geometry, these apical angles indicate an increase in volume in the NW cone (i.e. larger hydrocarbon reservoirs), compared to the central and SE cones. Theoretical considerations indicate that the curvature increases dramatically towards the point of the cone. In the case of the Cantarell structure, the apices of the cones are located at the conical‐cylindrical fold junctions, where the highest curvature may have resulted in a higher degree of fracturing. The coincidence of maximum curvature and the intersection of the conical and cylindrical fold axes in the fold culminations with porous and permeable reservoir rocks may have made these locations favourable for the accumulation of hydrocarbons. 相似文献