全文获取类型
收费全文 | 188094篇 |
免费 | 19623篇 |
国内免费 | 12345篇 |
专业分类
电工技术 | 15937篇 |
技术理论 | 5篇 |
综合类 | 22290篇 |
化学工业 | 24432篇 |
金属工艺 | 8211篇 |
机械仪表 | 14249篇 |
建筑科学 | 20604篇 |
矿业工程 | 7936篇 |
能源动力 | 9540篇 |
轻工业 | 8441篇 |
水利工程 | 11120篇 |
石油天然气 | 9720篇 |
武器工业 | 2519篇 |
无线电 | 11088篇 |
一般工业技术 | 21549篇 |
冶金工业 | 8076篇 |
原子能技术 | 3568篇 |
自动化技术 | 20777篇 |
出版年
2024年 | 658篇 |
2023年 | 2250篇 |
2022年 | 4485篇 |
2021年 | 5247篇 |
2020年 | 5735篇 |
2019年 | 4974篇 |
2018年 | 4687篇 |
2017年 | 6024篇 |
2016年 | 6767篇 |
2015年 | 7051篇 |
2014年 | 11103篇 |
2013年 | 11173篇 |
2012年 | 14067篇 |
2011年 | 14737篇 |
2010年 | 11120篇 |
2009年 | 11663篇 |
2008年 | 10756篇 |
2007年 | 13228篇 |
2006年 | 11802篇 |
2005年 | 10111篇 |
2004年 | 8335篇 |
2003年 | 7228篇 |
2002年 | 5974篇 |
2001年 | 5019篇 |
2000年 | 4430篇 |
1999年 | 3801篇 |
1998年 | 3025篇 |
1997年 | 2617篇 |
1996年 | 2245篇 |
1995年 | 2031篇 |
1994年 | 1697篇 |
1993年 | 1275篇 |
1992年 | 1111篇 |
1991年 | 749篇 |
1990年 | 662篇 |
1989年 | 616篇 |
1988年 | 438篇 |
1987年 | 266篇 |
1986年 | 209篇 |
1985年 | 94篇 |
1984年 | 111篇 |
1983年 | 67篇 |
1982年 | 60篇 |
1981年 | 62篇 |
1980年 | 36篇 |
1979年 | 49篇 |
1978年 | 21篇 |
1975年 | 19篇 |
1959年 | 50篇 |
1951年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
31.
One specific class of non-linear evolution equations, known as the Tzitzéica-type equations, has received great attention from a group of researchers involved in non-linear science. In this article, new exact solutions of the Tzitzéica-type equations arising in non-linear optics, including the Tzitzéica, Dodd–Bullough–Mikhailov and Tzitzéica–Dodd–Bullough equations, are obtained using the expa function method. The integration technique actually suggests a useful and reliable method to extract new exact solutions of a wide range of non-linear evolution equations. 相似文献
32.
33.
Surface wave breaking is a challenging two-phase flow process which plays an important role in numerous physical processes. A highly-turbulent unsteady breaking surge was investigated experimentally in a large facility, and substantial aeration occurred in the roller. The application of three optical flow techniques (Lucas-Kanade, Horn-Schunck and Farnback) to the air-water region was tested. The results indicated that the Farnback technique provided most accurate results, although some misleading results could be obtained near the air-water boundaries of the roller. The bore generation by a rapid gate closure showed a highly-unsteady complicated velocity field, with substantial free-surface deformations, wave breaking and formation of large coherent structures before the surge detached from the gate. Further upstream, the surge propagated as a hydraulic jump in translation and the data showed a marked shear region with a recirculation zone above, showing air-water flow features comparable to stationary hydraulic jumps. The upper and lower bounds of air-water flow region yielded data implying an air-to-water velocity ratio about 4–5 for a Froude number Fr1 = 2.1. 相似文献
34.
35.
反应堆屏蔽计算中经常出现厚屏蔽、小探测器问题,常规蒙特卡罗方法难以有效解决。基于自动重要抽样(AIS)方法,本文提出了小探测器自动重要抽样(SDAIS)方法,并针对小探测器问题,优化了AIS方法的虚粒子赌分裂算法。该方法在自主开发的蒙特卡罗屏蔽程序MCShield上进行了实现。使用NUREG/CR-6115 PWR基准题验证该方法的正确性和计算效率。结果表明,SDAIS方法可有效地解决厚屏蔽小探测器问题,相比AIS方法及传统的重要性方法,计算效率提升1~2个量级。 相似文献
36.
