全文获取类型
收费全文 | 445180篇 |
免费 | 4100篇 |
国内免费 | 648篇 |
专业分类
电工技术 | 7551篇 |
综合类 | 340篇 |
化学工业 | 71967篇 |
金属工艺 | 21665篇 |
机械仪表 | 15354篇 |
建筑科学 | 9034篇 |
矿业工程 | 4519篇 |
能源动力 | 8484篇 |
轻工业 | 32628篇 |
水利工程 | 6032篇 |
石油天然气 | 15372篇 |
武器工业 | 55篇 |
无线电 | 41078篇 |
一般工业技术 | 96700篇 |
冶金工业 | 71736篇 |
原子能技术 | 14687篇 |
自动化技术 | 32726篇 |
出版年
2021年 | 4239篇 |
2019年 | 4089篇 |
2018年 | 7532篇 |
2017年 | 7775篇 |
2016年 | 8226篇 |
2015年 | 4636篇 |
2014年 | 8060篇 |
2013年 | 18398篇 |
2012年 | 11956篇 |
2011年 | 15420篇 |
2010年 | 12392篇 |
2009年 | 13729篇 |
2008年 | 14237篇 |
2007年 | 14093篇 |
2006年 | 11962篇 |
2005年 | 10489篇 |
2004年 | 10241篇 |
2003年 | 9916篇 |
2002年 | 9908篇 |
2001年 | 9625篇 |
2000年 | 9442篇 |
1999年 | 8853篇 |
1998年 | 18663篇 |
1997年 | 13815篇 |
1996年 | 10629篇 |
1995年 | 8471篇 |
1994年 | 7705篇 |
1993年 | 7718篇 |
1992年 | 6379篇 |
1991年 | 6194篇 |
1990年 | 6452篇 |
1989年 | 6261篇 |
1988年 | 6018篇 |
1987年 | 5631篇 |
1986年 | 5583篇 |
1985年 | 6138篇 |
1984年 | 5927篇 |
1983年 | 5565篇 |
1982年 | 5251篇 |
1981年 | 5347篇 |
1980年 | 5274篇 |
1979年 | 5381篇 |
1978年 | 5569篇 |
1977年 | 5881篇 |
1976年 | 7093篇 |
1975年 | 5031篇 |
1974年 | 5038篇 |
1973年 | 5153篇 |
1972年 | 4494篇 |
1971年 | 4143篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
21.
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
22.
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
23.
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
24.
25.
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
26.
27.
The characteristics of pulsation processes in dc plasmatrons with the cathode located in the channel center and the anode in the form of a cylindrical or a conical channel wall are investigated in plasmas of argon and nitrogen at atmospheric pressure. The fast Fourier transform of signals and their subsequent computer processing are used to obtain the dependences of the frequency of fluctuations of the arcing voltage on the working parameters of the plasmatron, namely, the electric arc current, the flow rate of plasma-forming gas, and the channel diameter. For plasmatrons with the self-adjusting length of the electric arc, analysis is performed of the mechanism of reclosing of the anode region of the arc, i.e., of the electric arc shunting associated with the stretching of the current filament by a flow of gas and with the electrodynamic interaction of different filament regions. A formula is derived which defines the dependence of the characteristic frequency of fluctuations of the arcing voltage on the external parameters of the problem, namely, the arc current, the flow rate of the working gas, and the characteristic channel diameter. It is demonstrated that the pattern of the dependence of the frequency of voltage fluctuations on the gas flow rate may vary with the values of the parameter of magnetohydrodynamic interaction. The formula generalizes the experimental results of numerous researchers obtained in a wide range of variation of the external parameters. 相似文献
28.
The present work deals with the modelling of damage behaviour for sheet moulding compound (SMC) composite materials using a finite element analysis package. Specifically, a comparison is made between the results obtained experimentally for a three-point bending test, and those obtained from numerical simulation using a material model already implemented. The simulation has been performed for the material models available within the PAM-CRASH software. The simulation results are compared and validated with respect to experimentation. 相似文献
29.
Yu. V. Baldokhin V. V. Vavilova P. Ya. Kolotyrkin Yu. K. Kovneristyi N. A. Palii A. S. Solomatin 《Inorganic Materials》2003,39(6):562-567
Mössbauer effect measurements and physicochemical analysis demonstrate that annealing of amorphous Fe–P–Mn alloys leads to the formation of a nanocrystalline structure. 相似文献
30.
为了分析多水库系统中两座水库之间灌溉用水的分配问题,建立了基到动态规划的神经网络模型。为了研究从一座上游水库取水在下游两座之库之间进行水量分配的问题,提出了3个状态变量和4个决策变量的改进的动态规划算法。采用神经网络模型,用3个状态变量动态规划算法得出调度原则,就所研究的多水库系统实例来说,新的动态规划神经网络模型的性能很好,将该模型的性能与临时凑合的标准调度原则和以前推荐使用的约束动态规划神经网络模型进行了比较。 相似文献