全文获取类型
收费全文 | 130747篇 |
免费 | 16867篇 |
国内免费 | 6678篇 |
专业分类
电工技术 | 51000篇 |
技术理论 | 3篇 |
综合类 | 9934篇 |
化学工业 | 13543篇 |
金属工艺 | 5489篇 |
机械仪表 | 5547篇 |
建筑科学 | 6667篇 |
矿业工程 | 2511篇 |
能源动力 | 11205篇 |
轻工业 | 2945篇 |
水利工程 | 2920篇 |
石油天然气 | 2349篇 |
武器工业 | 1293篇 |
无线电 | 15568篇 |
一般工业技术 | 9230篇 |
冶金工业 | 3128篇 |
原子能技术 | 2803篇 |
自动化技术 | 8157篇 |
出版年
2024年 | 300篇 |
2023年 | 1939篇 |
2022年 | 3347篇 |
2021年 | 4140篇 |
2020年 | 4679篇 |
2019年 | 3981篇 |
2018年 | 3599篇 |
2017年 | 4929篇 |
2016年 | 5142篇 |
2015年 | 5660篇 |
2014年 | 9049篇 |
2013年 | 8152篇 |
2012年 | 10292篇 |
2011年 | 10974篇 |
2010年 | 8051篇 |
2009年 | 8234篇 |
2008年 | 7843篇 |
2007年 | 9385篇 |
2006年 | 8466篇 |
2005年 | 6757篇 |
2004年 | 5625篇 |
2003年 | 4522篇 |
2002年 | 3671篇 |
2001年 | 3158篇 |
2000年 | 2529篇 |
1999年 | 1870篇 |
1998年 | 1354篇 |
1997年 | 1133篇 |
1996年 | 1076篇 |
1995年 | 853篇 |
1994年 | 718篇 |
1993年 | 508篇 |
1992年 | 469篇 |
1991年 | 356篇 |
1990年 | 293篇 |
1989年 | 248篇 |
1988年 | 183篇 |
1987年 | 120篇 |
1986年 | 96篇 |
1985年 | 99篇 |
1984年 | 116篇 |
1983年 | 92篇 |
1982年 | 96篇 |
1981年 | 46篇 |
1980年 | 29篇 |
1979年 | 17篇 |
1978年 | 15篇 |
1977年 | 10篇 |
1959年 | 20篇 |
1951年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Tatsuro Tanaka Yoshifumi Maeda Shinji Yamamoto Toru Iwao 《Electrical Engineering in Japan》2019,207(1):15-23
The arc welding has been used in various welding methods because it is inexpensive and high in strength after welding. However, it is a problem that accidents such as collapse of the bridge occur because of the welding defects. The welding of low cost and high productivity is required without the welding defects. The pulsed TIG welding is inexpensive and capable of high‐quality welding. The electromagnetic force contributing to penetration changes because the transient response of arc temperature and iron vapor generated from anode occurs. However, the analysis of pulsed TIG welding with metal vapor has been elucidated only metal vapor concentration near anode with transient phenomenon and heat flux. Thus, the theoretical elucidation of penetration depth with control factor has not been researched. In this paper, the contribution of metal vapor mass at the periphery part of pulsed arc to the electromagnetic force in the weld pool is elucidated. As a result, the iron vapor mass at periphery part decreased with increasing the frequency. The iron vapor was stagnated at axial center within one cycle. The electromagnetic force to the penetration depth direction in weld pool increased at axial center. Therefore, the metal vapor mass at periphery part plays an important role for the electromagnetic force increment at axial center. 相似文献
92.
