全文获取类型
收费全文 | 188113篇 |
免费 | 26122篇 |
国内免费 | 23549篇 |
专业分类
电工技术 | 19093篇 |
技术理论 | 8篇 |
综合类 | 13742篇 |
化学工业 | 37387篇 |
金属工艺 | 7707篇 |
机械仪表 | 12313篇 |
建筑科学 | 8621篇 |
矿业工程 | 2168篇 |
能源动力 | 5956篇 |
轻工业 | 13522篇 |
水利工程 | 2495篇 |
石油天然气 | 4387篇 |
武器工业 | 2001篇 |
无线电 | 29356篇 |
一般工业技术 | 21110篇 |
冶金工业 | 3992篇 |
原子能技术 | 3264篇 |
自动化技术 | 50662篇 |
出版年
2024年 | 484篇 |
2023年 | 3043篇 |
2022年 | 5175篇 |
2021年 | 6960篇 |
2020年 | 6652篇 |
2019年 | 6017篇 |
2018年 | 5552篇 |
2017年 | 7607篇 |
2016年 | 8409篇 |
2015年 | 9830篇 |
2014年 | 9525篇 |
2013年 | 12765篇 |
2012年 | 14674篇 |
2011年 | 16533篇 |
2010年 | 11937篇 |
2009年 | 11773篇 |
2008年 | 13037篇 |
2007年 | 14448篇 |
2006年 | 13765篇 |
2005年 | 11813篇 |
2004年 | 9982篇 |
2003年 | 7847篇 |
2002年 | 5975篇 |
2001年 | 4359篇 |
2000年 | 3413篇 |
1999年 | 2847篇 |
1998年 | 2349篇 |
1997年 | 1854篇 |
1996年 | 1579篇 |
1995年 | 1400篇 |
1994年 | 1245篇 |
1993年 | 927篇 |
1992年 | 750篇 |
1991年 | 593篇 |
1990年 | 514篇 |
1989年 | 381篇 |
1988年 | 293篇 |
1987年 | 182篇 |
1986年 | 170篇 |
1985年 | 227篇 |
1984年 | 199篇 |
1983年 | 138篇 |
1982年 | 196篇 |
1981年 | 95篇 |
1980年 | 95篇 |
1979年 | 24篇 |
1978年 | 15篇 |
1977年 | 24篇 |
1959年 | 18篇 |
1957年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Serkan Nohut 《Ceramics International》2021,47(2):2270-2279
Strength distribution of advanced ceramics is commonly characterized by two-Parameter (2P) Weibull distribution. However, deviation of strength distribution from 2P-Weibull distribution may occur in ceramics due to various mechanisms. R-curve behavior is one of these mechanisms where increase of fracture resistance with the extension of crack occurs. In such cases, 2P-Weibull distribution may not be the best fitting distribution function based on the goodness-of-fitness tests. This article examines the effectiveness of three-parameter (3P) Weibull distribution function for fitting the strength variation due to R-curve effect by using experimental and virtual strength data. The effect of Weibull parameters, degree of increase in crack resistance and number of samples on effectiveness of fitting via 3P-Weibull distribution is investigated. It is reported that 3P-Weibull distribution function fits the strength distribution better than 2P-Weibull distribution function for materials showing R-curve behavior when the crack resistance curve is steep and Weibull modulus is high. Furthermore, it is shown that at least 100 samples should be used for a reliable estimate when the material exhibits R-curve behavior. 相似文献
992.
Chengbiao Ge Guilong Wang Jinchuan Zhao Guoqun Zhao 《Polymer Engineering and Science》2021,61(7):2137-2146
Freshwater resources are currently insufficient, and another form of freshwater resources, namely, ice, is very interesting except for the issue of how to use new materials for effective purification during the processing procedure. In this article, a new membrane material with multisize pore structure in the cross-section and intact thin skin layer on the upper and lower surfaces was successfully prepared by adding porogen, filler and setting heating environment during the phase separation process. The membrane exhibits excellent axial deformability, and its elongation at break can reach to 160% strain. Meanwhile, they all show elastic deformation behavior in the range from −60 to 100°C. Even if high content of hydrophobic filler is compounded into these membranes, that is, 5.7 wt% carbon tube content, water contact angle of membrane's surface is only 72.5°, demonstrating obvious hydrophilicity. In addition, in the water purification process, the adsorption rate constant reached ideal value of 0.26 s−1, and the equilibrium adsorption capacity was about 2.8 g/g, showing fast and efficient water purification ability. In the mode of external heating source or the membrane's heat dissipation, these prepared membranes can melt the ice to obtain purified water and exhibit a controllable purification ability in this process. 相似文献
993.
