全文获取类型
收费全文 | 2247篇 |
免费 | 213篇 |
国内免费 | 260篇 |
专业分类
电工技术 | 152篇 |
综合类 | 145篇 |
化学工业 | 232篇 |
金属工艺 | 105篇 |
机械仪表 | 132篇 |
建筑科学 | 45篇 |
矿业工程 | 13篇 |
能源动力 | 95篇 |
轻工业 | 35篇 |
水利工程 | 7篇 |
石油天然气 | 76篇 |
武器工业 | 30篇 |
无线电 | 645篇 |
一般工业技术 | 321篇 |
冶金工业 | 88篇 |
原子能技术 | 105篇 |
自动化技术 | 494篇 |
出版年
2024年 | 7篇 |
2023年 | 43篇 |
2022年 | 52篇 |
2021年 | 56篇 |
2020年 | 71篇 |
2019年 | 66篇 |
2018年 | 44篇 |
2017年 | 98篇 |
2016年 | 105篇 |
2015年 | 93篇 |
2014年 | 128篇 |
2013年 | 139篇 |
2012年 | 171篇 |
2011年 | 191篇 |
2010年 | 143篇 |
2009年 | 158篇 |
2008年 | 139篇 |
2007年 | 122篇 |
2006年 | 109篇 |
2005年 | 104篇 |
2004年 | 76篇 |
2003年 | 79篇 |
2002年 | 76篇 |
2001年 | 69篇 |
2000年 | 62篇 |
1999年 | 48篇 |
1998年 | 49篇 |
1997年 | 35篇 |
1996年 | 34篇 |
1995年 | 23篇 |
1994年 | 23篇 |
1993年 | 30篇 |
1992年 | 12篇 |
1991年 | 13篇 |
1990年 | 11篇 |
1989年 | 12篇 |
1988年 | 8篇 |
1987年 | 6篇 |
1986年 | 3篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1975年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有2720条查询结果,搜索用时 0 毫秒
101.
102.
为了提高Y-Gd-Hf-O压制式高温阴极的热发射性能,制备了Y2O3/HfO2摩尔比不同的S2O3掺杂Y-Gd-Hf-O直热式压制阴极。测试结果显示,当比值为5/2时,热发射能力最好,1500 ℃下发射电流为2.79 A/cm2。阴极支取直流发射电流密度1.0 A/cm2,在1500 ℃的工作温度下,已经稳定工作了1320 h,并在该温度下经过696 h的10 W连续电子轰击后,发射电流仍保持为初始值的86%,表现出良好的耐电子轰击能力。XPS结合深度刻蚀表明,发射活性层主要集中在距表面50 nm深度范围内。表层SEM、EDS分析表明,阴极经过激活、老炼,活性物质粒径变大,Y/Hf原子比低于初始值,且随着Y2O3含量的提高,阴极表层n型半导体Y2O3-x的含量相应地增加,对改善阴极表面的导电性、降低逸出功和提高阴极的热发射性能有促进作用 相似文献
103.
Herbert Stutz 《应用聚合物科学杂志》2004,91(3):1881-1886
The kinetics of thermal degradation of 4,4′‐diaminodiphenylsulfone (DDS)‐cured glycidylethers (DGBA) and glycidylamines (TGDDM) have been studied by isothermal annealing. Thermal degradation proceeds via first‐order kinetics with activation energies of 138 (DGBA/DDS) and 95 kJ/mol (TGDDM/DDS). From these data the temperature‐dependent lifetime can be calculated. Based on the heat distortion temperature and 20 years' service as criteria, the upper service temperature is found to be around 115–120°C. In spite of the different activation energies and bond stabilities, only marginal differences in the upper allowed service temperatures between these resins were found. Only slight improvements can be expected by optimizing the cure conditions. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1881–1886, 2004 相似文献
104.
The potential energy profile of the reaction between dimethyl disulfide and OH? radicals is explored by utilizing ab initio and hybrid meta density functional theory methods. Having the energies and structural data of the stationary points, statistical rate theories, such as transition state theory and variable reaction coordinate-transition state theory, are employed to compute the overall rate constants, and discuss the mechanism and product channels. On the basis of the calculations, the overall rate coefficient is predicted to be 2.49?×?10?10?cm3?molecule?1?s?1 at 298?K. It is found that in the most favorable pathway, the reaction proceeds via formation of the relatively unstable intermediate CH3S?(OH)SCH3 decomposing rapidly to yield CH3S?+CH3SOH. 相似文献
105.
