全文获取类型
收费全文 | 3249篇 |
免费 | 220篇 |
国内免费 | 238篇 |
专业分类
电工技术 | 61篇 |
综合类 | 151篇 |
化学工业 | 173篇 |
金属工艺 | 81篇 |
机械仪表 | 267篇 |
建筑科学 | 112篇 |
矿业工程 | 23篇 |
能源动力 | 56篇 |
轻工业 | 38篇 |
水利工程 | 36篇 |
石油天然气 | 37篇 |
武器工业 | 24篇 |
无线电 | 487篇 |
一般工业技术 | 519篇 |
冶金工业 | 34篇 |
原子能技术 | 39篇 |
自动化技术 | 1569篇 |
出版年
2024年 | 2篇 |
2023年 | 51篇 |
2022年 | 87篇 |
2021年 | 96篇 |
2020年 | 107篇 |
2019年 | 69篇 |
2018年 | 90篇 |
2017年 | 111篇 |
2016年 | 146篇 |
2015年 | 138篇 |
2014年 | 192篇 |
2013年 | 204篇 |
2012年 | 188篇 |
2011年 | 275篇 |
2010年 | 186篇 |
2009年 | 213篇 |
2008年 | 189篇 |
2007年 | 186篇 |
2006年 | 172篇 |
2005年 | 123篇 |
2004年 | 114篇 |
2003年 | 111篇 |
2002年 | 102篇 |
2001年 | 72篇 |
2000年 | 55篇 |
1999年 | 52篇 |
1998年 | 55篇 |
1997年 | 54篇 |
1996年 | 34篇 |
1995年 | 43篇 |
1994年 | 33篇 |
1993年 | 26篇 |
1992年 | 15篇 |
1991年 | 21篇 |
1990年 | 14篇 |
1989年 | 18篇 |
1988年 | 14篇 |
1987年 | 4篇 |
1986年 | 12篇 |
1985年 | 5篇 |
1984年 | 9篇 |
1983年 | 6篇 |
1982年 | 2篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有3707条查询结果,搜索用时 15 毫秒
11.
A new method for computing the node-pair reliability of network systems modeled by random graphs with nodes arranged in sequence is presented. It is based on a recursive algorithm using the “sliding window” technique, the window being composed of several consecutive nodes. In a single step, the connectivity probabilities for all nodes included in the window are found. Subsequently, the window is moved one node forward. This process is repeated until, in the last step, the window reaches the terminal node. The connectivity probabilities found at that point are used to compute the node-pair reliability of the network system considered. The algorithm is designed especially for graphs with small distances between adjacent nodes, where the distance between two nodes is defined as the absolute value of the difference between the nodes’ numbers. The maximal distance between any two adjacent nodes is denoted by Γ(G), where G symbolizes a random graph. If Γ(G)=2 then the method can be applied for directed as well as undirected graphs whose nodes and edges are subject to failure. This is important in view of the fact that many algorithms computing network reliability are designed for graphs with failure-prone edges and reliable nodes. If Γ(G)=3 then the method's applicability is limited to undirected graphs with reliable nodes. The main asset of the presented algorithms is their low numerical complexity—O(n), where n denotes the number of nodes. 相似文献
12.
The smooth fractionator 总被引:8,自引:0,他引:8
H. J. G. Gundersen 《Journal of microscopy》2002,207(3):191-210
A modification of the general fractionator sampling technique called the smooth fractionator is presented. It may be used in almost every situation in which sampling is performed from distinct items that are uniquely defined, often they are physically separated items or clusters like pieces, blocks, slabs, sections, etc. To each item is associated a ‘guesstimate’ or an associated variable with a more‐or‐less close – and possibly biased ? relationship to the content of the item. The smooth fractionator is systematic sampling among the items arranged according to the guesstimates in a unique, symmetric sequence with one peak and minimal jumps. The smooth fractionator is both very simple to implement and so efficient that it should probably always be used unless the natural sequence of the sampling items is equally smooth. So far, there is no theory for the prediction of the efficiency of smooth fractionator designs in general, and their properties are therefore illustrated with a range of real and simulated examples. At the cost of a slightly more elaborate sampling scheme, it is, however, always possible to obtain an unbiased estimate of the real precision and of some of the variance components. The only real practical problem for always obtaining a high precision with the smooth fractionator is specimen inhomogeneity, but that is detectable at almost no extra cost. With careful designs and for sample sizes of about 10, the sampling variation for the primary, smooth fractionator sampling step may in practice often be small enough to be ignored. 相似文献
13.