Darikha Kudasova Botagoz Mutaliyeva Kristina Vlahovi
ek-Kahlina Slaven Juri Marijan Marijan Svetlana V. Khalus Alexander V. Prosyanik Suzana egota Nikola pani Marko Vincekovi 《International journal of molecular sciences》2021,22(5)
A new copper complex, trans-diaqua-trans-bis [1-hydroxy-1,2-di (methoxycarbonyl) ethenato] copper (abbreviation Cu(II) complex), was synthesized and its plant growth regulation properties were investigated. The results show a sharp dependence of growth regulation activity of the Cu(II) complex on the type of culture and its concentration. New plant growth regulator accelerated the development of the corn root system (the increase in both length and weight) but showed a smaller effect on the development of the wheat and barley root systems. Stimulation of corn growth decreased with increasing Cu(II) complex concentration from 0.0001% to 0.01% (inhibition at high concentrations—0.01%). The development of corn stems was also accelerated but to a lesser extent. Chitosan-coated calcium alginate microcapsules suitable for delivery of Cu(II) complex to plants were prepared and characterized. Analysis of the FTIR spectrum showed that complex molecular interactions between functional groups of microcapsule constituents include mainly electrostatic interactions and hydrogen bonds. Microcapsules surface exhibits a soft granular surface structure with substructures consisting of abundant smaller particles with reduced surface roughness. Release profile analysis showed Fickian diffusion is the rate-controlling mechanism of Cu(II) complex releasing. The obtained results give new insights into the complexity of the interaction between the Cu(II) complex and microcapsule formulation constituents, which can be of great help in accelerating product development for the application in agriculture 相似文献
994.
Wen Ma Yuanming Gao Jingxin Zhang Yu Bai Ruiling Jia Hongying Dong Ruijun Wang Manyu Bao 《Journal of the European Ceramic Society》2021,41(4):2734-2745
Srx(Zr0.9Y0.05Yb0.05)O1.95+x (x=1.0, 0.9, 0.8, 0.7) ceramics were prepared by solid state reaction sintering. The sintered Sr1.0(Zr0.9Y0.05Yb0.05)O2.95 is a single-phase solid solution while the sintered Srx(Zr0.9Y0.05Yb0.05)O1.95+x (x=0.9?0.7) are composites, and a significant grain growth inhibition is observed in the sintered Srx(Zr0.9Y0.05Yb0.05)O1.95+x (x=1.0, 0.9). Rare-earth elements distribution in the bulk materials indicates that Yb and Y preferentially substitute Zr-sites in SrZrO3, and the highest solubility of RE2O3 in pure SrZrO3 is ~0.8 mol%. The sintered Srx(Zr0.9Y0.05Yb0.05)O1.95+x have high thermal expansion coefficients up to ~11.0×10?6 K-1 (1200°C). Sr0.8(Zr0.9Y0.05Yb0.05)O2.75 has the lowest thermal conductivity of 1.38 W·m-1·K-1 at 800°C. Srx(Zr0.9Y0.05Yb0.05)O1.95+x (x=1.0, 0.9, 0.8) show no phase transition from 600 to 1400°C, whereas Srx(Zr0.9Y0.05Yb0.05)O1.95+x (x=0.9, 0.8) have excellent high-temperature phase stability over the whole investigated temperature range. Therefore, Srx(Zr0.9Y0.05Yb0.05)O1.95+x (x=1.0, 0.9, 0.8) are considered as promising TBCs materials that might be operated at higher temperatures compared to YSZ. 相似文献
995.
Gregor D. Wehinger 《化学,工程师,技术》2021,93(7):1049-1057
This article introduces assistant professor Gregor D. Wehinger of the Institute of Chemical and Electrochemical Process Engineering at Clausthal University of Technology. Besides recent research projects and teaching activities, he gives an overview about his commitment to the community. He reports on current research results in the field of CFD modeling of packed-bed reactors, redox-flow batteries, and multiphase systems. Furthermore, the use of virtual reality in teaching is presented. 相似文献
996.
Koichi Shigeno Moyuan Li Hirotaka Fujimori 《Journal of the European Ceramic Society》2021,41(1):376-386
A new composition was developed using sintering to improve the dielectric properties of low-temperature co-fired alumina (LTCA) containing CuO–TiO2–Nb2O5–Ag2O. By substituting some alumina with rutile TiO2, the second-phase compound could be changed from AgNbO3 to the rutile phase. Further, low-temperature sintering at temperatures below 960 °C was possible, suppressing Al2TiO5 formation during firing. The dielectric characteristics, particularly the temperature coefficient of the resonant frequency (τf) and Q × f values, were improved without significantly reducing the sinterability and thermal conductivity. The dielectric properties of the developed 88Al2O3–12TiO2-based ceramic were εr: 14.7, τf: +0.8 ppm/K, and Q × f: 13,383 GHz (at ~10 GHz) at a firing temperature of 940 °C. The thermal conductivity was 18.5 W/mK, which is the highest value for reported temperature-stable low-temperature co-fired ceramics (LTCCs). These results provide one of the key technologies for the practical application of LTCCs with superior thermal conductivities. 相似文献
997.
