全文获取类型
收费全文 | 13667篇 |
免费 | 1959篇 |
国内免费 | 1347篇 |
专业分类
电工技术 | 1201篇 |
综合类 | 1670篇 |
化学工业 | 545篇 |
金属工艺 | 250篇 |
机械仪表 | 803篇 |
建筑科学 | 767篇 |
矿业工程 | 283篇 |
能源动力 | 506篇 |
轻工业 | 292篇 |
水利工程 | 381篇 |
石油天然气 | 226篇 |
武器工业 | 134篇 |
无线电 | 1143篇 |
一般工业技术 | 993篇 |
冶金工业 | 342篇 |
原子能技术 | 43篇 |
自动化技术 | 7394篇 |
出版年
2024年 | 36篇 |
2023年 | 123篇 |
2022年 | 223篇 |
2021年 | 307篇 |
2020年 | 390篇 |
2019年 | 366篇 |
2018年 | 353篇 |
2017年 | 394篇 |
2016年 | 506篇 |
2015年 | 612篇 |
2014年 | 868篇 |
2013年 | 889篇 |
2012年 | 1025篇 |
2011年 | 1198篇 |
2010年 | 936篇 |
2009年 | 978篇 |
2008年 | 1123篇 |
2007年 | 1123篇 |
2006年 | 977篇 |
2005年 | 841篇 |
2004年 | 670篇 |
2003年 | 595篇 |
2002年 | 435篇 |
2001年 | 342篇 |
2000年 | 289篇 |
1999年 | 238篇 |
1998年 | 173篇 |
1997年 | 155篇 |
1996年 | 143篇 |
1995年 | 137篇 |
1994年 | 97篇 |
1993年 | 61篇 |
1992年 | 62篇 |
1991年 | 58篇 |
1990年 | 52篇 |
1989年 | 46篇 |
1988年 | 31篇 |
1987年 | 19篇 |
1986年 | 8篇 |
1985年 | 10篇 |
1984年 | 8篇 |
1983年 | 13篇 |
1982年 | 5篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1976年 | 4篇 |
1963年 | 7篇 |
1961年 | 8篇 |
1960年 | 4篇 |
1957年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
A numerical solution of the inverse problem of the gravitational field at a single point is obtained using six field elements
for a point, a spherical cap, a differential spherical sector and a vertical segment. In the system of six equations obtained,
the unknowns are the mass of the body, the depth of its center, and the second, third, and fourth degree moments. The accuracy
of the solution of this system is ten times higher than when using three field elements.
__________
Translated from Izmeritel’naya Tekhnika, No. 5, pp. 3–8, May, 2007. 相似文献
23.
The paper is devoted to the effect of compressibility of the avalanche snow impacting an obstacle. Compression shocks generated by obstacle cause high pressure peaks at first instants of impact. That is why the account of compressibility is essential for the understanding of measurements and the design of structures. The main problem in calculation compression shocks in avalanches is to formulate an equation of state for moving snow in impact. Two different types of equations of state are proposed depending on the type of the avalanche (low-density and high-density flows). The approach is not totally new. It was earlier proposed mainly in Russian literature. Here a brief review of the previous work is given with discussion of some gaps in it. The theory is reformulated and further developed to account thermodynamical equations. The simplest case of a normal compression shock in an avalanche flow is studied. Examples of estimations of pressure and density behind a shock are given. It is important to emphasize that the Mach number plays an important role in the theory of compressible flows so it should be taken into account (together with the Froude number) in calculation and modelling an avalanche impact pressure. 相似文献
24.
An efficient algorithm for the random packing of spheres can significantly save the cost of the preparation of an initial configuration often required in discrete element simulations. It is not trivial to generate such random packing at a large scale, particularly when spheres of various sizes and geometric domains of different shapes are present. Motivated by the idea of compression complemented by an efficient physical process to increase packing density, shaking, a new approach, termed compression algorithm, is proposed in this work to randomly fill any arbitrary polyhedral or cylindrical domains with spheres of various sizes. The algorithm features both simplicity and high efficiency. Tests show that it takes 181 s on a 1.4-GHz PC to complete the filling of a cylindrical domain with a total number of 26,787 spheres, achieving a packing density of 52.89%. 相似文献
25.
In recent years, constructing a virtual backbone by nodes in a connected dominating set (CDS) has been proposed to improve the performance of ad hoc wireless networks. In general, a dominating set satisfies that every vertex in the graph is either in the set or adjacent to a vertex in the set. A CDS is a dominating set that also induces a connected sub‐graph. However, finding the minimum connected dominating set (MCDS) is a well‐known NP‐hard problem in graph theory. Approximation algorithms for MCDS have been proposed in the literature. Most of these algorithms suffer from a poor approximation ratio, and from high time complexity and message complexity. In this paper, we present a new distributed approximation algorithm that constructs a MCDS for wireless ad hoc networks based on a maximal independent set (MIS). Our algorithm, which is fully localized, has a constant approximation ratio, and O(n) time and O(n) message complexity. In this algorithm, each node only requires the knowledge of its one‐hop neighbours and there is only one shortest path connecting two dominators that are at most three hops away. We not only give theoretical performance analysis for our algorithm, but also conduct extensive simulation to compare our algorithm with other algorithms in the literature. Simulation results and theoretical analysis show that our algorithm has better efficiency and performance than others. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
26.
27.
A method is considered to solve a conditional optimization problem with a linear-fractional objective function over permutations.
The performance of sub algorithms to solve this problem is evaluated. The practical efficiency of the algorithm is analyzed
by conducting numerical experiments.
__________
Translated from Kibernetika i Sistemnyi Analiz, No. 4, pp. 133–146, July–August 2007. 相似文献
28.
L. M. CRUZ-ORIVE 《Journal of microscopy》2005,219(1):18-28
A new principle is presented to generate isotropic uniform random (IUR) test lines hitting a geometric structure in three-dimensional space (3D). The principle therefore concerns the estimation of surface area, volume, membrane thickness, etc., of arbitrary structures with piecewise smooth boundary. The principle states that a point-sampled test line on an isotropic plane through a fixed point in 3D is effectively an invariant test line in 3D. Particular attention is devoted to the stereology of particles, where an alternative to the surfactor method is obtained to estimate surface area. An interesting case arises when the particle is convex. The methods are illustrated with synthetic examples. 相似文献
29.
Garth Isaak 《Information Processing Letters》2004,92(3):107-111
Given a tournament with an acyclic tournament as a feedback arc set we give necessary and sufficient conditions for this feedback arc set to have minimum size. 相似文献
30.
基于VW2010芯片的嵌入式多媒体监控系统压缩/解压卡设计 总被引:5,自引:0,他引:5
在简要分析了多媒体监控系统发展现状的基础上,提出了一种基于VW2010压缩/解压芯片的多媒体压缩/解压卡的设计方案,给出了基于VW2010的多媒体监控系统压缩和解压卡的硬件结构图以及在Linux系统下VW2010的驱动程序,同时给出了在Linux Redhat7.3下编写的测试程序,并进行了全面的测试。 相似文献