全文获取类型
收费全文 | 111601篇 |
免费 | 8169篇 |
国内免费 | 2845篇 |
专业分类
电工技术 | 4372篇 |
技术理论 | 4篇 |
综合类 | 3732篇 |
化学工业 | 19799篇 |
金属工艺 | 5321篇 |
机械仪表 | 6837篇 |
建筑科学 | 5415篇 |
矿业工程 | 1799篇 |
能源动力 | 3899篇 |
轻工业 | 8010篇 |
水利工程 | 1418篇 |
石油天然气 | 3038篇 |
武器工业 | 554篇 |
无线电 | 16224篇 |
一般工业技术 | 17901篇 |
冶金工业 | 8496篇 |
原子能技术 | 1444篇 |
自动化技术 | 14352篇 |
出版年
2024年 | 311篇 |
2023年 | 1490篇 |
2022年 | 2556篇 |
2021年 | 3746篇 |
2020年 | 2792篇 |
2019年 | 2598篇 |
2018年 | 3112篇 |
2017年 | 3216篇 |
2016年 | 3435篇 |
2015年 | 3660篇 |
2014年 | 5010篇 |
2013年 | 6937篇 |
2012年 | 7163篇 |
2011年 | 8034篇 |
2010年 | 6576篇 |
2009年 | 6611篇 |
2008年 | 6180篇 |
2007年 | 5548篇 |
2006年 | 5133篇 |
2005年 | 4356篇 |
2004年 | 3682篇 |
2003年 | 3363篇 |
2002年 | 3397篇 |
2001年 | 2815篇 |
2000年 | 2425篇 |
1999年 | 2358篇 |
1998年 | 3006篇 |
1997年 | 2062篇 |
1996年 | 1808篇 |
1995年 | 1499篇 |
1994年 | 1105篇 |
1993年 | 1000篇 |
1992年 | 744篇 |
1991年 | 665篇 |
1990年 | 557篇 |
1989年 | 497篇 |
1988年 | 424篇 |
1987年 | 326篇 |
1986年 | 314篇 |
1985年 | 257篇 |
1984年 | 222篇 |
1983年 | 166篇 |
1982年 | 164篇 |
1981年 | 138篇 |
1980年 | 132篇 |
1979年 | 110篇 |
1978年 | 96篇 |
1977年 | 129篇 |
1976年 | 163篇 |
1975年 | 86篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
991.
Jeong Won Kim Hee Won Kang Dong-Hwan Hwang Sang Jeong Lee 《International Journal of Control, Automation and Systems》2012,10(3):529-535
A signal tracking method of GNSS receivers for spinning vehicles is proposed in order to eliminate the influence of spinning to the GNSS signal of a vehicle. In the proposed method, a rotation tracking loop is added into the carrier tracking loop of a conventional GNSS receiver. The proposed method was verified through computer simulations and an experiment for live GPS signals. The results show that the proposed method gives an accurate tracking performance. 相似文献
992.
Junhan Lee Chan Gook Park 《International Journal of Control, Automation and Systems》2012,10(3):506-516
This paper presents a new scheme for fault detection and isolation in a satellite system. The purpose of this paper is to develop detection, isolation and identification algorithms based on a cascade filter for both total and partial faults in a satellite attitude control system (ACS). The cascade filter consists of a decentralized Kalman filter (DKF) and a bank of interacting multiple model (IMM) filters. The cascade filter is utilized for detection and diagnosis of anticipated sensor and actuator faults in a satellite ACS. Other fault detection and isolation (FDI) schemes are compared with the proposed FDI scheme. The FDI procedure using a cascade filter was developed in three stages. In the first stage, two local filters and a master filter detect sensor faults. In the second stage, the FDI scheme checks sensor residuals to isolate sensor faults, and 11 Extended Kalman filters with actuator fault models detect wherever actuator faults occur. In the third stage of the FDI scheme, four filters identify the fault type, which is either a total or partial fault. An important feature of the proposed FDI scheme is that it can decrease fault isolation time and accomplish not only fault detection and isolation but also fault type identification using a scalar penalty in the conditional density function. 相似文献
993.
