全文获取类型
收费全文 | 491184篇 |
免费 | 5960篇 |
国内免费 | 1066篇 |
专业分类
电工技术 | 8526篇 |
综合类 | 424篇 |
化学工业 | 75839篇 |
金属工艺 | 23527篇 |
机械仪表 | 17091篇 |
建筑科学 | 10447篇 |
矿业工程 | 4487篇 |
能源动力 | 10103篇 |
轻工业 | 35420篇 |
水利工程 | 6374篇 |
石油天然气 | 14999篇 |
武器工业 | 92篇 |
无线电 | 51413篇 |
一般工业技术 | 106928篇 |
冶金工业 | 77467篇 |
原子能技术 | 14715篇 |
自动化技术 | 40358篇 |
出版年
2021年 | 4796篇 |
2019年 | 4737篇 |
2018年 | 8764篇 |
2017年 | 9023篇 |
2016年 | 9523篇 |
2015年 | 5570篇 |
2014年 | 9227篇 |
2013年 | 21445篇 |
2012年 | 13937篇 |
2011年 | 17578篇 |
2010年 | 14084篇 |
2009年 | 15471篇 |
2008年 | 16372篇 |
2007年 | 16026篇 |
2006年 | 13588篇 |
2005年 | 12225篇 |
2004年 | 11858篇 |
2003年 | 11613篇 |
2002年 | 11072篇 |
2001年 | 10880篇 |
2000年 | 10546篇 |
1999年 | 10088篇 |
1998年 | 21651篇 |
1997年 | 16113篇 |
1996年 | 12475篇 |
1995年 | 9852篇 |
1994年 | 8892篇 |
1993年 | 8954篇 |
1992年 | 7339篇 |
1991年 | 7130篇 |
1990年 | 7080篇 |
1989年 | 6763篇 |
1988年 | 6511篇 |
1987年 | 6088篇 |
1986年 | 5927篇 |
1985年 | 6539篇 |
1984年 | 6267篇 |
1983年 | 5786篇 |
1982年 | 5480篇 |
1981年 | 5611篇 |
1980年 | 5446篇 |
1979年 | 5506篇 |
1978年 | 5564篇 |
1977年 | 5984篇 |
1976年 | 7105篇 |
1975年 | 5135篇 |
1974年 | 5169篇 |
1973年 | 5260篇 |
1972年 | 4468篇 |
1971年 | 4125篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
21.
22.
Quasi-static stress fields for a crack inclined to the property gradation in functionally graded materials 总被引:3,自引:0,他引:3
Summary. Quasi-static stress fields for a crack inclined to the direction of property gradation in functionally graded materials (FGMs)
are obtained through an asymptotic analysis coupled with Westergaard's stress function approach. The elastic modulus of the
FGM is assumed to vary exponentially along the gradation direction. The mode mixity due to the inclination of the property
gradient is accommodated in the analysis through superposition of opening and shear modes. The first four terms in the expansion
of the stress field are derived to explicitly bring out the influence of nonhomogeneity on the structure of the stress field.
Using these stress field contours of constant maximum shear stress, constant maximum principal stress, constant first stress
invariant and constant out of plane displacement are generated, and the effect of inclination of the property gradation direction
on these contours is discussed.
Received September 22, 2002
Published online: May 20, 2003
The financial support of National Science Foundation (NSF) under grant no. CMS 99000138 is gratefully acknowledged. 相似文献
23.
24.
V. N. Tsygankov V. V. Safonov A. I. Kozlov V. P. Gavrilov 《Inorganic Materials》2003,39(10):1076-1078
The GeO2–NiO system is studied in the stability range of Ni2GeO4 by temperature-dependent resistivity measurements, in combination with x-ray diffraction, differential thermal analysis, and thermogravimetry. The resistivity of the starting mixtures and heat-treated samples is measured in the composition range 55–90 mol % NiO. The effect of air humidity on the resistivity of the samples is examined. 相似文献
25.
Thomy V. Dubois L. Vanoverschelde C. Sozanski J.P. Pribetich J. 《IEEE sensors journal》2004,4(6):772-778
This paper describes a novel planar antenna sensor created for the purpose of noninvasive temperature measurements using microwave radiometry. In order to improve radiometric measurements in industrial applications, a new generation of sensors is introduced, composed of a metallic sheet. Simulations based upon the method of moments is used both to design and to determine their electromagnetic performances. This paper also describes a radiometric device using these sensors to measure and control the temperature of food products during deep freezing processes. The results and discussions are presented. 相似文献
26.
27.
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
28.
Gas/liquid mass transfer has been investigated using a stirred vessel gas/liquid contactor using non‐Newtonian media and carbon dioxide as absorbent and gas phase, respectively. The volumetric mass transfer coefficients at different operational variables have been determined. Non‐Newtonian media (liquid phase) were prepared as aqueous solutions of sodium carboxymethyl cellulose salt. The influence of the rheological properties, polymer concentration, stirring rate, and gas flow rate on mass transfer was studied for these liquid phases. Kinematic viscosity and density experimental data were used to calculate the average molecular weight corresponding to the polymer employed. The Ostwald model has been used to fit the rheological behavior of aqueous solutions of the polymer employed as absorbent phase. Reasonably good agreement was found between the predictions of the proposed models and the experimental data of mass transfer coefficients. 相似文献
29.
30.
It is shown that, for the spectrum analysis of digital quasi-periodic signals, one must use a procedure based on approximating the sequence of data readouts by a first-order trigonometric polynomial with a varying frequency of its harmonic functions. 相似文献