全文获取类型
收费全文 | 26713篇 |
免费 | 2312篇 |
国内免费 | 1189篇 |
专业分类
电工技术 | 1584篇 |
技术理论 | 3篇 |
综合类 | 1668篇 |
化学工业 | 4430篇 |
金属工艺 | 1757篇 |
机械仪表 | 1666篇 |
建筑科学 | 2352篇 |
矿业工程 | 742篇 |
能源动力 | 690篇 |
轻工业 | 1760篇 |
水利工程 | 427篇 |
石油天然气 | 1480篇 |
武器工业 | 207篇 |
无线电 | 3097篇 |
一般工业技术 | 3396篇 |
冶金工业 | 1143篇 |
原子能技术 | 259篇 |
自动化技术 | 3553篇 |
出版年
2024年 | 129篇 |
2023年 | 449篇 |
2022年 | 788篇 |
2021年 | 1142篇 |
2020年 | 882篇 |
2019年 | 679篇 |
2018年 | 792篇 |
2017年 | 839篇 |
2016年 | 756篇 |
2015年 | 1013篇 |
2014年 | 1205篇 |
2013年 | 1518篇 |
2012年 | 1658篇 |
2011年 | 1745篇 |
2010年 | 1609篇 |
2009年 | 1487篇 |
2008年 | 1430篇 |
2007年 | 1445篇 |
2006年 | 1396篇 |
2005年 | 1310篇 |
2004年 | 901篇 |
2003年 | 792篇 |
2002年 | 804篇 |
2001年 | 638篇 |
2000年 | 728篇 |
1999年 | 753篇 |
1998年 | 621篇 |
1997年 | 494篇 |
1996年 | 505篇 |
1995年 | 391篇 |
1994年 | 323篇 |
1993年 | 253篇 |
1992年 | 207篇 |
1991年 | 134篇 |
1990年 | 89篇 |
1989年 | 89篇 |
1988年 | 71篇 |
1987年 | 42篇 |
1986年 | 35篇 |
1985年 | 16篇 |
1984年 | 16篇 |
1983年 | 11篇 |
1982年 | 10篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1970年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
In this paper, we propose a novel image recompression frame?work and image quality assessment (IQA) method to efficient?ly recompress Internet images. With this framework image size is significantly re... 相似文献
932.
Single event multiple-cell upsets (MCU) increase sharply with the semiconductor devices scaling. The impacts of several test factors on heavy ion single event MCU in 65 nm SRAM are studied based on the buildup of MCU test data acquiring and processing technique, including the heavy ion LET, the tilt angle, the device orientation, the test pattern and the supply voltage; the MCU physical bitmaps are extracted correspondingly. The dependencies of parameters such as the MCU percentage, MCU mean and topological pattern on these factors are summarized and analyzed. This work is meaningful for developing a more reasonable single event test method and assessing the effectiveness of anti-MCU strategies on nanometer-scale devices. 相似文献
933.
934.
分析1号变压器冷却器腐蚀渗漏油原因,采取有效措施解决盐雾对设备的腐蚀问题.通过盐雾试验,分别分析了盐雾腐蚀强度与工作环境温度、铝金属腐蚀速率的关系.结合盐雾腐蚀特点,对变压器冷却器进行全面检查,得出1号变压器冷却器渗漏油的主要原因是盐雾点腐蚀引起冷却器翘片和直管穿孔.提出的解决方法及防范措施为海边地区的设备选型与运维工作提供参考. 相似文献
935.
Catalytic hydrothermal liquefaction of D. tertiolecta for the production of bio‐oil over different acid/base catalysts 下载免费PDF全文
Yu Chen Yulong Wu Ranran Ding Pan Zhang Ji Liu Mingde Yang Pan Zhang 《American Institute of Chemical Engineers》2015,61(4):1118-1128
In this article, two acid catalysts (ZrO2/SO42? and HZSM‐5) and two base catalysts (MgO/MCM‐41 and KtB) were used in catalytic hydrothermal liquefaction (HTL) of Dunaliella tertiolecta (D. tertiolecta) for the production of bio‐oil. The results indicated that the acid/base property of the catalyst plays a crucial role in the catalytic HTL process, and the base catalyst is conducive to the improvement of conversion and bio‐oil yield. When KtB was used as the catalyst, the maximum conversion and bio‐oil yield was 94.84 and 49.09 wt %, respectively. The detailed compositional analysis of the bio‐oil was performed using thermogravimetric analysis, elemental analysis, FT‐IR, and GC‐MS. The compositional analysis results showed that the introduction of catalyst is beneficial for reducing the fixed carbon content in the bio‐oil, and the structure of catalyst influences on the bio‐oil composition and boiling point distribution. Based on our results and previous studies, the probable catalytic HTL microalgae model over various catalysts can be described that the main chemical reactions include ketonization, decarboxylic, dehydration, ammonolysis, and so forth. with HZSM‐5 and MgO/MCM‐41 as the catalyst; the cyclodimerization, decomposition, Maillard reaction, and ketonization are the main reactions with ZrO2/SO42? as the catalyst; the dehydration, ammonolysis, Maillard reaction, and ketonization can occur with KtB as the catalyst. Therefore, a plausible reaction mechanism of the main chemical component in D. tertiolecta is proposed. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1118–1128, 2015 相似文献
936.
937.
938.
为更深入地在微观角度上研究变压器绝缘纸老化机理,利用分子动力学仿真,对不同温度下纤维素无定形区的热力学性质进行了研究。结果表明:纤维素无定形区为各向同性弹性材料,其弹性系数和各模量随着模拟温度的升高均有减小的趋势,与晶区相比,温度对其影响较大;无定形区的刚性随温度升高出现较大减弱;随着温度升高,无定形区内氢键数量减少,并且分子内氢键数目较分子间氢键数目下降快。对比晶区内的氢键数目在相同模拟温度下的极小变化,可知纤维素的老化首先是从纤维素的无定形区内分子间的氢键被破坏开始的。随模拟温度的升高,纤维素分子链运动加剧,但其末端距无明显变化。温度对纤维素无定形区的力学性质和氢键的影响从分子层次上阐明了纤维素绝缘老化实验中结晶度升高及无不定形区先行老化的微观机理。 相似文献
939.
940.
Preparation of polyacrylamide grafted collagen extracted from leather wastes and their application in kaolin flocculation 下载免费PDF全文
This is probably the first report on the synthesis of a series of novel collagen‐based flocculants (CP11, CP12, and CP13) by grafting polyacrylamide (PAM) chains onto the collagen backbone, which was directly extracted from leather shavings via alkali hydrolysis. The results from FTIR, XRD, 1H NMR, and TGA well supported that PAM chains had been successfully grafted onto collagen backbone. In addition, the micrographs of SEM revealed that the PAM grafted collagen possessed much more porous and looser surface structures in comparison with virgin collagen. Zeta potential measurement showed that the introduction of branched PAM chains helped to improve the positively charge density. Furthermore, CP12 performed the best in the kaolin flocculation with the highest flocculation rate about 24%·min?1 and could induce the generation of much larger and denser floccs for the fast settling of kaolin particles. The corresponding flocculation mechanism was also presented by analyzing the collected flocs. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41556. 相似文献