全文获取类型
收费全文 | 126227篇 |
免费 | 11205篇 |
国内免费 | 8039篇 |
专业分类
电工技术 | 4052篇 |
技术理论 | 2篇 |
综合类 | 7453篇 |
化学工业 | 38309篇 |
金属工艺 | 15504篇 |
机械仪表 | 3705篇 |
建筑科学 | 2826篇 |
矿业工程 | 2141篇 |
能源动力 | 4729篇 |
轻工业 | 10593篇 |
水利工程 | 864篇 |
石油天然气 | 4763篇 |
武器工业 | 883篇 |
无线电 | 10985篇 |
一般工业技术 | 18055篇 |
冶金工业 | 7157篇 |
原子能技术 | 1549篇 |
自动化技术 | 11901篇 |
出版年
2024年 | 470篇 |
2023年 | 2294篇 |
2022年 | 4338篇 |
2021年 | 4807篇 |
2020年 | 3953篇 |
2019年 | 3551篇 |
2018年 | 3282篇 |
2017年 | 4007篇 |
2016年 | 4314篇 |
2015年 | 4287篇 |
2014年 | 6146篇 |
2013年 | 7126篇 |
2012年 | 8260篇 |
2011年 | 10214篇 |
2010年 | 7760篇 |
2009年 | 8834篇 |
2008年 | 7563篇 |
2007年 | 8964篇 |
2006年 | 8152篇 |
2005年 | 6398篇 |
2004年 | 5432篇 |
2003年 | 4641篇 |
2002年 | 3810篇 |
2001年 | 3040篇 |
2000年 | 2653篇 |
1999年 | 2001篇 |
1998年 | 1596篇 |
1997年 | 1236篇 |
1996年 | 1152篇 |
1995年 | 968篇 |
1994年 | 892篇 |
1993年 | 681篇 |
1992年 | 540篇 |
1991年 | 437篇 |
1990年 | 380篇 |
1989年 | 304篇 |
1988年 | 186篇 |
1987年 | 124篇 |
1986年 | 118篇 |
1985年 | 95篇 |
1984年 | 73篇 |
1983年 | 44篇 |
1982年 | 65篇 |
1981年 | 65篇 |
1980年 | 48篇 |
1979年 | 38篇 |
1977年 | 23篇 |
1976年 | 16篇 |
1975年 | 22篇 |
1951年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
82.
83.
用NaOH熔融样品,向标准溶液中加入同样量的KOH基体,建立工作曲线,试样酸化后,直接用ICP-AES法测定。 相似文献
84.
Granados M. López Galisteo F. Cabello Lambrou P. S. Alifanti M. Mariscal R. Gurbani A. Sanz J. Sobrados I. Efstathiou A. M. Fierro J. L. G. 《Topics in Catalysis》2007,42(1-4):443-447
The chemical nature of P-containing species of varying concentration present in CeO2 after impregnation with (NH4)2HPO4 and calcination at 1273 K, and their effects on the oxygen storage and release (OSR) properties of ceria are reported for
the first time. The samples were characterized by different techniques and the results were compared with those recently reported
on the same samples but calcined at 873 K. When P-containing ceria solids were calcined at 1273 K, CePO4 (monazite) was the predominant P-containing species on the surface of ceria, confirming previous studies that showed that
monazite exists for those samples in which the surface P loading (P atoms per nm−2) is larger than 5.5. For lower surface P concentrations, isolated orthophosphate units are present at the surface and within
the subsurface region of the solid. Severe sintering of CeO2 after calcination at 1273 K resulted in P concentrations >5.5 P atoms·nm−2 in all samples. Isolated PO4 units that could initially be present in the samples calcined at 873 K nucleated and CePO4 was formed when samples were calcined at 1273 K. OSR properties of CeO2 deteriorated progressively when P loading increased due to the presence of larger crystals of the very stable Ce(III) phase
of CePO4 at the surface of the P-containing ceria solids. 相似文献
85.
M. Pérez-Luna A. Cosultchi J. A. Toledo-Antonio C. Angeles-Chavez E. M. Arce-Estrada 《Catalysis Letters》2006,107(1-2):103-110
Three Ni/ZrO2–SO4=/Al2O3 catalysts with different concentrations of platinum (0.2, 0.3 and 0.4 wt%) were prepare and tested for n-butane isomerization reaction at 338 K, in absence and in presence of hydrogen. The results shown that, at low temperature,
platinum contributes to the olefin or butyl ion formation and the reaction follows a bimolecular pathway. However, when the
reaction occurs in the presence of hydrogen, the formation of butyl ions is inhibited. The main feature of platinum addition
is the stabilization of the catalytic activity, which is indicated by the slow deactivation constants compared to that of
the unpromoted catalyst. 相似文献
86.
87.
采用反相高效液相色谱法测定合成meso-四苯基卟啉钴的纯度;以甲醇乙腈二氯甲烷(体积比为55∶35∶10)为流动相,ShimpackCLCODS柱(150mm×6.0mmi.d,5μm)为分离柱,流速为1.5mL/min,检测波长420nm;meso四苯基卟啉钴的测定在1.0~10μg/mL时线性关系良好(相关系数r=0.9993),加标回收率为97.03%~101.42%,重复进样的相对标准偏差RSD为0.64%~2.92%(n=5)。方法的准确度高,精密度好,实际应用效果好。 相似文献
88.
添加物对ZrO2系快离子导体烧结性能的影响 总被引:1,自引:0,他引:1
本文介绍了1320℃下,CaO,Y2O3等稳定剂,低融物组成及1-6价阳离子化合物对ZrO2烧结性能的影响并列举出材料的晶型及某些主要性能。 相似文献
89.
莫达非尼的绿色化学合成 总被引:1,自引:0,他引:1
采用[bm im]BF4离子液体作为反应溶剂,以二苯甲硫醇为原料,经醚化、氨解、氧化得到新型提神醒脑药物莫达非尼。讨论了不同的氯乙酸酯和反应温度对醚化反应收率的影响,讨论了不同的二苯甲硫乙酸酯对氨解反应收率的影响,及离子液体的回收使用。研究表明,采用氯乙酸甲酯作为醚化试剂,反应时间4 h,反应温度100℃,二苯甲硫醇∶氯乙酸甲酯=1∶1.5(摩尔比),室温下氨解反应20 h,二苯甲硫乙酰胺收率76%;采用过氧化氢作为氧化试剂,反应时间3 h,反应温度60℃,过氧化氢∶二苯甲硫乙酰胺=1∶1(摩尔比),莫达非尼收率79%,反应总收率可达48%。 相似文献
90.
The PbO2 and F−-doped PbO2 (F-PbO2) film electrodes have been prepared by an electrodeposition process onto platinum substrate. The changes of their electrochemical activity for oxygen evolution (OE) reaction with accelerated electrolysis time have been studied. The results show that the activity of the electrodes decreases with increasing electrolysis time. This can be attributed to the conductivity variations, which are caused by the decrease of the oxygen vacancy concentration in PbO2 films during OE. The mechanism of the decrease of the oxygen vacancies has been investigated. For F-PbO2 film electrodes, though its electrochemical activity is somewhat lower than that of undoped one, its activity stability is much higher in comparison with that of PbO2. The influence of F− doping on the activity of PbO2 film electrodes has been also discussed. 相似文献