全文获取类型
收费全文 | 33845篇 |
免费 | 4115篇 |
国内免费 | 2426篇 |
专业分类
电工技术 | 3366篇 |
技术理论 | 2篇 |
综合类 | 4270篇 |
化学工业 | 4674篇 |
金属工艺 | 620篇 |
机械仪表 | 1604篇 |
建筑科学 | 1399篇 |
矿业工程 | 469篇 |
能源动力 | 1052篇 |
轻工业 | 3936篇 |
水利工程 | 785篇 |
石油天然气 | 861篇 |
武器工业 | 321篇 |
无线电 | 2994篇 |
一般工业技术 | 4204篇 |
冶金工业 | 772篇 |
原子能技术 | 251篇 |
自动化技术 | 8806篇 |
出版年
2024年 | 168篇 |
2023年 | 686篇 |
2022年 | 946篇 |
2021年 | 1254篇 |
2020年 | 1225篇 |
2019年 | 1216篇 |
2018年 | 1183篇 |
2017年 | 1303篇 |
2016年 | 1377篇 |
2015年 | 1360篇 |
2014年 | 1899篇 |
2013年 | 2308篇 |
2012年 | 2507篇 |
2011年 | 2598篇 |
2010年 | 1777篇 |
2009年 | 1933篇 |
2008年 | 1827篇 |
2007年 | 2078篇 |
2006年 | 1889篇 |
2005年 | 1551篇 |
2004年 | 1332篇 |
2003年 | 1200篇 |
2002年 | 1002篇 |
2001年 | 795篇 |
2000年 | 727篇 |
1999年 | 636篇 |
1998年 | 536篇 |
1997年 | 432篇 |
1996年 | 455篇 |
1995年 | 364篇 |
1994年 | 315篇 |
1993年 | 234篇 |
1992年 | 200篇 |
1991年 | 158篇 |
1990年 | 159篇 |
1989年 | 119篇 |
1988年 | 103篇 |
1987年 | 64篇 |
1986年 | 49篇 |
1985年 | 47篇 |
1984年 | 53篇 |
1983年 | 41篇 |
1982年 | 59篇 |
1981年 | 35篇 |
1980年 | 26篇 |
1979年 | 29篇 |
1978年 | 21篇 |
1977年 | 24篇 |
1964年 | 11篇 |
1961年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
This paper proposes an original method for obtaining analytical approximations of the invariant probability density function of multi-dimensional Hamiltonian dissipative dynamic systems under Gaussian white noise excitations, with linear non-conservative parts and nonlinear conservative parts. The method is based on an exact result and a heuristic argument. Its pertinence is attested by numerical tests. 相似文献
52.
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
53.
54.
The motional transition and heterogeneity of semi‐interpenetrating networks (SIPNs) based on polyurethane (PU) with carboxylic groups and methacrylic copolymer (PM) with tertiary amine groups were studied by the electron spin resonance (ESR) spin probe method. The concentration of functional groups in both prepolymers varied from 0 to 0.45 mmol g?1. Spin‐probed SIPNs show that the temperature‐dependent spectra are sensitive to polymer interactions imposed by functional groups. These interactions determine the free volume distribution in the matrix and temperature at which motional transition takes place. The fraction of free volume increases with functional group concentration and reaches its maximum at 0.25 mmol g?1. Further increases in the functional group concentration reduce the free volume. The results of the networks with strong interactions are discussed in terms of the interference of the plasticizing effect of the PU component and the formation of possible cluster cross‐links, which restricts segmental motions. Copyright © 2003 Society of Chemical Industry 相似文献
55.
The scale along the coordinate axes in the equations of motion hitherto used for an H-maser (in relative units) is shown to depend on Q as the quality factor for an H-maser. This hinders both analysis of the operation of the H-maser and optimization of its parameters. The modified equations of motion proposed here do not have that shortcoming. We determine the atomic flux into the bulb that gives the H-maser the best metrological characteristics. 相似文献
56.
57.
本文提出了全真信息、信息的亲善性等概念,讨论了信息的有关性质及运算的关系,得到了信息的运算与普通集合运算之间存在着差异的结论,说明了引起该差异的原因.同时,以认知模式为基础,定义了信息函数,并得到了有关的命题及运算. 相似文献
58.
For completely observed continuous time constant parameter stochastic linear systems, an indirect adaptive control law is presented which, subject principally to a weak location hypothesis concerning the true parameter, and a persistent excitation hypothesis, generates ε-consistent recursive least squares parameter estimates and ensures the system is mean square sample path stable. The adaptive control algorith mentails (i) recursively calculating the least squares estimate of the system parameter, and (ii) recursively generating the LQR feedback gain matrix lying in a set of matrix gains γ known to contain a stabilizing gain. The a.s. non-explosion of the system is a direct consequence of this construction. 相似文献
59.
设计并研制了一种用于压缩式致冷设备的电子式定温域多功能控制装置。它除具有控温范围宽、精度高、控温参数易调等优点外,还实现了低成本的温度显示、半自动除霜控制、加电延时保护、过欠压保护等功能。全部采用无触点控制方式,有良好的性能/价格比。 相似文献
60.
运放滞回比较电路在差动式温度控制中的应用研究 总被引:1,自引:0,他引:1
从差动式温度控制的角度研究了两种由集成运算放大器构成的滞回比较器(基型和交叉耦合型)的传输特性,发现它们均能用作闭环差动式控温单元,并都具有在温度设置点转换速度快、抗干扰能力强、控制单元设计简单等优点。分析和比较了这两种控温单元的控制参数的调节性能和参数的稳定性,获知后者的预置温度(Th或TL)和差动温度范围(△T)的设置值均能各自独立地调节,且系统的Th,TL,△T的实际值几乎仅决定于设置电路本身,因而显得更为优越。文中还讨论了应用中的有关问题,并给出了相关的应用实例。 相似文献