Hanaa A. H. Asfour 《亚洲传热研究》2021,50(4):3366-3387
As thermal radiation is one of the fundamental means of heat transfer, therefore, this study analyzes the impacts of thermal radiation and magnetic field on the peristaltic transport of a Jeffrey nanofluid in a nonuniform asymmetric channel. Further, Two models of viscosity are debated: Model (I), in which all parameters dependent on viscosity behave as a constant (as treated before in nanofluid research); Model (II), in which these known parameters are considered to vary with the temperature of the flow. Under the condition of long wavelength and low Reynolds number, the problem is rearranged. The resulting system of partial differential equations (PNE) is solved with aid of Mathematica 11. Furthermore, the streamline graphs are presented by significance of trapping bolus phenomenon. To emphasize the quality of solutions, comparisons between the previous results and recent published results by Reddy et al. have been made and signified. The comparisons are shown in Table 1 and are found to be in good agreement. As the thermal radiation increases, the diameter of nanoparticles rises (thermal radiation is a diminishing function of temperature, and with a decrease in the temperature, the diameter of the nanoparticles increases, that is, the size of nanoparticles increases and they become more active near malignant tumor tissues). Therefore, its work as agents for radiation remedy, produce limited radiation quantities, and selectively target malignant tumor for controlled mutilation (radiotherapy of oncology). Such a model is appropriate for the transportation of physiological flows in the arteries with heat and mass transfer (blood flow models). 相似文献
93.
Zhen Wu Jing Yao Pengfei Zhu Fusheng Yang Xiangyu Meng Sandra Kurko Zaoxiao Zhang 《International Journal of Hydrogen Energy》2021,46(19):11183-11198
Advanced biogas power generation technology has been attracting attentions, which contributes to the waste disposal and the mitigation of greenhouse gas emissions. This work proposes and models a novel biogas-fed hybrid power generation system consisting of solid oxide fuel cell, water gas shift reaction, thermal swing adsorption and proton exchange membrane fuel cell (SOFC-WGS-TSA-PEMFC). The thermodynamic, exergetic, and thermo-economic analyses of this hybrid system for power generation were conducted to comprehensively evaluate its performance. It was found that the novel biogas-fed hybrid system has a gross energy conversion efficiency of 68.63% and exergy efficiency of 65.36%, indicating high efficiency for this kind of hybrid power technology. The market sensitivity analysis showed that the hybrid system also has a low sensitivity to market price fluctuation. Under the current subsidy level for the distributed biogas power plant, the levelized cost of energy can be lowered to 0.02942 $/kWh for a 1 MW scale system. Accordingly, the payback period and annual return on investment can reach 1.4 year and about 20%, respectively. These results reveal that the proposed hybrid system is promising and economically feasible as a distributed power plant, especially for the small power scale (no more than 2 MW). 相似文献
94.
In this work, the interdiffusion between a MCrAlY-bond coat and two different nickel-based superalloys is evaluated at three temperatures, 950 °C, 980 °C, and 1,050 °C. Of primary interest is the evolution of Kirkendall-porosity, the β-depleted zone in the bond coat and the β’- depleted zone in the superalloy. The three phenomena arise near the interface between bond coat and superalloy as a result of interdiffusion between both materials and are detrimental to the coating-substrate system. The evolution of the interdiffusion phenomena is highly dependent on the alloy composition of the materials as well as the annealing temperature. It has been found that not only the temperature dependency of the diffusion coefficient but also the temperature dependent element activities are an important factor when evaluating the interdiffusion phenomena. It has further been shown that at lower temperatures the amount of Kirkendall-porosity per volume fraction is higher than at higher temperatures, even though the overall amount of porosity is lower. Different equilibrium concentrations of main alloying elements and a correspondingly lower over-saturation of vacancies have been identified as the main explanation. 相似文献
95.
Jiayi Su Chang Tan Yang Gao Ying Feng 《International Journal of Food Science & Technology》2021,56(4):1896-1904
Liquid chromatography coupled with tandem mass spectrometry (LC–MS/MS) was employed to investigate free phenols that were released from purple sweet potato (PSP) by alkaline, acid and enzymatic hydrolysis. Four phenolic acids, including ferulic, isoferulic, 4-hydroxybenzoic and caffeic acids, were identified. Based on their effects on the characteristics of purple sweet potato starch (PSPS), the four phenolic acids were studied. Furthermore, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT–IR) and X-ray diffraction (XRD) techniques were employed to explore the microstructures of the complexes of the phenolic acids and PSPS. The obtained results demonstrated that the pasting, thermal, retrogradation, as well as digestive properties of PSPS were all influenced by the phenolic acids which interacted with PSPS through noncovalent hydrogen bonds. The influence of the four phenolic acids on the properties of PSPS was in the descending order: 4-hydroxybenzoic acid > ferulic acid > caffeic acid > isoferulic acid. 相似文献
96.
