全文获取类型
收费全文 | 1585389篇 |
免费 | 26449篇 |
国内免费 | 7080篇 |
专业分类
电工技术 | 34606篇 |
综合类 | 6551篇 |
化学工业 | 274438篇 |
金属工艺 | 65154篇 |
机械仪表 | 44559篇 |
建筑科学 | 48211篇 |
矿业工程 | 11481篇 |
能源动力 | 50433篇 |
轻工业 | 123688篇 |
水利工程 | 16139篇 |
石油天然气 | 37482篇 |
武器工业 | 140篇 |
无线电 | 198464篇 |
一般工业技术 | 297864篇 |
冶金工业 | 202170篇 |
原子能技术 | 34000篇 |
自动化技术 | 173538篇 |
出版年
2021年 | 15720篇 |
2020年 | 11972篇 |
2019年 | 14747篇 |
2018年 | 16199篇 |
2017年 | 15512篇 |
2016年 | 21828篇 |
2015年 | 17557篇 |
2014年 | 28961篇 |
2013年 | 88371篇 |
2012年 | 37680篇 |
2011年 | 51015篇 |
2010年 | 43665篇 |
2009年 | 51439篇 |
2008年 | 47393篇 |
2007年 | 44854篇 |
2006年 | 46735篇 |
2005年 | 41213篇 |
2004年 | 43519篇 |
2003年 | 43328篇 |
2002年 | 42074篇 |
2001年 | 39496篇 |
2000年 | 37611篇 |
1999年 | 37304篇 |
1998年 | 57340篇 |
1997年 | 46645篇 |
1996年 | 40255篇 |
1995年 | 33810篇 |
1994年 | 31534篇 |
1993年 | 31026篇 |
1992年 | 27007篇 |
1991年 | 24270篇 |
1990年 | 24413篇 |
1989年 | 23491篇 |
1988年 | 22056篇 |
1987年 | 20232篇 |
1986年 | 19771篇 |
1985年 | 23045篇 |
1984年 | 22942篇 |
1983年 | 20845篇 |
1982年 | 19638篇 |
1981年 | 19760篇 |
1980年 | 18378篇 |
1979年 | 18921篇 |
1978年 | 18094篇 |
1977年 | 18641篇 |
1976年 | 21066篇 |
1975年 | 16252篇 |
1974年 | 15748篇 |
1973年 | 15823篇 |
1972年 | 13306篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
A nonstationary model of SO2 absorption from a gas phase to a countercurrent falling film of absorbing slurry was developed. Laminar, wavy and turbulent film structures were considered based on published information. Resistances to the mass transfer on the gas and the liquid sides of the interphase were considered, together with chemical reactions in the liquid phase. Relevant chemical equilibria in the liquid phase were modeled. Original experimental data on the neutralization reagent dissolution rate presented as a polydispersed two‐phase system of solids and on the rate of dissolved sulfite oxidation were used. The model was verified with experimental data from a laboratory‐scale falling‐film absorber using a single vertical tube under various geometrical and operating conditions, and a very good agreement was found with the experiment. Parametric sensitivity analysis showed the critical parts of the model. 相似文献
992.
The microstructure evolution in nonstoichiometric titanium carbide is studied during high-temperature deformation at high strain rates and low strains (shock compression) and at slow strain rates and high strains (superplastic regime). The results demonstrate that high-temperature deformation in a broad range of strain rates offers a means of controlling the microstructure of titanium carbide. By varying deformation conditions, one can obtain materials differing in microstructure and chemical composition, in particular, with equilibrium and nonequilibrium microstructures. Accordingly, the physicochemical properties of such materials also differ. 相似文献
993.
An analysis is made of the characteristic features and problems of the optimal processing of the results of measurements in the case of a random observation function utilizing a nonlinear Kalman filter. A method is proposed for increasing the convergence domain of the filter with additional processing of measurements in the frequency domain. 相似文献
994.
