全文获取类型
收费全文 | 49242篇 |
免费 | 3918篇 |
国内免费 | 2035篇 |
专业分类
电工技术 | 2596篇 |
技术理论 | 8篇 |
综合类 | 3029篇 |
化学工业 | 8642篇 |
金属工艺 | 2709篇 |
机械仪表 | 3228篇 |
建筑科学 | 3701篇 |
矿业工程 | 1709篇 |
能源动力 | 1430篇 |
轻工业 | 2766篇 |
水利工程 | 781篇 |
石油天然气 | 3859篇 |
武器工业 | 443篇 |
无线电 | 5324篇 |
一般工业技术 | 5909篇 |
冶金工业 | 2490篇 |
原子能技术 | 489篇 |
自动化技术 | 6082篇 |
出版年
2024年 | 242篇 |
2023年 | 910篇 |
2022年 | 1486篇 |
2021年 | 2014篇 |
2020年 | 1566篇 |
2019年 | 1325篇 |
2018年 | 1490篇 |
2017年 | 1647篇 |
2016年 | 1463篇 |
2015年 | 1932篇 |
2014年 | 2370篇 |
2013年 | 2898篇 |
2012年 | 2938篇 |
2011年 | 3314篇 |
2010年 | 2767篇 |
2009年 | 2683篇 |
2008年 | 2765篇 |
2007年 | 2526篇 |
2006年 | 2602篇 |
2005年 | 2289篇 |
2004年 | 1438篇 |
2003年 | 1350篇 |
2002年 | 1224篇 |
2001年 | 1099篇 |
2000年 | 1212篇 |
1999年 | 1428篇 |
1998年 | 1126篇 |
1997年 | 947篇 |
1996年 | 848篇 |
1995年 | 763篇 |
1994年 | 632篇 |
1993年 | 471篇 |
1992年 | 360篇 |
1991年 | 262篇 |
1990年 | 220篇 |
1989年 | 152篇 |
1988年 | 136篇 |
1987年 | 87篇 |
1986年 | 63篇 |
1985年 | 35篇 |
1984年 | 29篇 |
1983年 | 31篇 |
1982年 | 24篇 |
1981年 | 15篇 |
1980年 | 11篇 |
1979年 | 4篇 |
1978年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Gui-Jia Gao Mei-Qi Zeng En-Liang Zhang Rong-Chang Zeng Lan-Yue Cui Dao-kui Xu Feng-Qin Wang M.Bobby Kannan 《材料科学技术学报》2021,83(24):161-178
The microstructure and chemical compositions of the solid solution-treated Mg-3Nd-1Li-0.2Zn alloy were characterized using optical microscope,scanning electron microscope(SEM),transmission electron microscope(TEM),electron probe micro-analyzer(EPMA)and X-ray photoelectron spectroscopy(XPS).The corrosion behaviour of the alloy was investigated via electrochemical polarization,electrochemical impedance spectroscopy(EIS),hydrogen evolution test and scanning Kelvin probe(SKP).The results showed that the microstructure of the as-extruded Mg-3Nd-1Li-0.2Zn alloy contained α-Mg matrix and nanometric second phase Mg41 Nd5.The grain size of the alloy increased significantly with the increase in the heat-treatment duration,whereas the volume fraction of the second phase decreased after the solid solution treatment.The surface film was composed of oxides(Nd2O3,MgO,Li2O and ZnO)and carbonates(MgCO3 and Li2CO3),in addition to Nd.The as-extruded alloy exhibited the best corrosion resistance after an initial soaking of 10 min,whereas the alloy with 4h-solution-treatment possessed the lowest corrosion rate after a longer immersion(1 h).This can be attributed to the formation of Nd-containing oxide film on the alloys and a dense corrosion product layer.The dealloying corrosion of the second phase was related to the anodic Mg41Nd5 with a more negative Volta potential relative to α-Mg phase.The preferential corrosion of Mg41Nd5 is proven by in-situ observation and SEM.The solid solution treatment of Mg-3Nd-1Li-0.2Zn alloy led to a shift in corrosion type from pitting corrosion to uniform corrosion under long-term exposure. 相似文献
992.
993.
