全文获取类型
收费全文 | 32508篇 |
免费 | 6759篇 |
国内免费 | 5744篇 |
专业分类
电工技术 | 4338篇 |
技术理论 | 3篇 |
综合类 | 3990篇 |
化学工业 | 1211篇 |
金属工艺 | 763篇 |
机械仪表 | 1987篇 |
建筑科学 | 847篇 |
矿业工程 | 486篇 |
能源动力 | 621篇 |
轻工业 | 560篇 |
水利工程 | 423篇 |
石油天然气 | 459篇 |
武器工业 | 505篇 |
无线电 | 6724篇 |
一般工业技术 | 3165篇 |
冶金工业 | 489篇 |
原子能技术 | 142篇 |
自动化技术 | 18298篇 |
出版年
2024年 | 318篇 |
2023年 | 842篇 |
2022年 | 1313篇 |
2021年 | 1413篇 |
2020年 | 1653篇 |
2019年 | 1545篇 |
2018年 | 1493篇 |
2017年 | 1673篇 |
2016年 | 1756篇 |
2015年 | 1894篇 |
2014年 | 2305篇 |
2013年 | 2658篇 |
2012年 | 2718篇 |
2011年 | 2990篇 |
2010年 | 2319篇 |
2009年 | 2289篇 |
2008年 | 2357篇 |
2007年 | 2456篇 |
2006年 | 1949篇 |
2005年 | 1590篇 |
2004年 | 1252篇 |
2003年 | 1064篇 |
2002年 | 836篇 |
2001年 | 741篇 |
2000年 | 598篇 |
1999年 | 500篇 |
1998年 | 417篇 |
1997年 | 374篇 |
1996年 | 330篇 |
1995年 | 249篇 |
1994年 | 209篇 |
1993年 | 197篇 |
1992年 | 145篇 |
1991年 | 103篇 |
1990年 | 112篇 |
1989年 | 80篇 |
1988年 | 56篇 |
1987年 | 26篇 |
1986年 | 22篇 |
1985年 | 21篇 |
1984年 | 41篇 |
1983年 | 22篇 |
1982年 | 16篇 |
1981年 | 14篇 |
1980年 | 9篇 |
1979年 | 14篇 |
1978年 | 7篇 |
1977年 | 6篇 |
1960年 | 3篇 |
1959年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
Mobile networks are becoming nothing but a way to allow ubiquitous access to multimedia services. To allow efficient use of
resources, new systems provide flexible bandwidth and different error protection techniques to match channel behavior. As
the backbone network is increasingly becoming based on packet techniques and in particular on IP and related transport protocols,
end to end service quality must be analyzed considering both the fixed and the mobile part. Source scalability may help in
coping with a mixed and heterogeneous environment. In this work we present some results of a transmission chain comprising
a scalable MPEG-2 coder, an IP network and a radio access exploiting the availability of satellites. It is shown that for
a given target rate, differentiated coding can be exploited to achieve decodability and good quality at a channel SNR much
lower that single layer streams.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
93.
M. R. JOYCE K. K. LEE S. SYNGELLAKIS P. A. S. REED 《Fatigue & Fracture of Engineering Materials & Structures》2004,27(11):1025-1036
Complex multi‐phase Al–Sn–Si alloys are commonly employed in the manufacture of small automotive plain bearings. The fundamental fatigue initiation behaviour of this class of alloys is currently not well understood. A range of analytical techniques were applied to investigate preferential initiation site location and to attempt to identify critical microstructural features. It was apparent from experimental studies that points of fatigue crack initiation are associated with the Si secondary phase. Using tessellation approaches and subsequently both adaptive numerical modelling and micro‐scale finite element modelling allowed the identification of features affecting the probability that a given Si phase would initiate a fatigue crack. 相似文献
94.
自适应RBF神经网络在CDMA移动通信上行链路功率控制中的应用研究 总被引:1,自引:0,他引:1
提出了一种自适应RBF神经网络功率控制方案。详细研究了该网络在DS-CDMA通信中,进行上行链路闭环功率控制(基于信扰比(SIR))的应用理论,给出了该网络参数的计算方法。最后用计算机仿真法模拟出该控制器的运行性能。结果表明基于SIR的自适应RBF神经网络功率控制器能自适应地调整移动台的发射功率,使基站接收信号的信扰比始终非常接近于一个常数,且有比定步长功率控制更小的SIR跟踪误差,从而可以降低接收信号的中断概率、提高信道容量。 相似文献
95.
