全文获取类型
收费全文 | 26489篇 |
免费 | 2359篇 |
国内免费 | 1047篇 |
专业分类
电工技术 | 1443篇 |
技术理论 | 1篇 |
综合类 | 1549篇 |
化学工业 | 4562篇 |
金属工艺 | 1565篇 |
机械仪表 | 1545篇 |
建筑科学 | 2137篇 |
矿业工程 | 791篇 |
能源动力 | 777篇 |
轻工业 | 1911篇 |
水利工程 | 476篇 |
石油天然气 | 1285篇 |
武器工业 | 207篇 |
无线电 | 2958篇 |
一般工业技术 | 3432篇 |
冶金工业 | 1235篇 |
原子能技术 | 360篇 |
自动化技术 | 3661篇 |
出版年
2024年 | 140篇 |
2023年 | 534篇 |
2022年 | 900篇 |
2021年 | 1240篇 |
2020年 | 979篇 |
2019年 | 773篇 |
2018年 | 806篇 |
2017年 | 1006篇 |
2016年 | 864篇 |
2015年 | 1103篇 |
2014年 | 1299篇 |
2013年 | 1603篇 |
2012年 | 1636篇 |
2011年 | 1797篇 |
2010年 | 1496篇 |
2009年 | 1411篇 |
2008年 | 1346篇 |
2007年 | 1255篇 |
2006年 | 1241篇 |
2005年 | 1209篇 |
2004年 | 763篇 |
2003年 | 661篇 |
2002年 | 587篇 |
2001年 | 503篇 |
2000年 | 530篇 |
1999年 | 631篇 |
1998年 | 591篇 |
1997年 | 474篇 |
1996年 | 511篇 |
1995年 | 420篇 |
1994年 | 348篇 |
1993年 | 270篇 |
1992年 | 207篇 |
1991年 | 173篇 |
1990年 | 125篇 |
1989年 | 103篇 |
1988年 | 99篇 |
1987年 | 66篇 |
1986年 | 45篇 |
1985年 | 34篇 |
1984年 | 33篇 |
1983年 | 15篇 |
1982年 | 12篇 |
1981年 | 12篇 |
1980年 | 10篇 |
1979年 | 9篇 |
1978年 | 4篇 |
1976年 | 5篇 |
1972年 | 3篇 |
1959年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
991.
Thermal management and catalytic combustion stability characteristics of premixed methane/air in heat recirculation meso‐combustors 下载免费PDF全文
Yunfei Yan Shuai Feng Zizhen Huang Li Zhang Wenli Pan Lixian Li Zhongqing Yang 《国际能源研究杂志》2018,42(3):999-1012
In order to illuminate heat recirculation effect on catalytic combustion stability and further improve energy conversion efficiency in meso‐combustor, the catalytic combustion characteristics of the combustor with/without preheating channels are numerically studied at steady conditions. It is found that methane conversion rate and combustion efficiency increases by 2% to 3% and approximately 9% in the heat recirculation meso‐combustor, indicating that heat recirculation effect facilitates more complete combustion of methane and medium components. Preheating channels show positive effects on improving combustion stability in the heat recirculation meso‐combustor. On one hand, preheating channels facilitate heat recirculation effect, and heat recirculation rate exceeds 10% for all cases and reaches 31.8% with an inlet velocity of 0.5 m/s, leading to significant increment of methane‐specific enthalpy at the preheating channel outlet. On the other hand, Rh(s)/O(s) ratios of catalytic surface and catalytic surface temperature in main reaction zone are enlarged by the preheating channels, facilitating methane adsorption at catalytic surface. Specially, most of fuels are consumed in a shorter distance with higher methane conversion speed, which brings benefits to promote combustion efficiency and may be helpful to inhibit the combustion instability in heat recirculation meso‐combustors. 相似文献
992.
随着我国经济的高速发展,人们对供电安全可靠性的要求日益提高。通过分析现阶段供电企业安全用电管理和服务的现状,提出了改进用户安全用电管理和服务的办法,以供参考。 相似文献
993.
994.
