全文获取类型
收费全文 | 5391篇 |
免费 | 702篇 |
国内免费 | 286篇 |
专业分类
电工技术 | 543篇 |
综合类 | 290篇 |
化学工业 | 894篇 |
金属工艺 | 393篇 |
机械仪表 | 431篇 |
建筑科学 | 445篇 |
矿业工程 | 195篇 |
能源动力 | 300篇 |
轻工业 | 713篇 |
水利工程 | 124篇 |
石油天然气 | 11篇 |
武器工业 | 4篇 |
无线电 | 299篇 |
一般工业技术 | 634篇 |
冶金工业 | 123篇 |
原子能技术 | 41篇 |
自动化技术 | 939篇 |
出版年
2024年 | 20篇 |
2023年 | 181篇 |
2022年 | 268篇 |
2021年 | 298篇 |
2020年 | 285篇 |
2019年 | 200篇 |
2018年 | 187篇 |
2017年 | 161篇 |
2016年 | 178篇 |
2015年 | 144篇 |
2014年 | 297篇 |
2013年 | 401篇 |
2012年 | 693篇 |
2011年 | 628篇 |
2010年 | 419篇 |
2009年 | 489篇 |
2008年 | 239篇 |
2007年 | 475篇 |
2006年 | 373篇 |
2005年 | 121篇 |
2004年 | 39篇 |
2003年 | 26篇 |
2002年 | 27篇 |
2001年 | 28篇 |
2000年 | 30篇 |
1999年 | 35篇 |
1998年 | 13篇 |
1997年 | 11篇 |
1996年 | 12篇 |
1995年 | 6篇 |
1994年 | 11篇 |
1993年 | 4篇 |
1992年 | 6篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 10篇 |
1987年 | 27篇 |
1986年 | 12篇 |
1985年 | 7篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1951年 | 3篇 |
排序方式: 共有6379条查询结果,搜索用时 31 毫秒
961.
962.
963.
Wu Wenwei Cai Jinchao Wu Xuehang Liao Sen Wang Kaituo Tao Lin 《Advanced Powder Technology》2013,24(1):154-159
Precursor of nanocrystalline LaMnO3 was synthesized by solid-state reaction at low heat using La(NO3)3·6H2O, MnSO4·H2O, and Na2CO3·10H2O as raw materials. XRD analysis showed that precursor was a mixture containing orthorhombic La2(CO3)3·8H2O and rhombohedral MnCO3. When the precursor was calcined at 800 °C for 2 h, pure phase LaMnO3 with rhombohedral structure was obtained. Magnetic characterization indicated that rhombohedral LaMnO3 behaved weak magnetic properties. The thermal process of the precursor experienced four steps, which involved the dehydration of crystallization water at first, and then decomposition of manganese carbonate into MnO2, and decomposition of La2(CO3)3 and MnO2 together into La2O2CO3 and Mn2O3, and lastly reaction of monoclinic La2O2CO3 with Mn2O3 and formation of rhombohedral LaMnO3. Based on the Kissinger equation, the value of the activation energy associated with the formation of rhombohedral LaMnO3 was determined to be 260 kJ mol?1. The value of the Avrami exponent, n, was equal to 1.68, which suggested that crystallization process of LaMnO3 was the random nucleation and growth of nuclei reaction. 相似文献
964.
Changrong Zhou Huabin Yang Qin Zhou Guohua Chen Weizhou Li Hua Wang 《Journal of Materials Science: Materials in Electronics》2013,24(5):1685-1689
BiFeO3–BTiO3(BF–BT) ceramics as a promising candidate for lead-free high-temperature piezoelectric ceramics were studied with a special emphasis on the compositional dependence of piezoelectric properties. Excess Bi was added to compensate for the evaporation of Bi3+ ions during sintering and this addition was found to be effective in improving the piezoelectric properties of BF–BT ceramics. The microstructure, dielectric and piezoelectric properties of excess Bi doped BF–BT ceramics were investigated. Maximum piezoelectric constant d 33 = 142 pC/N and k p = 0.302 were obtained with 0.04 Bi doping. At the same time, an enhanced Curie temperature T c, 452 °C, was obtained. The combination of improved piezoelectric properties and increased T c makes these ceramics suitable for elevated temperature piezoelectric devices. 相似文献
965.
