全文获取类型
收费全文 | 12428篇 |
免费 | 798篇 |
国内免费 | 258篇 |
专业分类
电工技术 | 437篇 |
综合类 | 361篇 |
化学工业 | 1855篇 |
金属工艺 | 480篇 |
机械仪表 | 590篇 |
建筑科学 | 706篇 |
矿业工程 | 149篇 |
能源动力 | 333篇 |
轻工业 | 964篇 |
水利工程 | 123篇 |
石油天然气 | 179篇 |
武器工业 | 25篇 |
无线电 | 2135篇 |
一般工业技术 | 1780篇 |
冶金工业 | 1448篇 |
原子能技术 | 115篇 |
自动化技术 | 1804篇 |
出版年
2024年 | 29篇 |
2023年 | 156篇 |
2022年 | 309篇 |
2021年 | 383篇 |
2020年 | 269篇 |
2019年 | 230篇 |
2018年 | 303篇 |
2017年 | 276篇 |
2016年 | 347篇 |
2015年 | 371篇 |
2014年 | 472篇 |
2013年 | 747篇 |
2012年 | 729篇 |
2011年 | 769篇 |
2010年 | 573篇 |
2009年 | 664篇 |
2008年 | 670篇 |
2007年 | 602篇 |
2006年 | 596篇 |
2005年 | 471篇 |
2004年 | 351篇 |
2003年 | 385篇 |
2002年 | 323篇 |
2001年 | 309篇 |
2000年 | 252篇 |
1999年 | 269篇 |
1998年 | 567篇 |
1997年 | 322篇 |
1996年 | 263篇 |
1995年 | 234篇 |
1994年 | 142篇 |
1993年 | 162篇 |
1992年 | 104篇 |
1991年 | 85篇 |
1990年 | 70篇 |
1989年 | 62篇 |
1988年 | 61篇 |
1987年 | 51篇 |
1986年 | 43篇 |
1985年 | 64篇 |
1984年 | 31篇 |
1983年 | 30篇 |
1982年 | 39篇 |
1981年 | 43篇 |
1980年 | 35篇 |
1979年 | 27篇 |
1977年 | 28篇 |
1976年 | 51篇 |
1975年 | 20篇 |
1973年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 3 毫秒
21.
22.
Performance model of interactive video-on-demand systems 总被引:5,自引:0,他引:5
Li V.O.K. Wanjiun Liao Xiaoxin Qiu Wong E.W.M. 《Selected Areas in Communications, IEEE Journal on》1996,14(6):1099-1109
An interactive video-on-demand (VoD) system allows users to access video services, such as movies, electronic encyclopedia, interactive games, and educational videos from video servers on a broadband network. This paper develops a performance evaluation tool for the system design. In particular, a user activity model is developed to describe the usage of system resources, i.e., network bandwidth and video server usage, by a user as it interacts with the service. In addition, we allow batching of user requests, and the effect of such batching is captured in a batching model. Our proposed queueing model integrates both the user activity and the batching model. This model can be used to determine the requirements of network bandwidth and video server and, hence, the trade-off in communication and storage costs for different system resource configurations 相似文献
23.
HS Wong 《Canadian Metallurgical Quarterly》1997,38(11):459-464
24.
A genetic algorithm for multiple molecular sequence alignment 总被引:1,自引:0,他引:1
MOTIVATION: Multiple molecular sequence alignment is among the most important and most challenging tasks in computational biology. The currently used alignment techniques are characterized by great computational complexity, which prevents their wider use. This research is aimed at developing a new technique for efficient multiple sequence alignment. APPROACH: The new method is based on genetic algorithms. Genetic algorithms are stochastic approaches for efficient and robust searching. By converting biomolecular sequence alignment into a problem of searching for optimal or near-optimal points in an 'alignment space', a genetic algorithm can be used to find good alignments very efficiently. RESULTS: Experiments on real data sets have shown that the average computing time of this technique may be two or three orders lower than that of a technique based on pairwise dynamic programming, while the alignment qualities are very similar. AVAILABILITY: A C program on UNIX has been written to implement the technique. It is available on request from the authors. 相似文献
25.
