全文获取类型
收费全文 | 59680篇 |
免费 | 5245篇 |
国内免费 | 2647篇 |
专业分类
电工技术 | 3777篇 |
技术理论 | 3篇 |
综合类 | 4071篇 |
化学工业 | 9975篇 |
金属工艺 | 3455篇 |
机械仪表 | 3930篇 |
建筑科学 | 4703篇 |
矿业工程 | 1899篇 |
能源动力 | 1740篇 |
轻工业 | 3949篇 |
水利工程 | 1087篇 |
石油天然气 | 4059篇 |
武器工业 | 562篇 |
无线电 | 6470篇 |
一般工业技术 | 7160篇 |
冶金工业 | 2686篇 |
原子能技术 | 600篇 |
自动化技术 | 7446篇 |
出版年
2024年 | 294篇 |
2023年 | 1159篇 |
2022年 | 1952篇 |
2021年 | 2654篇 |
2020年 | 2080篇 |
2019年 | 1645篇 |
2018年 | 1820篇 |
2017年 | 2012篇 |
2016年 | 1718篇 |
2015年 | 2364篇 |
2014年 | 3063篇 |
2013年 | 3397篇 |
2012年 | 3694篇 |
2011年 | 4147篇 |
2010年 | 3570篇 |
2009年 | 3353篇 |
2008年 | 3280篇 |
2007年 | 3049篇 |
2006年 | 3129篇 |
2005年 | 2620篇 |
2004年 | 1881篇 |
2003年 | 1665篇 |
2002年 | 1641篇 |
2001年 | 1426篇 |
2000年 | 1337篇 |
1999年 | 1564篇 |
1998年 | 1312篇 |
1997年 | 1136篇 |
1996年 | 1031篇 |
1995年 | 840篇 |
1994年 | 676篇 |
1993年 | 487篇 |
1992年 | 424篇 |
1991年 | 273篇 |
1990年 | 219篇 |
1989年 | 167篇 |
1988年 | 128篇 |
1987年 | 88篇 |
1986年 | 74篇 |
1985年 | 45篇 |
1984年 | 38篇 |
1983年 | 32篇 |
1982年 | 31篇 |
1981年 | 19篇 |
1980年 | 17篇 |
1979年 | 6篇 |
1940年 | 3篇 |
1933年 | 1篇 |
1929年 | 1篇 |
1928年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
32.
Guangbo Zeng Dongqing Zhang Liuming Yan Baohua Yue Ting Pan Yidong Hu Shufa He Hongbin Zhao Jiujun Zhang 《International Journal of Hydrogen Energy》2021,46(39):20664-20677
Side-chain optimized poly (2,6-dimethyl-1,4-phenylene oxide)-g-poly (styrene sulfonic acid) (PPO-g-PSSA) is designed with balanced water-resistance and sulfonation degree. The PPO-g-PSSA is synthesized by controlled atom-transfer radical polymerization (ATRP) from brominated poly (2,6-dimethyl-1,4-phenylene oxide) (PPO-xBr) and ethyl styrene-4-sulfonate and followed by hydrolysis. A series of PPO-g-PSSA are prepared possessing different bromination degree (x) of PPO-xBr and polymerization degree (m) of the side-chains and the water-resistances of the fabricated membranes are investigated. The results show that a PPO-g-PSSA at relatively low x (x < 0.2) and high m (m > 4) exhibits good balance between the water-resistance and the sulfonation degree. Namely, it displays suitable proton conductivity with compromised water-resistance. Moreover, a maximum ion exchange capacity (IEC) of 3.24 mmol g?1 is reached without the sacrifice of water-resistance. In addition, PPO-g-0.08PSSA-13 and PPO-g-0.14PSSA-4 are chosen characterized by thermogravimetric analysis, proton conductivities and mechanical properties. At 90% RH, the optimized PPO-g-0.08PPSA-13 possesses a proton conductivity of 37.9 mS cm?1 at 40 °C and 45.5 mS cm?1 at 95 °C, respectively. 相似文献
33.
