全文获取类型
收费全文 | 2258篇 |
免费 | 222篇 |
国内免费 | 112篇 |
专业分类
电工技术 | 162篇 |
综合类 | 226篇 |
化学工业 | 33篇 |
金属工艺 | 14篇 |
机械仪表 | 216篇 |
建筑科学 | 20篇 |
矿业工程 | 15篇 |
能源动力 | 34篇 |
轻工业 | 7篇 |
水利工程 | 3篇 |
石油天然气 | 18篇 |
武器工业 | 24篇 |
无线电 | 1027篇 |
一般工业技术 | 331篇 |
冶金工业 | 13篇 |
原子能技术 | 21篇 |
自动化技术 | 428篇 |
出版年
2024年 | 14篇 |
2023年 | 23篇 |
2022年 | 35篇 |
2021年 | 40篇 |
2020年 | 51篇 |
2019年 | 45篇 |
2018年 | 46篇 |
2017年 | 76篇 |
2016年 | 81篇 |
2015年 | 100篇 |
2014年 | 132篇 |
2013年 | 132篇 |
2012年 | 202篇 |
2011年 | 175篇 |
2010年 | 145篇 |
2009年 | 144篇 |
2008年 | 157篇 |
2007年 | 187篇 |
2006年 | 162篇 |
2005年 | 155篇 |
2004年 | 98篇 |
2003年 | 89篇 |
2002年 | 51篇 |
2001年 | 53篇 |
2000年 | 39篇 |
1999年 | 37篇 |
1998年 | 33篇 |
1997年 | 17篇 |
1996年 | 23篇 |
1995年 | 18篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 5篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有2592条查询结果,搜索用时 15 毫秒
41.
LI Jing GE JianHua WANG Yong & YAO Hao State Key Laboratory of Integrated Service Networks Xidian University Xi’an China State Key Laboratory of Rail Traffic Control Safety Beijing Jiaotong University Beijing Department of Electronics Information Engineering Huazhong University of Science Technology Wuhan 《中国科学:信息科学(英文版)》2010,(5):1044-1055
An adaptive decode-and-forward (DF) cooperative diversity system based on quadrature modulation is proposed, in which each user is allowed to transmit its own and the partner’s data simultaneously via the in-phase and quadrature components of M -ary quadrature amplitude modulation (MQAM) constellation. Cooperative transmission in this way can avoid the bandwidth expansion in traditional cooperative systems. The closed form expression of the average bit error rate (BER) performance is derived in terms of the... 相似文献
42.
Francesco Tornabene 《Computer Methods in Applied Mechanics and Engineering》2009,198(37-40):2911-2935
Based on the First-order Shear Deformation Theory (FSDT) this paper focuses on the dynamic behavior of moderately thick functionally graded conical, cylindrical shells and annular plates. The last two structures are obtained as special cases of the conical shell formulation. The treatment is developed within the theory of linear elasticity, when materials are assumed to be isotropic and inhomogeneous through the thickness direction. The two-constituent functionally graded shell consists of ceramic and metal. These constituents are graded through the thickness, from one surface of the shell to the other. A generalization of the power-law distribution presented in literature is proposed. Two different four-parameter power-law distributions are considered for the ceramic volume fraction. Some material profiles through the functionally graded shell thickness are illustrated by varying the four parameters of power-law distributions. For the first power-law distribution, the bottom surface of the structure is ceramic rich, whereas the top surface can be metal rich, ceramic rich or made of a mixture of the two constituents and on the contrary for the second one. Symmetric and asymmetric volume fraction profiles are presented in this paper. The homogeneous isotropic material can be inferred as a special case of functionally graded materials (FGM). The governing equations of motion are expressed as functions of five kinematic parameters, by using the constitutive and kinematic relationships. The solution is given in terms of generalized displacement components of the points lying on the middle surface of the shell. The discretization of the system equations by means of the Generalized Differential Quadrature (GDQ) method leads to a standard linear eigenvalue problem, where two independent variables are involved without using the Fourier modal expansion methodology. Numerical results concerning six types of shell structures illustrate the influence of the power-law exponent, of the power-law distribution and of the choice of the four parameters on the mechanical behaviour of shell structures considered. 相似文献
43.
44.
Sam J. Cipolla 《Computer Physics Communications》2011,(11):2439-2440
In this new version of ISICS, called ISICS2011, a few omissions and incorrect entries in the built-in file of electron binding energies have been corrected; operational situations leading to un-physical behavior have been identified and flagged.
