全文获取类型
收费全文 | 2657篇 |
免费 | 309篇 |
国内免费 | 174篇 |
专业分类
电工技术 | 61篇 |
综合类 | 138篇 |
化学工业 | 766篇 |
金属工艺 | 207篇 |
机械仪表 | 28篇 |
建筑科学 | 13篇 |
矿业工程 | 16篇 |
能源动力 | 213篇 |
轻工业 | 17篇 |
水利工程 | 1篇 |
石油天然气 | 8篇 |
武器工业 | 5篇 |
无线电 | 633篇 |
一般工业技术 | 799篇 |
冶金工业 | 163篇 |
原子能技术 | 31篇 |
自动化技术 | 41篇 |
出版年
2024年 | 1篇 |
2023年 | 64篇 |
2022年 | 84篇 |
2021年 | 74篇 |
2020年 | 104篇 |
2019年 | 172篇 |
2018年 | 168篇 |
2017年 | 136篇 |
2016年 | 98篇 |
2015年 | 107篇 |
2014年 | 138篇 |
2013年 | 122篇 |
2012年 | 148篇 |
2011年 | 215篇 |
2010年 | 144篇 |
2009年 | 158篇 |
2008年 | 118篇 |
2007年 | 137篇 |
2006年 | 147篇 |
2005年 | 117篇 |
2004年 | 100篇 |
2003年 | 88篇 |
2002年 | 73篇 |
2001年 | 58篇 |
2000年 | 51篇 |
1999年 | 49篇 |
1998年 | 44篇 |
1997年 | 39篇 |
1996年 | 35篇 |
1995年 | 36篇 |
1994年 | 30篇 |
1993年 | 22篇 |
1992年 | 20篇 |
1991年 | 10篇 |
1990年 | 11篇 |
1989年 | 9篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1985年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有3140条查询结果,搜索用时 31 毫秒
101.
采用高温固相反应法制备了一系列镝离子掺杂Bi2ZnB2O7(BZBO)光催化剂。通过XRD、TEM和HRTEM等手段对BZBO: xDy3+材料的结构及形貌等进行了表征,通过RhB溶液在紫外灯下的光降解实验研究了不同浓度镝离子掺杂对BZBO光催化性能的影响。RhB光降解实验结果表明,当Dy3+在BZBO中的掺杂量为4%时,BZBO: 4%Dy3+具有最好的光降解活性,其光降解活性为纯BZBO的1.56倍。通过光吸收性能分析可知,Dy3+的引入增强了BZBO的紫外吸收强度,并稍降低了其禁带宽度。光吸收性能、光致发光光谱、光电流和EIS实验结果表明,BZBO: 4%Dy3+的光催化活性增强的主要原因是BZBO中掺杂的镝不仅提高了BZBO光催化剂的光吸收能力,更促进了光生电子-空穴对的分离和转移。因此,在稀土元素和极化电场的作用下,BZBO: 4%Dy3+的光催化活性要高于其他所制备的样品。 相似文献
102.
Andreja Žužić Filip Car Jelena Macan Vesna Tomašić Andreja Gajović 《International Journal of Applied Ceramic Technology》2022,19(5):2891-2904
Strontium-doped lanthanum manganites, La1-xSrxMnO3 (LSMO), are promising and affordable catalysts for oxidative degradation of volatile organic compounds. LSMO catalysts (x = 0, .1, .2, and .3) were prepared by the citrate-nitrate autocombustion (CNA) and coprecipitation synthesis. The phase composition was confirmed by X-ray diffraction and Rietveld refinement analysis, while the oxygen content was determined by Mohr's salt permanganate titration. Morphology and porosity of prepared catalysts was correlated to catalytic oxidation of benzene, toluene, ethylbenzene and o-xylene. It was observed that both synthesis methods yielded catalysts of similar average pore size diameter and specific surface area, but the pore size distribution differed: CNA-prepared catalysts had a multimodal pore size distribution, while the coprecipitated ones had a single maximum at 4 nm. Catalysts prepared by the CNA method have shown a higher catalytic activity in the temperature range 373–723 K, as the presence of Mn3+/Mn4+ mixed valences increased their reducibility. 相似文献
103.
Kumar Siddharth Yian Wang Jing Wang Fei Xiao Gabriel Sikukuu Nambafu Usman Bin Shahid Fei Yang Ernest Pahuyo Delmo Minhua Shao 《Frontiers of Chemical Science and Engineering》2022,16(6):930
Ammonia electrooxidation reaction involving multistep electron-proton transfer is a significant reaction for fuel cells, hydrogen production and understanding nitrogen cycle. Platinum has been established as the best electrocatalyst for ammonia oxidation in aqueous alkaline media. In this study, Pt/nitrogen-doped graphene (NDG) and Pt/tungsten monocarbide (WC)/NDG are synthesized by a wet chemistry method and their ammonia oxidation activities are compared to commercial Pt/C. Pt/NDG exhibits a specific activity of 0.472 mA∙cm–2, which is 44% higher than commercial Pt/C, thus establishing NDG as a more effective support than carbon black. Moreover, it is demonstrated that WC as a support also impacts the activity with further 30% increase in comparison to NDG. Surface modification with Ir resulted in the best electrocatalytic activity with Pt-Ir/WC/NDG having almost thrice the current density of commercial Pt/C. This work adds insights regarding the role of NDG and WC as efficient supports along with significant impact of Ir surface modification. 相似文献
104.
