全文获取类型
收费全文 | 10504篇 |
免费 | 1080篇 |
国内免费 | 667篇 |
专业分类
电工技术 | 644篇 |
综合类 | 1048篇 |
化学工业 | 1479篇 |
金属工艺 | 1573篇 |
机械仪表 | 202篇 |
建筑科学 | 1334篇 |
矿业工程 | 671篇 |
能源动力 | 207篇 |
轻工业 | 222篇 |
水利工程 | 586篇 |
石油天然气 | 278篇 |
武器工业 | 56篇 |
无线电 | 439篇 |
一般工业技术 | 968篇 |
冶金工业 | 2271篇 |
原子能技术 | 76篇 |
自动化技术 | 197篇 |
出版年
2024年 | 40篇 |
2023年 | 179篇 |
2022年 | 272篇 |
2021年 | 294篇 |
2020年 | 354篇 |
2019年 | 247篇 |
2018年 | 251篇 |
2017年 | 262篇 |
2016年 | 294篇 |
2015年 | 285篇 |
2014年 | 447篇 |
2013年 | 445篇 |
2012年 | 613篇 |
2011年 | 703篇 |
2010年 | 574篇 |
2009年 | 564篇 |
2008年 | 525篇 |
2007年 | 627篇 |
2006年 | 681篇 |
2005年 | 621篇 |
2004年 | 535篇 |
2003年 | 566篇 |
2002年 | 438篇 |
2001年 | 425篇 |
2000年 | 354篇 |
1999年 | 304篇 |
1998年 | 249篇 |
1997年 | 202篇 |
1996年 | 187篇 |
1995年 | 167篇 |
1994年 | 127篇 |
1993年 | 102篇 |
1992年 | 88篇 |
1991年 | 63篇 |
1990年 | 46篇 |
1989年 | 34篇 |
1988年 | 20篇 |
1987年 | 23篇 |
1986年 | 13篇 |
1985年 | 6篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1975年 | 1篇 |
1959年 | 1篇 |
1957年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
《Ceramics International》2022,48(8):10885-10894
Lead-free bismuth sodium titanate-strontium titanate (NBT-ST) dielectric ceramic materials have been extensively investigated energy storage materials because of their relaxor characteristics. In this study, four different lanthanide elements were introduced into the ferroelectric NBT-ST ceramic to improve their relaxor properties. The introduction of the lanthanide resulted in an increase in disorder at location A within the perovskite lattice and improved relaxor characteristics, leading to a stored energy density of more than 3.5 J/cm3. In particular, an ultrahigh recoverable stored energy density of 4.94 J/cm3 and efficiency of 88.45% were achieved at 440 kV/cm when the NBT-ST ceramic was modified with neodymium. The modified ceramic also exhibited good thermal stability in the range of 30–120 °C, as well as a fast discharge time of ~153 ns, indicating that Nd-incorporated NBT-ST is a promising candidate for electrical energy storage ceramic. 相似文献
3.
Power transformers are protected by different relays that operate independently. Malfunction of each relay has a major role in reducing the reliability of the protection system. In order to mitigate the main drawbacks of the power transformer relays, an overall protection scheme is presented in this paper. This scheme proposes a novel multi criterion algorithm using decision-making based on fuzzy logic. In this paper the outputs of restricted earth fault relay and a directional check unit, are combined with the output of the differential protection relay. Therefore, problems that are pertaining to independent operation of each relay have been mitigated and the relays cover protection blind spots of each other. The improved power transformer protection (IPTP) scheme enhances the sensitivity and reliability of the power transformer protection. Extensive simulations are used to measure the effectiveness and merit of the proposed IPTP relay. The above efforts result in a multi criteria approach for protection of power transformers. 相似文献
4.
O.N. Kondrateva G.E. Nikiforova A.V. Tyurin M.A. Ryumin V.M. Gurevich A.P. Kritskaya K.S. Gavrichev 《Ceramics International》2018,44(15):18103-18107
The heat capacity of ytterbium orthovanadate was first measured by adiabatic calorimetry in the temperature range T?=?12.28–344.06?K. No obvious anomalies were observed on the curve obtained. The values of standard thermodynamic functions in the temperature range T?=?0–400 K were calculated. Based on low-temperature calorimetry data obtained, previously published data on the high-temperature heat capacity of ytterbium orthovanadate were corrected. The anomalous contribution to heat capacity for YbVO4 was compared with the data known for YbPO4. 相似文献
5.
Milli Suchita Kujur Vyasaraj Manakari Gururaj Parande Khin Sandar Tun Ashis Mallick Manoj Gupta 《Ceramics International》2018,44(13):15035-15043
Magnesium (Mg)-based nanocomposites owing to their low density and biocompatibility are being targeted for transportation and biomedical sectors. In order to support a sustainable environment, the prime aim of this study was to develop non-toxic magnesium-based nanocomposites for a wide spectrum of applications. To support this objective, cerium oxide nanoparticles (0.5?vol%, 1?vol%, and 1.5?vol%) reinforced Mg composites are developed in this study using blend-press-sinter powder metallurgy technique. The microstructural studies exhibited limited amounts of porosity in Mg and Mg-CeO2 samples (< 1%). Increasing presence of CeO2 nanoparticles (up to 1.5?vol%) led to a progressive increase in microhardness, dimensional stability, damping capacity and ignition resistance of magnesium. The compressive strengths increased with the increasing addition of the nanoparticles with a significant enhancement in the fracture strain (up to ~48%). Superior energy absorption was observed for all the composite samples prior to compressive fracture. Further, enhancement in thermal, mechanical and damping characteristics of pure Mg is correlated with microstructural changes due to the presence of the CeO2 nanoparticles. 相似文献
6.
7.
8.
9.
基于对地观测激光回波特征的目标特性研究 总被引:5,自引:0,他引:5
本文研究了对地观测激光回波特征与地面目标特征之间的关系模型,分析了分类地面目标的激光回波特征,提出一种基于查表法的目标特性计算方法并给出了仿真结果。 相似文献
10.
Effect of Stoichiometry on Properties of Rare-Earth-Based Hydrogen Storage Alloy for Nickel-Metal Hydride Secondary Battery 总被引:2,自引:0,他引:2
Effect of stoichiometry on microstructures, electrochemical properties and PCT characteristics of the alloys MI(Ni0.71Co0.15-Al0.06Mn0.08)x (MI=Lanthanum-rich Michmetal, x=4.6~5.2) have been investigated. The lattice constants a, c, and cellvolumes of non-stoichiometric alloys are bigger than those of the stoichiometric alloy. With the increasing stoichiometry x,the value of a decreases, and the value of c and cell volume increases except for those of the stoichiometric alloy; the plateaupressure of PCT curve, discharge capacity and cycling stability all increase. The alloy with x=5.2 shows the highest dischargecapacity and the best cycling stability among the studied alloys. 相似文献