首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   7946篇
  免费   763篇
  国内免费   593篇
电工技术   261篇
综合类   392篇
化学工业   1761篇
金属工艺   1784篇
机械仪表   103篇
建筑科学   27篇
矿业工程   93篇
能源动力   518篇
轻工业   83篇
水利工程   2篇
石油天然气   60篇
武器工业   39篇
无线电   1440篇
一般工业技术   2191篇
冶金工业   401篇
原子能技术   48篇
自动化技术   99篇
  2024年   4篇
  2023年   305篇
  2022年   303篇
  2021年   443篇
  2020年   404篇
  2019年   402篇
  2018年   336篇
  2017年   378篇
  2016年   283篇
  2015年   310篇
  2014年   395篇
  2013年   423篇
  2012年   475篇
  2011年   642篇
  2010年   397篇
  2009年   473篇
  2008年   384篇
  2007年   469篇
  2006年   435篇
  2005年   302篇
  2004年   311篇
  2003年   206篇
  2002年   231篇
  2001年   162篇
  2000年   155篇
  1999年   101篇
  1998年   88篇
  1997年   76篇
  1996年   58篇
  1995年   48篇
  1994年   55篇
  1993年   46篇
  1992年   37篇
  1991年   42篇
  1990年   32篇
  1989年   18篇
  1988年   16篇
  1987年   4篇
  1986年   9篇
  1985年   4篇
  1984年   7篇
  1983年   3篇
  1982年   9篇
  1981年   5篇
  1980年   4篇
  1979年   5篇
  1977年   2篇
  1976年   2篇
  1975年   3篇
排序方式: 共有9302条查询结果,搜索用时 15 毫秒
1.
To improve the safety of wet dust removal systems for processing magnesium-based alloys, a new method is proposed for preventing hydrogen generation. In this paper, hydrogen generation by Mg–Zn alloy dust was inhibited with six common metal corrosion inhibitors. The results showed that sodium dodecylbenzene sulfonate was the best hydrogen inhibitor, while CeCl3 enhanced hydrogen precipitation. The film-forming stability of sodium dodecylbenzene sulfonate was tested with different contents, temperatures, Cl? concentrations and perturbation rates. The results showed that this inhibitor formed stable protective films on the surfaces of Mg–Zn alloy particles, and adsorption followed the Langmuir adsorption model.  相似文献   
2.
MgB2 superconductor pellets were synthesized through Mg gas infiltration method using nanosized- and microsized B powders. There was a marked difference in the superconducting properties of the two samples, particularly in the pinning force and dominant pinning mechanism. The microstructures of the samples were observed using HR-TEM and STEM-HAADF, and the results showed that the primary reason for the difference in the superconducting properties is the distribution of the nanosized second-phase particle MgO. Additionally, a feasible reaction model for the Mg gas infiltration method was established. Compared to the Mg liquid infiltration method, the gas infiltration showed better penetrability ability with a small amount of residual Mg. This study presents a novel synthesis process to fabricate an MgB2 pellet with superior density and superconducting properties. This method can be used in multiple applications such as superconducting bearings, compact superconductor magnets, and magnetic shielding.  相似文献   
3.
采用铸造法制备原位自生亚共晶Al-10Mg2Si复合材料,研究Cu和T6热处理对该复合材料组织与力学性能的影响。结果表明:适量Cu的添加能显著减小共晶Mg2Si相晶粒尺寸,使其晶体结构由粗大的长条状和汉字状转变为细小的条状和纤维状;同时使针状的β-Al5Fe Si相转变为细小的不规则富Cu颗粒。经T6热处理后,质量分数为1.5%的Cu复合材料中的共晶Mg2Si相完全球化。质量分数为1.5%的Cu添加同时提高了材料铸态下的抗拉强度(Rm)、屈服强度(Rp0.2)和伸长率(A),达317、169 MPa和2.3%,比未添加Cu提高了42.2%、24.3%和53.3%;经T6热处理的Rm和Rp0.2值分别增至332、181 MPa,而A值保持不变。同时,材料由脆性断裂完全转变为韧性断裂。  相似文献   
4.
Oxygen evolution reaction (OER) plays a decisive role in electrolytic water splitting. However, it is still challengeable to develop low-cost and efficient OER electrocatalysts. Herein, we present a combination strategy via heteroatom doping, hetero-interface engineering and introducing conductive skeleton to synthesize a hybrid OER catalyst of CNT-interconnected iron-doped NiP2/Ni2P (Fe-(NiP2/Ni2P)@CNT) heterostructural nanoflowers by a simple hydrothermal reaction and subsequent phosphorization process. The optimized Fe-(NiP2/Ni2P)@CNT catalyst delivers an ultralow Tafel slope of 46.1 mV dec?1 and overpotential of 254 mV to obtain 10 mA cm?2, which are even better than those of commercial OER catalyst RuO2. The excellent OER performance is mainly attributed to its unique nanoarchitecture and the synergistic effects: the nanoflowers constructed by a 2D-like nanosheets guarantee large specific area and abundant active sites; the highly conductive CNT skeleton and the electronic modulation by the heterostructural NiP2/Ni2P interface and the hetero-atom doping can improve the catalytic activity; porous nanostructure benefits electrolyte penetration and gas release; most importantly, the rough surface and rich defects caused by phosphorization process can further enhance the OER performance. This work provides a deep insight to boost catalytic performance by heteroatom doping and interface engineering for water splitting.  相似文献   
5.
