全文获取类型
收费全文 | 1543416篇 |
免费 | 27613篇 |
国内免费 | 7092篇 |
专业分类
电工技术 | 34648篇 |
综合类 | 6578篇 |
化学工业 | 272453篇 |
金属工艺 | 64808篇 |
机械仪表 | 43901篇 |
建筑科学 | 46846篇 |
矿业工程 | 11514篇 |
能源动力 | 50388篇 |
轻工业 | 116859篇 |
水利工程 | 15542篇 |
石油天然气 | 37670篇 |
武器工业 | 190篇 |
无线电 | 197920篇 |
一般工业技术 | 290843篇 |
冶金工业 | 182858篇 |
原子能技术 | 34084篇 |
自动化技术 | 171019篇 |
出版年
2021年 | 15650篇 |
2020年 | 11933篇 |
2019年 | 14679篇 |
2018年 | 16625篇 |
2017年 | 16031篇 |
2016年 | 21779篇 |
2015年 | 17464篇 |
2014年 | 28811篇 |
2013年 | 88100篇 |
2012年 | 36321篇 |
2011年 | 49468篇 |
2010年 | 43383篇 |
2009年 | 51404篇 |
2008年 | 45977篇 |
2007年 | 43205篇 |
2006年 | 45449篇 |
2005年 | 40215篇 |
2004年 | 42211篇 |
2003年 | 42148篇 |
2002年 | 40920篇 |
2001年 | 38212篇 |
2000年 | 36503篇 |
1999年 | 36031篇 |
1998年 | 51563篇 |
1997年 | 42928篇 |
1996年 | 37750篇 |
1995年 | 32241篇 |
1994年 | 30117篇 |
1993年 | 29922篇 |
1992年 | 26582篇 |
1991年 | 23801篇 |
1990年 | 23996篇 |
1989年 | 23022篇 |
1988年 | 21610篇 |
1987年 | 19857篇 |
1986年 | 19320篇 |
1985年 | 22512篇 |
1984年 | 22562篇 |
1983年 | 20531篇 |
1982年 | 19435篇 |
1981年 | 19556篇 |
1980年 | 18158篇 |
1979年 | 18684篇 |
1978年 | 17887篇 |
1977年 | 17910篇 |
1976年 | 19437篇 |
1975年 | 16121篇 |
1974年 | 15647篇 |
1973年 | 15717篇 |
1972年 | 13143篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Co-browsing is an activity in which a group of users navigate their way through of a set of Web pages together for a shared
purpose. Effective co-browsing among users with different device capabilities requires a shared understanding of those Web
pages. This paper demonstrates the concept of shared viewpoints (SVPs), and personal viewpoints (PVPs), for co-browsing, before
detailing a framework for implementing these concepts. Finally, the effectiveness of the framework is presented through a
perceptual experiment. 相似文献
992.
993.
Djoumessi E.E. Marsan E. Caloz C. Chaker M. Wu K. 《Microwave and Wireless Components Letters, IEEE》2006,16(11):603-605
A tunable dual-band quadrature hybrid coupler for mobile GSM bands (900 and 1800MHz) is proposed and characterized. The structure is composed of four quarter-wavelength sections at a frequency located between the two operating frequencies and two pairs of open-ended stubs. Frequency tuning is achieved by modifying the electrical length of the open-ended stubs with varactor-diode capacitors. A dual-band tunability of 33% and 10% is obtained for the first and the second bands, respectively 相似文献
994.
Koizumi H. Kurokawa K. Mori S. 《IEEE transactions on circuits and systems. I, Regular papers》2006,53(3):677-687
This paper presents an analysis of Class D inverter when irregular driving patterns are given to the gate drive of the switch devices. The analysis has been carried out with focusing on the waveforms, harmonics, low-frequency components, output power, and equivalent dc resistance, which are numerically analyzed and discussed. Class D inverters with six different Q factors from 0.1 to 20 are analyzed about 2/sup 16/ driving patterns for each Q. Superior four models of the six inverters are built and tested in circuit experiments. The calculated waveforms are compared to the experimental results. Both of them are agreed well in time domain and frequency domain. Analytical results show a possibility of a novel control method with irregular driving patterns. In spite of discontinuous control, the output power or voltage can be strictly changed as if continuous using the selected driving patterns in some ranges. 相似文献
995.
