全文获取类型
收费全文 | 18566篇 |
免费 | 477篇 |
国内免费 | 18篇 |
专业分类
电工技术 | 245篇 |
综合类 | 9篇 |
化学工业 | 3616篇 |
金属工艺 | 284篇 |
机械仪表 | 319篇 |
建筑科学 | 1133篇 |
矿业工程 | 109篇 |
能源动力 | 515篇 |
轻工业 | 1412篇 |
水利工程 | 158篇 |
石油天然气 | 194篇 |
武器工业 | 1篇 |
无线电 | 1117篇 |
一般工业技术 | 2936篇 |
冶金工业 | 4367篇 |
原子能技术 | 165篇 |
自动化技术 | 2481篇 |
出版年
2022年 | 140篇 |
2021年 | 222篇 |
2020年 | 171篇 |
2019年 | 227篇 |
2018年 | 269篇 |
2017年 | 266篇 |
2016年 | 321篇 |
2015年 | 242篇 |
2014年 | 387篇 |
2013年 | 1119篇 |
2012年 | 668篇 |
2011年 | 880篇 |
2010年 | 681篇 |
2009年 | 667篇 |
2008年 | 864篇 |
2007年 | 881篇 |
2006年 | 695篇 |
2005年 | 728篇 |
2004年 | 573篇 |
2003年 | 578篇 |
2002年 | 517篇 |
2001年 | 338篇 |
2000年 | 312篇 |
1999年 | 315篇 |
1998年 | 365篇 |
1997年 | 335篇 |
1996年 | 318篇 |
1995年 | 343篇 |
1994年 | 277篇 |
1993年 | 319篇 |
1992年 | 281篇 |
1991年 | 173篇 |
1990年 | 243篇 |
1989年 | 295篇 |
1988年 | 213篇 |
1987年 | 220篇 |
1986年 | 219篇 |
1985年 | 271篇 |
1984年 | 265篇 |
1983年 | 232篇 |
1982年 | 222篇 |
1981年 | 217篇 |
1980年 | 175篇 |
1979年 | 191篇 |
1978年 | 182篇 |
1977年 | 181篇 |
1976年 | 159篇 |
1975年 | 184篇 |
1974年 | 171篇 |
1973年 | 137篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Investigation of the thermal, mechanical, and fracture properties of alumina-epoxy composites 总被引:1,自引:0,他引:1
A combination of dynamic shear rheology, thermomechanical analysis (TMA), scanning electron microscopy (SEM), Near-Edge X-ray Absorption Fine Structure (NEXAFS), and fracture toughness testing was utilized to characterize the thermal, mechanical, chemical, and fracture properties of alumina (α-Al2O3)-filled epoxy resins as a function of average filler size, size distribution, particle shape, loading, and epoxy crosslink density. In general the cured properties of the filled composites were robust. Small changes in particle size, shape, and size distribution had little impact on the final properties. Resin crosslink density and filler loading were the most critical variables, causing changes in all properties. However, most applications could likely tolerate small changes in these variables also. SEM and NEXAFS characterization of the fracture surfaces revealed that the fracture occurs at the filler interface and the interfacial epoxy composition is similar to the bulk resin, indicating a weak epoxy-alumina interaction. These results are critical for implementation of particulate-filled polymer composites in practical applications because relaxed material specifications and handling procedures can be incorporated in production environments to improve efficiency. 相似文献
102.
Liew Jeffrey; Eisenberg Nancy; Losoya Sandra H.; Fabes Richard A.; Guthrie Ivanna K.; Murphy Bridget C. 《Canadian Metallurgical Quarterly》2003,17(4):584
Relations of heart rate and skin conductance reactions to mildly evocative empathy-inducing slides with socioemotional functioning were examined for 154 children (mean age = 9 years, 5 months). In addition, maternal expressivity was tested as a moderator of these relations. Parents and teachers rated children's socioemotional functioning, and a behavioral measure of children's regulation was obtained. Boys who exhibited higher skin conductance and higher heart rate to slides depicting negative emotions were better regulated, less emotionally intense, and better adjusted than their peers. Furthermore, boys' regulation and adjustment were positively related to such physiological responding to negative slides if maternal negative expressivity was relatively low or moderate, but not high. Fewer findings were obtained for girls or for positive slides. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
103.
A 1-D transient model (RESHEAT), developed by the writers, was used to study the thermal performance of a highly reflective paint applied sequentially to the outer walls and roof of a simulated residence in a hot and arid region of the southwestern United States. The model uses climatological inputs from a file that includes hourly data on ambient temperatures, insolation, cloud cover, and so on, at the particular location. The model focuses particularly on the potential cooling load reduction due to the reduced heat pickup from the inside attic surfaces to the outer surfaces of the supply duct. This simulation showed that a reduction of 33.6% (cooling load) on the average is achieved over the base case where no reflective paint is used when the outer surface of the roof and walls are painted. Alternatively, only a 11% reduction would be achieved if the reflective paint is applied only to the roof. Savings of $42 per month are conservatively estimated from calculations made when applying this technology to a typical residence (roof and walls) equipped with a 4 ton refrigeration unit in the Southwest. 相似文献
104.
