全文获取类型
收费全文 | 103418篇 |
免费 | 1367篇 |
国内免费 | 1230篇 |
专业分类
电工技术 | 1926篇 |
综合类 | 139篇 |
化学工业 | 10622篇 |
金属工艺 | 5489篇 |
机械仪表 | 3223篇 |
建筑科学 | 2037篇 |
矿业工程 | 159篇 |
能源动力 | 2974篇 |
轻工业 | 6081篇 |
水利工程 | 704篇 |
石油天然气 | 669篇 |
武器工业 | 15篇 |
无线电 | 16007篇 |
一般工业技术 | 21867篇 |
冶金工业 | 25320篇 |
原子能技术 | 1388篇 |
自动化技术 | 7395篇 |
出版年
2022年 | 461篇 |
2021年 | 714篇 |
2020年 | 531篇 |
2019年 | 691篇 |
2018年 | 1146篇 |
2017年 | 1110篇 |
2016年 | 1185篇 |
2015年 | 941篇 |
2014年 | 1511篇 |
2013年 | 4713篇 |
2012年 | 2620篇 |
2011年 | 3885篇 |
2010年 | 3127篇 |
2009年 | 3741篇 |
2008年 | 3917篇 |
2007年 | 4097篇 |
2006年 | 3702篇 |
2005年 | 3344篇 |
2004年 | 3185篇 |
2003年 | 3042篇 |
2002年 | 2682篇 |
2001年 | 2979篇 |
2000年 | 2725篇 |
1999年 | 3085篇 |
1998年 | 9472篇 |
1997年 | 6176篇 |
1996年 | 4769篇 |
1995年 | 3166篇 |
1994年 | 2791篇 |
1993年 | 2727篇 |
1992年 | 1632篇 |
1991年 | 1593篇 |
1990年 | 1519篇 |
1989年 | 1323篇 |
1988年 | 1171篇 |
1987年 | 862篇 |
1986年 | 887篇 |
1985年 | 917篇 |
1984年 | 803篇 |
1983年 | 700篇 |
1982年 | 699篇 |
1981年 | 681篇 |
1980年 | 567篇 |
1979年 | 476篇 |
1978年 | 414篇 |
1977年 | 533篇 |
1976年 | 960篇 |
1975年 | 300篇 |
1974年 | 276篇 |
1973年 | 256篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
12.
L. Vu‐Quoc V. Srinivas Y. Zhai 《International journal for numerical methods in engineering》2003,58(3):397-461
We establish a systematic methodology to design and analyse electromagnetic components such as advanced multilayer ceramic capacitors (MLCCs) using the finite element (FE) method. We employ a coupled formulation to compute the interaction between the electric and magnetic fields. Unlike a linear distribution of current assumed in the circuit model, an accurate electrostatic solution to model the entire advanced MLCCs (4 × 4 × 27 = 432 cells) is presented. The FE solution is used to compute the lumped parameters for a range of frequencies. These lumped parameters are then used to compute the parasitic elements of the MLCCs. We introduce two algorithms to efficiently analyse the behaviour of a capacitor with changing frequency. The lower frequency (much below the self‐resonant frequency of the capacitor) algorithm separates the effect of the electric and magnetic fields and reduces the computational effort required to solve the FE problem, whereas, the high‐frequency algorithm couples the effect between the electric and the magnetic fields. We use these algorithms in conjunction with a new multiple scale technique to effectively determine the small values of R, L and C in MLCCs. The formulation, the implementation, and the numerical results demonstrate the efficacy of the present FE formulation and establish a systematic methodology to design and analyse advanced electromagnetic components. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
13.
14.
On the effect of spatial variances in historical rainfall time series to CSO performance evaluation.