Baofu Qiu Xiaoming Duan Zhuo Zhang Delong Cai Ning Liao Peigang He Dechang Jia Yu Zhou 《Ceramics International》2021,47(1):73-79
The effects of La2O3–Al2O3–SiO2 addition on the thermal conductivity, coefficient of thermal expansion (CTE), Young's modulus and cyclic thermal shock resistance of hot-pressed h-BN composite ceramics were investigated. The samples were heated to 1000 °C and then quenched to room temperature with 1–50 cycles, and the residual flexural strength was used to evaluate cyclic thermal shock resistance. h-BN composite ceramics containing 10 vol% La2O3–Al2O3 and 20 vol% SiO2 addition exhibited the highest flexural strength, thermal conductivity and relatively low CTE, which were beneficial to the excellent thermal shock resistance. In addition, the viscous amorphous phase of ternary La2O3–Al2O3–SiO2 system could accommodate and relax thermal stress contributing to the high thermal shock resistance. Therefore, the residual flexural strength still maintained the value of 234.3 MPa (86.9% of initial strength) after 50 cycles of thermal shock. 相似文献
34.
Wang Zhicheng Xu Kangwei Ruan Shangshang He Chenliang Zhang Lidong Liu Fuyi 《Catalysis Letters》2022,152(9):2695-2704
Catalysis Letters - A series of mesoporous cobalt–manganese catalysts were successfully synthesized by sol–gel method as efficient catalysts for the propane oxidation. A significant... 相似文献
35.
Basins with various mineral resources coexisting and enriching often occupy an important strategic position. The exploration of various mineral resources is repetitive at present due to unshared data and imperfect management mechanism. This situation greatly increases the cost of energy exploitation in the country. Traditional data-sharing mode has several disadvantages, such as high cost, difficulty in confirming the right of data, and lack of incentive mechanism, which make achieving real data sharing difficult. In this paper, we propose a data-sharing mechanism based on blockchain and provide implementation suggestions and technical key points. Compared with traditional data-sharing methods, the proposed data-sharing mechanism can realize data sharing, ensure data quality, and protect intellectual property. Moreover, key points in the construction are stated in the case study section to verify the feasibility of the data-sharing system based on blockchain proposed in this paper. 相似文献
36.
37.
针对大型旋转机械通过临界转速时振动过大及运行中故障频发等问题,搭建转子试验台,模拟启停机过程和碰摩、不对中故障。不改变原有支撑形式,安装自主设计的磁流变阻尼器,在不停机的情况下,试验研究阻尼器抑制转子通过临界转速时振动过大及各类故障振动。试验结果表明,阻尼器可以有效抑制转子系统临界转速附近的振动,降幅在60%以上;转子发生碰摩或不对中故障时,阻尼器可以降低其高倍频振动。 相似文献
38.
Synergistic flame retardant effects of activated carbon and molybdenum oxide in poly(vinyl chloride) 下载免费PDF全文
Mengjiao Zhang Weihong Wu Shaorui He Xue Wang Yunhong Jiao Hongqiang Qu Jianzhong Xu 《Polymer International》2018,67(4):445-452
The synergistic effects of activated carbon (AC) and molybdenum oxide (MoO3) in improving the flame retardancy of poly(vinyl chloride) (PVC) were investigated. The effects of AC, MoO3 and their mixture with a mass ratio of 1:1 on the flame retardancy and smoke suppression properties of PVC were studied using the limiting oxygen index and cone calorimeter tests. It was found that the flame retardancy of the relatively cheaper AC was slightly weaker than that of MoO3. In addition, the incorporation of AC and MoO3 greatly reduced the total heat release and improved smoke suppressant property of PVC composites. When the total content of AC and MoO3 was 10 phr, PVC/AC/MoO3 had the lowest peak heat release rate and peak smoke production rate values of 173.80 kW m?2 and 0.1472 m2 s?1, which represented reductions of 47.3 and 59.9%, respectively, compared with those of PVC. Furthermore, thermogravimetric analysis and gel content tests were used to analyze the flame retardant mechanism of AC and MoO3, with results showing that AC could promote early crosslinking in PVC. Char residue left after heating at 500 °C was analyzed using scanning electron microscopy and Raman spectroscopy, and the results showed that MoO3 produced the most compact char, with the smallest and most organized carbonaceous microstructures. © 2017 Society of Chemical Industry 相似文献
39.
40.
设计了一种以STM32F103微控制器为控制核心,基于24位高精度模数转换器的钻孔深度测量仪器。利用弹性波回波测距原理,通过测量出钻孔中钻杆的长度,实现钻孔深度的快速、无损、准确的测量,主要用于井下瓦斯抽放钻孔、探放水钻孔等煤矿通防工作的施工验收。仪器小巧轻便,操作简单,单人即可完成测量工作,节约下井的人力物力,提高生产效率,最长测量长度可达250米,误差不超过1米。 相似文献