Huabin Yang Changrong Zhou Qin Zhou Changlai Yuan Weizhou Li Hua Wang 《Journal of Materials Science》2013,48(7):2997-3002
Lead-free (1 ? x)(K0.475Na0.475Li0.05)(Nb0.95Sb0.05)O3–xBi(Ni0.5Ti0.5)O3 [(1 ? x)KNNL–xBNiT] piezoelectric ceramics were prepared by conventional solid-state sintering. The effect of BNiT addition and sintering temperature on phase structure, microstructure, and dielectric and piezoelectric properties of (1 ? x)KNNL–xBNiT ceramics was investigated. The results reveal that the addition of small amounts of BNiT causes significant changes in microstructures, crystalline structures, and dielectric and piezoelectric properties. The T c values and dielectric constant at T c of (1 ? x)KNNL–xBNiT ceramics are increased obviously with 0.2 % BNiT addition and decreased with further increasing BNiT content. Enhanced piezoelectric properties are obtained for the sample with x = 0.4 % and synthesized at optimal temperature of 1100 °C, in which d 33 and k p are 253 pC/N and 0.52, respectively. These results show that (1 ? x)KNNL–xBNiT ceramics are promising lead-free piezoelectric materials. 相似文献
966.
Phase diagrams of the RE (rare earth)-IV-VI systems are very important for the design of rare earth doped diluted magnetic semiconductors (DMSs), but related information is very limited. In this work, ... 相似文献
967.
假乙内酰硫脲酸在铜-钼浮选分离中的抑制性能(英文) 总被引:3,自引:0,他引:3
将合成的假乙内酰硫脲酸(PGA)用作铜-钼分离抑制剂。该药剂闭路实验结果表明:假乙内酰硫脲酸在较小的用量下对黄铜矿有较强的抑制作用,经一次粗选、一次扫选、两次精选,可获得Mo品位大于26%、回收率大于89%的浮选指标,而用Na2S做抑制剂时钼的回收率下降了2%。药剂吸附量测试结果表明,PGA与丁基黄药在矿物表面发生竞争吸附,PGA在黄铜矿表面上的吸附量远大于在辉钼矿表面的。红外光谱分析表明,PGA在黄铜矿表面是化学吸附,而在辉钼矿表面属于物理吸附。前线轨道计算结果表明,在PAG分子中,硫原子是反应活性的中心。利用矿物、丁黄药及PGA的费米能级能量大小可以从电化学作用角来度解释PGA的抑制机理。 相似文献
968.
Hui Feng Hui Guo Xiaoma Tao Hongmei Chen Yifang Ouyang Yong Du Yuehui He 《Journal of Phase Equilibria and Diffusion》2013,34(2):116-121
The phase equilibrium of the Al-Fe-Gd plays an important role of development of bulk amorphous alloys and magnetocaloric materials. The entire isothermal section of the phase diagram for Al-Fe-Gd ternary system at 773 K has been investigated by means of x-ray powder diffraction, scanning electron microscopy with energy dispersive analysis, and optical microscopy. The existences of 13 binary compounds for the Al-Fe, Al-Gd, and Fe-Gd binary systems were confirmed. The binary phases, i.e., Al2Gd, Fe2Gd, and α-Fe17Gd2 present appreciable ternary solubility. Three ternary compounds: τ1-Al10Fe2Gd, τ2-Al8+x Fe4-x Gd (0 ≤ x ≤ 2), and λ-Al2?x Fe x Gd (0.951 ≤ x ≤ 1.245) were determined. The isothermal section consists of 19 single-phase regions, 40 binary-phase regions, and 20 ternary-phase regions. 相似文献
969.
简要介绍了一种煤矿工业锅炉的专用DCS监控系统设计方案,并进行了造价预算。实践证明采用专用DCS设计的煤矿工业锅炉监控系统较传统的PLC监控系统而言,具有更高的稳定性和更好的易用性,即插即用的设计非常适合现有技术人员。 相似文献
970.
文章结合某煤矿自备电厂锅炉给水系统扰动因素分析,在传统三冲量给水控制策略的基础上,提出以汽包压力微分迟滞信号作为给水流量跟踪副环的前馈量,并延迟给水指令。通过燃烧扰动、蒸发量扰动试验证明,该控制方案具有较强的抗扰动能力。 相似文献