Shao-Fang Li Zhen-Yi Gu Jin-Zhi Guo Xian-Kun Hou Xu Yang Bo Zhao Xing-Long Wu 《材料科学技术学报》2021,78(19):176-182
In recent years,sodium-ion batteries(SIBs)have been considered as one of the most promising alterna-tives to lithium-ion batteries(LIBs).Here,a new Na-super-ionic conductor(NASICON)cathode material NaFe2PO4(SO4)2 is successfully prepared through solid state method for SIBs.While the poor electronic conductivity of iron-based materials results in its poor rate and cycle performance.Then the electro-chemical is effectively promoting via Ca2+doping.Na0.84Ca0.08Fe2PO4(SO4)2 have achieved considerable electrochemical properties.The first discharge specific capacity is 121.6mAhg-1 at 25mAg-1 with the voltage platform(~3.1 V)corresponding to Fe2+/3+.After 100 cycles,the capacity retention is 55.1%.The excellent electrochemical performance is caused by some Na+is substituted by Ca2+and leading to the fast sodium kinetics,which is well proved by the powder X-ray diffraction pattern and well corresponding to the galvanostatic intermittent titration technique and cyclic voltammetry testing result(the diffusivity values are around at 10-12 cm2 s-1). 相似文献
998.
The development of T-spherical fuzzy (T-SF) sets in qualitative multiple-criteria choice analysis has been well investigated, but little is explored about how the VIKOR (i.e., VIšekriterijumsko KOmpromisno Rangiranje in Serbian) mechanism is generalized into intricate T-SF environments. This paper has the objective of propounding a creative T-SF VIKOR methodology for compromise ranking modeling in multiple criteria analysis. The exploitation of the T-SF configuration brings about superior information space representation in response to intricate realistic environments. However, because of the increased complexity of decision situations involving T-spherical fuzziness, treatment with the T-SF information arises a pragmatic difficulty in developing methodological approaches to T-SF VIKOR. In light of this concern, this paper unfolds an analytical framework for the T-SF VIKOR method predicated on new notions of an evolved T-SF score function and the Minkowski-type T-SF distance measure along with its special cases of the Manhattan-, Euclidean-, and Chebyshev-type distances. The aspired and despised T-SF characteristics can be identified supported by the evolved T-SF score function of T-SF performance ratings. This paper gives a new delineation of the group utility, individual regret, and joint generalized measures with the aid of the Minkowski-type T-SF distance measure relative to the aspired/despised T-SF characteristics. A synthetic mechanism is built to validate the standards of acceptable advantage and stability and yield the ultimate compromise choices for multiple criteria decision aiding. The practicality of the T-SF VIKOR methodology in down-to-earth decision situations has been well demonstrated through the selection issues of warehouse locations and advertisement strategies. Moreover, the developed approach has shown better application outcomes than the past methods did. The comparative study with parametric analysis has revealed the steadiness and effectiveness of the compromise choice results in T-SF circumstances. 相似文献
999.
《International Journal of Hydrogen Energy》2022,47(9):6388-6403
The influence of electrochemical charging of hydrogen at j = ?5 mA/cm2 for 6, 12, 48 and 96 h on the structural and the mechanical behavior of wrought and electron beam melting (EBM) Ti–6Al–4V alloys containing 6 wt% β and similar impurities level was investigated. The length of the α/β interphase boundaries in the EBM alloy was larger by 34% compared to that in the wrought alloy. The small punch test (SPT) technique was used to characterize the mechanical behavior of the non-hydrogenated and hydrogenated specimens. It was found that the maximum load and the displacement at maximum load of the wrought alloy remained nearly stable after 6 h of charging, showing a maximum decrease of ~32% and 11%, respectively. Similarly, hydrogenation of the EBM alloy resulted in a gradual degradation in mechanical properties with charging time, up to ~81% and 86% in pop-in load and displacement at the “pop-in” load, respectively. The mode of fracture of the wrought alloy changed from ductile to semi-brittle with mud-cracking in all hydrogenated specimens. In contrast, the mode of fracture of the EBM alloy changed from a mixed mode ductile-brittle fracture to brittle fracture with star-like morphology. The degraded mechanical properties of the EBM alloy are attributed to its α/β lamellar microstructure which acted as a short-circuit path and enhanced hydrogen diffusion into the bulk as well as δa and δb hydride formation on the surface. In contrast, a surface layer with higher concentration of δa and δb hydrides in the wrought alloy served as a barrier to hydrogen uptake into the bulk and increased the alloy resistivity to hydrogen embrittlement (HE). This study shows that EBM Ti–6Al–4V alloy is more susceptible to mechanical degradation due to HE than wrought Ti–6Al–4V alloy. 相似文献
1000.
Additive manufacturing (AM) has rapidly changed both large- and small-scale production environments across many industries. By re-envisioning parts from the ground up, not limited to the challenges presented by traditional manufacturing techniques, researchers and engineers have developed new design strategies to solve large-scale materials and design problems worldwide. This is particularly true in the world of alloy design, where new metallic materials have historically been developed through tedious processes and procedures based primarily on casting methodologies. With the onset of directed energy deposition (DED) and powder bed fusion (PBF)-based AM, new alloys can be innovated and evaluated rapidly at a lower cost and considerably shorter lead time than has ever been achieved. This article details the advantages, challenges, applications, and perspectives of alloy design using primarily laser-based AM. It is envisioned that researchers in industry and academia can utilize this work to design new alloys leveraging metallic AM processes for various current and future applications. 相似文献