New version program summary
Program title: ISICS2011Catalogue identifier: ADDS_v5_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADDS_v5_0.htmlProgram obtainable from: CPC Program Library, Queen?s University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 6011No. of bytes in distributed program, including test data, etc.: 130 587Distribution format: tar.gzProgramming language: CComputer: 80486 or higher-level PCsOperating system: WINDOWS XP and all earlier operating systemsClassification: 16.7Catalogue identifier of previous version: ADDS_v4_0Journal reference of previous version: Comput. Phys. Commun. 180 (2009) 1716.Does the new version supersede the previous version?: YesNature of problem: Ionization and X-ray production cross section calculations for ion–atom collisions.Solution method: Numerical integration of form factor using a logarithmic transform and Gaussian quadrature, plus exact integration limits.Reasons for new version: General need for higher precision in output format for projectile energies; some built-in binding energies needed correcting; some anomalous results occur due to faulty read-in data or calculated parameters becoming un-physical; erroneous calculations could result for the L and M shells when restricted K-shell options are inadvertently chosen; to achieve general compatibility with ISICSoo, a companion C++ version that is portable to Linux and MacOS platforms, has been submitted for publication in the CPC Program Library approximately at the same time as this present new standalone version of ISICS [1].Summary of revisions: The format field for projectile energies in the output has been expanded from two to four decimal places in order to distinguish between closely spaced energy values. There were a few entries in the executable binding energy file that needed correcting; K shell of Eu, M shells of Zn, M1 shell of Kr. The corrected values were also entered in the ENERGY.DAT file. In addition, an alternate data file of binding energies is included, called ENERGY_GW.DAT, which is more up-to-date [2]. Likewise, an alternate atomic parameters data file is now included, called FLOURE_JC.DAT, which is more up-to-date [3] fluorescence yields for the K and L shells and Coster–Kronig parameters for the L shell. Both data files can be read in using the -f usage option. To do this, the original energy file should be renamed and saved (e.g., ENERGY_BB.DAT) and the new file (ENERGY_GW.DAT ) should be duplicated as ENERGY.DAT to be read in using the -f option. Similarly for reading in an alternate FLOURE.DAT file. As with previous versions, the user can also simply input different values of any input quantity by invoking the “specify your own parameters” option from the main menu. You can also use this option to simply check the values of the built-in values of the parameters. If it still happens that a zero binding energy for a particular sub-shell is read in, the program will not completely abort, but will calculate results for the other sub-shells while setting the affected sub-shell output to zero. In calculating the Coulomb deflection factor, if the quantity inside the radical sign of the parameter zs becomes zero or negative, to prevent the program from aborting, the PWBA cross sections are still calculated while the ECPSSR cross sections are set to zero. This situation can happen for very low energy collisions, such as were noticed for helium ions on copper at energies of E?11.2 keV. It was observed during the engineering of ISICSoo [1] that erroneous calculations could result for the L- and M-shell cases when restricted K-shell R or HSR scaling options were inappropriately chosen. The program has now been fixed so that these inappropriate options are ignored for the L and M shells. In the previous versions, the usage for inputting a batch data file was incorrectly stated in the Users Manual as -Bxxx; the correct designation is -Fxxx, or alternatively, -Ixxx, as indicated on the usage screen in running the program.A revised Users Manual is also available.Restrictions: The consumed CPU time increases with the atomic shell (K, L, M), but execution is still very fast.Running time: This depends on which shell and the number of different energies to be used in the calculation. The running time is not significantly changed from the previous version.References:[1]
M. Batic, M.G. Pia, S. Cipolla, Comput. Phys. Commun. (2011), submitted for publication. [2]
http://www.jlab.org/~gwyn/ebindene.html. [3]
J. Campbell, At. Data Nucl. Data Tables 85 (2003) 291.
45.
文章介绍了双向工频通信系统的基本原理及入站信号的调制和解调方法,详细地介绍了采用FIR滤波器及数字差分方法对入站信号进行提取的方法,并用Matlab/Simulink建立了基于配电网的仿真模型。对入站信号调制与提取的仿真研究验证了文中所述方法的正确性。 相似文献
46.
正交试验设计及其在电厂化学中的应用 总被引:3,自引:0,他引:3
在火力发电厂化学的生产和科研中,为了改革旧工艺和试验新方法,经常要做许多多因素试验。如何安排多因素试验,是一个值得研究的问题。正交试验设计是研究和处理多因素试验的一种科学方法,已在火力发电厂化学中获得了有效的应用。文中结合国内外的有关资料及作者在试验设计中的一点体会,论术字正交试验设计的原理和方法,以及其在电厂化学研究中应用的诸多方面,并指出了目前应用中存在的不足和解决方法。 相似文献
47.
48.
《国际计算机数学杂志》2012,89(3):679-689
In this paper, quadrature formulas with remaining term in integral form for functions partially holomorphic with respect to each variable in a Jordan polydomain in C 2 and a complex double integral formula are given. For this, we used the Cauchy Integral formula for Jordan polydomain in C 2. 相似文献
49.
《国际计算机数学杂志》2012,89(5):1097-1121
This paper presents the mechanical quadrature methods (MQMs) for solving the boundary integral equations of steady-state anisotropic heat conduction equation on the smooth domains and polygons, respectively. The costless and high-accurate Sidi–Israeli quadrature formula are applied to deal with the integrals in which the kernels have a logarithmic singularity. Especially, the Sidi transformation is used for the polygon cases in order to obtain a rapid convergence by degrading the singularity at the corners on the boundary. The convergence and stability of the MQMs solution are proved based on Anselone's collective compact theory. In addition, asymptotic error expansion of the MQMs shows that the approximation order is of O(h3), where h is the partition size of the boundary. Finally, numerical examples are tested and results verify the theoretical analysis. 相似文献
50.
A new radial basis functions method for pricing American options under Merton's jump-diffusion model
《国际计算机数学杂志》2012,89(9):1164-1185
A new radial basis functions (RBFs) algorithm for pricing financial options under Merton's jump-diffusion model is described. The method is based on a differential quadrature approach, that allows the implementation of the boundary conditions in an efficient way. The semi-discrete equations obtained after approximation of the spatial derivatives, using RBFs based on differential quadrature are solved, using an exponential time integration scheme and we provide several numerical tests which show the superiority of this method over the popular Crank–Nicolson method. Various numerical results for the pricing of European, American and barrier options are given to illustrate the efficiency and accuracy of this new algorithm. We also show that the option Greeks such as the Delta and Gamma sensitivity measures are efficiently computed to high accuracy. 相似文献