全文获取类型
收费全文 | 111487篇 |
免费 | 7444篇 |
国内免费 | 4138篇 |
专业分类
电工技术 | 5360篇 |
技术理论 | 5篇 |
综合类 | 5745篇 |
化学工业 | 18135篇 |
金属工艺 | 7507篇 |
机械仪表 | 6384篇 |
建筑科学 | 8304篇 |
矿业工程 | 2620篇 |
能源动力 | 3200篇 |
轻工业 | 6453篇 |
水利工程 | 1713篇 |
石油天然气 | 5596篇 |
武器工业 | 688篇 |
无线电 | 11994篇 |
一般工业技术 | 16897篇 |
冶金工业 | 8234篇 |
原子能技术 | 1363篇 |
自动化技术 | 12871篇 |
出版年
2024年 | 364篇 |
2023年 | 1537篇 |
2022年 | 2540篇 |
2021年 | 3532篇 |
2020年 | 2750篇 |
2019年 | 2414篇 |
2018年 | 2921篇 |
2017年 | 3233篇 |
2016年 | 2868篇 |
2015年 | 3589篇 |
2014年 | 4650篇 |
2013年 | 6508篇 |
2012年 | 6389篇 |
2011年 | 7253篇 |
2010年 | 6058篇 |
2009年 | 6181篇 |
2008年 | 5977篇 |
2007年 | 5804篇 |
2006年 | 5945篇 |
2005年 | 5327篇 |
2004年 | 3705篇 |
2003年 | 3256篇 |
2002年 | 3009篇 |
2001年 | 2727篇 |
2000年 | 2966篇 |
1999年 | 3378篇 |
1998年 | 3612篇 |
1997年 | 2791篇 |
1996年 | 2693篇 |
1995年 | 2024篇 |
1994年 | 1649篇 |
1993年 | 1220篇 |
1992年 | 931篇 |
1991年 | 790篇 |
1990年 | 558篇 |
1989年 | 498篇 |
1988年 | 387篇 |
1987年 | 268篇 |
1986年 | 178篇 |
1985年 | 147篇 |
1984年 | 94篇 |
1983年 | 67篇 |
1982年 | 66篇 |
1981年 | 63篇 |
1980年 | 39篇 |
1979年 | 14篇 |
1978年 | 10篇 |
1976年 | 19篇 |
1975年 | 11篇 |
1973年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
121.
A new torque estimator for switched reluctance motor (SRM) drives based on 2-D rotary regression analysis is presented in this paper. The proposed torque estimator is composed of a bicubic regressive polynomial as a function of rotor position and input current. The regressive coefficients can be computed offline or online from the torque characteristics acquired either experimentally or from numerical computation. Furthermore, a torque estimation method by taking mutual coupling into consideration is proposed. It can be seen that the estimated and experimentally obtained self-coupling and mutual-coupling torque characteristics are in good agreement with each other. In addition, the dynamic torque waveforms with and without the mutual coupling, estimated by the proposed estimator, are found to be virtually the same as those obtained from the bicubic spline interpolation for SRM drives with single-pulse voltage, hysteresis current chopping, as well as with voltage pulse width modulation control. The success of all the case studies being reported is a good validation of the usefulness and accuracy of the proposed real-time torque estimator that, as described in this paper, can be used to quickly estimate the instantaneous output torque of SRM drives. 相似文献
122.
We present a numerical study of the packing of uniform spheres under three-dimensional vibration using the discrete element method (DEM), focusing on the effects of vibration condition (amplitude and frequency) and inter-particle frictions (sliding and rolling frictions). The results are analysed in terms of packing density, coordination number (CN), radial distribution function (RDF) and pore structure. It is shown that increasing either the vibration amplitude or frequency causes packing density to increase initially to a maximum and then decrease. Both vibration frequency and amplitude should be considered to characterize the effect of vibration process on packing structure. The sliding and rolling frictions between particles can decrease packing density since they dissipate energy, although the effect of rolling friction is less significant. In line with the change of packing density, microstructural properties such as CN, RDF and pore distribution also change: a looser packing often corresponds to smaller CN, less peaked RDF and larger but more widely distributed pores. 相似文献
123.