Historical, high-resolution rain series are the backbone of modern combined sewer overflow (CSO) structure design. These rain series are the input to the computational estimation of the performance of the measures with respect to CSO pollution abatement. However, those historical precipitation measurements are available at only a few locations. Frequently rain series have to be used from gauging stations at a significant distance. In order to judge and to compensate for this influence an estimate between rain characteristics and combined sewer outflow (CSO) performance indicators would be useful. In this paper such correlations have been sought for a collection of 37 rain series covering large areas of Europe. It was found that the mean annual rain volume can explain most of the variances for the performance indicators Number of overflows and CSO volume. For explaining the spatial differences in the efficiency of the CSO structure another rain characteristic, i.e. the maximum event with a return period of one year, is to be used. 相似文献
15.
H. L. Du S. R. Rose Z. D. Xiang P. K. Datta X. Y. Li 《Materialwissenschaft und Werkstofftechnik》2003,34(4):421-426
The oxidation/sulphidation behaviour of a Ti‐46.7Al‐1.9W‐0.5Si alloy with a TiAl3 diffusion coating was studied in an environment of H2/H2S/H2O at 850oC. The kinetic results demonstrate that the TiAl3 coating significantly increased the high temperature corrosion resistance of Ti‐46.7Al‐1.9W‐0.5Si. The SEM, EDX, XRD and TEM analysis reveals that the formation of an Al2O3 scale on the surface of the TiAl3‐coated sample was responsible for the enhancement of the corroison resistance. The Ti‐46.7Al‐1.9W‐0.5Si alloy was also modified by Nb ion implantation. The Nb ion implanted and as received sampels were subjected to cyclic oxidation in an open air at 800oC. The Nb ion implantation not only increased the oxidation resistance but also substantially improved the adhesion of scale to the substrate. 相似文献
16.
The aim of this study was to evaluate the use of total coliforms (TC) and faecal coliforms (FC) using a membrane filtration method for precise monitoring of faecal pollution in Korean surface water. The samples were collected in Korea from both main rivers and their tributaries. Presumptive TC * FC were enumerated. The ratios of presumptive FC to TC were not constant, but varied widely, and TC were difficult to enumerate because of overgrowth by background colonies. For FC this was not the case. Seven hundred and three purified strains of presumptive TC * FC and their background colonies were biotyped using API 20E. Among 272 presumptive TC, non-faecal related species, Aeromonas hydrophila dominated (34.6%) and E. coli accounted for only 5.1%. In contrast, E. coli made up 89% of the 209 presumptive FC. Furthermore, of 164 background colonies on Endo Agar LES, 54.9% was A. hydrophila, while background colonies on m-FC Agar were few (58 strains), and despite their atypical colony appearance, most of them were biotyped as enteric bacteria. These results reveal that the detection of FC rather than TC using m-FC Agar is more appropriate for faecal pollution monitoring in eutrophicated surface water located in a temperate region. 相似文献
17.
Using a corrected sum rule and a generalized virial identity, we study the analytical expression for entire modes of the collective elementary excitation spectrum in a trapped Bose–Einstein condensate at any atom number. Explicit analytical formulas for the spectrum are obtained for the harmonic traps with both spherical symmetry and axial symmetry using the gaussian approximation for the N-body ground-state wave function of the condensate. These formulas give the simple dependence of all energy levels on the atom numbers, their interaction strength and trap geometry parameters. 相似文献
18.
R. Murgan F. Razak D. R. Tilley T. Y. Tan J. Osman M. N. A. Halif 《Computational Materials Science》2004,30(3-4):468-473
We derive an expression for transmittivity (TSHG) of second harmonic generation (SHG) signals from a ferroelectric (FE) film. Intensities of up and down fields in the medium are investigated in relation to TSHG. The derivations are made based on undepletion of input fields and nonlinear wave equation derived from the Maxwell equations. We present two cases: film without mirrors and with partial mirrors. Expressions for the newly derived nonlinear susceptibility coefficients of SHG for real crystal symmetry [J. Opt. Soc. Am. B 19 (2002) 2007] are used to get more realistic results. Variations in TSHG with respect to film thickness are illustrated. 相似文献
19.
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
20.