全文获取类型
收费全文 | 68983篇 |
免费 | 9772篇 |
国内免费 | 4487篇 |
专业分类
电工技术 | 10472篇 |
技术理论 | 7篇 |
综合类 | 7121篇 |
化学工业 | 10997篇 |
金属工艺 | 2177篇 |
机械仪表 | 4595篇 |
建筑科学 | 8939篇 |
矿业工程 | 1521篇 |
能源动力 | 6255篇 |
轻工业 | 1611篇 |
水利工程 | 1967篇 |
石油天然气 | 1764篇 |
武器工业 | 632篇 |
无线电 | 4966篇 |
一般工业技术 | 6981篇 |
冶金工业 | 2133篇 |
原子能技术 | 942篇 |
自动化技术 | 10162篇 |
出版年
2024年 | 423篇 |
2023年 | 1272篇 |
2022年 | 2200篇 |
2021年 | 2409篇 |
2020年 | 2618篇 |
2019年 | 2216篇 |
2018年 | 2079篇 |
2017年 | 2462篇 |
2016年 | 2619篇 |
2015年 | 2876篇 |
2014年 | 4289篇 |
2013年 | 4411篇 |
2012年 | 4927篇 |
2011年 | 5430篇 |
2010年 | 4060篇 |
2009年 | 4163篇 |
2008年 | 4020篇 |
2007年 | 4615篇 |
2006年 | 4196篇 |
2005年 | 3719篇 |
2004年 | 2904篇 |
2003年 | 2703篇 |
2002年 | 2150篇 |
2001年 | 1771篇 |
2000年 | 1497篇 |
1999年 | 1229篇 |
1998年 | 962篇 |
1997年 | 875篇 |
1996年 | 775篇 |
1995年 | 640篇 |
1994年 | 503篇 |
1993年 | 402篇 |
1992年 | 347篇 |
1991年 | 255篇 |
1990年 | 252篇 |
1989年 | 218篇 |
1988年 | 169篇 |
1987年 | 105篇 |
1986年 | 89篇 |
1985年 | 69篇 |
1984年 | 87篇 |
1983年 | 58篇 |
1982年 | 41篇 |
1981年 | 18篇 |
1980年 | 17篇 |
1979年 | 10篇 |
1978年 | 6篇 |
1966年 | 8篇 |
1959年 | 15篇 |
1951年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
《International Journal of Hydrogen Energy》2022,47(2):1217-1228
In this article, pre-assembly hot-press pressure and thermal expansion effects in gas-diffusion layers (GDLs) are addressed to explore the practicalities of the constitutive model reported in the companion article. A facile technique is proposed to include deformation history dependent residual strain effects. The model is implemented in the numerical environment and compared with widely followed conventional models such as isotropic and orthotropic material models. With the normal and accelerated thermal expansion effects no significant variation in stresses or strains is reported with the compressible GDL model in contrast to the conventional incompressible form of the GDL model. The present work identifies the critical differences with advanced and extended variants of the model along with conventional GDL material models in terms of planar stress/strain distribution and the membrane response. Finally, the model is simulated for micro-cyclic stress loads of varying amplitudes that imitate the real working conditions of fuel cell. The inelastic energy dissipation in GDLs is predicted using the proposed model, which is utilized further to distinguish the safe (elastic) and unsafe (inelastic shakedown) operating limits. The inelastic collapse of GDLs is shown to be a active function of high amplitude micro-cyclic load with high initial clamping load. 相似文献
2.
3.
《International Journal of Hydrogen Energy》2022,47(75):32031-32038
The activity of catalysts with various sizes was compared in a fixed-bed Fischer–Tropsch reactor under similar operating conditions by determining the deactivation model. Catalyst size had no impact on the type of deactivation model. The smaller catalyst showed a smaller deactivation constant of catalyst (kd) and a lower deactivation rate in the initial stage. The decline in the activities of the catalyst with a mesh size of 40 was lower than the other catalysts, suggesting its higher long-term stability (ass). Larger catalyst sizes led to the fouling of carbon and heavy hydrocarbons, decreasing the specific surface of the catalyst, thus increasing the pore diffusion resistance and further decrementing the catalyst activities. 相似文献
4.