Kerlavage A.R. FitzHugh W. Gladek A. Kelley J. Scott J. Shirley R. Sutton G. Man Wai-Chiu White O. Adams D. 《IEEE engineering in medicine and biology magazine》1995,14(6):710-717
The rapid advances in molecular biology have begun to shift many of the bottlenecks in genome research from the laboratory to the data analysis facility. The pace at which this has occurred creates a situation in which software development always has to catch up with the flow of data. Since such large-scale processes were not anticipated, the analysis infrastructure has not been fully established. Furthermore, most systems that have been built were designed by the biologists who collected the data. More recently, computer scientists, mathematicians, and engineers have taken an interest in this problem. This has had a positive effect, since it has created a tight synergy between the informatics and the biology. Several principles affected the design of the system developed at TIGR. Each of the sample preparation, sequencing, and analysis steps had to be managed, scheduled, and tracked. This information had to be made readily available to those who needed it for carrying out their tasks. Different skill levels of the users had to be taken into account. The degree of human intervention at each step had to be evaluated and built into the design. A mixed processing environment of Macintosh and Unix platforms had to be integrated. Most importantly, the system had to save time, reduce error, and ensure uniformity of the analysis and quality of the results. In the authors' experience, the tools they have built work well because of their early decisions as to which systems to use for development. The authors settled on a robust relational database management system (Sybase) and a portable development environment (C, C++) 相似文献
26.
A structured genetic algorithm (SGA) approach is developed for robust controller design based on the concept of an H∞ loop-shaping technique and the method of inequalities. Such an SGA is capable of simultaneously searching the orders and coefficients of the precompensator and postcompensator for the weighted plant. It is, therefore, not necessary to predefine the order of compensators as in usual practice. A multiple objective ranking approach is also incorporated so that the design criteria of extreme plants can be easily achieved. The effectiveness of such a technique is illustrated by a high-purity distillation column design example 相似文献
27.
This paper introduces genetic algorithms (GA) as a complete entity, in which knowledge of this emerging technology can be integrated together to form the framework of a design tool for industrial engineers. An attempt has also been made to explain “why” and “when” GA should be used as an optimization tool 相似文献
28.
The problem of joint estimation of time delay and Doppler shift is considered from the point of view of the Wigner distribution of the signal. A very efficient method of obtaining the optimum signal with minimum estimation error based on the convexity of the design region is developed. Practical applications, however, require the signal to satisfy other constraints which present complications in acquiring the optimum signal. A design approach based on the method of simulated annealing is suggested to solve for the optimum signal under constraints. The performance of the signals so obtained is evaluated and compared with that of signals obtained by synthesis 相似文献
29.
根据转炉炼钢的物理化学反应机理,从质量平衡和能量平衡的计算出发,通过小参数变动,导出了增量式静态模型中矿石方程和供氧方程的系数。所得结论与新日铁资料基本相符。同时,还进行了炉料和产物的计算,分析了改变废钢比对生产的影响。 相似文献
30.
D.A. van Beek K.L. Man M.A. Reniers J.E. Rooda R.R.H. Schiffelers 《The Journal of Logic and Algebraic Programming》2006,68(1-2):129
The hybrid χ (Chi) formalism integrates concepts from dynamics and control theory with concepts from computer science, in particular from process algebra and hybrid automata. It integrates ease of modeling with a straightforward, structured operational semantics. Its ‘consistent equation semantics’ enforces state changes to be consistent with delay predicates, that combine the invariant and flow clauses of hybrid automata. Ease of modeling is ensured by means of the following concepts: (1) different classes of variables: discrete and continuous, of subclass jumping or non-jumping, and algebraic; (2) strong time determinism of alternative composition in combination with delayable guards; (3) integration of urgent and non-urgent actions; (4) differential algebraic equations as a process term as in mathematics; (5) steady-state initialization; and 6) several user-friendly syntactic extensions. Furthermore, the χ formalism incorporates several concepts for complex system specification: (1) process terms for scoping that integrate abstraction, local variables, local channels and local recursion definitions; (2) process definition and instantiation that enable process re-use, encapsulation, hierarchical and/or modular composition of processes; and (3) different interaction mechanisms: handshake synchronization and synchronous communication that allow interaction between processes without sharing variables, and shared variables that enable modular composition of continuous-time or hybrid processes. The syntax and semantics are illustrated using several examples. 相似文献