全文获取类型
收费全文 | 77271篇 |
免费 | 8224篇 |
国内免费 | 4826篇 |
专业分类
电工技术 | 5930篇 |
技术理论 | 5篇 |
综合类 | 8551篇 |
化学工业 | 9843篇 |
金属工艺 | 4625篇 |
机械仪表 | 3808篇 |
建筑科学 | 8252篇 |
矿业工程 | 4934篇 |
能源动力 | 3088篇 |
轻工业 | 5207篇 |
水利工程 | 3226篇 |
石油天然气 | 4286篇 |
武器工业 | 938篇 |
无线电 | 6690篇 |
一般工业技术 | 6519篇 |
冶金工业 | 5216篇 |
原子能技术 | 1246篇 |
自动化技术 | 7957篇 |
出版年
2024年 | 266篇 |
2023年 | 992篇 |
2022年 | 1958篇 |
2021年 | 2333篇 |
2020年 | 2553篇 |
2019年 | 2209篇 |
2018年 | 2043篇 |
2017年 | 2591篇 |
2016年 | 2894篇 |
2015年 | 3076篇 |
2014年 | 5009篇 |
2013年 | 4710篇 |
2012年 | 5968篇 |
2011年 | 6127篇 |
2010年 | 4632篇 |
2009年 | 4658篇 |
2008年 | 4196篇 |
2007年 | 5184篇 |
2006年 | 4584篇 |
2005年 | 3909篇 |
2004年 | 3313篇 |
2003年 | 2894篇 |
2002年 | 2412篇 |
2001年 | 2088篇 |
2000年 | 1780篇 |
1999年 | 1461篇 |
1998年 | 1139篇 |
1997年 | 999篇 |
1996年 | 877篇 |
1995年 | 770篇 |
1994年 | 598篇 |
1993年 | 430篇 |
1992年 | 386篇 |
1991年 | 278篇 |
1990年 | 231篇 |
1989年 | 190篇 |
1988年 | 120篇 |
1987年 | 95篇 |
1986年 | 60篇 |
1985年 | 48篇 |
1984年 | 55篇 |
1983年 | 36篇 |
1982年 | 24篇 |
1981年 | 23篇 |
1980年 | 32篇 |
1979年 | 13篇 |
1978年 | 8篇 |
1977年 | 7篇 |
1975年 | 12篇 |
1959年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
《International Journal of Hydrogen Energy》2022,47(54):22981-22992
In this study, a three-dimensional model was established using the lattice Boltzmann method (LBM) to study the internal ice melting process of the gas diffusion layer (GDL) of the proton exchange membrane fuel cell (PEMFC). The single-point second-order curved boundary condition was adopted. The effects of GDL carbon fiber number, growth slope of the number of carbon fibers and carbon fiber diameter on ice melting were studied. The results were revealed that the temperature in the middle and lower part of the gradient distribution GDL is significantly higher than that of the no-gradient GDL. With the increase of the growth slope of the number of carbon fiber, the temperature and melting rate gradually increase, and the position of the solid-liquid interface gradually decreases. The decrease in the number of carbon fibers has a similar effect as the increase in the growth slope of the number of carbon fibers. In addition, as the diameter of the carbon fiber increases, the position of the solid-liquid interface gradually decreases first and then increases. 相似文献
4.
William M. Pitts Martin Werrel Marco Fernandez Mary A. Long Evan A. Eisenberg James Filliben Cory D. Runyon 《火与材料》2021,45(1):127-154
Fire spread and growth on real‐scale four cushion mock‐ups of residential upholstered furniture (RUF) were investigated with the goal of identifying whether changes in five classes of materials (barrier, flexible polyurethane foam, polyester fiber wrap, upholstery fabric, and sewing thread), referred to as factors, resulted in statistically significant changes in burning behavior. A fractional factorial experimental design plus practical considerations yielded a test matrix with 20 material combinations. Experiments were repeated a minimum of two times. Measurements included fire spread rates derived from video recordings and heat release rates (HRRs). A total of 13 experimental parameters (3 based on the videos and 10 on the HRR results), referred to as responses, characterized the measurements. Statistical analyses based on Main Effects Plots (main effects) and Block Plots (main effects and factor interactions) were used. The results showed that three of the factors resulted in statistically significant effects on varying numbers of the 13 responses. The Barrier and Fabric factors had the strongest main effects with roughly comparable magnitudes. Foam was statistically significant for fewer of the responses and its overall strength was weaker than for Barrier and Fabric. No statistically significant main effects were identified for Wrap or Thread. Multiple two‐term interactions between factors were identified as being statistically significant. The Barrier*Fabric interaction resulted in the highest number of and strongest statistically significant effects. The existence of two‐term interactions means that it will be necessary to consider their effects in approaches designed to predict the burning behavior of RUF. 相似文献
5.
