全文获取类型
收费全文 | 4794篇 |
免费 | 257篇 |
国内免费 | 14篇 |
专业分类
电工技术 | 70篇 |
综合类 | 1篇 |
化学工业 | 933篇 |
金属工艺 | 90篇 |
机械仪表 | 110篇 |
建筑科学 | 190篇 |
矿业工程 | 6篇 |
能源动力 | 163篇 |
轻工业 | 388篇 |
水利工程 | 37篇 |
石油天然气 | 13篇 |
无线电 | 500篇 |
一般工业技术 | 942篇 |
冶金工业 | 687篇 |
原子能技术 | 47篇 |
自动化技术 | 888篇 |
出版年
2023年 | 31篇 |
2022年 | 79篇 |
2021年 | 112篇 |
2020年 | 96篇 |
2019年 | 95篇 |
2018年 | 148篇 |
2017年 | 142篇 |
2016年 | 136篇 |
2015年 | 119篇 |
2014年 | 170篇 |
2013年 | 290篇 |
2012年 | 264篇 |
2011年 | 307篇 |
2010年 | 237篇 |
2009年 | 277篇 |
2008年 | 257篇 |
2007年 | 233篇 |
2006年 | 175篇 |
2005年 | 137篇 |
2004年 | 134篇 |
2003年 | 126篇 |
2002年 | 116篇 |
2001年 | 78篇 |
2000年 | 77篇 |
1999年 | 96篇 |
1998年 | 201篇 |
1997年 | 149篇 |
1996年 | 110篇 |
1995年 | 57篇 |
1994年 | 66篇 |
1993年 | 48篇 |
1992年 | 47篇 |
1991年 | 38篇 |
1990年 | 35篇 |
1989年 | 31篇 |
1988年 | 34篇 |
1987年 | 19篇 |
1986年 | 31篇 |
1985年 | 28篇 |
1984年 | 20篇 |
1983年 | 18篇 |
1982年 | 17篇 |
1981年 | 13篇 |
1980年 | 20篇 |
1979年 | 16篇 |
1978年 | 8篇 |
1977年 | 16篇 |
1976年 | 34篇 |
1974年 | 12篇 |
1973年 | 12篇 |
排序方式: 共有5065条查询结果,搜索用时 875 毫秒
71.
K doped YBa2Cu2O
x
powders have been obtained by incorporating K2CO3 to previously coprecipitated amorphous hydroxide mixtures. Synthesis was performed at 900C and an orthorhombic 1 2 3 phase was the final product. Sintering of isopressed bars was carried out from 920 to 940C. K doping up to 5 at % led to the development of dense bodies with good superconducting behaviour. Oxygen pick-up during the cooling step following sintering was well accomplished despite the high density of the samples. Transition temperatures 90 K were measured. Doping above that percentage led to samples with lower density values. The presence of non-superconducting phases, such as CuO and a green phase, was very significant, and suppressed the superconducting transition. 相似文献
72.
Ernest B. Cady Ann Lorek Yakito Takei John S. Wyatt Juliet M. Penrice A. David Edwards Donald Peebles Marzena Wylezinska Huw Owen-Reece Vincent Kirkbride Christopher E. Cooper Richard F. Aldridge Simon C. Roth Guy Brown David T. Delpy E. Osmund R. Reynolds 《Magma (New York, N.Y.)》1994,2(3):437-439
The aim of this study was to reproduce the delayed (secondary) cerebral energy failure previously described in birth-asphyxiated newborn infants and to investigate relationships between primary insult severity and the extent of the delayed energy failure. Phosphorus (31P) magnetic resonance spectroscopy (MRS) at 7 T was used to study the brains of 12 newborn piglets during an acute, reversible, cerebral hypoxic-ischemic episode which continued until nucleotide triphosphates (NTP) were depleted. After reperfusion and reoxygenation, spectroscopy was continued for 48 h. High-energy metabolite concentrations returned to near normal levels after the insult, but later they fell as delayed energy failure developed. The time integral of NTP depletion in the primary insult correlated strongly with the minimum [phosphocreatine (PCr)]/[inorganic orthophosphate (Pi)] observed 24–48 h after the insult. (Linear regression analysis gave slope –8.04 h–1; ordinate intercept=1.23;r=0.92;P<0.0001.) This model is currently being used to investigate the therapeutic potential of various cerebroprotective strategies including hypothermia. 相似文献
73.