制备了Mg改性Cr2O3/Al2O3催化剂,利用XRD,UV-Vis,XPS,H2-TPR,NH3-TPD,TG等方法考察了新鲜和再生后催化剂的结构与性能。实验结果表明,助剂Mg的添加有利于催化剂再生后的物相结构稳定;随再生次数的增加,催化剂孔径增大,比表面积降低,催化剂表面Cr6+含量降低,Cr6+组分逐渐不可逆还原为Cr3+等稳定状态;催化剂表面主要为弱酸和中强酸,随再生次数的增加,酸量减少,但酸强度增加,Cr物种价态及其与载体的相互作用影响了表面酸性进而影响了催化剂活性;新鲜催化剂催化活性略高于再生催化剂,经多次再生后催化剂性能趋于稳定,丙烷转化率稳定在30%左右,丙烯选择性在88%以上。  相似文献   
6.
以盐酸胍为前驱体,硝酸锆为锆源,通过热聚合法制备了Zr掺杂的Zr/g-C3N4光催化剂。运用XRD、SEM、UV-Vis DRS、PL、XPS、BET等手段对催化剂的结构、形貌、光学性能进行了表征分析。结果表明:Zr掺杂改性的Zr/g-C3N4光催化剂拓宽了可见光的吸收,增大了比表面积,且降低了光生电子-空穴的复合率,具有较好的光催化活性。可见光照射下,在60 min内,5Zr/g-C3N4对罗丹明B(RhB)的光催化降解率达99.29%,光催化降解过程符合一级动力学方程,其速率常数k= 0.08647 min-1,是纯g-C3N4的8.3倍。捕获剂实验发现降解RhB的主要活性物种为超氧自由基,并推测了可能的反应机理。  相似文献   
7.
为提高催化剂抗砷能力,采用密度泛函理论(DFT)方法研究As2O3在α-Fe2O3(001)表面的吸附行为以及掺杂Mo、Mn、Ni对α-Fe2O3(001)表面As2O3吸附行为的影响。建立As2O3在α-Fe2O3(001)表面吸附模型和Mo、Mn、Ni掺杂的吸附模型,计算As2O3在催化剂表面的吸附能,分析成键态密度以及掺杂前后的As2O3在α-Fe2O3(001)表面的电荷布局。结果表明:这4种体系均发生电子转移,Mo掺杂活化了As2O3分子,使得As2O3倾向于吸附在Mo活性位点上,保护了Fe活性位点,...  相似文献   
8.
Non-noble metal catalyst with high catalytic activity and stability towards oxygen reduction reaction (ORR) is critical for durable bioelectricity generation in air-cathode microbial fuel cells (MFCs). Herein, nitrogen-doped (iron-cobalt alloy)/cobalt/cobalt phosphide/partly-graphitized carbon ((FeCo)/Co/Co2P/NPGC) catalysts are prepared by using cornstalks via a facile method. Carbonization temperature exerts a great effect on catalyst structure and ORR activity. FeCo alloys are in-situ formed in the catalysts above 900 °C, which are considered as the highly-active component in catalyzing ORR. AC-MFC with FeCo/Co/Co2P/NPGC (950 °C) cathode shows the highest power density of 997.74 ± 5 mW m?2, which only declines 8.65% after 90 d operation. The highest Coulombic efficiency (23.3%) and the lowest charge transfer resistance (22.89 Ω) are obtained by FeCo/Co/Co2P/NPGC (950 °C) cathode, indicating that it has a high bio-electrons recycling rate. Highly porous structure (539.50 m2 g?1) can provide the interconnected channels to facilitate the transport of O2. FeCo alloys promote charge transfer and catalytic decomposition of H2O2 to ?OH and ?O2?, which inhibits cathodic biofilm growth to improve ORR durability. Synergies between metallic components (FeCo/Co/Co2P) and N-doped carbon energetically improve the ORR catalytic activity of (FeCo)/Co/Co2P/NPGC catalysts, which have the potential to be widely used as catalysts in MFCs.  相似文献   
9.
10.
Photocatalytic technology can solve various environmental pollution problems, especially antibiotic pollution. A novel La-doped MIL-53(Al)/ZnO composite material was successfully synthesized by a combination of hydrothermal method and calcination, showing high photocatalytic degradation percent of sulfamethazine (SMT). The 2 mol% La MIL-53(Al)/ZnO photocatalyst shows the highest degradation efficiency toward SMT (92%) within 120 min, which is 4.1 times higher than pure ZnO (increased from 18% to 92%). In addition, the degradation analysis of SMT by high performance liquid chromatography proves that the products are CO2 and H2O. The improved photocatalytic activity is mostly caused by the following factors. (1) Doping La ions can decrease the band gap of ZnO, enhance light response, and effectively enhance the separation rate of photo-generated holes and electrons. (2) MIL-53(Al) can adsorb SMT and promote the separation of electron. This work shows that the synthesized La-doped MIL-53(Al)/ZnO photocatalyst is expected to be used as a green and effective method for treatment of environment water pollution.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号