全文获取类型
收费全文 | 25540篇 |
免费 | 1734篇 |
国内免费 | 1194篇 |
专业分类
电工技术 | 259篇 |
综合类 | 1263篇 |
化学工业 | 10416篇 |
金属工艺 | 4293篇 |
机械仪表 | 361篇 |
建筑科学 | 924篇 |
矿业工程 | 574篇 |
能源动力 | 1469篇 |
轻工业 | 2840篇 |
水利工程 | 200篇 |
石油天然气 | 1361篇 |
武器工业 | 92篇 |
无线电 | 561篇 |
一般工业技术 | 2279篇 |
冶金工业 | 1261篇 |
原子能技术 | 225篇 |
自动化技术 | 90篇 |
出版年
2024年 | 109篇 |
2023年 | 520篇 |
2022年 | 655篇 |
2021年 | 802篇 |
2020年 | 858篇 |
2019年 | 823篇 |
2018年 | 753篇 |
2017年 | 832篇 |
2016年 | 752篇 |
2015年 | 712篇 |
2014年 | 1147篇 |
2013年 | 1349篇 |
2012年 | 1401篇 |
2011年 | 1737篇 |
2010年 | 1300篇 |
2009年 | 1545篇 |
2008年 | 1349篇 |
2007年 | 1640篇 |
2006年 | 1476篇 |
2005年 | 1248篇 |
2004年 | 1064篇 |
2003年 | 948篇 |
2002年 | 816篇 |
2001年 | 749篇 |
2000年 | 657篇 |
1999年 | 427篇 |
1998年 | 405篇 |
1997年 | 325篇 |
1996年 | 345篇 |
1995年 | 224篇 |
1994年 | 212篇 |
1993年 | 201篇 |
1992年 | 183篇 |
1991年 | 165篇 |
1990年 | 142篇 |
1989年 | 81篇 |
1988年 | 58篇 |
1987年 | 60篇 |
1986年 | 52篇 |
1985年 | 49篇 |
1984年 | 48篇 |
1983年 | 21篇 |
1982年 | 42篇 |
1981年 | 36篇 |
1980年 | 31篇 |
1979年 | 20篇 |
1978年 | 24篇 |
1977年 | 18篇 |
1976年 | 17篇 |
1975年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
91.
介绍了以Ta/Ta2O5/Cu为结构的平板MIM电容器的制备方法和性能测试,探究金属Cu直接作为钽电解电容器阴极层的可行性。通过阳极氧化法在钽箔表面制备非晶态的Ta2O5薄膜,以化学镀铜、磁控溅射镀铜两种镀铜工艺制备Ta/Ta2O5/Cu结构,并对所得结构进行结构表征和性能测试。实验结果表明:不同镀铜方式制备的Ta/Ta2O5/Cu结构在电学性能测试过程中都没有表现出电容特性,正负极之间的电阻仅有0.7Ω;以金属Cu直接作为钽电容器的阴极层会导致金属铜在测试过程中被氧化成铜离子从而进入Ta2O5介质层中,进而导致Ta2O5的击穿,因此金属铜不适合直接作为钽电容的阴极层。 相似文献
92.
93.
Bin Yao Youzhou He Song Wang Hongfei Sun Xingyan Liu 《International journal of molecular sciences》2022,23(11)
Oxygen evolution reaction (OER) plays a pivotal role in the development of renewable energy methods, such as water-splitting devices and the use of Zn–air batteries. First-row transition metal complexes are promising catalyst candidates due to their excellent electrocatalytic performance, rich abundance, and cheap price. Metalloporphyrins are a class of representative high-efficiency complex catalysts owing to their structural and functional characteristics. However, OER based on porphyrin systems previously have been paid little attention in comparison to the well-described oxygen reduction reaction (ORR), hydrogen evolution reaction, and CO2 reduction reaction. Recently, porphyrin-based systems, including both small molecules and porous polymers for electrochemical OER, are emerging. Accordingly, this review summarizes the recent advances of porphyrin-based systems for electrochemical OER. Firstly, the electrochemical OER for water oxidation is discussed, which shows various methodologies to achieve catalysis from homogeneous to heterogeneous processes. Subsequently, the porphyrin-based catalytic systems for bifunctional oxygen electrocatalysis including both OER and ORR are demonstrated. Finally, the future development of porphyrin-based catalytic systems for electrochemical OER is briefly prospected. 相似文献
94.
