全文获取类型
收费全文 | 61394篇 |
免费 | 7051篇 |
国内免费 | 3221篇 |
专业分类
电工技术 | 4597篇 |
技术理论 | 7篇 |
综合类 | 5094篇 |
化学工业 | 13520篇 |
金属工艺 | 2010篇 |
机械仪表 | 2923篇 |
建筑科学 | 5337篇 |
矿业工程 | 1669篇 |
能源动力 | 8404篇 |
轻工业 | 2374篇 |
水利工程 | 1360篇 |
石油天然气 | 2790篇 |
武器工业 | 506篇 |
无线电 | 6216篇 |
一般工业技术 | 6195篇 |
冶金工业 | 2445篇 |
原子能技术 | 1288篇 |
自动化技术 | 4931篇 |
出版年
2024年 | 294篇 |
2023年 | 1091篇 |
2022年 | 1794篇 |
2021年 | 2122篇 |
2020年 | 2222篇 |
2019年 | 2006篇 |
2018年 | 1839篇 |
2017年 | 2119篇 |
2016年 | 2333篇 |
2015年 | 2452篇 |
2014年 | 3719篇 |
2013年 | 4150篇 |
2012年 | 4172篇 |
2011年 | 4632篇 |
2010年 | 3519篇 |
2009年 | 3570篇 |
2008年 | 3367篇 |
2007年 | 3745篇 |
2006年 | 3470篇 |
2005年 | 3017篇 |
2004年 | 2451篇 |
2003年 | 2273篇 |
2002年 | 1865篇 |
2001年 | 1527篇 |
2000年 | 1338篇 |
1999年 | 1048篇 |
1998年 | 898篇 |
1997年 | 785篇 |
1996年 | 711篇 |
1995年 | 582篇 |
1994年 | 461篇 |
1993年 | 367篇 |
1992年 | 337篇 |
1991年 | 257篇 |
1990年 | 222篇 |
1989年 | 192篇 |
1988年 | 137篇 |
1987年 | 106篇 |
1986年 | 93篇 |
1985年 | 69篇 |
1984年 | 82篇 |
1983年 | 53篇 |
1982年 | 38篇 |
1981年 | 26篇 |
1980年 | 10篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1966年 | 7篇 |
1959年 | 18篇 |
1951年 | 31篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
In this work, the longitudinal permeability of squarely packed dual-scale fiber preforms is studied theoretically. These fiber preforms are composed of aligned porous tows and the tows are tightly packed. The effective permeability is calculated as a parallel-like network of intra-tow permeability and inter-tow permeability, which are quantified by Darcy’s law and the inscribed radius between tows, respectively. The jump velocity at the interface between inter-tow fluids and porous tows is considered, as derived by substituting Beavers and Joseph’s correlation into Brinkman’s equation. We further examine the effects of intra-tow permeability on the effective permeability of the fibrous system with three interface conditions: (1) interface velocity = 0, (2) interface velocity = mean intra-tow velocity, and (3) interface velocity = jump velocity. The jump-velocity-based model is found to be closest to numerical data. The influence of the fiber volume fraction of tows on the effective permeability is also analyzed. 相似文献
3.
《低温学》2015
The development of a high cooling power and high efficiency 4.2 K two stage G-M cryocooler is critically important given its broad applications in low temperature superconductors, MRI, infrared detector and cryogenic electronics. A high efficiency 1.5 W/4.2 K pneumatic-drive G-M cryocooler has recently been designed and developed by ARS. The effect of expansion volume rate and operation conditions on the cooling performance has been experimentally investigated. A typical cooling performance of 1.5 W/4.2 K has been achieved, and the minimum temperature of the second stage is 2.46 K. The steady input power of the compressor at 60 Hz is 6.8 kW, while the operation speed of the rotary valve is 30 rpm. A maximum cooling power of 1.75 W/4.2 K has been obtained in test runs. 相似文献
4.
5.