《International Journal of Hydrogen Energy》2022,47(80):33955-33965
We report the study of conductive polyaniline (PANI) chain embedded Ti-MOF functionalized with CoS as a cocatalyst for hydrogen evolution reaction (HER) application. The post synthetically modified hybrid photocatalyst PANI/Ti-MOF/CoS greatly influences the redox and e? ? h+ separation process and exhibits an impressive rate of HER (~1322 μmol h?1g?1), suppressing the pristine Ti-MOF (~62 μmol h?1g?1) with apparent quantum yield (AQY) of ~3.2 and transient current response of ~46.4 μA cm?2. In this system, Ti-MOF provides the circulation of Ti3+ and Ti4+ to the reaction of photocatalytic H2 generation, where the additional PANI and CoS amended the performance of H2 production through electron enrichment and thereby improving the stability and integrity of Ti-MOF. The Electrochemical studies demonstrated increased photocurrent by interweaving Ti-MOF crystal with PANI through cation-π interaction thereby enhancing interface connection and then promoting electron transfers. The charge dynamics revealed the initial charge transfer from photoexcited PANI to encapsulated MOF framework to boost the photocatalytic performance of the system. Further, the electron movement at the Ti-MOF/CoS interface is investigated through work function and electrochemical potential of electrons (Fermi level). DFT results demonstrate the importance of CoS in improving the photocatalytic performance of hybrid Ti-MOF catalyst, which leads to superior catalytic behaviour. These results establish that the encapsulation of catalytic active sites inside MOFs with desirable energy band gaps would be an ideal choice for the production of solar fuels. 相似文献
5.
Today, utility meters for water are tested for measurement behavior at stable operating conditions at specified flow rates as part of the approval process. The measurement error that occurs during start and stop or when changing between flow rates may not be taken into account. In addition, there are new technologies whose measuring behavior under real-world conditions is only known to a limited extend. To take these facts into account, a new method has been developed and tested to determine the measurement behavior of water meters under dynamic load profiles as they occur in the real application. For this purpose, a test rig for flow rate measurement was extended by a cavitation nozzle apparatus and the generation of dynamic load profiles was validated. For the cavitation nozzles used, possible factors influencing the flow rate, such as temperature and purity of the water as well as the upstream pressure were investigated. Using different types of domestic water meters, the applicability of the dynamic test procedure was demonstrated and the measurement behavior of the meters was characterised. 相似文献
6.
《Ceramics International》2022,48(9):12281-12290
Following the rapid growth of lightning technology, the development of red-emitting phosphors is effective for improving color temperature and color rendering index for w-LEDs devices. Herein, a single phased garnet phosphor with cation and polyhedron substitution modification was firstly prepared. For Mg3Gd2Ge3O12: Bi3+, Eu3+, the intensity has been remarkably improved by about 16% compared to the one without Bi3+ sensitization. The energy transfer mechanism is identified in this work. Based on cation and polyhedron substitution strategies, novel phosphors with different compositions were obtained and further modified the PL properties. With Lu3+ substitution, the bond lengths between Bi3+ ion and anion ligands are decreased and the site symmetry has been strengthened, which leads to a 21 nm blue shift when Lu3+ totally replaced Gd3+ ions. In addition, Lu3+ and [SiO4] substitution strategies both effectively increased symmetric rigid structure, which leads to a significant improvement in thermal stability, indicating the samples own great potential in optical applications This work provides a new insight to synthesis red-emitting phosphors for warm white-LEDs. 相似文献
7.
围绕人工智能与智慧海洋建设这条主线,论述人工智能、智慧海洋的概念,列举当前较为成熟的人工智能与海洋科技在海洋观测方面融合的切入点,初步展现一种海洋技术与装备智能化的发展路径,提出加快人工智能技术向智慧海洋建设赋能的几点建议。 相似文献
8.
In this investigation, low-cement castables were prepared using 70% alumina grog aggregates obtained from crushed alumina brick waste. The aggregates were thermally treated at 1550 °C for 3 h. Four types of low-cement castables were prepared with various types of aggregates (alumina grog with or without thermal treatment) and fillers (with or without zircon addition), and they were evaluated in terms of their physical, thermal, and chemical properties. Microstructural analysis via scanning electron microscopy (SEM) was performed on the castables before and after slag attack. Compared to the other fabricated castables, the thermally treated alumina grog castables with zircon showed better physical properties, such as a higher bulk density, cold crushing strength, and modulus of rupture and a lower apparent porosity and water absorption. In addition, they had a higher positive linear thermal expansion, refractoriness under load, permanent linear change, and hot modulus of rupture. The results of the SEM with energy dispersive X-ray analysis of the prepared castables confirmed that the mullite and anorthite phases were predominant when zircon was not added and the zircon–mullite phase additionally appeared upon the incorporation of zircon. A quantitative elemental analysis via X-ray fluorescence spectroscopy was employed to determine the composition of the castables. X-ray diffraction analysis showed that the alumina grog castables had a high mullite and low anorthite content, and the thermally treated alumina grog had a high anorthite, low mullite, and high zircon content. The improvement in the mechanical and thermo-mechanical properties of the castables with thermally treated alumina grog and added zircon can be attributed to the formation of the zircon–mullite phase with a low mullite phase content. 相似文献
9.
A new method for the polygonal approximation is presented. The method is based on the search for break points through a context-free grammar, that accepts digital straight segments with loss of information, as well as the decrease in the error committed employing the comparison of a tolerable error. We present an application of our method to different sets of objects widely used, as well as a comparison of our results with the best results reported in the literature, proving that our method achieves better values of error criteria. Besides, a new way to find polygonal approximations, with context-free grammars to recognize digital straight segments without loss of pixels, it is also addressed. 相似文献