不同给液方式对铜电解过程中有重要的影响,不同的循环方式会影响槽内温度分布、电解液成分及阳极泥沉降等,因此,根据铜电解生产不同情况的需要,分析对比了多种给液方式在贵冶电解车间的应用,总结了这几种给液方式的优缺点和适用条件。 相似文献
37.
Transmission system restoration with co-optimization of repairs,load pickups,and generation dispatch
This paper studies the restoration of a transmission system after a significant disruption such as a natural disaster. It considers the co-optimization of repairs, load pickups, and generation dispatch to produce a sequencing of the repairs that minimizes the size of the blackout over time. The core of this process is a Restoration Ordering Problem (ROP), a non-convex mixed-integer nonlinear program that is outside the capabilities of existing solver technologies. To address this computational barrier, the paper examines two approximations of the power flow equations: The DC model and the recently proposed LPAC model. Systematic, large-scale testing indicates that the DC model is not sufficiently accurate for solving the ROP. In contrast, the LPAC power flow model, which captures line losses, reactive power, and voltage magnitudes, is sufficiently accurate to obtain restoration plans that can be converted into AC-feasible power flows. An experimental study also suggests that the LPAC model provides a robust and appealing tradeoff between accuracy and computational performance for solving the ROP. 相似文献
38.
A 2D computational fluid dynamics (Eulerian–Eulerian) multiphase flow model coupled with a population balance model (CFD-PBM) was implemented to investigate the fluidization structure in terms of entrance region in an industrial-scale gas phase fluidized bed reactor. The simulation results were compared with the industrial data, and good agreement was observed. Two cases including perforated distributor and complete sparger were applied to examine the flow structure through the bed. The parametric sensitivity analysis of time step, number of node, drag coefficient, and specularity coefficient was carried out. It was found that the results were more sensitive to the drag model. The results showed that the entrance configuration has significant effect on the flow structure. While the dead zones are created in both corners of the distributors, the perforated distributor generates more startup bubbles, heterogeneous flow field, and better gas–solid interaction above the entrance region due to jet formation. 相似文献
39.
《International Journal of Hydrogen Energy》2021,46(69):34449-34462
Three-dimensional Bödewadt flow (fluid rotates at a large enough distance from the stationary plate) of carbon nanomaterial is examined. Single walled and multi walled CNTs are dissolved in water and gasoline oil baseliquids. Darcy-Forchheimer porous medium is considered. Stationary disk is further stretched linearly in radial direction. Heat transfer effect is examined in presence of radiation and convection. Effect of viscous dissipation is accounted. Entropy generation rate is studied. By using adequate transformation (von Kármán relations), the flow field equations (PDEs) are transmitted into ODEs. Solutions to these ODEs are constructed via implementation of shooting method (bvp4c). In addition to Entropy generation rate, Bejan number, heat transfer rate (Nusselt number), skin friction and temperature of fluid are examined through involved physical parameters. Axial component of velocity intensifies with increment in nanoparticles volume fraction and ratio of stretching rate to angular velocity parameter while it decays with higher porosity parameter. Higher nanoparticles volume fraction and porosity parameter lead to decay in radial as well as tangential component of velocity. However it enhances with higher ratio of stretching rate to angular velocity parameter. Temperature of fluid directly varies with higher ratio of stretching rate to angular velocity parameter, radiation parameter, Eckert number, Biot number and nanoparticles volume fraction. Rate of Entropy generation is reduced with higher estimations of porosity parameter, nanoparticles volume fraction and radiation parameter. Skin friction coefficient decays with higher porosity parameter and ratio of stretching rate to angular velocity parameter. Intensification in porosity parameter, nanoparticles volume fraction and Biot number leads to higher Nusselt number. Prominent impact is shown by multiple-walled CNTs with gasoline oil basefluid than single-walled CNTs with water basefluid. 相似文献
40.