全文获取类型
收费全文 | 22733篇 |
免费 | 2028篇 |
国内免费 | 1294篇 |
专业分类
电工技术 | 303篇 |
技术理论 | 1篇 |
综合类 | 2474篇 |
化学工业 | 940篇 |
金属工艺 | 1593篇 |
机械仪表 | 1698篇 |
建筑科学 | 6707篇 |
矿业工程 | 519篇 |
能源动力 | 281篇 |
轻工业 | 263篇 |
水利工程 | 418篇 |
石油天然气 | 372篇 |
武器工业 | 138篇 |
无线电 | 4087篇 |
一般工业技术 | 3748篇 |
冶金工业 | 627篇 |
原子能技术 | 1121篇 |
自动化技术 | 765篇 |
出版年
2024年 | 69篇 |
2023年 | 200篇 |
2022年 | 350篇 |
2021年 | 450篇 |
2020年 | 557篇 |
2019年 | 508篇 |
2018年 | 494篇 |
2017年 | 641篇 |
2016年 | 625篇 |
2015年 | 727篇 |
2014年 | 1259篇 |
2013年 | 1273篇 |
2012年 | 1585篇 |
2011年 | 1827篇 |
2010年 | 1394篇 |
2009年 | 1532篇 |
2008年 | 1425篇 |
2007年 | 1657篇 |
2006年 | 1428篇 |
2005年 | 1209篇 |
2004年 | 1004篇 |
2003年 | 888篇 |
2002年 | 758篇 |
2001年 | 683篇 |
2000年 | 588篇 |
1999年 | 496篇 |
1998年 | 430篇 |
1997年 | 358篇 |
1996年 | 307篇 |
1995年 | 252篇 |
1994年 | 225篇 |
1993年 | 164篇 |
1992年 | 130篇 |
1991年 | 119篇 |
1990年 | 97篇 |
1989年 | 72篇 |
1988年 | 64篇 |
1987年 | 50篇 |
1986年 | 52篇 |
1985年 | 20篇 |
1984年 | 27篇 |
1983年 | 14篇 |
1982年 | 14篇 |
1981年 | 5篇 |
1980年 | 11篇 |
1979年 | 4篇 |
1959年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
《Journal of the European Ceramic Society》2020,40(10):3577-3584
In this work, the grain boundaries composition of the polycrystalline CaCu3Ti4O12 (CCTO) was investigated. A Focused Ion Beam (FIB)/lift-out technique was used to prepare site-specific thin samples of the grain boundaries interface of CCTO ceramics. Scanning transmission electron microscopy (STEM) coupled with energy dispersive X-ray spectrometry (EDXS) and Electron Energy Loss Spectroscopy (EELS) systems were used to characterize the composition and nanostructure of the grain and grain boundaries region. It is known that during conventional sintering, discontinuous grain growth occurs and a Cu-rich phase appears at grain boundaries. This Cu-rich phase may affect the final dielectric properties of CCTO but its structure and chemical composition remained unknown. For the first time, this high-resolution FIB-TEM-STEM study of CCTO interfacial region highlights the composition of the phases segregated at grain boundaries namely CuO, Cu2O and the metastable phase Cu3TiO4. 相似文献
2.
Cyclic tension and bend tests were performed on heat-resistant 12Cr1MoV steel specimens in as-supplied condition as well as after Zr+ ion beam surface irradiation. Distinct differences in strain induced relief, as well in cracking pattern of modified surface layer were observed by optical microscopy and interference profilometry. Changes in subsurface layer are characterized by means of nano- and microindentation and fractography of fracture surfaces (with the help of scanning electron microscopy). It is shown that the main influence on mechanical properties is mostly induced by thermal treatment during irradiation rather than formation of a 2 μm thick layer doped with Zr. The differences in deformation behavior may be explained by physical mesomechanics concepts. 相似文献
3.