Sixiong Han Yasuaki Ichikawa 《International journal for numerical methods in engineering》1995,38(24):4081-4100
In this paper, a mathematical model is proposed for the problem of the scattering of plane waves in a three-dimensional cracked materials. Instead of obtaining closed-form solutions as in conventional theoretical analysis methods, this approach, called the Equivalent Nodal Force (ENF) method formulates the mechanical effects of cracks as an equivalent nodal force in a numerical procedure, and physically translates cracked material into an equivalent continuous one. Several mechanical relations between waves and cracks are evident from this method. Also the results of several numerical calculations are presented and these are compared with those obtained by the conventional methods. 相似文献
96.
The design of an adaptive nonlinear controller for the control of a fluidized bed reactor is derived by using exact linearization techniques. Reset action and parameter adaptation are used to make more robust the precise compensation of nonlinear terms, which is called for in the linearization technique. A nonlinear antiwindup mechanism is introduced to handle reset windup problem and to provide fast response without large overshoot. Simulation results show that the proposed adaptive controller guarantees good setpoint tracking. The developed estimation algorithm allows accurate estimation of the parameters for which the regressor component is not zero. 相似文献
97.
Ramon R. Costa Liu Hsu 《International Journal of Adaptive Control and Signal Processing》1992,6(1):19-33
A variable structure model reference adaptive controller (VS-MRAC) using only input and output measurements was recently proposed and shown to be globally asymptotically stable with superior transient behaviour and disturbance rejection properties. In this paper a singular perturbation approach is used in order to establish the robustness of the controller in the presence of unmodelled dynamics (parasitics) and disturbances. We develop a new Lyapunov-based technique to analyse the overall system and show that for sufficiently small parasitics the system remains stable and the output error is small in some sense. 相似文献
98.
Atilla Bilgin 《国际能源研究杂志》2002,26(11):987-1000
Flame front surface area and enflamed volume (the volume enclosed with flame front) is theoretically analysed for a spark‐ignition engine, having cylindrical disc‐shaped combustion chamber with two spark plugs located axisymmetrically on cylinder head, between cylinder axis and cylinder wall. Spherical flame front assumption is used. A computer code is developed based on purely geometric consideration of the flame development process in combustion chamber, and is used to investigate the effects of variations of spark plugs' locations on geometric features of the flame front. A comparison has also been made with a spark‐ignition engine having one spark plug at the same location. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
99.
Abstract— In response to the increasing structural applications in duplex steels for welded structures, fatigue behaviour of a SAF 2304 grade duplex stainless steel was investigated, considering both the base metal and GTAW welded joints. Fatigue curves and fatigue limits under rotary bending fatigue were obtained. The study focused attention on the microstructural features of fatigue crack propagation of the two series of experiments, thereby permitting an evaluation of the tortuous crack path of welded joints and the mechanisms related to threshold microstructural barriers. 相似文献
100.
Ibrahim H. Osman Nicos Christofides 《International Transactions in Operational Research》1994,1(3):317-336
The capacitated clustering problem (CCP) is the problem in which a given set of weighted objects is to be partitioned into clusters so that the total weight of objects in each cluster is less than a given value (cluster ‘capacity’). The objective is to minimize the total scatter of objects from the ‘centre’ of the cluster to which they have been allocated. A simple constructive heuristic, a R-interchange generation mechanism, a hybrid simulated annealing (SA) and tabu search (TS) algorithm which has computationally desirable features using a new non-monotonic cooling schedule, are developed. A classification of the existing SA cooling schedules is presented. The effects on the final solution quality of the initial solutions, the cooling schedule parameters and the neighbourhood search strategies are investigated. Computational results on randomly generated problems with size ranging from 50 to 100 customers indicate that the hybrid SA/TS algorithm out-performs previous simulated annealing algorithms, a simple tabu search and local descent algorithms. 相似文献