全文获取类型
收费全文 | 88781篇 |
免费 | 8748篇 |
国内免费 | 5084篇 |
专业分类
电工技术 | 6428篇 |
技术理论 | 5篇 |
综合类 | 7029篇 |
化学工业 | 13391篇 |
金属工艺 | 5426篇 |
机械仪表 | 5682篇 |
建筑科学 | 7016篇 |
矿业工程 | 2631篇 |
能源动力 | 2456篇 |
轻工业 | 8937篇 |
水利工程 | 2060篇 |
石油天然气 | 4046篇 |
武器工业 | 977篇 |
无线电 | 9896篇 |
一般工业技术 | 9347篇 |
冶金工业 | 3523篇 |
原子能技术 | 1065篇 |
自动化技术 | 12698篇 |
出版年
2024年 | 301篇 |
2023年 | 1479篇 |
2022年 | 2762篇 |
2021年 | 3843篇 |
2020年 | 3023篇 |
2019年 | 2337篇 |
2018年 | 2634篇 |
2017年 | 2985篇 |
2016年 | 2709篇 |
2015年 | 3965篇 |
2014年 | 4799篇 |
2013年 | 5779篇 |
2012年 | 6673篇 |
2011年 | 7224篇 |
2010年 | 6429篇 |
2009年 | 6082篇 |
2008年 | 6119篇 |
2007年 | 5602篇 |
2006年 | 5095篇 |
2005年 | 4293篇 |
2004年 | 2993篇 |
2003年 | 2506篇 |
2002年 | 2357篇 |
2001年 | 1996篇 |
2000年 | 1578篇 |
1999年 | 1372篇 |
1998年 | 1052篇 |
1997年 | 852篇 |
1996年 | 799篇 |
1995年 | 668篇 |
1994年 | 521篇 |
1993年 | 400篇 |
1992年 | 292篇 |
1991年 | 266篇 |
1990年 | 194篇 |
1989年 | 138篇 |
1988年 | 121篇 |
1987年 | 82篇 |
1986年 | 64篇 |
1985年 | 41篇 |
1984年 | 39篇 |
1983年 | 16篇 |
1982年 | 16篇 |
1981年 | 22篇 |
1980年 | 31篇 |
1979年 | 14篇 |
1977年 | 4篇 |
1976年 | 9篇 |
1972年 | 4篇 |
1959年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
41.
ABSTRACT This study investigates the effects of strain, strain rates, and forming directions (RD-rolling direction, TD-transverse direction, and ND-normal direction) on adiabatic shear, via dynamic impact compression tests using the Split Hopkinson Pressure Bar (SHPB) apparatus. A modified Johnson-Cook (J-C) constitutive model is proposed, which used to analyse the influence of the constitutive parameters on the sensitivity of adiabatic shear, employing a finite element software. The different sensitivities of adiabatic shear under different directions are explained by combining microscopic analysis and results from mechanical responses. The results show that the sensitivity of adiabatic shear can be related to the time of stress collapse in the following trend: ND?>?TD?>?RD; the sensitivities of these constitutive parameters on adiabatic shear are calculated and compared. 相似文献
42.
To realize joint optimization of spatial diversity and equalization combining in the intersymbol interference (ISI) channel, an iterative equalization combining algorithm is proposed. The proposed algorithm uses the coefficients of Turbo equalization to calculate the combination weights without estimating the signal to noise ratio in each diversity branch. The equalized symbols from different diversity branches are combined, and the extrinsic information output from the decoder is fed back to the equalizers, so as to exchange soft information between the equalizers and the decoder. The performance of the proposed algorithm is analyzed using the extrinsic information transfer (EXIT) chart and verified by simulations. Results show that our approach fully exploits time domain information from the multipath channel and spatial domain information from multi receiving antennas, which efficiently improve the performance of the receiver in the severe ISI channel. 相似文献
43.
Ting Liu Huimin Zhang Panfei Ma Aimin Chang Hui Jiang 《Journal of the American Ceramic Society》2019,102(8):4393-4398
Core–shell structures have been proposed to improve the electrical properties of negative-temperature coefficient (NTC) thermistor ceramics. In this work, Al2O3-modified Co1.5Mn1.2Ni0.3O4 NTC thermistor ceramics with adjustable electrical properties were prepared through citrate-chelation followed by conventional sintering. Co1.5Mn1.2Ni0.3O4 powder was coated with a thin Al2O3 shell layer to form a core–shell structure. Resistivity (ρ) increased rapidly with increasing thickness of the Al2O3 layer, and the thermal constant (B) varied moderately between 3706 and 3846 K. In particular, Co1.5Mn1.2Ni0.3O4@Al2O3 ceramic with 0.08 wt% Al2O3 showed the increase of ρ double, and the change in its B was less than 140 K. The Co1.5Mn1.2Ni0.3O4@Al2O3 NTC ceramics showed high stability, and their grain size was relatively uniform due to the protection offered by the shell. The aging coefficient of the ceramic was less than 0.2% after aging for 500 hours at 125°C. Taken together, the results indicate that as-prepared Co1.5Mn1.2Ni0.3O4@Al2O3 NTC ceramics with a core–shell structure may be promising candidates for application as wide-temperature NTC thermistor ceramics. 相似文献
44.