The mobile agent is a fundamental building block of the mobile computing paradigm. In mobile agent security, oblivious transfer
(OT) from a trusted party can be used to protect the agent’s privacy and the hosts’ privacy. In this paper, we introduce a
new cryptographic primitive called Verifiable Distributed Oblivious Transfer (VDOT), which allows us to replace a single trusted party with a group of threshold trusted servers. The design of VDOT uses a novel
technique called consistency verification of encrypted secret shares. VDOT protects the privacy of both the sender and the receiver against malicious attacks of the servers. We also show the
design of a system to apply VDOT to protect the privacy of mobile agents. Our design partitions an agent into the general
portion and the security-sensitive portion. We also implement the key components of our system. As far as we know, this is
the first effort to implement a system that protects the privacy of mobile agents. Our preliminary evaluation shows that protecting
mobile agents not only is possible, but also can be implemented efficiently.
This work was supported in part by the DoD University Research Initiative (URI) program administered by the Office of Naval
Research under grant N00014-01-1-0795. Sheng Zhong was supported by ONR grant N00014-01-1-0795 and NSF grants ANI-0207399
and CCR-TC-0208972. Yang Richard Yang was supported in part by NSF grant ANI-0207399. A preliminary version of this paper
was presented at the DialM-POMC Joint Workshop on Foundations of Mobile Computing in 2003.
Sheng Zhong received his Ph.D. in computer science from Yale University in the year of 2004. He holds an assistant professor position
at SUNY Buffalo and is currently on leave for postdoctoral research at the Center for Discrete Mathematics and Theoretical
Computer Science (DIMACS). His research interests, on the practical side, are security and incentives in data mining, databases,
and wireless networks. On the theoretical side, he is interested in cryptography and game theory.
Yang Richard Yang is an Assistant Professor of Computer Science at Yale University. His research interests include computer networks, mobile
computing, wireless networking, sensor networks, and network security. He leads the LAboratory of Networked Systems (LANS)
at Yale. His recent awards include a Schlumberger Fellowship and a CAREER Award from the National Science Foundation. He received
his B.E. degree from Tsinghua University (1993), and his M.S. and Ph.D. degrees from the University of Texas at Austin (1998
and 2001). 相似文献
105.
Thailand has recently introduced net metering legislation that provides streamlined procedures for small renewable energy generators to connect to the grid, and guarantees both a market and good prices. The new laws create income opportunities for rural communities based on locally produced, clean, renewable energy supplies and offer significant potential to reduce Thailand's dependence on imported oil and coal. Chris Greacen, Chuenchom Sangarasri Greacen and Rich Plevin report. 相似文献
106.
Makarand Hastak Amir Mirmiran Richard Miller Ronak Shah Reid Castrodale 《Canadian Metallurgical Quarterly》2003,8(5):267-272
Precast bridges are often constructed as single span for dead load, but continuous for live load. A diaphragm connection is provided for negative moment continuity. However, the connection may also be subjected to positive moments due to time-dependent effects. Because these moments may be large enough to damage the diaphragm or even the girders, a positive moment connection is often provided. This paper reports on a study to determine the types of positive moment connections used across the country and to identify potential problems with these types of connections. A questionnaire survey was conducted to assess the state of practice for precast prestressed concrete bridges made continuous. The survey provides valuable information on this type of bridge and updates a previous survey on this subject. 相似文献
107.
108.
Richard Ennals 《AI & Society》1997,11(1-2):155-165
This article introduces the theme of the special issue, linking current concerns in European social and industrial relations
policy with the research traditions covered byAI & Society. Human centredness, skill and technology, and the central importance of education and learning are emphasised as we build
new development coalitions. 相似文献
109.
110.
The use of block coding and errors-and-erasures decoding can enhance performance in frequency-hop (FH) communication systems, provided that a good scheme is employed to determine which symbols to erase. The problem of making erasure decisions from collections of receiver outputs is investigated in this paper. Methods to determine which received symbols to erase are derived from Bayesian decision theory. Decision rules are developed for a system with M-ary orthogonal signaling, noncoherent demodulation, and frequency-selective fading. One result is a class of Bayesian schemes in which erasure decisions are made independently from symbol to symbol. Within this class is a rule that uses signal amplitude estimates for improved performance. A second result is a Bayesian technique in which erasure decisions are mutually dependent and are made collectively for each codeword. These techniques are analyzed and compared with the performance of receivers that use erasure techniques that require multiple applications of bounded distance decoding. The performance of the Bayesian techniques for dependent erasures are also compared with the performance of receivers that do not permit erasures. It is found that each of the Bayesian techniques offers substantial performance gains over errors-only decoding, and the dependent erasure scheme provides the best performance among the techniques of lower complexity 相似文献