Filamentary preforms of aluminium-13 wt % Si alloy reinforced with TiC-coated carbon fibres were obtained by liquid metal infiltration using K2ZrF6 as wetting agent. The interfacial structure was investigated using analytical electron microscopy (TEM, SEM) and the fibre strength measured following each step of processing. The reaction between the K2ZrF6 deposit and the molten alloy is discussed on the basis of the reaction products formed at the fibre-matrix interface, which mainly consisted of fluoride compounds (K3AlF6), different zirconium-rich suicides (Si2Zr, SiZr (Al), (Al, Si)2Zr) and crystalline -alumina. Large amounts and/or inhomogeneous distributions of the K2ZrF6 deposit should be avoided, because the massive precipitation of colonies of intermetallics around fibres is conducive for the formation of harmful aluminium carbides and favours brittle fracture of the composite. The utilization of TiC-coatings formed by the reactive chemical vapour deposition process gave satisfactory results, both in terms of composite elaboration and fibre protection during liquid infiltration. 相似文献
74.
Faisal Ahmed Carlos Rodríguez-Fernández Henry A. Fernandez Yi Zhang Abde Mayeen Shafi Md Gius Uddin Xiaoqi Cui Hoon Hahn Yoon Naveed Mehmood Andreas C. Liapis Lide Yao Humeyra Caglayan Zhipei Sun Harri Lipsanen 《Advanced functional materials》2023,33(33):2302051
Developing selective and coherent polymorphic crystals at the nanoscale offers a novel strategy for designing integrated architectures for photonic and optoelectronic applications such as metasurfaces, optical gratings, photodetectors, and image sensors. Here, a direct optical writing approach is demonstrated to deterministically create polymorphic 2D materials by locally inducing metallic 1T′-MoTe2 on the semiconducting 2H-MoTe2 host layer. In the polymorphic-engineered MoTe2, 2H- and 1T′- crystalline phases exhibit strong optical contrast from near-infrared to telecom-band ranges (1–1.5 µm), due to the change in the band structure and increase in surface roughness. Sevenfold enhancement of third harmonic generation intensity is realized with conversion efficiency (susceptibility) of ≈1.7 × 10−7 (1.1 × 10−19 m2 V−2) and ≈1.7 × 10−8 (0.3 × 10−19 m2 V−2) for 1T′ and 2H-MoTe2, respectively at telecom-band ultrafast pump laser. Lastly, based on polymorphic engineering on MoTe2, a Schottky photodiode with a high photoresponsivity of 90 AW−1 is demonstrated. This study proposes facile polymorphic engineered structures that will greatly benefit realizing integrated photonics and optoelectronic circuits. 相似文献
75.
Ji Qian Yang Ha Krishna Prasad Koirala Di Huang Zhi Huang Vincent S. Battaglia Chongmin Wang Wanli Yang Wei Tong 《Advanced functional materials》2023,33(22):2205972
The recently developed Li-excess cation-disordered rock salts (DRXs) exhibit an excellent chemical diversity for the development of alternative Co/Ni-free high-energy cathodes. Herein, the synthesis of a highly fluorinated DRX cathode, Li1.2Mn0.6Ti0.2O1.8F0.2, based on cost-effective and earth-abundant transition metals, via a solid-state reaction, is reported. The fluorinated DRX cathode using ammonium fluoride precursor exhibits more uniform particle size and delivers a specific discharge capacity of 233 mAh g−1 and specific energy of 754 Wh kg−1, with 206 mAh g−1 retained after 200 cycles. The combined synchrotron X-ray absorption spectroscopy and resonant inelastic X-ray scattering spectroscopy analysis reveals that the remarkable cycling performance is attributed to the high fluorination and thus enhanced Mn content, enabling the utilization of more Mn redox than the oxide analog. This study demonstrates a great promise to develop next-generation cost-effective DRX cathodes with enhanced capacity retention for high-energy Li-ion batteries. 相似文献
76.