Ming-Puu Chen Asta Y. Z. Lord Yu-Yao Cheng Ku-Chou Tai Wen-Harn Pan 《Journal of Computer Assisted Learning》2020,36(3):383-396
Reflective judgement is crucial for medical-related practitioners in dealing with controversial issues. However, the conformity phenomenon is likely to occur and interfere with reflective judgement learning during interactive activities. Effective strategies are required to moderate the conformity behaviour tendency (CBT) and improve reflective judgement performance (RJP). This study demonstrates two significant results: (a) Compared with the guided self-reflection learning strategy, the online collective reflection (OCR) learning strategy effectively weakened the learners' general CBT while dealing with professional controversial issues; and (b) a significantly negative correlation between the RJP achieved and the change of CBT in online environment was detected in the OCR group. The implications and potential applications in higher education were discussed. Further studies are needed to confirm the long-term effects and the extending application to other professional studies. 相似文献
45.
为进一步摸清国家核应急医学救援分队能力建设现状,国家核应急响应技术支持中心建立了评估指标体系、评分标准,对依托苏州大学附属第二医院(核工业总医院)设立的国家核应急医学救援分队开展能力评估。评估重点包括政策法规、组织机构、预案方案、指挥控制、应急设施与装备、应急响应行动和培训演练等7项一级指标。通过评估,摸清了现状,查找了问题,同时对救援方案、物资装备配备及管理、培训演练等国家核应急医学救援分队能力建设以及核应急能力评估等工作提出改进建议。 相似文献
46.
为确保原CO压缩机在净化系统升级改造项目实施后能安全稳定运行,采取了流程优化、工艺条件论证、设备缺陷排查、联锁指标重新确定等一系列措施。改造措施实施后,CO压缩机出口压力稳定在3.23 MPa左右,有效缓解了前后工序压力波动对压缩机稳定运行的影响,各级水冷却器的换热效果也得到了较大的改善。 相似文献
47.
Mineralization of Para-Chlorobenzoic Acid in Water by Cobalt-Incorporated MCM-41 Catalyzed Ozonation
Cobalt-incorporated MCM-41(Co-MCM-41) was used as a heterogeneous catalyst for the ozonation of para-chlorobenzoic acid (p-CBA) in aqueous solution. Cobalt oxide supported on MCM-41(Co/MCM-41) was synthesized for comparison. Their textural properties were elucidated by various characterization techniques to understand the relationship between surface texture and catalytic activity. TOC removal at 60 min reached 91% with Co-MCM-41, 83% with Co/MCM-41 and only 52% with ozone alone, respectively. Observations from diffuse reflection spectroscopy demonstrated that different metal phases were formed in these cobalt-modified molecular sieves samples. Radical scavenger experiments indicated the formation of hydroxyl radicals that were responsible for the effective degradation of p-CBA. An integrated approach to the catalytic mechanism was proposed by considering the variation of pH in the course of ozonation as well as its subsequent influence on the dissociation of targeted compounds and surface charge of the catalyst. In the reusability experiments, the reused Co-MCM-41 was able to regain the same catalytic capability as the fresh one within 5 cycles. X-ray photoelectron spectroscopy results indicated that a part of Co2+ was oxidized to Co3+ after oxidation reaction. 相似文献
48.
Initialization speed is one of the most important factors in network real time kinematic (NRTK) performance. Owing to the low correlation among the error s 相似文献
49.
Lei He Yan Xuan Feng Zhang Xue Wang Huaqing Pan Junfeng Ren Meina Chen 《International Journal of Hydrogen Energy》2021,46(1):1096-1105
Bulk and surface properties of proton stability and transportation in Y and Nd co-doped BaCeO3 (BCYN), especially the effect of Nd segregation, were investigated by first-principles calculations. Since the structure of doped BaCeO3 at the operating temperature of proton-conducting has been unclear for a long time, we have summarized the latest experimental results and calculated the structure of the asymmetric BCYN for the first time. The results show that compared with Y, Nd doping promotes oxygen vacancy formation, however reduces proton stability. Our calculation can also provide a possible explanation for the formation of space charge layer at the grain boundary of doped BaCeO3 in experiment. Unlike the stable Y in BCYN, Nd is calculated to be easily segregated, which can facilitate both proton hydration and proton transportation near the surface. Moreover, Nd segregation at the grain boundary is predicted to be beneficial for proton transportation between grains. 相似文献
50.
在高压耐压实验中,由于施加耐压较大(可达额定电压的3倍),因此常遇到实验线路对设备或对地距离不够导致实验中发生放电或实验数据测试异常的情况.为了保证实验线路对设备或对地有足够的距离,常用绝缘操作杆将高压实验线路挑起或用绝缘带拉紧高压实验线使其悬空,既费时费力又不安全,尤其在刮风天气极易造成绝缘杆滑落、塑料带摆动等,导致实验数据不准确,影响判断.这种情况下,就必须进行多次实验,降低了工作效率.为此研制一款功能完善、能有效解决现场实验困难的实验线支撑工具,以达到提高工作效率和安全性的目的. 相似文献