The limited research on the geopolymer concrete mix design for targeting a specific strength is identified an obstacle for their effective design and wide use. In this paper, a mix design procedure has been proposed for fly-ash based geopolymer concrete and its use as infill hybrid composite beam is investigated. Then, the structural performance of geopolymer concrete filled hybrid composite beam is investigated to determine their possible application in civil infrastructure. Firstly, a detailed procedure of mix design for fly-ash based geopolymer concrete is presented. Secondly, three hybrid beams filled with geopolymer concrete were prepared and tested in a four-point bending setup to evaluate their flexural modulus and modulus of rupture. Numerical and analytical evaluation of the behaviour of hybrid beam were performed and results showed a good agreement with the experimental investigation. Thirdly, the suitability of the beam for a composite railway sleeper is evaluated and compared with existing timber and composite sleepers. Finally, the beams’ performance in a ballast railway track is analysed using Strand7 finite element simulation software and the results showed that the new concept of using geopolymer concrete as infill to pultruded composite section satisfied the stiffness and strength requirements for a railway sleeper. 相似文献
4.
Neural Machine Translation (NMT) is an end-to-end learning approach for
automated translation, overcoming the weaknesses of conventional phrase-based translation
systems. Although NMT based systems have gained their popularity in commercial
translation applications, there is still plenty of room for improvement. Being the most
popular search algorithm in NMT, beam search is vital to the translation result. However,
traditional beam search can produce duplicate or missing translation due to its target
sequence selection strategy. Aiming to alleviate this problem, this paper proposed neural
machine translation improvements based on a novel beam search evaluation function. And
we use reinforcement learning to train a translation evaluation system to select better
candidate words for generating translations. In the experiments, we conducted extensive
experiments to evaluate our methods. CASIA corpus and the 1,000,000 pairs of bilingual
corpora of NiuTrans are used in our experiments. The experiment results prove that the
proposed methods can effectively improve the English to Chinese translation quality. 相似文献
5.
6.
7.
8.
Albul V. I. Bychkov V. B. Gusev K. E. Demidov V. S. Demidova E. V. Kurchanov A. F. Luk'yashin V. E. Sokolov A. Yu. 《Measurement Techniques》2003,46(8):810-814
A monitor is proposed based on ultrasonic production when ionizing radiation passes through a medium. The recording element is a 0.2 mm aluminum plate mounted in a ceramic acoustic converter AC in the form of a wedge of thickness 2 mm. The low plate thickness minimizes the beam parameter distortion, while special technology used in the AC provides high sensitivity. The device has been calibrated in the proton beam from the ITEP accelerator at 200 MeV with 2·109–6·1010 particles in a pulse and a pulse length of 70 nsec. 相似文献
9.
游梁式抽油机二次平衡分析 总被引:1,自引:0,他引:1
为解决游梁式抽油机能耗大、效率低的问题,设计了二次平衡装置。这种装置通过是挂在抽油机后端的平衡重的平衡作用,降低一次平衡曲柄轴净扭矩的两个峰值,达到减少能耗提高效率的目的。对抽油机的二次平衡作了较详尽的理论分析,给出了实行二次平衡后曲柄轴净扭矩的计算公式和安装二次平衡装置前后曲柄轴净扭矩曲线图。在大庆油田两口井上进行的现场试验结果表明,安装二次平衡装置后,两口井年节约电费分别为0.25万元和1.17万元,经济效益明显。 相似文献
10.
把瞬态记录仪Biomation8l00与微型计算机IBM─pC/XT联接建成了一个高速数据采集系统,本文介绍了系统的硬件接口设计及软件设计。在超声分子束条件下,把它应用于环氧乙烷(C_2H_4O)的多光子电离与离解飞行时间(MPID─TOF)质谱的实验研究中,并给出了实验结果;本系统在微观基元化学反应动力学实验研究中广泛适用于对时间分辨微弱信号的探测。 相似文献