Qingzhao Yao Yuming Zhou Yanqing Sun Xiaoyun Ye 《Journal of Inorganic and Organometallic Polymers and Materials》2008,18(4):477-484
TiO2 hybrid molecular imprinted polymer (MIP) for ethofumesate using methacrylic acid (MAA) as the functional monomer and silane
coupling agent 3-(trimethoxysilyl) propylmethacrylate (KH570) as organic–inorganic connective bridge was synthesized via photo-excitation
method. Hydrogen bond was proved to act between MAA and ethofumesate for pre- and post-polymerization binding properties as
testified by UV spectrometric method. KH570 modified TiO2 nanoparticles were prepared via sonochemical reaction, which can accelerate hydrolysis, increase collision chance for the
reactive system and improve the dispersion of the nanoparticles. Scanning electron microscope (SEM), transmission electron
microscope (TEM), binding and the adsorption kinetics experiments as well as thermogravimetric analysis (TGA) were employed
for characterization. The results indicated that the hybrid MIP revealed a larger surface area and more ordered imprinting
cavities with improved thermal stability compared to organic-only MIP. Furthermore, faster adsorption kinetics and enhancive
adsorption capacity were achieved, which made it promising in chemical sensor applications. 相似文献
124.
J. L. Barron R. E. Mercer X. Chen P. Joe 《International journal of imaging systems and technology》2005,15(3):189-198
We present local least squares and regularization frameworks for computing 3D velocity (3D optical flow) from 3D radial velocity measured by a Doppler radar. We demonstrate the performance of our algorithms quantitatively on synthetic radial velocity data and qualitatively on real radial velocity data, obtained from the Doppler radar at Kurnell Radar station, Botany Bay, New South Wales, Australia. Radial velocity can be used to predict the future positions of storms in sequences of Doppler radar datasets.© 2005 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 15, 189–198, 2005 相似文献
125.
Synthesis of 21R AlN polytypoids was investigated using Al and ultrafine SiO2 powder in a flowing nitrogen atmosphere by means of thermal gravity (TG), differential scanning calorimeter (DSC), X-ray diffractometer (XRD) and scanning electronic microscope (SEM) linked with energy dispersive spectrometer (EDS). The results showed that the formation mechanism of AlN polytypoids was different from that in reaction sintering process using Si3N4, AlN, Al2O3 and other sintering additive as raw materials. It was suggested that firstly Al reduce SiO2 into Si and is also nitrided into AlN, then AlN, Al2O3 and SiO2 dissolve into silicon liquid until the AlN polytypoids precipitate in saturated liquid in a flowing nitrogen atmosphere at lower than 1700 °C. 相似文献
126.
127.
128.
川西平原属沉积平原,不到2m厚的表土下面全是沙卵石,沙卯石厚度达二、三十米。地面覆盖农田,沟垄纵横,限制了车载钻机的进入。以往地震勘探多采取浅井组合方式激发,所获得的地震资料能量差、面波强,对农田破坏面积大。若使用SH30—2A型轻便工程钻机,配上自制的冲击管,采取冲击钻进,从管中下药柱的方式,可实现沙卵石地区的深井激发,提高资料采集质量,且效率高、成本低。 相似文献
129.
Water treatment using TiO2 semiconductor as a durable heterogeneous photocatalyst has been the focus of environmentalists in recent years. Currently, we developed an inexpensive and highly efficient approach for synthesizing nitrogen-doped TiO2 with lower band-gap energy that can respond to visible light. Doping on the molecular scale led to an enhanced nitrogen concentration of up to 21.8%. Reflectance measurements showed the synthesized N-doped TiO2 nanoparticles are catalytically active with the absorbance that extends into the visible region up to 600 nm. The water purification potential of this new class of compound was evaluated by studying the photodegradation of Acid Orange 7 (AO7) and E. coli. Experiments were conducted to compare the photocatalytic activities of N-doped TiO2 nanocatalysts and commercially available Degussa P25 power under identical solar light exposure. N-doped TiO2 demonstrated superior photocatalytic activities in both chemical compound degradation and bactericidal reactions. The result of this study shows the potential of applying new generations of catalyst for wastewater purification and disinfection. 相似文献
130.
Charalambous C.D. Bultitude R.J.C. Li X. Zhan J. 《Wireless Communications, IEEE Transactions on》2008,7(2):434-439
This paper is concerned with modeling and identification of wireless channels using noisy measurements. The models employed are governed by stochastic differential equations (SDEs) in state space form, while the identification method is based on the expectation-maximization (EM) algorithm and Kalman filtering. The algorithm is tested against real channel measurements. The results presented include state space models for the channels, estimates of inphase and quadrature components, and estimates of the corresponding Doppler power spectral densities (DPSDs), from sample noisy measurements. Based on the available measurements, it is concluded that state space models of order two are sufficient for wireless flat fading channel characterization. 相似文献