The heat transfer and flow characteristics of MWCNT-R141b nanorefrigerant with different mass fractions have been studied through experiments. Experimental results were compared with existing correlations. A two-step method was used to prepare the nanorefrigerants. Span-80 was used as surfactant with an average particle diameter of 20 nm. Transmittance method was used to evaluate the stability of nanorefrigerants. Results showed that the stability of MWCNT-R141b nanorefrigerant, which is the added dispersant, was good during the experiments. The 0.3 wt% MWCNT-R141b nanorefrigerants had optimal heat transfer enhancement effects compared with pure refrigerants. The maximum Nusselt number increased by 40%. The specific pressure drop of nanorefrigerant increased as the Reynolds number (Re) increased, and the specific pressure drop of the pure refrigerant was minimum, which is similar to R141b. 相似文献
6.
Nazir Kizzie‐Hayford Doris Jaros Yvonne Schneider Harald Rohm 《International Journal of Food Science & Technology》2015,50(2):381-388
A standard method for the extraction of tiger nut milk has been introduced. It has been shown that, although milling duration improves the yield of tiger nut milk solids and its nutrient composition, there is a quantifiable loss of nutrient in the pressing residue during milk extraction. Milling duration improved the colloidal stability of the milk against creaming during 16 h of storage. A higher milling intensity resulted in the aggregation of biological polymers which resulted in colloidal destabilisation. Milling improved the lightness and stability and reduced browning rate of the tiger nut milk during storage. This report is important for the production of tiger nut milk of consistent and comparable characteristics. Milling has been introduced as a processing method for the qualitative and quantitative modulation of the properties of tiger nut milk. It is recommended to develop further strategies to improve the colloidal stability of tiger nut milk as a beverage. 相似文献
7.
In this paper, a model taking into account the effects of carrier loss mechanisms has been developed. The model simulates the photovoltaic properties of the graphene/n-type silicon Schottky barrier solar cells (G/n-Si_SBSC), and it can reproduce the experimentally determined parameters of the G/n-Si_SBSC. To overcome the low efficiencies of G/n-Si_SBSC, their performances have been optimized by modifying the work function of graphene and Si properties, accounted for variation of its thickness and doping level. The obtained results show that the work function of graphene has the major impact on the device performance. Also, the temperature dependence of the G/n-Si_SBSC performance is investigated. 相似文献
8.
To realize joint optimization of spatial diversity and equalization combining in the intersymbol interference (ISI) channel, an iterative equalization combining algorithm is proposed. The proposed algorithm uses the coefficients of Turbo equalization to calculate the combination weights without estimating the signal to noise ratio in each diversity branch. The equalized symbols from different diversity branches are combined, and the extrinsic information output from the decoder is fed back to the equalizers, so as to exchange soft information between the equalizers and the decoder. The performance of the proposed algorithm is analyzed using the extrinsic information transfer (EXIT) chart and verified by simulations. Results show that our approach fully exploits time domain information from the multipath channel and spatial domain information from multi receiving antennas, which efficiently improve the performance of the receiver in the severe ISI channel. 相似文献
9.
文章通过对黑龙江省高效节水现状,存在问题的分析,结合黑龙江省高效节水发展的支撑能力,阐述黑龙江省节水增粮目标、任务及总体布局,为黑龙江省2012—2015年节水增粮实施提供依据。 相似文献
10.
We investigate the problem of efficient wireless power transfer in wireless sensor networks. In our approach, special mobile entities (called the Mobile Chargers) traverse the network and wirelessly replenish the energy of sensor nodes. In contrast to most current approaches, we envision methods that are distributed and use limited network information. We propose four new protocols for efficient charging, addressing key issues which we identify, most notably (i) what are good coordination procedures for the Mobile Chargers and (ii) what are good trajectories for the Mobile Chargers. Two of our protocols (DC, DCLK) perform distributed, limited network knowledge coordination and charging, while two others (CC, CCGK) perform centralized, global network knowledge coordination and charging. As detailed simulations demonstrate, one of our distributed protocols outperforms a known state of the art method, while its performance gets quite close to the performance of the powerful centralized global knowledge method. 相似文献