Dinesh Kalyanasundaram Shinnosuke Inoue Jong-Hoon Kim Hyun-Boo Lee Zenko Kawabata Woon-Hong Yeo Gerard A. Cangelosi Kieseok Oh Dayong Gao Kyong-Hoon Lee Jae-Hyun Chung 《Microfluidics and nanofluidics》2012,13(2):217-225
Simple, high-yield concentration of DNA is important for high-throughput genetic analysis and disease diagnosis. Glass-based microfilters are popular but the process requires centrifugation steps with cumbersome chemical processes. As an alternative, a concentration method using an electric field has been explored previously, but with limited efficiency. In this paper, electric field-induced concentration and capture of DNA are studied by using high-aspect-ratio microtips coated with a gold layer. The microtips are immersed longitudinally into a solution of 100???L containing ??-phage DNA. After DNA concentration using an electric field, the microtips are withdrawn from the solution. Under AC- and biased AC fields, DNA is concentrated by electrophoresis (EP), dielectrophoresis (DEP), and electroosmotic flow (EOF). To reduce capillary effects in the withdrawal process, the microtips are coated with positively charged poly-l-lysine (PLL). The pattern of captured DNA is analyzed by fluorescence microscopy. DEP attracts DNA molecules at the edges of microtips, where the highest gradient of electric field exists. EP attracts DNA onto the surface of microtips following the vectors of an electric field. EOF generates vortexes that deliver DNA onto microtips. Using this method, 85% of DNA is captured on the PLL-coated microtips after three sequential captures. The concentration mechanism can potentially facilitate rapid and simple preparation of DNA for downstream analysis. 相似文献
994.
We report an active micromixer utilizing vortex generation due to non-equilibrium electrokinetics near micro/nanochannel interfaces.
Its design is relatively simple, consisting of a U-shaped microchannel and a set of nanochannels. We fabricated the micromixer
just using a two-step reactive ion etching process. We observed strong vortex generation in fluorescent microscopy experiments.
The mixing performance was evident in a combined pressure-driven and electroosmotic flows, compared with the case with a pure
pressure-driven flow. We characterized the micromixer for several conditions: different applied voltages, ion concentrations,
flow rates, and nanochannel widths. The experimental results show that the mixing performance is better with a higher applied
voltage, a lower ion concentration, and a wider nanochannel width. We quantified the mixing characteristics in terms of mixing
time. The lowest mixing time was 2 milliseconds with the voltage of 230 V and potassium chloride solutions of 0.1 mM. We expect
that the micromixer is beneficial in several applications requiring rapid mixing. 相似文献
995.
Jun-Tae Lee Aamir Abid Ka Ho Cheung L. Sudheendra Ian M. Kennedy 《Microfluidics and nanofluidics》2012,13(3):461-468
The dynamics of superparamagnetic particles subject to competing magnetic and viscous drag forces have been examined with a uniform, stationary, external magnetic field. In this approach, competing drag and magnetic forces were created in a fluid suspension of superparamagnetic particles that was confined in a capillary tube; competing viscous drag and magnetic forces were established by rotating the tube. A critical Mason number was determined for conditions under which the rotation of the capillary prevents the formation of chains from individual particles. The statistics of chain length was investigated by image analysis while varying parameters such as the rotation speed and the viscosity of the liquid. The measurements showed that the rate of particle chain formation was decreased with increased viscosity and rotation speed; the particle dynamics could be quantified by the same dimensionless Mason number that has been demonstrated for rotating magnetic fields. The potential for enhancement of mixing in a bioassay was assessed using a fast chemical reaction that was diffusion-limited. Reducing the Mason number below the critical value, so that chains were formed in the fluid, gave rise to a modest improvement in the time to completion of the reaction. 相似文献
996.