以Ce掺杂的TiO2粉体为载体,MNOx为活性组分,制备了MNOx/Ce-TiO2体系SCR催化剂,利用TG-DSC,XRD,SEM及EDS考察了Ce的掺杂对MNOx/TiO2体系活性的影响,采用模拟烟气分析装置测试催化剂的活性。结果表明:Ce离子的掺杂阻碍了TiO2粒子由锐钛矿型向金红石型的转变,拓宽了锐钛矿型TiO2的使用温度范围。TiO2粉体粒子在锐钛矿型状态下,颗粒分散较为均匀,并且无明显团聚现象,保证了较高的比表面积,催化剂的SCR催化活性比未掺杂的催化剂活性有明显的提高。 相似文献
105.
106.
107.
Amalia Mesaros Cristina D. Ghitulica Mihaela Popa Raluca Mereu Adriana Popa Traian Petrisor Jr. Mihai Gabor Adrian Ionut Cadis Bogdan S. Vasile 《Ceramics International》2014
Zn1−xCoxO (x==0.05, 0.10, 0.15) nanoparticles have been synthesized by an alternative wet-chemical synthesis route using the SimAdd technique. The as-obtained powders were investigated by FT-IR spectroscopy, X-ray diffraction and thermal analysis correlated with evolved gas analysis (TG–DTA–FT-IR) in order to determine their chemical nature, crystalline structure and to establish the decomposition sequences. The precipitates are generally amorphous, but low-intensity reflection peaks assigned both to the zinc oxalate dihydrate, and zinc hydroxide can be observed in the recorded patterns, indicating that hydroxy-oxalate precipitates were obtained. The structure, morphology and magnetic properties of the thermally treated samples have been investigated by X-ray diffraction, FT-IR, HRTEM, SAED, UV–vis and EPR. XRD studies reveal a hexagonal wurtzite-type structure for all Zn1−xCoxO samples. TEM investigations show particle size between 28 and 37 nm, with spherical and polyhedral shapes and with tendency to form aggregates. The presence of a Co3O4 secondary phase was evidenced by XRD, UV–vis and EPR for the Zn0.85Co0.15O sample. The ferromagnetic behavior of the samples was revealed. The paper highlights that by varying the cobalt concentration it is possible to modulate the structural, morphological, optical and magnetic properties. 相似文献
108.
《Journal of the European Ceramic Society》2014,34(10):2217-2227
The point defects and the structural and dielectric properties of Dy-doped BaTiO3 ceramics prepared at 1400 °C were investigated. The solubility of Dy in the self-compensation mode was determined to be x = 0.07 for (Ba1−xDyx)(Ti1−xDyx)O3, and no EPR signals associated with the Dy3+ Kramers ion or the Ba and Ti vacancies were detected using the electron paramagnetic resonance (EPR) technique. As x increases, the dielectric behavior changed from a first-order phase transition to a diffuse phase transition to a Y7R dielectric-temperature stability. A strong EPR signal at g = 1.974, which is rare among rare-earth-doped BaTiO3 ceramics appeared unexpectedly in the single-phase (Ba1−xDyx)Ti1−x/4O3 ceramics with deliberately designed Ti vacancies. This signal was attributed to ionized Ba vacancy defects. A preference for the self-compensation mode of Dy3+ ions is responsible for the appearance of Ba vacancies. The real formula of the nominal (Ba1−xDyx)Ti1−x/4O3 is expressed as (Ba1−xDy3x/4)(Ti1−x/4Dyx/4)O3. In addition, the defect chemistry is discussed. 相似文献
109.
以碘掺杂聚苯胺为催化剂,对叔丁醇与乙酸酐之间的酰化反应进行了研究,考察了反应温度、反应时间、催化剂质量分数以及酐醇摩尔比对乙酸叔丁酯收率的影响。实验结果表明,碘掺杂聚苯胺有着较好的催化活性,当反应条件为:反应温度为55℃,反应时间为6 h,酐醇摩尔比为1∶1,催化剂质量分数为7.0%时乙酸叔丁酯的分离收率可达到87.6%,且所得产品无色透明。产品经红外光谱进行了表征。 相似文献
110.
在水/甲苯/十二烷基磺酸(DBSA)体系中采用乳化剂复配技术乳液合成工艺,能显著改善聚苯胺的溶解性能.在确定DBSA/苯胺、过硫酸铵/苯胺的量的合理比例及过硫酸铵的最佳滴加时间的基础上,乳液合成聚苯胺.产物的红外光谱、X射线衍射、热重-差热、光电子能谱测试和分析表明:DBSA对PANI进行了有效的掺杂,产物的主要结构为M acD iarm id完全掺杂态,且醌式结构的氮原子全部质子化.聚合物具有一定的结晶性,热稳定性好,但易被空气氧化,溅射条件对聚合物有明显脱掺杂影响.产物的产率成倍提高,PAN-DBSA已经部分晶化并具有很高的热稳定性. 相似文献