ZrNi与ZrCo合金具有高储氢量、抗杂质气体毒化能力较强、吸放氢速率快等优点,用于氚处理材料有广阔的应用前景,但ZrNi与ZrCo在高温高压下容易发生歧化反应这一缺点制约其实际应用。采用Sievert’s体积法测量合金的PCT(压力-容量-温度)曲线以及歧化动力学曲线以研究用Ti替代Zr对ZrNi0.6Co0.4合金储氢特性的影响,并采用X射线衍射物相分析(XRD)对合金在歧化反应前后的物相进行分析。研究表明,用Ti替代Zr后ZrNi0.6Co0.4合金随Ti含量的增大,其吸氢平台压增大。通过Van’t Hoff方程拟合并计算出Ti0.05Zr0.95Ni0.6Co0.4,Ti0.1Zr0.9Ni0.6Co0.4和Ti0.2Zr0.8Ni0.6Co0.4室温下的吸氢平台压分别为0.0146,0.0244和0.2960 Pa。TixZr1-xNi0.6Co0.4合金随Ti含量的增大,合金在773 K下发生歧化反应变得缓慢。合金吸氢平台压提高后,合金要发生歧化反应需要更高的温度作为驱动力,因此合金抗歧化性能随Ti含量的增大得到提高。 相似文献
995.
根据拉格朗日方程推导了结构设置FPS调谐质量系统地震动力反应分析计算公式,并考虑了接触面滞滑效应的影响。分析与计算结果表明:设置质量调谐系统之后,结构动力反应层间位移有所减小。当接触面滑动摩擦系数为0.15左右、滑道半径为0.7 m、调谐附加质量为楼层质量的1.4倍以上时,质量调谐系统具有较好的减振效果、消能效果与复位能力。 相似文献
996.
This paper proposes a Gaussian approximation recursive filter (GASF) for a class of nonlinear stochastic systems in the case that the process and measurement noises are correlated with each other. Through presenting the Gaussian approximations about the two-step state posterior predictive probability density function (PDF) and the one-step measurement posterior predictive PDF, a general GASF framework in the minimum mean square error (MMSE) sense is derived. Based on the framework, the GASF implementation is transformed into computing the multi-dimensional integrals, which is solved by developing a new divided difference filter (DDF) with correlated noises. Simulation results demonstrate the superior performance of the proposed DDF as compared to the standard DDF, the existing UKF and EKF with correlated noises. 相似文献
997.
Structural performance in direct (pure) shear and three-point bending was investigated for sandwich panels with a carbon fiber pyramidal truss core. Analytical estimates for sandwich panel strength for each loading condition were presented for possible competing failure modes. In the experimental part of the study, pyramidal truss cores were made using the hot press molding technique and then attached to flat carbon fiber composite face sheets to build all-composite sandwich panels. Panels with different configurations (e.g., core relative density and face sheet thickness) were tested to probe different failure modes and investigate the mechanical properties. In general, measured failure loads showed good agreement with the analytical predictions. Failure mechanism maps illustrate the controlling failure mechanisms in various regions of parameter space. 相似文献
998.
999.
Looking to increase the functionality of current wireless platforms and to improve their quality of service, we have explored the merits of using frequency-reconfigurable antennas as an alternative for multiband antennas. Our study included an analysis of various reconfigurable and multiband structures such as patches, wires, and combinations. Switches, such as radio-frequency microelectromechanical systems (RFMEMS) and p-i-n diodes, were also studied and directly incorporated onto antenna structures to successfully form frequency-reconfigurable antennas. 相似文献
1000.
Abstract The feasibility analysis of integrating methanol to olefins (MTO) with fluidized catalytic cracking (FCC) process is based on their similarities and compatibility. Feeding methanol in FCC is proposed to produce more light olefins. According to the characters of FCC, the effects of reaction temperature, water co-feed, and the coke content of catalyst in methanol conversion were studied systematically. It is concluded that high light olefins yields from methanol conversion were obtained on the FCC condition. Feeding methanol in FCC at the bottom of riser as the proper position was suggested on the ground of comparison with MGD process of FCC. The research proved the feasibility of feeding methanol in FCC and provided important reference for its commercial application in a certain degree. 相似文献