全文获取类型
收费全文 | 244945篇 |
免费 | 19636篇 |
国内免费 | 12730篇 |
专业分类
电工技术 | 14574篇 |
技术理论 | 11篇 |
综合类 | 18272篇 |
化学工业 | 48358篇 |
金属工艺 | 9882篇 |
机械仪表 | 13058篇 |
建筑科学 | 18390篇 |
矿业工程 | 7414篇 |
能源动力 | 10645篇 |
轻工业 | 21550篇 |
水利工程 | 19816篇 |
石油天然气 | 28985篇 |
武器工业 | 1355篇 |
无线电 | 15889篇 |
一般工业技术 | 17550篇 |
冶金工业 | 6470篇 |
原子能技术 | 2426篇 |
自动化技术 | 22666篇 |
出版年
2024年 | 699篇 |
2023年 | 2950篇 |
2022年 | 5181篇 |
2021年 | 6724篇 |
2020年 | 6629篇 |
2019年 | 6295篇 |
2018年 | 5734篇 |
2017年 | 7244篇 |
2016年 | 7949篇 |
2015年 | 7995篇 |
2014年 | 13180篇 |
2013年 | 14271篇 |
2012年 | 16330篇 |
2011年 | 17485篇 |
2010年 | 13560篇 |
2009年 | 14483篇 |
2008年 | 13448篇 |
2007年 | 16289篇 |
2006年 | 15675篇 |
2005年 | 13745篇 |
2004年 | 11545篇 |
2003年 | 10778篇 |
2002年 | 9150篇 |
2001年 | 7511篇 |
2000年 | 6480篇 |
1999年 | 5092篇 |
1998年 | 3882篇 |
1997年 | 3177篇 |
1996年 | 2639篇 |
1995年 | 2388篇 |
1994年 | 1919篇 |
1993年 | 1573篇 |
1992年 | 1254篇 |
1991年 | 868篇 |
1990年 | 606篇 |
1989年 | 565篇 |
1988年 | 358篇 |
1987年 | 290篇 |
1986年 | 246篇 |
1985年 | 253篇 |
1984年 | 218篇 |
1983年 | 145篇 |
1982年 | 112篇 |
1981年 | 72篇 |
1980年 | 60篇 |
1979年 | 50篇 |
1978年 | 32篇 |
1977年 | 30篇 |
1976年 | 39篇 |
1951年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
中国石化海南炼油化工有限公司0.2 Mt/a C5/C6烷烃异构化装置以连续重整装置的拔头油为原料,使用NNI-1催化剂,采用一次通过流程,不设脱异戊烷塔和稳定塔,经设在连续重整装置内的脱丁烷塔稳定处理后作为汽油调合组分。该装置于2006年9月开工投产,截至2015年3月已连续运行3个周期。长周期运行分析结果表明:前两个周期中NNI-1催化剂具有较高的异构化活性及选择性,C5异构化率为60%左右,C6异构化率为80%左右,C6选择性为15%左右,产品辛烷值基本达到技术指标要求(RON≥78);而在第三周期运行中,催化剂积炭增加等原因导致其异构化活性及选择性降低,异构化产品辛烷值提升能力呈现逐步衰减的趋势,提高反应苛刻度已不能弥补催化剂活性下降造成的产品辛烷值降低。为保证装置长周期运行,建议择机停工对催化剂进行再生,或是直接换用与装置原料性质匹配的异构化催化剂。 相似文献
52.
53.
54.
55.
56.
The main objective of the present work is to improve the performance of bonded joints in carbon fiber composite structures through introducing Multi-Walled Carbon Nanotubes (MWCNTs) into Epocast 50-A1/946 epoxy, which was primarily developed for joining and repairing of composite aircraft structures. Results from tension characterizations of structural adhesive joints (SAJs) with different scarf angles (5–45°) showed improvement up to 40% compared to neat epoxy (NE)–SAJs. Special attention was considered to investigate the performance of SAJs with 5° scarf angle under different environments. The tensile strength and stiffness of both NE-SAJs and MWCNT/E-SAJs were dramatically decreased at elevated temperature. Water absorption showed a marginal drop of about 2.0% in the tensile strength of the moist SAJs compared to the dry one. Cracks initiation and propagation were detected effectively using instrumented-SAJs with eight strain gauges. The experimental results agree well with the predicted using three-dimensional finite element analysis model. 相似文献
57.
SPEEK/cSMM membrane for simultaneous electricity generation and wastewater treatment in microbial fuel cell
下载免费PDF全文
![点击此处可从《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
58.
This short communication presents a generic mathematical programming formulation for computer-aided molecular design (CAMD). A given CAMD problem, based on target properties, is formulated as a mixed integer linear/non-linear program (MILP/MINLP). The mathematical programming model presented here, which is formulated as an MILP/MINLP problem, considers first-order and second-order molecular groups for molecular structure representation and property estimation. It is shown that various CAMD problems can be formulated and solved through this model. 相似文献
59.
《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
60.
Qingna Gong Songtao Cao Yu Zhou Ruixin Wang Weizhou Jiao 《International Journal of Hydrogen Energy》2021,46(41):21442-21453
Ni2P nanoparticles and CdS nanorods were grew together on a mesoporous g-C3N4 through a facile in-situ solvothermal approach. Under visible light (λ > 400 nm), the as-prepared ternary PCN–CdS-5% Ni2P composite displays a high H2 evolution rate with 2905.86 μmol g?1 h?1, which is about 14, 18 and 279 times that of PCN–CdS, PCN–Ni2P and PCN, respectively. The enhanced photocatalytic activity is mainly attributed to the improved separation efficiency of the photocarriers by the type II PCN–CdS heterojunction and the effective extraction of photogenerated electrons by Ni2P. Meanwhile, Ni2P acts as co-catalyst to provide the photocatalytic active site for hydrogen reduction. In addition, PCN–CdS-5% Ni2P composite exerts good stability in 12-h cycles. 相似文献