全文获取类型
收费全文 | 281211篇 |
免费 | 5353篇 |
国内免费 | 1071篇 |
专业分类
电工技术 | 4548篇 |
综合类 | 219篇 |
化学工业 | 42973篇 |
金属工艺 | 8767篇 |
机械仪表 | 7855篇 |
建筑科学 | 7632篇 |
矿业工程 | 609篇 |
能源动力 | 7755篇 |
轻工业 | 33299篇 |
水利工程 | 2392篇 |
石油天然气 | 1945篇 |
武器工业 | 10篇 |
无线电 | 34541篇 |
一般工业技术 | 51033篇 |
冶金工业 | 53153篇 |
原子能技术 | 3467篇 |
自动化技术 | 27437篇 |
出版年
2022年 | 1326篇 |
2021年 | 2492篇 |
2020年 | 1958篇 |
2019年 | 2368篇 |
2018年 | 3766篇 |
2017年 | 3732篇 |
2016年 | 4106篇 |
2015年 | 3110篇 |
2014年 | 4765篇 |
2013年 | 14228篇 |
2012年 | 8476篇 |
2011年 | 11195篇 |
2010年 | 8750篇 |
2009年 | 9544篇 |
2008年 | 10041篇 |
2007年 | 9979篇 |
2006年 | 8964篇 |
2005年 | 8092篇 |
2004年 | 7772篇 |
2003年 | 7591篇 |
2002年 | 7102篇 |
2001年 | 7356篇 |
2000年 | 6648篇 |
1999年 | 7174篇 |
1998年 | 18236篇 |
1997年 | 12663篇 |
1996年 | 9434篇 |
1995年 | 7051篇 |
1994年 | 6103篇 |
1993年 | 6039篇 |
1992年 | 4182篇 |
1991年 | 3964篇 |
1990年 | 3682篇 |
1989年 | 3503篇 |
1988年 | 3419篇 |
1987年 | 2717篇 |
1986年 | 2593篇 |
1985年 | 3282篇 |
1984年 | 2915篇 |
1983年 | 2648篇 |
1982年 | 2466篇 |
1981年 | 2524篇 |
1980年 | 2349篇 |
1979年 | 2125篇 |
1978年 | 1956篇 |
1977年 | 2443篇 |
1976年 | 3312篇 |
1975年 | 1632篇 |
1974年 | 1538篇 |
1973年 | 1617篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
The current Internet and wireless networks are harsh environments for transporting high-bandwidth multimedia data. We examine the technical issues involved, and describe an end-to-end solution to support a Web-based learn-on-demand system that operates in a wireless campus environment. 相似文献
33.
Thomy V. Dubois L. Vanoverschelde C. Sozanski J.P. Pribetich J. 《IEEE sensors journal》2004,4(6):772-778
This paper describes a novel planar antenna sensor created for the purpose of noninvasive temperature measurements using microwave radiometry. In order to improve radiometric measurements in industrial applications, a new generation of sensors is introduced, composed of a metallic sheet. Simulations based upon the method of moments is used both to design and to determine their electromagnetic performances. This paper also describes a radiometric device using these sensors to measure and control the temperature of food products during deep freezing processes. The results and discussions are presented. 相似文献
34.
35.
Eduardo Freire Teodiano Bastos-Filho Mário Sarcinelli-Filho Ricardo Carelli 《IEEE transactions on systems, man, and cybernetics. Part B, Cybernetics》2004,34(1):419-429
This paper proposes an alternative approach to address the problem of coordinating behaviors in mobile robot navigation: fusion of control signals. Such approach is based on a set of two decentralized information filters, which accomplish the data fusion involved. Besides these two fusion engines, control architectures designed according to this approach also embed a set of different controllers that generate reference signals for the robot linear and angular speeds. Such signals are delivered to the two decentralized information filters, which estimate suitable overall reference signals for the robot linear and angular speeds, respectively. Thus, the background for designing such control architectures is provided by the nonlinear systems theory, which makes this approach different from any other yet proposed. This background also allows checking control architectures designed according to the proposed approach for stability. Such analysis is carried out in the paper, and shows that the robot always reaches its final destination, in spite of either obstacles along its path or the environment layout. As an example, a control architecture is designed to guide a mobile robot in an experiment, whose results allows checking the good performance of the control architecture and validating the design approach proposed as well. 相似文献
36.