Subcritical crack growth behavior of a perovskite‐structured Ba0.5Sr0.5Co0.8Fe0.2O3−δ oxygen transport membrane 下载免费PDF全文
Li Wang Rui Dou Gong Wang Yizhe Li Mingwen Bai David Hall Ying Chen 《International Journal of Applied Ceramic Technology》2018,15(1):63-73
This paper herein studies subcritical crack growth (SCG) behavior of a perovskite‐structured Ba0.5Sr0.5Co0.8Fe0.2O3?δ (BSCF) as an oxygen transport membrane material. The SCG behavior of BSCF is evaluated by a constant load method and constant stress rate method at room temperature (RT) and 800°C in air, respectively. The low crack velocity measurements are carried out by ring‐on‐ring bending tests while the high crack velocity measurements by compact tension tests. The stress rates vary approximately from 0.1012 to 101.2 MPa/min. The fracture stress increases with increasing stress rate at 800°C. The SCG parameter, n, of BSCF is determined to be 24.32 and 13.83 at RT and 800°C in air, respectively. This indicates that BSCF is more susceptible to SCG at 800°C. The strength‐probability‐time (SPT) diagram is constructed for design proposes. The stress for a lifetime of 40 years should not exceed 27.21 MPa at RT or 4.53 MPa at 800°C to assure a failure probability below 1%. 相似文献
106.
对链板材料的疲劳强度、链板孔表面加工质量、链板应力集中、整链预拉强化、链板喷丸强化等影响滚子链疲劳寿命的规律进行了深入的研究,给出了提高滚子链疲劳寿命的工艺参数。 相似文献
107.
The properties and thickness of the bubbles in the froth control the flotation process. There is no work showing how to measure bubble film composition and thickness by a straightforward manner. In this work, a novel approach, a custom-designed bubble cell associated with layer interferometry(in the UV-vis region) and FT-IR spectroscopy was used to investigate the effect of solid particle type(hydrophilic vs hydrophobic), concentration and bubble diameter on stability of a bubble blown in air. Stability was quantified by measuring bubble lifetime and hydrated film thickness. Kerosene with silicone oil as a foaming agent was used to evaluate the impact of bubble diameter(test series I). Frother solutions(MIBC, Dowfroth 250, Hexanol and F-150) were used for the solid type concentration experiments(test series II). In the first series of experiments, it was determined that as the diameter of a bubble increased from 10 to 25 mm, so did the hydrated film thickness from 350 to 1000 nm. In the second series, as the silica concentration increased(0 to 10%), an increase in bubble lifetime and hydrated film thickness was resulted(130%-250%). An impact of solid hydrophobicity was found but to a lesser degree than expected. It is possible that the small particle size(〈0.1 m) of silica was responsible for this behavior. The findings are used to interpret the effect of solids in flotation froth. 相似文献
108.
为快速检测船用电缆的剩余使用寿命,尝试应用硬度这一可以快速检测的特征量来建立一种船舶电缆绝缘老化寿命快速检测方法。对船用丁苯橡胶电缆开展了加速老化实验,并对老化后的试样进行了硬度测试,并对所得数据进行处理,提出基于硬度的船用电缆剩余寿命快速检测方法,最后通过标准的基于断裂伸长保留率的寿命检测方法对所提出的快速检测方法进行检验。结果表明,2种方法具有高度的一致性,从而为船用电缆剩余寿命快速评估提供一种新的思路。 相似文献
109.
本文介绍了根据光纤动态疲劳试验的测定数据,通过 Weibull 分布统计推断处理进行光纤特性参数、光纤动态疲劳寿命的计算。 相似文献
110.
《Ceramics International》2019,45(12):14896-14907
Failure of plasma-sprayed thermal barrier coatings (TBCs) is very complicated upon temperature cycling, therefore, to ascertain the crack propagation behavior is beneficial to understand the failure mechanism and life prediction of TBCs. In this paper, a finite element model is developed by coupling the dynamic growth of thermally grown oxide and dynamic crack propagation to explore the failure of TBCs induced by the instability of the interface between top coat (TC) and bond coat (BC). The thermal cyclic lifetime is deduced by obtaining the thermal cycles corresponding to the occurrence of complete delamination. The influence of the non-uniformity of the interface on thermal cyclic lifetime is quantitatively evaluated. Sensitivity studies including the effects of constituent properties and crack distance to the interface on the thermal cyclic lifetime are further examined. The results show that the incipient cracks usually nucleate above the valley due to the large tensile stress, and the shear stress near the peak plays a very crucial role. The crack growth involves three stages with different fracture dominated-mode. The crack propagation behavior obtained by simulation is in line with that observed by experiments. The TBCs system with a uniform interface exhibits a longer thermal cyclic lifetime compared to the non-uniform interface. Coating optimization methods proposed in this work may provide an alternative option for developing a TBCs system with longer service lifetime. 相似文献