全文获取类型
收费全文 | 1559207篇 |
免费 | 24664篇 |
国内免费 | 7030篇 |
专业分类
电工技术 | 34559篇 |
综合类 | 6385篇 |
化学工业 | 273356篇 |
金属工艺 | 65095篇 |
机械仪表 | 44126篇 |
建筑科学 | 47232篇 |
矿业工程 | 11536篇 |
能源动力 | 50377篇 |
轻工业 | 119431篇 |
水利工程 | 15728篇 |
石油天然气 | 37751篇 |
武器工业 | 140篇 |
无线电 | 197938篇 |
一般工业技术 | 293254篇 |
冶金工业 | 188150篇 |
原子能技术 | 34132篇 |
自动化技术 | 171711篇 |
出版年
2021年 | 15595篇 |
2020年 | 11896篇 |
2019年 | 14694篇 |
2018年 | 16617篇 |
2017年 | 16014篇 |
2016年 | 21894篇 |
2015年 | 17456篇 |
2014年 | 28748篇 |
2013年 | 88023篇 |
2012年 | 36754篇 |
2011年 | 49896篇 |
2010年 | 43380篇 |
2009年 | 51715篇 |
2008年 | 46358篇 |
2007年 | 43932篇 |
2006年 | 45697篇 |
2005年 | 40661篇 |
2004年 | 42691篇 |
2003年 | 42409篇 |
2002年 | 41351篇 |
2001年 | 38434篇 |
2000年 | 36738篇 |
1999年 | 36069篇 |
1998年 | 52431篇 |
1997年 | 43782篇 |
1996年 | 38472篇 |
1995年 | 32709篇 |
1994年 | 30401篇 |
1993年 | 30176篇 |
1992年 | 26763篇 |
1991年 | 24000篇 |
1990年 | 24212篇 |
1989年 | 23372篇 |
1988年 | 21880篇 |
1987年 | 20010篇 |
1986年 | 19539篇 |
1985年 | 22896篇 |
1984年 | 22705篇 |
1983年 | 20724篇 |
1982年 | 19518篇 |
1981年 | 19646篇 |
1980年 | 18309篇 |
1979年 | 18838篇 |
1978年 | 17969篇 |
1977年 | 18326篇 |
1976年 | 20088篇 |
1975年 | 16189篇 |
1974年 | 15696篇 |
1973年 | 15791篇 |
1972年 | 13268篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
231.
We consider the effect of multiple fibers on wavelength division multiplexing networks without wavelength conversion. We study networks with dynamic wavelength routing and develop accurate analytical models to compare various possible options using single- and multiple-fiber networks. We use results of an analytical model and simulation-based studies to evaluate the blocking performance and cost of multifiber networks. The number of fibers required providing high performance in multifiber networks and their costs are compared. A case is made for using multiple fibers in each link with fewer wavelengths instead of using a single fiber with many wavelengths. In particular, we show that a network with four fibers per link and with four wavelengths on each fiber without any wavelength conversion on any node yields similar same performance as the networks with one fiber per link and 16 wavelengths per fiber on each link and with full wavelength conversion capability on all nodes. In addition, the multifiber network may also offer the cost advantage depending on the relative cost of components. We develop a parametric cost model to show that multiple fibers in each link are an attractive option. Finally, such multifiber networks also has fault tolerance, with respect to a single fiber failure, already built into the system. 相似文献
232.
We present a stable and practical algorithm that uses QR factors of the Sylvester matrix to compute the greatest common divisor (GCD) of univariate approximate polynomials over /spl Ropf/[x] or /spl Copf/[x]. An approximate polynomial is a polynomial with coefficients that are not known with certainty. The algorithm of this paper improves over previously published algorithms by handling the case when common roots are near to or outside the unit circle, by splitting and reversal if necessary. The algorithm has been tested on thousands of examples, including pairs of polynomials of up to degree 1000, and is now distributed as the program QRGCD in the SNAP package of Maple 9. 相似文献
233.
In this paper, the moving least-squares differential quadrature (MLSDQ) method is employed for free vibration of thick antisymmetric laminates based on the first-order shear deformation theory. The generalized displacements of the laminates are independently approximated with the centered moving least-squares (MLS) technique within each domain of influence. The MLS nodal shape functions and their partial derivatives are computed quickly through back-substitutions after only one LU decomposition. Subsequently, the weighting coefficients in the MLSDQ discretization are determined with the nodal partial derivatives of the MLS shape functions. The MLSDQ method combines the merits of both the differential quadrature and meshless methods which can be conveniently applied to complex domains and irregular discretizations without loss of implementation efficiency and numerical accuracy. The natural frequencies of the laminates with various edge conditions, ply angles, and shapes are calculated and compared with the existing solutions to study the numerical accuracy and stability of the MLSDQ method. Effects of support size, order of completeness of basis functions, and node irregularity on the numerical accuracy are investigated in detail. 相似文献
234.
235.
Derivation of a second-order switching surface in the boundary control of buck converters 总被引:1,自引:0,他引:1
A second-order switching surface in the boundary control of buck converters is derived in this letter. The formulated switching surface can make the overall converter exhibit better steady-state and transient behaviors than the one with a first-order switching surface. The switching surface is derived by estimating the state trajectory movement after a switching action, resulting in a high state trajectory velocity along the switching surface. This phenomenon accelerates the trajectory moving toward the target operating point. The proposed control scheme has been successfully applied to a 120-W buck converter. The large-signal performance and a comparison with the first-order switching surface have been studied. 相似文献
236.
G. Martinez 《Journal of Low Temperature Physics》2003,133(1-2):61-95
High magnetic fields are one of the most powerful tools available to scientists for the study, modification and control of matter. This includes the knowledge on correlations effects, interaction mechanisms, structural information and understanding of mesoscopic effects. In this context, a review of recent scientific achievements at the Grenoble High Magnetic Laboratory is given to illustrate, on specific examples, the power of the Magnetic Field probe. 相似文献
237.
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
238.
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
239.
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
240.
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