DNA methylation is one of the major epigenetic modifications and has been involved in a number of biological processes in mammalian cells. Yeast is widely used as a model organism for studying cell metabolism, cell cycle regulation, and signal transduction. However, it remains controversial whether methylated cytosine (5-methylcytosine, 5mC) exists in the yeast genome. In the current study, we developed a highly sensitive method based on gas chromatography/mass spectrometry (GC/MS) and systematically examined the incidence of 5mC in 19 yeast strains, which represent 16 yeast species. Our results showed that DNA methylation is widespread in yeast and the genome-wide DNA methylation of the studied yeast strains ranged from 0.014 to 0.364%, which were 1 to 2 orders of magnitude lower than that in mammalian cells (i.e., 3-8%). Furthermore, we found that the 5mC content in yeast varied considerably at different growth stages and DNA methylation inhibitor 5-azacytidine could induce a decrease in genome-wide DNA methylation as that in mammalian cells. The demonstration of the universal presence of DNA cytosine methylation in yeast constituted the first and essential step toward understanding the functions of this methylation in yeast. 相似文献
994.
阴离子本体开环聚合反应挤出合成聚三氟丙基甲基硅氧烷 总被引:4,自引:0,他引:4
以同向紧啮合双螺杆挤出机为反应器,硅醇钠/乙酸乙酯(EA)为引发体系,通过三氟丙基甲基环三硅氧烷(F3)阴离子本体开环聚合,制备了聚三氟丙基甲基硅氧烷(PMTFPS)。采用红外光谱(FT-IR),核磁共振(1H-NMR)和凝胶渗透色谱(GPC)确认了聚合物的结构与分子量,用电离飞行时间质谱分析了副产物的组成。研究表明,提高反应温度和EA用量可使反应平衡点提前到达。而螺杆转速对反应的主要影响在于改变聚合反应时间。因此,控制适当反应条件,使反应在平衡点到来时间之前终止,可得到高分子量以及高收率的PMTFPS。所得产物的数均分子量为2.41×105,分子量分散指数为1.12,产率为90.5%。 相似文献
995.
Alumina‐Supported CoFe Alloy Catalysts Derived from Layered‐Double‐Hydroxide Nanosheets for Efficient Photothermal CO2 Hydrogenation to Hydrocarbons 下载免费PDF全文
Guangbo Chen Rui Gao Yufei Zhao Zhenhua Li Geoffrey I. N. Waterhouse Run Shi Jiaqing Zhao Mengtao Zhang Lu Shang Guiyang Sheng Xiangping Zhang Xiaodong Wen Li‐Zhu Wu Chen‐Ho Tung Tierui Zhang 《Advanced materials (Deerfield Beach, Fla.)》2018,30(3)
A series of novel CoFe‐based catalysts are successfully fabricated by hydrogen reduction of CoFeAl layered‐double‐hydroxide (LDH) nanosheets at 300–700 °C. The chemical composition and morphology of the reaction products (denoted herein as CoFe‐x) are highly dependent on the reduction temperature (x). CO2 hydrogenation experiments are conducted on the CoFe‐x catalysts under UV–vis excitation. With increasing LDH‐nanosheet reduction temperature, the CoFe‐x catalysts show a progressive selectivity shift from CO to CH4, and eventually to high‐value hydrocarbons (C2+). CoFe‐650 shows remarkable selectivity toward hydrocarbons (60% CH4, 35% C2+). X‐ray absorption fine structure, high‐resolution transmission electron microscopy, Mössbauer spectroscopy, and density functional theory calculations demonstrate that alumina‐supported CoFe‐alloy nanoparticles are responsible for the high selectivity of CoFe‐650 for C2+ hydrocarbons, also allowing exploitation of photothermal effects. This study demonstrates a vibrant new catalyst platform for harnessing clean, abundant solar‐energy to produce valuable chemicals and fuels from CO2. 相似文献
996.
997.
998.
Co3O4 Hexagonal Platelets with Controllable Facets Enabling Highly Efficient Visible‐Light Photocatalytic Reduction of CO2
下载免费PDF全文
999.
文章从洗涤性能、环境和成本方面,阐述了生物酶能够优化洗涤剂配方的可能性.鉴于新兴市场愈发受人瞩目,且液体洗涤剂正经历高速增长,因此研究重点放在面向亚太市场的液体洗涤产品.结果表明,使用酶作为表面活性剂的替代品可以提升去污效果、让洗涤剂更绿色,且不会导致成本增加.原因在于,酶的使用量要比它所替代的表面活性剂少得多,而酶的... 相似文献
1000.