97.
A. M. Patki 《Polymer-Plastics Technology and Engineering》2021,60(1):70-83
ABSTRACT Poly(ether-ketone)/hexagonal boron nitride (h-BN) composites reinforced with micrometer-sized h-BN particles were investigated. The composites exhibited glass transition temperature (Tg) and thermal stability over 160°C and 560°C, respectively. The melting point and peak crystallization temperatures of the composites decreased up to 17°C and 12°C, respectively. The linear CTE of the composites decreased both below and above the Tg. The storage modulus increased with increasing h-BN content at all temperatures (50–250°C). The composites possessed excellent dielectric properties with insignificant dispersion with increasing frequency. Thus, resultant composites are promising candidates for the printed circuit boards/electronic substrates. 相似文献
98.
In the past decade, remarkable progress has been made in the domain of augmented reality/virtual reality (AR/VR). The need for realistic and immersive augmentation has propelled the development of haptics interfaces-enabled AR/VR. The haptics interfaces facilitate direct interaction and manipulation with both real and virtual objects, thus augmenting the perception and experiences of the users. The level of augmentation can be significantly improved by thermal stimulation or sensing, which facilitates a higher degree of object identification and discrimination. This review discusses the thermal technology-enabled augmented reality and summarizes the recent progress in the development of different thermal technology such as thermal haptics including thermo-resistive heater and Peltier devices, thermal sensors including resistive, pyroelectric, and thermoelectric sensors, which can be utilized to improve the realism of augmentation. The fundamental mechanism, design strategies, and the rational guidelines for the adoption of these technologies in AR/VR is explicitly discussed. The conclusion provides an outlook on the existing challenges and outlines the future roadmap for the realization of next-generation thermo-haptics enabled augmented reality. 相似文献
99.
文中提出了一种利用有限数量的相量测量单元(PMU)和相量数据集中器(PDC)设计最优监控结构的方法。通过在大量的设定值场景下,使电力系统可观测性曲线的期望值最大化,同时使通信基础设施成本最小化,最终确定PMU和PDC的最佳位置。提出了一种非线性动态扩展卡尔曼滤波(EFK)状态观测器。这种状态观测器可以将暂态行为转换为由代数微分方程描述的广域电力系统,而无需非线性反演技术。最后以IEEE-5电力系统为例,说明了该方法的有效性。 相似文献
100.
Jiatong Zhu Xuanyu Meng Ping Zhang Zhuolun Li Jie Xu Michael J. Reece Feng Gao 《Journal of the European Ceramic Society》2021,41(4):2861-2869
A series of rare earth zirconates (RE2Zr2O7) high-entropy ceramics with single- and dual-phase structure were prepared. Compared with La2Zr2O7 and Yb2Zr2O7, the smaller “rattling” ions (Yb3+, Er3+, Y3+) have been incorporated into pyrochlore lattice in (La0.2Nd0.2Y0.2Er0.2Yb0.2)2Zr2O7 (LNYEY) while larger ions (La3+, Nd3+, Sm3+, Eu3+) incorporated into fluorite lattice in (La0.2Nd0.2Sm0.2Gd0.2Yb0.2)2Zr2O7 (LNSGY). Due to high-entropy lattice distortion and resonant scattering derived from smaller ions Yb3+, Er3+, and Y3+, LNYEY shows a lower glass-like thermal conductivity (1.62-1.59 W m-1 K-1, 100-600℃) than LNSGY (1.74-1.75 W m-1 K-1, 100-600℃). Moreover, LNYEY and LNSGY exhibit enhanced Vickers’ hardness (LNYEY, Hv = 11.47 ± 0.41 GPa; LNSGY, Hv = 10.96 ± 0.26 GPa) and thermal expansion coefficients (LNYEY, 10.45 × 10-6 K-1, 1000℃; LNSGY, 11.02 × 10-6 K-1, 1000℃). These results indicate that dual-phase rare-earth-zirconate high-entropy ceramics could be desirable for thermal barrier coatings. 相似文献