全文获取类型
收费全文 | 773856篇 |
免费 | 9174篇 |
国内免费 | 2050篇 |
专业分类
电工技术 | 13026篇 |
综合类 | 2896篇 |
化学工业 | 116332篇 |
金属工艺 | 34994篇 |
机械仪表 | 25200篇 |
建筑科学 | 17756篇 |
矿业工程 | 5588篇 |
能源动力 | 18222篇 |
轻工业 | 56374篇 |
水利工程 | 9353篇 |
石油天然气 | 18362篇 |
武器工业 | 50篇 |
无线电 | 81645篇 |
一般工业技术 | 159549篇 |
冶金工业 | 128018篇 |
原子能技术 | 17983篇 |
自动化技术 | 79732篇 |
出版年
2021年 | 6701篇 |
2020年 | 4910篇 |
2019年 | 6384篇 |
2018年 | 24629篇 |
2017年 | 23602篇 |
2016年 | 21138篇 |
2015年 | 8172篇 |
2014年 | 12938篇 |
2013年 | 31230篇 |
2012年 | 22331篇 |
2011年 | 34769篇 |
2010年 | 28228篇 |
2009年 | 28307篇 |
2008年 | 29856篇 |
2007年 | 30240篇 |
2006年 | 19822篇 |
2005年 | 18990篇 |
2004年 | 18347篇 |
2003年 | 18164篇 |
2002年 | 16667篇 |
2001年 | 16316篇 |
2000年 | 15398篇 |
1999年 | 15528篇 |
1998年 | 37762篇 |
1997年 | 26961篇 |
1996年 | 20586篇 |
1995年 | 15659篇 |
1994年 | 13755篇 |
1993年 | 13623篇 |
1992年 | 10179篇 |
1991年 | 9793篇 |
1990年 | 9745篇 |
1989年 | 9395篇 |
1988年 | 8771篇 |
1987年 | 8054篇 |
1986年 | 7857篇 |
1985年 | 8624篇 |
1984年 | 8159篇 |
1983年 | 7416篇 |
1982年 | 6949篇 |
1981年 | 7127篇 |
1980年 | 6879篇 |
1979年 | 6906篇 |
1978年 | 6884篇 |
1977年 | 7786篇 |
1976年 | 9769篇 |
1975年 | 6069篇 |
1974年 | 5914篇 |
1973年 | 5985篇 |
1972年 | 5122篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
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
42.
Diphenylzinc, alone or in combination with water and butanone as coinitiators, was used as a polymerization initiator system for a variety of lactones at varying temperatures. The resulting data indicate that the course of the polymerization is greatly influenced by the lactone structure, as well as by the molar ratio of coinitiator to diphenylzinc. When used alone, diphenylzinc exhibited high activity as an initiator in δ‐valerolactone polymerizations, although it was less efficient when used in the β‐butyrolactone and the β‐propiolactone polymerizations. Activity in the polymerization of β‐lactones was increased by adding small amounts of butanone or water. It was also observed that the diphenylzinc–butanone combination was more effective than the diphenylzinc–water mixture in the polymerizations of β‐butyrolactone and β‐propiolactone. Copyright © 2003 Society of Chemical Industry 相似文献
43.
44.
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
45.
The catalytic activities of alumina prepared from an Al alkoxide-amine adduct monomer for the reaction of cyclopentene oxide with piperidine was determined after various pretreatments, including calcination and exposure to moisture. They were compared with the activity of alumina prepared by the conventional hydrolysis method. It was found that the as-prepared sample from the alkoxide-amine monomer preparation was five times more active than a conventional preparation, suggesting that it has a higher density of surface Lewis acid sites. However, its activity was much more severely suppressed by exposure to moisture. 相似文献
46.
S.M. Savaresi F.L. Taroni F. Previdi S. Bittanti 《Mechatronics, IEEE/ASME Transactions on》2004,9(3):569-579
The problem considered in this paper is the design and tuning of the control system of a power-split continuously variable transmission (CVT) used in high-power tractors. Power-split CVTs are characterized by the combination of a traditional mechanical transmission and by a continuously-variable transmission. This guarantees, at the same time, smooth variations of the transmission-ratio and high efficiency of the overall transmission system. The control architecture of an hydrostatic power-split CVT is constituted by three main parts: 1) servo-controller on the current of the valve which drives the hydraulic transmission; 2) a servo-controller on the hydraulic transmission-ratio; and 3) a synchronizer which coordinates the hydraulic and the mechanical parts of the CVT. In this work, these three controllers are fully developed, including: design, implementation, and evaluation on an experimental system. 相似文献
47.
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
48.
This paper describes techniques for the on-chip measurement of high-frequency and/or high-bandwidth electrical phenomena in ultra large-scale integration environments. The techniques rely on the integration of multiple compact and robust electronic test devices, or cores, at various locations within an integrated circuit. The cores consist primarily of signal generators that approximate the output of a sigma-delta modulator using finite repetitious bit patterns and a small set of highly robust analog components. They are capable of digitizing on-chip signals at gigahertz rates even using low-cost manufacturing processes. Simple communication between the multiple cores enables the migration of many "board-level" type measurements down to the chip level. 相似文献
49.
50.
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