全文获取类型
收费全文 | 903篇 |
免费 | 41篇 |
国内免费 | 81篇 |
专业分类
化学 | 761篇 |
晶体学 | 21篇 |
力学 | 5篇 |
综合类 | 2篇 |
物理学 | 236篇 |
出版年
2024年 | 1篇 |
2023年 | 18篇 |
2022年 | 15篇 |
2021年 | 18篇 |
2020年 | 23篇 |
2019年 | 11篇 |
2018年 | 13篇 |
2017年 | 11篇 |
2016年 | 35篇 |
2015年 | 36篇 |
2014年 | 23篇 |
2013年 | 92篇 |
2012年 | 35篇 |
2011年 | 41篇 |
2010年 | 33篇 |
2009年 | 48篇 |
2008年 | 53篇 |
2007年 | 57篇 |
2006年 | 51篇 |
2005年 | 45篇 |
2004年 | 34篇 |
2003年 | 41篇 |
2002年 | 26篇 |
2001年 | 26篇 |
2000年 | 30篇 |
1999年 | 23篇 |
1998年 | 20篇 |
1997年 | 27篇 |
1996年 | 21篇 |
1995年 | 25篇 |
1994年 | 18篇 |
1993年 | 17篇 |
1992年 | 14篇 |
1991年 | 7篇 |
1990年 | 9篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 4篇 |
1986年 | 5篇 |
1985年 | 1篇 |
1984年 | 4篇 |
1981年 | 2篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有1025条查询结果,搜索用时 15 毫秒
71.
采用0.2 mol/L的NaOH溶液对HZSM-5分子筛进行了不同时间的碱改性处理, 并对分子筛的结构和酸性进行表征, 考察了碱改性对HZSM-5催化剂的低碳烃芳构化活性的影响. 结果表明, HZSM-5分子筛经碱改性后会产生少量介孔, 且随改性时间延长, 介孔数量增加, 平均孔径增大, 总酸量降低, B酸/L酸比值降低. 120 min碱改性HZSM-5催化剂的活性、 稳定性以及目标产物苯、 甲苯、 乙苯和二甲苯(统称BTEX)的选择性最高. 相似文献
72.
在萃取研究过程中,合成了10种由四溴(或碘)合铟(Ⅲ)配阴离子与苯并-15-冠-5或二苯并-18-冠-6合钾(或钠)配阳离子相结合所形成的新型固体配合物。经元素分析、红外光谱及差热-热重等方法对配合物进行了表征。通过与相应的冠醚碱金属苦味酸盐配合物结构性质的对比,较合理地解释了这两类萃取体系之间存在的某些差别。 相似文献
73.
74.
T. N. Galkova B. Pacewska V. V. Samuskevich J. Pysiak N. V. Shulga 《Journal of Thermal Analysis and Calorimetry》2000,60(3):1019-1032
The isothermal and non-isothermal transformations of polycrystalline CuNH4PO4⋅H2O in vacuum and in various gas atmospheres (in open air and in gaseous ammonia atmosphere) were studied at 20–800°C by means
of differential thermal analysis, thermogravimetry, X-ray diffraction, paper chromatography, optical microscopy and chemical
analyses. The effects of the gas phase composition on the kinetic peculiarities of total gas evolution and on the partial
processes of dehydration, ammonia removal and rearrangement of the anionic sub-lattice were considered.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
75.
A new resin incorporating benzimidazolylazo group into a matrix of polystyrene divinylbenzene has been prepared. The exchange capacity of the resin for the ions mercury(II), silver(I) and palladium(II) as a function of pH has been determined. The resin exhibits no affinity for alkali or alkaline earth metals. It is highly selective for Hg(II), Ag(I) and Pd(II). In column operation, it has been observed that Hg(II), Ag(I) and Pd(II) in trace quantities can be selectively separated from geological, medicinal and environmental samples. 相似文献
76.
首次合成了酰基异硫氰酸酯4,并将其与各种芳胺、脂肪胺和肼衍生物加成,得到了22种未见文献报道的含双环笼状磷酸酯结构的酰基硫脲化合物(5a-5x)。4与丁胺反应未得到预期的加成产物,而得到相应的取代产物6。研究了5的结构。 相似文献
77.
Using LEED and angle resolved photoemission for characterisation we have prepared graphite overlayers with down to monolayer thickness by heating SiC crystals and monitored alkali metal intercalation for the multilayer films. The valence band structure of the monolayer is similar to that calculated for graphene though downshifted by around 0.8 eV and with a small gap at the zone corner. The shift suggests that the transport properties, which are of much present interest, are similar to that of a biased graphene sample. Upon alkali metal deposition the 3D character of the π states is lost and the resulting band structure becomes graphene like. A comparison with data obtained for ex situ prepared intercalation compounds indicates that the graphite film has converted to the stage 1 compounds C8K or C8Rb. Advantages with the present preparation method is that the graphite film can be recovered by desorbing small amounts of alkali metal and that the progress of compound formation can be monitored. The energy shifts measured after different deposits indicate that saturation is reached in three steps. Our interpretation is that in the first the alkali atoms are dispersed while the final steps are characterized by the formation of first one and then a second (2 × 2) ordered alkali metal layer adjacent to the uppermost carbon layer. 相似文献
78.
Alexander V. Artem’evNina K. Gusarova Svetlana F. MalyshevaVictor I. Mamatyuk Yurii V. GatilovBoris A. Trofimov 《Tetrahedron letters》2011,52(3):398-400
Primary phosphines readily react with elemental sulfur and alkali metal hydroxides (MOH, M = Na, K, Cs) in the molar ratio 1:3:2 under mild conditions (70 °C, 0.5 h, ethanol) to afford alkali metal trithiophosphonates in good to high yields (72-90%). 相似文献
79.
J. S. Schilling 《高压研究》2013,33(3):145-163
At ambient pressure there are 29 elemental superconductors in the periodic table, none of which is an alkali metal. The first alkali metal to become superconducting under high pressure is Cs followed years later by Li. Alkali metals are believed to be exemplary free-electron systems. The fact that an alkali metal becomes superconducting at all is surprising and is a result of the fact that under pressure it shows marked deviations from free-electron behaviour where, counterintuitively, bands narrow and gaps widen. For this reason the alkali metals are among the most interesting systems known to study in high-pressure experiments and superconductivity is one of their most fascinating properties. 相似文献
80.