全文获取类型
收费全文 | 40433篇 |
免费 | 5249篇 |
国内免费 | 1709篇 |
专业分类
电工技术 | 2071篇 |
综合类 | 3548篇 |
化学工业 | 2980篇 |
金属工艺 | 11725篇 |
机械仪表 | 3484篇 |
建筑科学 | 4439篇 |
矿业工程 | 2377篇 |
能源动力 | 925篇 |
轻工业 | 1532篇 |
水利工程 | 1069篇 |
石油天然气 | 2194篇 |
武器工业 | 318篇 |
无线电 | 1827篇 |
一般工业技术 | 3525篇 |
冶金工业 | 2424篇 |
原子能技术 | 277篇 |
自动化技术 | 2676篇 |
出版年
2024年 | 110篇 |
2023年 | 379篇 |
2022年 | 776篇 |
2021年 | 810篇 |
2020年 | 933篇 |
2019年 | 926篇 |
2018年 | 939篇 |
2017年 | 1319篇 |
2016年 | 1503篇 |
2015年 | 1468篇 |
2014年 | 2446篇 |
2013年 | 2499篇 |
2012年 | 2726篇 |
2011年 | 2982篇 |
2010年 | 2348篇 |
2009年 | 2399篇 |
2008年 | 2073篇 |
2007年 | 2868篇 |
2006年 | 2829篇 |
2005年 | 2356篇 |
2004年 | 2170篇 |
2003年 | 1837篇 |
2002年 | 1541篇 |
2001年 | 1367篇 |
2000年 | 1104篇 |
1999年 | 903篇 |
1998年 | 688篇 |
1997年 | 650篇 |
1996年 | 558篇 |
1995年 | 456篇 |
1994年 | 350篇 |
1993年 | 229篇 |
1992年 | 196篇 |
1991年 | 156篇 |
1990年 | 117篇 |
1989年 | 116篇 |
1988年 | 66篇 |
1987年 | 64篇 |
1986年 | 22篇 |
1985年 | 13篇 |
1984年 | 21篇 |
1983年 | 17篇 |
1982年 | 7篇 |
1981年 | 10篇 |
1980年 | 14篇 |
1979年 | 7篇 |
1977年 | 3篇 |
1975年 | 3篇 |
1968年 | 2篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
1.
2.
3.
Nicolas Larché Benoit Emo Audrey Allion Elisabeth Johansson Dominique Thierry 《工业材料与腐蚀》2021,72(8):1338-1349
With lower alloying cost and higher mechanical properties, lean duplex stainless steels can be an alternative to the more commonly used austenitic stainless steels. However, these alloys are still not the preferred choice, probably due to a lack of field experience. A study was thus initiated in view of defining the limits of use of selected (lean) duplexes for urban wastewater treatment units. The present paper shows the localized corrosion performance of selected lean duplexes in chloride contaminated solutions. The results are compared with austenitic S30403 and S31603 and with the more standard duplexes S82441 and S32205. The effect of welding was also investigated. Exposures in field municipal wastewater plants were conducted for 1 year in low and high chloride content units. The results show that lean duplexes S32101 and S32202 can be used as alternatives to S30403 and S31603 in low chloride electrolytes. At 500 ppm of chloride content, duplex stainless steel S32304 showed better corrosion resistance than S30403 and S31603. For higher chloride contents (1000 ppm and above) the standard duplexes S82441 and S32205 shall be preferred. 相似文献
4.
《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
5.
为研究钢管套筒灌浆连接轴向受拉破坏过程及破坏机理,试验中设计了16组48个钢管套筒灌浆连接试件,试件采用钢板代替圆钢管,并进行静载试验。分析了灌浆料裂缝扩展过程、荷载-相对位移曲线,并对抗剪键高距比、灌浆料厚度、侧向力等因素对破坏过程及承载力的影响进行分析。结果表明:对于不设置抗剪键的套筒灌浆连接试件,斜裂缝随机产生,裂缝分布不均匀;对于设置抗剪键的套筒灌浆连接试件,裂缝首先出现在底部抗剪键位置处,与水平方向夹角约为30°,随后在中部和上部抗剪键位置处分别出现斜裂缝。由于每个抗剪键上荷载分担并不均匀,与抗剪键接触的灌浆料逐渐达到极限压应力,达到极限状态时,承载力全部由抗剪键间的机械咬合力承担,在连接承载力中,可忽略摩擦力和胶结力作用。随着抗剪键高距比h/s增大,各试件初始剪切刚度相差不大,承载力增大,但增幅逐渐减小,建议抗剪键高距比0.06g/s>0.3,同时需要满足灌浆料灌注的施工要求。 相似文献
6.
7.
The existing analytical average bit error rate (ABER) expression of conventional generalised spatial modulation (CGSM) does not agree well with the Monte Carlo simulation results in the low signal‐to‐noise ratio (SNR) region. Hence, the first contribution of this paper is to derive a new and easy way to evaluate analytical ABER expression that improves the validation of the simulation results at low SNRs. Secondly, a novel system termed CGSM with enhanced spectral efficiency (CGSM‐ESE) is presented. This system is realised by applying a rotation angle to one of the two active transmit antennas. As a result, the overall spectral efficiency is increased by 1 bit/s/Hz when compared with the equivalent CGSM system. In order to validate the simulation results of CGSM‐ESE, the third contribution is to derive an analytical ABER expression. Finally, to improve the ABER performance of CGSM‐ESE, three link adaptation algorithms are developed. By assuming full knowledge of the channel at the receiver, the proposed algorithms select a subset of channel gain vector (CGV) pairs based on the Euclidean distance between all CGV pairs, CGV splitting, CGV amplitudes, or a combination of these. 相似文献
8.
As a solid state joining process, ultrasonic spot welding has been proven to be a promising technique for joining copper alloys. However, challenges still remain in employing ultrasonic spot welding to join copper alloys. This article comprehensively reviews the current state of ultrasonic spot welding of copper alloys with a number of critical issues including materials flow, plastic deformation, temperature distribution, vibration, relative motion, vertical displacement, interface friction coefficient, online monitoring technique, coupled with the macrostructure and microstructure, the mechanical properties and electrical conductivity. In addition, the future trends in this field are provided. 相似文献
9.
The Vehicle Routing Problem with Simultaneous Pickup and Delivery (VRPSPD) is an extension to the classical Vehicle Routing Problem (VRP), where customers may both receive and send goods simultaneously. The Vehicle Routing Problem with Mixed Pickup and Delivery (VRPMPD) differs from the VRPSPD in that the customers may have either pickup or delivery demand. However, the solution approaches proposed for the VRPSPD can be directly applied to the VRPMPD. In this study, an adaptive local search solution approach is developed for both the VRPSPD and the VRPMPD, which hybridizes a Simulated Annealing inspired algorithm with Variable Neighborhood Descent. The algorithm uses an adaptive threshold function that makes the algorithm self-tuning. The proposed approach is tested on well-known VRPSPD and VRPMPD benchmark instances derived from the literature. The computational results indicate that the proposed algorithm is effective in solving the problems in reasonable computation time. 相似文献
10.
从电焊机自身电气特点及建筑工地工作环境入手,探讨电焊机安全技术的实施方法。分析电焊机安全隐患及事故的分类以及电焊机在使用过程中产生危险的原因。介绍电焊机在安装以及作业过程中的安全措施。 相似文献