Kontogiannopoulos N. Psychalinos C. 《Circuits and Systems II: Express Briefs, IEEE Transactions on》2006,53(12):1373-1377
In this brief, the well-known switched-current (SI) filtering technique is revisited using the concept of the square-root domain (SRD) filtering. It is proved that SI filters are a subclass of the SRD filters, where sampled-data signal processing is performed. This is achieved by considering typical lossless and lossy SRD sampled-data integrator configurations, using a set of complementary SRD operators which are based on the quadratic I-V relationship of MOS transistor operated in the saturation. Circuit examples are given, where linear-domain integrator and third-order filter configurations were derived using appropriate SRD sampled-data building blocks 相似文献
37.
Enrique Alexandre Antonio Pena Manuel Sobreira 《IEEE transactions on information technology in biomedicine》2006,10(4):809-811
This paper discusses the convenience of using two-dimensional (2-D) coding techniques for the compression of electrocardiogram (ECG) signals. These signals present a very clear periodicity that can be exploited by the use of a 2-D time/frequency transform to decorrelate it as much as possible. A brief theoretical approach is given to justify the use of this technique, and a comparison is made between a 2-D and a one-dimensional (1-D) uniform quantization scenarios. The influence of the error as well as the frame size on the estimation of the fundamental period is studied. 相似文献
38.
Pallem C. Chowdhuri P. Demko J.A. Gouge M.J. 《Applied Superconductivity, IEEE Transactions on》2006,16(1):31-37
The objective of this work was to determine the significant parameters of a 3-GW 200-kV dc superconducting cable system which influence the transient voltage distribution in the various parts of the cable. The cable system consists of four coaxial metallic cylinders. It was found that the dielectric constant and the electrical resistivity of the soil significantly affect the severity of the transient voltages; lower dielectric constant and higher resistivity of the soil will increase the magnitudes of the transient voltages by increasing the earth-return impedance. It was also found that the effect of the conductor internal impedances of the cable is insignificant. Shorting the coaxial cylinders of the cryogen flow and the cryostat will lessen the severity of the transient voltages. Grounding the second, third, and fourth cylinders at regular intervals with low-impedance grounding impedance will also improve the transient performance of the cable. More research is needed to evaluate these procedures. 相似文献
39.
The Boundary Element Method (BEM) incorporating the Embedded Cell Approach (ECA) has been used to analyse the effects of constituent material properties, fibre spatial distribution and microcrack damage on the localised behaviour of transversely fractured, unidirectional fibre-reinforced composites. Three specific composites, i.e., glass fibre reinforced polyester, carbon fibre reinforced epoxy and a glass-carbon hybrid, are considered. The geometrical structures examined were perfectly periodic, uniformly spaced fibre arrangements in square and hexagonal embedded cells. In addition, numerical simulations were also conducted using embedded cells containing randomly distributed fibres. The models involve both elastic fibres and matrix, with the interfaces between the different phases being fully bonded. The results indicate that the constituent material properties (two phase composite) and spatial distribution have a significant effect on the localised stress distributions around the primary crack tip. However, the strain energy release rate associated with crack propagation is predominantly influenced by the material composition. The three-phase hybrid composite exhibited an apparent intermediate fracture toughness value, compared to the all-glass and all-carbon models. Furthermore, the strain energy release rate for the macrocrack lowers as it enters a zone of localised damage (microcracking). The presence of microcracks relaxes the stress field, which can result in a significant reduction in the energetics of the primary crack. 相似文献
40.