全文获取类型
收费全文 | 150962篇 |
免费 | 23371篇 |
国内免费 | 13090篇 |
专业分类
电工技术 | 19879篇 |
技术理论 | 13篇 |
综合类 | 17776篇 |
化学工业 | 7939篇 |
金属工艺 | 2882篇 |
机械仪表 | 7830篇 |
建筑科学 | 10524篇 |
矿业工程 | 5541篇 |
能源动力 | 3230篇 |
轻工业 | 2776篇 |
水利工程 | 4700篇 |
石油天然气 | 5630篇 |
武器工业 | 1414篇 |
无线电 | 28699篇 |
一般工业技术 | 6675篇 |
冶金工业 | 3065篇 |
原子能技术 | 639篇 |
自动化技术 | 58211篇 |
出版年
2024年 | 1033篇 |
2023年 | 2826篇 |
2022年 | 5403篇 |
2021年 | 5969篇 |
2020年 | 6260篇 |
2019年 | 4701篇 |
2018年 | 4268篇 |
2017年 | 4981篇 |
2016年 | 5341篇 |
2015年 | 6006篇 |
2014年 | 12774篇 |
2013年 | 10505篇 |
2012年 | 13897篇 |
2011年 | 14309篇 |
2010年 | 11441篇 |
2009年 | 11246篇 |
2008年 | 9851篇 |
2007年 | 10019篇 |
2006年 | 8346篇 |
2005年 | 7300篇 |
2004年 | 6000篇 |
2003年 | 5304篇 |
2002年 | 4152篇 |
2001年 | 3521篇 |
2000年 | 2711篇 |
1999年 | 2213篇 |
1998年 | 1586篇 |
1997年 | 1291篇 |
1996年 | 1035篇 |
1995年 | 818篇 |
1994年 | 610篇 |
1993年 | 424篇 |
1992年 | 304篇 |
1991年 | 195篇 |
1990年 | 168篇 |
1989年 | 139篇 |
1988年 | 98篇 |
1987年 | 49篇 |
1986年 | 61篇 |
1985年 | 60篇 |
1984年 | 36篇 |
1983年 | 39篇 |
1982年 | 38篇 |
1981年 | 34篇 |
1980年 | 15篇 |
1979年 | 15篇 |
1975年 | 3篇 |
1959年 | 8篇 |
1956年 | 3篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Abstract. Locally stationary processes are non‐stationary stochastic processes the second‐order structure of which varies smoothly over time. In this paper, we develop a method to bootstrap the local periodogram of a locally stationary process. Our method generates pseudo local periodogram ordinates by combining a parametric time and non‐parametric frequency domain bootstrap approach. We first fit locally a time varying autoregressive model so as to capture the essential characteristics of the underlying process. A locally calculated non‐parametric correction in the frequency domain is then used so as to improve upon the locally parametric autoregressive fit. As an application, we investigate theoretically the asymptotic properties of the bootstrap method proposed applied to the class of local spectral means, local ratio statistics and local spectral density estimators. Some simulations demonstrate the ability of our method to give accurate estimates of the quantities of interest in finite sample situations and an application to a real‐life data‐set is presented. 相似文献
82.
J. L. Barron R. E. Mercer X. Chen P. Joe 《International journal of imaging systems and technology》2005,15(3):189-198
We present local least squares and regularization frameworks for computing 3D velocity (3D optical flow) from 3D radial velocity measured by a Doppler radar. We demonstrate the performance of our algorithms quantitatively on synthetic radial velocity data and qualitatively on real radial velocity data, obtained from the Doppler radar at Kurnell Radar station, Botany Bay, New South Wales, Australia. Radial velocity can be used to predict the future positions of storms in sequences of Doppler radar datasets.© 2005 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 15, 189–198, 2005 相似文献
83.
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
84.
川西平原属沉积平原,不到2m厚的表土下面全是沙卵石,沙卯石厚度达二、三十米。地面覆盖农田,沟垄纵横,限制了车载钻机的进入。以往地震勘探多采取浅井组合方式激发,所获得的地震资料能量差、面波强,对农田破坏面积大。若使用SH30—2A型轻便工程钻机,配上自制的冲击管,采取冲击钻进,从管中下药柱的方式,可实现沙卵石地区的深井激发,提高资料采集质量,且效率高、成本低。 相似文献
85.
Average consensus in networks of dynamic agents with switching topologies and multiple time-varying delays 总被引:5,自引:0,他引:5
In this paper, we discuss average consensus problem in undirected networks of dynamic agents with fixed and switching topologies as well as multiple time-varying communication delays. By employing a linear matrix inequality method, we prove that all the nodes in the network achieve average consensus asymptotically for appropriate communication delays if the network topology is connected. Particularly, several feasible linear matrix inequalities are established to determine the maximal allowable upper bound of time-varying communication delays. Numerical examples are given to demonstrate the effectiveness and the sharpness of the theoretical results. 相似文献
86.
87.
Simonetta Balsamo Vittoria De Nitto Person Paola Inverardi 《Performance Evaluation》2003,51(2-4):269-288
A review is carried out on how queueing network models with blocking have been applied so far into the performance evaluation and prediction of Software Architectures (SA). Queueing network models with finite capacity queues and blocking have recently been introduced and applied as more realistic models of systems with finite capacity resources and population constraints. Queueing network models have been often adopted as models for the evaluation of software performance. Starting from our own experience, we observe the need of a more accurate definition of the performance models of SA to capture some features of the communication systems. We consider queueing networks with finite capacity and blocking after service (BAS) to represent some synchronization constraints that cannot be easily modeled with queueing network models with infinite capacity queues. We investigate the use of queueing networks with blocking as performance models of SA with concurrent components and synchronous communication. Queueing theoretic analysis is used to solve the queueing network model and study the synchronous communication and performance of concurrent software components. Our experience is supported by other approaches that also propose the use of queueing networks with blocking. Directions for future research work in the field are included. 相似文献
88.
介绍了一种基于人工神经网络(ANN)的声目标识别系统,概述了用MATLAB专用工具箱对神经网络权值进行训练及仿真的过程,叙述了ANN目标识别系统的数字信号处理器(DSP)实时实现过程,并着重分析定点实现过程中程序变量的定标、非线性运算的实现、溢出的处理等关键步骤.对不同字长的识别结果进行比较表明,基于定点实时实现的系统数据保持很高的精度,可以得到与浮点处理相同的识别率. 相似文献
89.
90.
通过分析PHS网络中各寻呼区的统计指标,剖析指标劣化的根本原因,采取修改相应的参数配置、移站、调整天线等措施进行网络优化,优化实施后再次收集统计指标做对比分析,总结经验。 相似文献