6.
为缓解我国水、能源和粮食资源紧张问题,促进资源可持续利用,构建水-能源-粮食系统,利用耦合协调度模型对我国的30个省(自治区、直辖市)进行测算,并利用空间杜宾模型分析主要影响因素。结果表明:2003—2017年,我国能源、粮食评价[JP]指数高于水资源评价指数,系统综合评价指数逐年递增;大部分省份耦合协调度处于初级协调水平且呈现逐年上升的态势,个别省份耦合协调度濒临失调;耦合协调度空间自相关性较强,虽有明显波动,但是呈现逐年加强的态势;影响耦合协调度的主要因素有从业人口数、固定资产投资额、人均生产总值、人口总数、[JP]文盲人口占比、工业污染排放、城镇化。 相似文献
7.
8.
《Ceramics International》2021,47(23):33353-33362
High thermal conductivity Si3N4 ceramics were fabricated using a one-step method consisting of reaction-bonded Si3N4 (RBSN) and post-sintering. The influence of Si content on nitridation rate, β/(α+β) phase rate, thermal conductivity and mechanical properties was investigated in this work. It is of special interest to note that the thermal conductivity showed a tendency to increase first and then decrease with increasing Si content. This experimental result shows that the optimal thermal conductivity and fracture toughness were obtained to be 66 W (m K)-1 and 12.0 MPa m1/2, respectively. As a comparison, the nitridation rate and β/(α+β) phase rate in a static pressure nitriding system, i.e., 97% (MS10), 97% (MS15), 97% (MS20) and 8.3% (MS10), 8.3% (MS15), 8.9% (MS20), respectively, have obvious advantages over those in a flowing nitriding system, i.e., 91% (MS10), 91% (MS15), 93% (MS20) and 3.1% (MS10), 3.3% (MS15), 3.3% (MS20), respectively. Moreover, high lattice integrity of the β-Si3N4 phase was observed, which can effectively confine O atoms into the β-Si3N4 lattice using MgO as a sintering additive. This result indicates that one-step sintering can provide a new route to prepare Si3N4 ceramics with a good combination of thermal conductivity and mechanical properties. 相似文献
9.
L.J. Espinoza-Pérez S. Esquivel-Medina E. López-Honorato 《Ceramics International》2021,47(11):15527-15532
The influence of the microstructure on the corrosion rate of three monolithic SiC samples in FLiNaK salt at 900 °C for 250 h was studied. The SiC samples, labeled as SiC-1, SiC-2, and SiC-3, had corrosion rates of 0.137, 0.020, and 0.043 mg/cm2h, respectively. Compared with grain size and the presence of special grain boundaries (i.e., Σ3), the content of high-angle grain boundaries (HAGBs) appeared to have the strongest influence on the corrosion rate of SiC in FLiNaK salt, since the corrosion rate increased six times as the concentration of high-angle grain boundaries increased from 19 to 32% for SiC-2 and SiC-1, respectively. These results stress the importance of controlling the content of HAGBs during the production process of SiC. 相似文献
10.
《International Journal of Hydrogen Energy》2022,47(19):10747-10761
To obtain the mixing enhancement mechanism of H2–Water combined jets in supersonic crossflows in a combustor with expanded section for rotating detonation ramjet, the flow field shape and spray structure were studied by experimental and numerical methods. The Eulerian–Lagrangian method was used to investigate the diffusion mechanism and H2–Water interaction law of combined jets with different sequences. At the same time, high-speed photography and the schlieren technique were used to capture the flow field. The effects of jet pressure drop, orifice diameter, orifice spacing, incoming Mach number, and other parameters on the penetration depth of water jets were studied. The results of experiment and simulation show that using H2–Water combined jets, the penetration depth of the jet spray can be greatly increased and the jet mixing effect can be significantly improved, which will contribute to the engine's ignition and stable combustion. In the case of pre-water/post-H2, the penetration depth of the hydrogen jet is greater. In the case of pre-H2/post-water, the hydrogen jet raises the water spray mainly by protecting the integrity of the water column. 相似文献