Ho-Chan Kim Hardian Reza Dharmayanda Taesam Kang Agus Budiyono Gigun Lee Widyawardana Adiprawita 《International Journal of Control, Automation and Systems》2012,10(1):88-101
Rigorous control synthesis for an unmanned aerial vehicle necessitates the availability of a good, reasonable model for such
a vehicle. The work reported in this paper focuses on the modeling of a rotary unmanned aerial vehicle (RUAV) and the development
of a robust controller that can handle parameter uncertainties and disturbances. The parameters of the plant model are obtained
through the use of the prediction error method with real flight data. The response of the identified linear model shows a
good match with the measured flight data. The H
∞ control scheme is applied to obtain a robustly stable controller using the identified model. The proposed controller is analyzed
using frequency-domain analysis and time-domain simulations. The performance of the proposed H
∞ controller is better than that of the conventional proportional derivative controller in that the proposed controller has
a shorter settling time and less overshoot. Furthermore, the degradation of the proposed controller performance is negligible
and stability is maintained when the input gains to the plant are doubled, which demonstrates the good performance and robustness
of the controller. 相似文献
997.
Dong?Seop?LeeEmail author J.?Periaux L.?F.?Gonzalez K.?Srinivas E.?Onate 《Structural and Multidisciplinary Optimization》2012,45(3):433-450
There are many applications in aeronautical/aerospace engineering where some values of the design parameters/states cannot
be provided or determined accurately. These values can be related to the geometry (wingspan, length, angles) and or to operational
flight conditions that vary due to the presence of uncertainty parameters (Mach, angle of attack, air density and temperature,
etc.). These uncertainty design parameters cannot be ignored in engineering design and must be taken into the optimisation
task to produce more realistic and reliable solutions. In this paper, a robust/uncertainty design method with statistical
constraints is introduced to produce a set of reliable solutions which have high performance and low sensitivity. Robust design
concept coupled with Multi-Objective Evolutionary Algorithms (MOEAs) is defined by applying two statistical sampling formulas;
mean and variance/standard deviation associated with the optimisation fitness/objective functions. The methodology is based
on a canonical evolution strategy and incorporates the concepts of hierarchical topology, parallel computing and asynchronous
evaluation. It is implemented for two practical Unmanned Aerial System (UAS) design problems; the first case considers robust
multi-objective (single-disciplinary: aerodynamics) design optimisation and the second considers a robust multidisciplinary
(aero-structures) design optimisation. Numerical results show that the solutions obtained by the robust design method with
statistical constraints have a more reliable performance and sensitivity in both aerodynamics and structures when compared
to the baseline design. 相似文献
998.
Karen A. Lee Margaret A. Frerking 《Journal of Infrared, Millimeter and Terahertz Waves》1989,10(7):789-802
A quasi-optical reflection cavity intended to be used as the resonant load of a submillimeter wavelength oscillator has been designed, constructed, and tested. The resonator consists of three elements in cascade: a high Q, high finesse folded Fabry-Perot resonator, a lower Q, low finesse Fabry-Perot resonator, and a Littrow mounted diffraction grating. The resonator exhibits a Q of 6600 and 2.5 dB of loss at 63 GHz. The design can be scaled to 1 THz, where waveguide structures become impractical, to serve as the resonator for high frequency quantum well resonant tunneling device oscillators. 相似文献
999.
1000.
Mechanical alloying was used to synthesize NixZr1–x alloys from mixtures of intermetallic compound powders, and also from mixtures of intermetallic compound powders and pure elemental powders. The mechanically alloyed powders were amorphous in the range 0.24 x 0.85. This range is larger than amorphous alloys produced by the melt-spinning technique and mechanical alloying of elemental crystalline powders. Two-phase mixtures of the amorphous phase and the corresponding crystalline terminal solid solution were formed in the range 0.10 x 0.22, and x=0.90. It is found that the morphological development during mechanical alloying of these powders is different from mechanical alloying using only pure ductile crystalline elemental powders. The thermal stability has been investigated. The enthalpy and activation energy of crystallization for Ni-Zr amorphous powders prepared by mechanical alloying are lower than those for melt-spun samples of the same composition. The crystallization temperature of the mechanically alloyed Ni-Zr amorphous powders is higher than that of meltspun samples in the composition range Ni20Zr80 to Ni33Zr67 and Ni40Zr60 to Ni60Zr40. The presence of tiny crystallites as nucleation centres and high oxygen levels in the mechanically alloyed amorphous alloys might be responsible for the differences in crystallization behaviour. A new crystalline metastable phase was observed during crystallization studies of Ni24Zr76 amorphous powder. 相似文献