Srivastava Rachna Gaudet Vincent C. Mitran Patrick 《Journal of Signal Processing Systems》2022,94(1):101-116
Journal of Signal Processing Systems - This paper describes a field-programmable gate array (FPGA) implementation of a fixed-point low-density lattice code (LDLC) decoder where the Gaussian mixture... 相似文献
77.
El Baz Didier Fakih Bilal Sanchez Nigenda Romeo Boyer Vincent 《The Journal of supercomputing》2022,78(3):3122-3151
The Journal of Supercomputing - The multiplication of computing cores in modern processor units permits revisiting the design of classical algorithms to improve computational performance in complex... 相似文献
78.
Milou van Harsel Vincent Hoogerheide Peter Verkoeijen Tamara van Gog 《Journal of Computer Assisted Learning》2022,38(1):19-39
Nowadays, students often practice problem-solving skills in online learning environments with the help of examples and problems. This requires them to self-regulate their learning. It is questionable how novices self-regulate their learning from examples and problems and whether they need support. The present study investigated the open questions (1) to what extent students' (novices) task selections align with instructional design principles and (2) whether informing them about these principles would improve their task selections, learning outcomes, and motivation. Higher education students (N = 150) learned a problem-solving procedure by fixed sequences of examples and problems (FS-condition), or by self-regulated learning (SRL). The SRL participants selected tasks from a database, varying in format, complexity, and cover story, either with (ISRL-condition) or without (SRL-condition) watching a video detailing the instructional design principles. Students' task-selection patterns in both SRL conditions largely corresponded to the principles, although tasks were built up in complexity more often in the ISRL-condition than in the SRL-condition. Moreover, there was still room for improvement in students' task selections after solving practice problems. The video instruction helped students to better apply certain principles, but did not enhance learning and motivation. Finally, there were no test performance or motivational differences among conditions. Although these findings might suggest it is relatively ‘safe’ to allow students to independently start learning new problems-solving tasks using examples and problems, caution is warranted: It is unclear whether these findings generalize to other student populations, as the students participating in this study have had some experience with similar tasks or learning with examples. Moreover, as there was still room for improvement in students' task selections, follow-up research should investigate how we can further improve self-regulated learning from examples and practice problems. 相似文献
79.
Mental workload is considered to be strongly linked to human performance, and the ability to measure it accurately is key for balancing human health and work. In this study, brain signals were elicited by mental arithmetic tasks of varying difficulty to stimulate different levels of mental workload. In addition, a finite impulse response (FIR) filter, independent component analysis (ICA), and multiple artifact rejection algorithms (MARAs) were used to filter event-related potentials (ERPs). Then, the data consisting of ERPs, subjective ratings of mental workload, and task performance, were analyzed through the use of variance and Spearman’s correlation during a simulated computer task. We found that participants responded faster and performed better in the easy task condition, followed by the medium and high-difficulty conditions, which verifies the validity of the ERP filtering. Moreover, larger P2 and P3 waveforms were evoked as the task difficulty increased, and a higher task difficulty elicited a more enhanced N300. Correlation analysis revealed a negative relationship between the amplitude of P3 and the subjective ratings, and a positive relationship between the P3 amplitude and accuracy. The results presented in this paper demonstrate that a combination of FIR, ICA, and MARA methods can filter ERPs in the non-invasive real-time measurement of workload. Additionally, frontocentral P2, N3, and parietal P3 components showed differences between genders. The proposed measurement of mental workload can be useful for real-time identification of mental states and can be applied to human–computer interaction in the future. 相似文献
80.
Manipulating Electrical and Fluidic Access in Integrated Nanopore‐Microfluidic Arrays Using Microvalves
下载免费PDF全文
![点击此处可从《Small (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)