全文获取类型
收费全文 | 48193篇 |
免费 | 13211篇 |
国内免费 | 35篇 |
专业分类
电工技术 | 843篇 |
综合类 | 11篇 |
化学工业 | 19098篇 |
金属工艺 | 732篇 |
机械仪表 | 1314篇 |
建筑科学 | 1811篇 |
矿业工程 | 2篇 |
能源动力 | 1357篇 |
轻工业 | 7744篇 |
水利工程 | 311篇 |
石油天然气 | 60篇 |
无线电 | 8427篇 |
一般工业技术 | 13064篇 |
冶金工业 | 1168篇 |
原子能技术 | 173篇 |
自动化技术 | 5324篇 |
出版年
2024年 | 8篇 |
2023年 | 129篇 |
2022年 | 187篇 |
2021年 | 502篇 |
2020年 | 1583篇 |
2019年 | 3309篇 |
2018年 | 3309篇 |
2017年 | 3634篇 |
2016年 | 4112篇 |
2015年 | 4103篇 |
2014年 | 4194篇 |
2013年 | 5517篇 |
2012年 | 3313篇 |
2011年 | 3133篇 |
2010年 | 3140篇 |
2009年 | 3065篇 |
2008年 | 2516篇 |
2007年 | 2280篇 |
2006年 | 1993篇 |
2005年 | 1705篇 |
2004年 | 1587篇 |
2003年 | 1579篇 |
2002年 | 1503篇 |
2001年 | 1299篇 |
2000年 | 1259篇 |
1999年 | 624篇 |
1998年 | 348篇 |
1997年 | 214篇 |
1996年 | 194篇 |
1995年 | 161篇 |
1994年 | 133篇 |
1993年 | 116篇 |
1992年 | 87篇 |
1991年 | 89篇 |
1990年 | 76篇 |
1989年 | 64篇 |
1988年 | 44篇 |
1987年 | 47篇 |
1986年 | 45篇 |
1985年 | 34篇 |
1984年 | 33篇 |
1983年 | 23篇 |
1982年 | 23篇 |
1981年 | 16篇 |
1980年 | 20篇 |
1979年 | 8篇 |
1978年 | 9篇 |
1977年 | 14篇 |
1976年 | 17篇 |
1975年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 14 毫秒
61.
We propose a new service for digital mobile communication systems. The service enables two or more users to hold a secure conference. Two requirements must be considered: privacy and authentication. Privacy involves ensuring that an eavesdropper cannot intercept the conversations of the parties holding the conference. Authentication involves ensuring that service is not obtained fraudulently in order to avoid usage charges. We present two new conference key distribution schemes for digital mobile communication systems. In these schemes, a group of users can generate a common secret keg over a public channel so that they may hold a secure conference 相似文献
62.
The paper addresses the design of two-level power system stabilizers using an optimal reduced order model whose state variables are torque angles and speeds. The reduced order model retains their physical meaning and is used to design a two-level linear feedback controller that takes into account the realities and constraints of electrical power systems. The two-level control strategy is used, and a global control signal is generated from the output variables to minimize the effect of interactions. The effectiveness of this controller is evaluated and a multimachine system is given as an example to illustrate the advantages of the proposed method. Responses of the system with a two-level scheme and an optimal reduced order scheme are included for comparative analysis. 相似文献
63.
J. Weise Dr.‐Ing. O. Yezerska M. Busse M. Haesche V. Zanetti‐Bueckmann M. Schmitt 《Materialwissenschaft und Werkstofftechnik》2007,38(11):901-906
Micro‐porous syntactic foams were produced by means of integration of glass bubbles into aluminium and zinc matrices. Preforms of glass bubbles were pressure infiltrated with the alloys AlSi9Cu9 ans ZnAl4Cu using squeeze casting. The preforms were sintered thermically without the use of bonding agents. Using the combination of different sintering steps syntactic foams with locally different densities could be produced. The mechanical properties of the foams were tested indicating a high compression strength of the foams and a very good compression energy absorption. Furthermore, corrosion behaviour and behaviour at higher temperatures were investigated. 相似文献
64.