P. Cofta 《BT Technology Journal》2006,24(2):214-218
Trust is the key element of commerce, both for traditional models and — more recently — for eCommerce. Unlike its traditional
counterpart, eCommerce relies on trust being created and maintained with the help of digital devices and services. Convergence
brings significant changes to the way people interact through digital media by offering ubiquitous and seamless communication.
This has a significant impact on the way trust is established and maintained, with consequent impact upon eCommerce. This
paper identifies a number of the most important challenges to trust in eCommerce as well as trust-related aspects of key enablers
of eCommerce. From this perspective, the paper studies an impact of convergence on trust within eCommerce to identify several
positive relationships. 相似文献
996.
This paper introduces a wide-spectrum specification logic νZ. The minimal core logic is extended to a more expressive specification logic which includes a schema calculus similar (but not equivalent) to Z, new additional schema operators, and extensions to programming and program development logics. 相似文献
997.
998.
The derivation, verification, and implication of the nonlinear dynamic and frequency response of electrostatic actuator due to the double frequency effect (DFE) were reported in this study. In particular, an extra mode called half mode was observed and measured in various studies. However, a complete in-depth discussion of the effect was not reported in the past. In the present study, a second-order dynamical equation was adapted firstly to model the dynamic and frequency response of electrostatic actuator where typical harmonic input signal with a dc bias was used. Secondly, by solving the equation, complex waveform in dynamic response and an extra half mode in frequency response due to the double frequency effect can be observed and discussed. To verify the simulated result, an electrostatic driving device was fabricated using PolyMUMPS© process. Note that in frequency response, when dc bias is equal to the amplitude of ac signal, simulated and experimental results indicated that the amplitude of half mode was one-fourth of first mode. 相似文献
999.
An adaptive numerical dissipation control in a class of high order filter methods for compressible MHD equations is systematically discussed. The filter schemes consist of a divergence-free preserving high order spatial base scheme with a filter approach which can be divergence-free preserving depending on the type of filter operator being used, the method of applying the filter step, and the type of flow problem to be considered. Some of these filter variants provide a natural and efficient way for the minimization of the divergence of the magnetic field (∇·B) numerical error in the sense that commonly used divergence cleaning is not required. Numerical experiments presented emphasize the performance of the ∇·B numerical error. Many levels of grid refinement and detailed comparison of the filter methods with several commonly used compressible MHD shock-capturing schemes will be illustratedA condensed version appears in the Proceedings of the International Conference on High Performance Scientific Computing, March 10-14, 2003, Hanoi, Vietnam. This is a revised version of a longer internal report, Feb. 19, 2004. The longer internal report was published as a RIACS Technical Report TR03.10, July 2003, NASA Ames Research Center 相似文献
1000.
Intensive use of the benchmark simulation model No. 1 (BSM1), a protocol for objective comparison of the effectiveness of control strategies in biological nitrogen removal activated sludge plants, has also revealed a number of limitations. Preliminary definitions of the long-term benchmark simulation model No. 1 (BSM1_LT) and the benchmark simulation model No. 2 (BSM2) have been made to extend BSM1 for evaluation of process monitoring methods and plant-wide control strategies, respectively. Influent-related disturbances for BSM1_LT/BSM2 are to be generated with a model, and this paper provides a general overview of the modelling methods used. Typical influent dynamic phenomena generated with the BSM1_LT/BSM2 influent disturbance model, including diurnal, weekend, seasonal and holiday effects, as well as rainfall, are illustrated with simulation results. As a result of the work described in this paper, a proposed influent model/file has been released to the benchmark developers for evaluation purposes. Pending this evaluation, a final BSM1_LT/BSM2 influent disturbance model definition is foreseen. Preliminary simulations with dynamic influent data generated by the influent disturbance model indicate that default BSM1 activated sludge plant control strategies will need extensions for BSM1_LT/BSM2 to efficiently handle 1 year of influent dynamics. 相似文献