14.
介绍了采用双通道FFT分析仪进行振动传感器随机校准的方法。校准系统采用2种方法,闭环控制,单振动台全频段校准。经理论分析和试验研究,其校准结果准确可靠。 相似文献
15.
本文重点讨论了在平稳m相依噪声中弱随机信号的最佳无记忆Robust检测问题;并且以渐近功效函数为测度准则得到了最大最小无记忆非线性Robust检测器。 相似文献
16.
羰基铁类随机混合吸波材料等效电磁参数的计算 总被引:3,自引:0,他引:3
本文为计及多重散射偶极子间的相互作用,引入参量εh和μh,导得一组公式。它不仅能计算铁氧体类也能计算羰基铁类的随机混合吸波材料的等效电磁参数,均与实验结果吻合良好。 相似文献
17.
A. Palmeri F. Ricciardelli G. Muscolino A. De Luca 《Canadian Metallurgical Quarterly》2004,130(9):1052-1061
The equation of motion of linear dynamic systems with viscoelastic memory is usually expressed in a integrodifferential form, and its numerical solution is computationally heavy. In two recent papers, the writers suggested that the system memory be accounted for through the introduction of a number of additional internal variables. Following this approach, the motion of the system is governed by a set of first-order, linear differential equations, whose solution is quite easy. In this paper, the approach is extended to single-degree-of-freedom systems subjected to random, nonstationary excitation. The equations governing the time variation of the second-order statistics are derived, and an effective step-by-step solution procedure is proposed. Numerical example shows the accuracy of the procedure for white and nonwhite excitations. 相似文献
18.
19.
A separation distance between adjacent buildings is provided to reduce the risk of pounding of adjacent buildings under seismic excitations. It should be recognized that the evaluation of the critical separation distance is a one-sided barrier crossing problem while the problem of structural design under seismic excitations is a two-sided crossing problem. A procedure for assessing the required separation distance with or without considering possible uncertainty in structural properties was presented based on the reliability methods and random vibration theory. The procedure was used to carry out parametric analyses. It is shown that use of the complete quadratic combination (CQC) rule with the modal responses employed for designing structures may over- or underestimate the critical separation distance, depending on the damping ratios and the closeness of the natural vibration periods of adjacent buildings. This is due to not only one-sided versus two-sided crossing problem but also the approximation in the CQC rule. Further, the effect of the uncertainty in structural properties on the estimated separation is investigated. The results indicate that this uncertainty tends to increase the required critical separation distance. 相似文献
20.
A new functional perturbation method (FPM) for calculating the probabilistic response of stochastically heterogeneous, linear elastic structures is developed. The method is based on treating the governing differential operator as well as the unknown displacement function as a functional of material modulus field. By executing a functional perturbation around the homogeneous case, a set of successive differential equations is obtained and solved, from which the average and variance of any local parameter (displacements, stresses, strains) can be found. For a linear problem, the equations to be solved in each approximation order differ from the one for the homogeneous case by a pseudo external loading (right hand side) part only. Thus, only the Green function for the homogeneous case is needed for an analytical solution of the corresponding heterogeneous problem. A one dimensional stochastically heterogeneous rod embedded in a uniform shear resistant elastic medium is solved as an example. The statistical variance of displacements and stresses are found analytically, including the edge regions. Morphological (grain size) and material (modulus) effects on the stochastic response are demonstrated. The above results are essential for estimating the stochastic features of local stress concentrations, which are the source for many strength-related macro properties of materials. Extensive usage of generalized functions (Dirac operator and its derivatives) is needed for the analysis. 相似文献