Kilchytska V. Neve A. Vancaillie L. Levacq D. Adriaensen S. van Meer H. De Meyer K. Raynaud C. Dehan M. Raskin J.-P. Flandre D. 《Electron Devices, IEEE Transactions on》2003,50(3):577-588
This work presents a systematic comparative study of the influence of various process options on the analog and RF properties of fully depleted (FD) silicon-on-insulator (SOI), partially depleted (PD) SOI, and bulk MOSFET's with gate lengths down to 0.08 /spl mu/m. We introduce the transconductance-over-drain current ratio and Early voltage as key figures of merits for the analog MOS performance and the gain and the transition and maximum frequencies for RF performances and link them to device engineering. Specifically, we investigate the effects of HALO implantation in FD, PD, and bulk devices, of film thickness in FD, of substrate doping in SOI, and of nonstandard channel engineering (i.e., asymmetric Graded-channel MOSFETs and gate-body contacted DTMOS). 相似文献
995.
We consider the problem of designing a network of optical cross-connects (OXCs) to provide end-to-end lightpath services to large numbers of label switched routers (LSRs). We present a set of heuristic algorithms to address the combined problem of physical topology design (i.e., determine the number of OXCs required and the fiber links among them) and logical topology design (i.e., determine the routing and wavelength assignment for the lightpaths among the LSRs). Unlike previous studies which were limited to small topologies with a handful of nodes and a few tens of lightpaths, we have applied our algorithms to networks with hundreds or thousands of LSRs and with a number of lightpaths that is an order of magnitude larger than the number of LSRs. In order to characterize the performance of our algorithms, we have developed lower bounds which can be computed efficiently. We present numerical results for up to 1000 LSRs and for a wide range of system parameters such as the number of wavelengths per fiber, the number of transceivers per LSR, and the number of ports per OXC. The results indicate that it is possible to build large-scale optical networks with rich connectivity in a cost-effective manner, using relatively few but properly dimensioned OXCs. 相似文献
996.
997.
A hybrid optical fibre amplifier is described that consists of a fluoride-based thulium-doped fibre amplifier and a silica-based erbium-doped fibre amplifier connected in a cascade. The amplifier has a gain of more than 25 dB and a noise figure of less than 9 dB over a wide wavelength region of 1458-1540 nm. 相似文献
998.
Static energy reduction techniques for microprocessor caches 总被引:1,自引:0,他引:1
Hanson H. Hrishikesh M.S. Agarwal V. Keckler S.W. Burger D. 《Very Large Scale Integration (VLSI) Systems, IEEE Transactions on》2003,11(3):303-313
Microprocessor performance has been improved by increasing the capacity of on-chip caches. However, the performance gain comes at the price of static energy consumption due to subthreshold leakage current in cache memory arrays. This paper compares three techniques for reducing static energy consumption in on-chip level-1 and level-2 caches. One technique employs low-leakage transistors in the memory cell. Another technique, power supply switching, can be used to turn off memory cells and discard their contents. A third alternative is dynamic threshold modulation, which places memory cells in a standby state that preserves cell contents. In our experiments, we explore the energy and performance tradeoffs of these techniques. We also investigate the sensitivity of microprocessor performance and energy consumption to additional cache latency caused by leakage-reduction techniques. 相似文献
999.
The paper presents an improved statistical analysis of the least mean fourth (LMF) adaptive algorithm behavior for a stationary Gaussian input. The analysis improves previous results in that higher order moments of the weight error vector are not neglected and that it is not restricted to a specific noise distribution. The analysis is based on the independence theory and assumes reasonably slow learning and a large number of adaptive filter coefficients. A new analytical model is derived, which is able to predict the algorithm behavior accurately, both during transient and in steady-state, for small step sizes and long impulse responses. The new model is valid for any zero-mean symmetric noise density function and for any signal-to-noise ratio (SNR). Computer simulations illustrate the accuracy of the new model in predicting the algorithm behavior in several different situations. 相似文献
1000.
2-D symmetry: theory and filter design applications 总被引:1,自引:0,他引:1
In this comprehensive review article, we present the theory of symmetry in two-dimensional (2-D) filter functions and in 2-D Fourier transforms. It is shown that when a filter frequency response possesses symmetry, the realization problem becomes relatively simple. Further, when the frequency response has no symmetry, there is a technique to decompose that frequency response into components each of which has the desired symmetry. This again reduces the complexity of two-dimensional filter design. A number of filter design examples are illustrated. 相似文献