We define the very rich language of composed conditionals on a three‐valued logic and use this language as the communication tool between man and machine. Communication takes place for three reasons: knowledge acquisition, query, and response. Learning, thinking, and answering questions are of a pure information theoretical nature. The pivot of this knowledge processing concept is the amount of information (bit) we receive if a conditional becomes true. We follow an axiomatic approach to information theory rather than the classical probabilistic approach of Shannon; information comes first, and then comes probability. In the light of this philosophy, query and response experience new interpretations. Both, acquisition and response are realized by maximizing entropy and minimizing relative entropy, respectively. The iterative solution of these mathematical optimization problems gives new insights into the adaptation of prior knowledge to new information. Our expert system shell SPIRIT supports this kind of knowledge processing, which will be established by suitable examples. © 2003 Wiley Periodicals, Inc. 相似文献
65.
Mathews V.K. Maddox R.L. Fazan P.C. Rosato J. Hwang H. Lee J. 《Electron Device Letters, IEEE》1992,13(12):648-650
Nitrided gate oxides offer several electrical and reliability advantages over conventional oxides and also provide a good barrier against impurity diffusion. Oxidation in nitrous oxide (N2O) has been very successful in overcoming some of the problems associated with nitridation in ammonia. The authors have observed that the extent of N2O oxidation has a strong detrimental effect on the drain leakage current of MOS transistors in the off state. This phenomenon has been identified to be caused by an increase in the active area junction leakage current 相似文献
66.
Hwang H.-K. Lee L.-S. Chen S.-H. 《Selected Areas in Communications, IEEE Journal on》1989,7(9):1450-1461
Multi-H phase-coded modulation (MHPM) is a bandwidth-efficient modulation scheme which offers substantial coding gain over conventional digital modulation schemes. MHPM with asymmetric modulation indices corresponding to the bipolar data +1 and -1 is considered, and numerical results for the minimum Euclidean distances are provided. It is shown that performance improvements on the error probability over conventional MHPM are gained with essentially the same bandwidth and a very slight modification in implementation. The upper bounds on the error probabilities as functions of observation intervals and received E b/N 0 are also investigated in detail. It is concluded that the concept of asymmetric modulation indices for MHPM is attractive for bandwidth and power-efficient modulation 相似文献
67.
Wood has long traditions as a building material, and is often used in construction elements, and as interior and exterior surfaces in the Nordic countries. In most applications, there are reaction to fire requirements to products used as surfaces, e.g. in escape routes and larger public spaces. Most wood products will therefore have to be treated with fire retardant (FR) agents to fulfil the strict requirements to properties connected to heat release and flame spread. Unfortunately, FR agents usually also increase the smoke production, as they cause a more incomplete combustion of the wood. The wood product manufacturers seek to find the optimal amount of FR additives where both heat release and smoke production in the classifying test are within the requirements given in the building regulations. This paper describes models for prediction of the European reaction to fire classes of wood products. The models are based on multivariate statistical analysis, and use test results from the cone calorimeter test as input. The presented models are, with very good precision, able to predict which Euroclass and additional smoke class a wood based product would obtain if it were to be tested in the single burning item test. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
68.
Suk Lee Kyung Chang Lee Man Hyung Lee Harashima F. 《Industrial Electronics, IEEE Transactions on》2002,49(3):693-701
This paper focuses on a method to integrate mobile devices such as a mobile robot, automated guided vehicle, and unmanned container transporter to form an automated material handling system. In this paper, the stationary devices are connected via a Profibus network while the mobile devices are communicating via an IEEE 802.11 wireless LAN. In order to integrate these two networks, a protocol converter is developed on a PC platform that runs two interacting processes with shared internal buffers. The protocol converter performs a role of translator between two different protocols by converting the format of a data frame. In addition to this basic conversion function, the protocol converter has a virtual polling algorithm to reduce the uncertainty involved in accessing the wireless network. Finally, the integrated network. of Profibus and IEEE 802.11 is experimentally evaluated for its data latency and throughput, which shows the feasibility of the Profibus-IEEE 802.11 network for industrial applications involving mobile devices 相似文献
69.
70.