Tong Gu Zhenghu Tong Xue Zhang Zhiyong Wang Zhen Zhang Tzann-Shun Hwang Lin Li 《International journal of molecular sciences》2022,23(11)
Mn(II)-oxidizing microorganisms are generally considered the primary driving forces in the biological formation of Mn oxides. However, the mechanistic elucidation of the actuation and regulation of Mn oxidation in soilborne bacteria remains elusive. Here, we performed joint multiple gene-knockout analyses and comparative morphological and physiological determinations to characterize the influence of carbon metabolism on the Mn oxide deposit amount (MnODA) and the Mn oxide formation of a soilborne bacterium, Escherichia coli MB266. Different carbon source substances exhibited significantly varied effects on the MnODA of MB266. A total of 16 carbon metabolism-related genes with significant variant expression levels under Mn supplementation conditions were knocked out in the MB266 genome accordingly, but only little effect on the MnODA of each mutant strain was accounted for. However, a simultaneous four-gene-knockout mutant (namely, MB801) showed an overall remarkable MnODA reduction and an initially delayed Mn oxide formation compared with the wild-type MB266. The assays using scanning/transmission electron microscopy verified that MB801 exhibited not only a delayed Mn-oxide aggregate processing, but also relatively smaller microspherical agglomerations, and presented flocculent deposit Mn oxides compared with normal fibrous and crystalline Mn oxides formed by MB266. Moreover, the Mn oxide aggregate formation was highly related to the intracellular ROS level. Thus, this study demonstrates that carbon metabolism acts as a pronounced modulator of MnODA in MB266, which will provide new insights into the occurrence of Mn oxidation and Mn oxide formation by soilborne bacteria in habitats where Mn(II) naturally occurs. 相似文献
95.
96.
Marta Valkov Pavel Letinský Lenka Matjov Kateina Klemencov Michal Ritz Christian Schimpf Mykhailo Motylenko David Rafaja Jakub Blík 《International journal of molecular sciences》2022,23(15)
Hematite (α-Fe2O3) catalysts prepared using the precipitation methods was found to be highly effective, and therefore, it was studied with methane (CH4), showing an excellent stable performance below 500 °C. This study investigates hematite nanoparticles (NPs) obtained by precipitation in water from the precursor of ferric chloride hexahydrate using precipitating agents NaOH or NH4OH at maintained pH 11 and calcined up to 500 °C for the catalytic oxidation of low concentrations of CH4 (5% by volume in air) at 500 °C to compare their structural state in a CH4 reducing environment. The conversion (%) of CH4 values decreasing with time was discussed according to the course of different transformation of goethite and hydrohematites NPs precursors to magnetite and the structural state of the calcined hydrohematites. The phase composition, the size and morphology of nanocrystallites, thermal transformation of precipitates and the specific surface area of the NPs were characterized in detail by X-ray powder diffraction, transmission electron microscopy, infrared spectroscopy, thermal TG/DTA analysis and nitrogen physisorption measurements. The results support the finding that after goethite dehydration, transformation to hydrohematite due to structurally incorporated water and vacancies is different from hydrohematite α-Fe2O3. The surface area SBET of Fe2O3_NH-70 precipitate composed of protohematite was larger by about 53 m2/g in comparison with Fe2O3_Na-70 precipitate composed of goethite. The oxidation of methane was positively influenced by the hydrohematites of the smaller particle size and the largest lattice volume containing structurally incorporated water and vacancies. 相似文献
97.
98.
采用溶胶凝胶-喷雾干燥法制备微球TiO2,其粒径为0.5~3μm,平均沉淀速度为5mm/s,为晶体粒径为8.3nm的锐钛型纳米TiO2的聚合体,比表面积较大。具有与纳米TiO2相似的催化活性,较好地解决了催化剂活性和分离之间的矛盾。 相似文献
99.
F.J. Liu M.C. Zhang J.X. Dong Y. W. Zhang 《金属学报(英文版)》2007,20(2):102-110
High temperature oxidation behaviors of FGH96 P/M superalloy have been studied in air at temperatures ranging from 600 to 1000℃. By means of isothermal oxidation testing,X-ray diffraction,SEM(scanning electron microscopy),and EDS(energy dispersive X-ray spectroscopy) analyses,the oxidation kinetics as well as the composition and morphology of scales were investigated. Thermodynamic calculations were used to explain the oxidation mechanism. The results showed that as the oxidation temperature increased,the oxidation rate,the scale thickness,and scale spallation increased. FGH96 P/M superalloy exhibits good oxidation resistance at temperature below 800℃. The oxidation kinetics follows an approximately parabolic rate law,and the oxide layer was mainly composed of Cr2O3,TiO2,and a little amount of NiCr2O4. The oxidation is controlled by the transmission of chromium,titanium,and oxygen through the oxide scale. 相似文献
100.