全文获取类型
收费全文 | 451379篇 |
免费 | 4242篇 |
国内免费 | 1280篇 |
专业分类
化学 | 231597篇 |
晶体学 | 6936篇 |
力学 | 21066篇 |
综合类 | 14篇 |
数学 | 52595篇 |
物理学 | 144693篇 |
出版年
2021年 | 3968篇 |
2020年 | 4238篇 |
2019年 | 4732篇 |
2018年 | 6291篇 |
2017年 | 6510篇 |
2016年 | 9280篇 |
2015年 | 5410篇 |
2014年 | 8835篇 |
2013年 | 20958篇 |
2012年 | 16194篇 |
2011年 | 19707篇 |
2010年 | 14283篇 |
2009年 | 14180篇 |
2008年 | 17649篇 |
2007年 | 17665篇 |
2006年 | 16262篇 |
2005年 | 14364篇 |
2004年 | 13252篇 |
2003年 | 11689篇 |
2002年 | 11676篇 |
2001年 | 13558篇 |
2000年 | 10177篇 |
1999年 | 7920篇 |
1998年 | 6671篇 |
1997年 | 6501篇 |
1996年 | 6070篇 |
1995年 | 5398篇 |
1994年 | 5330篇 |
1993年 | 5095篇 |
1992年 | 5719篇 |
1991年 | 5978篇 |
1990年 | 5567篇 |
1989年 | 5508篇 |
1988年 | 5261篇 |
1987年 | 5331篇 |
1986年 | 5000篇 |
1985年 | 6393篇 |
1984年 | 6546篇 |
1983年 | 5488篇 |
1982年 | 5663篇 |
1981年 | 5324篇 |
1980年 | 5229篇 |
1979年 | 5609篇 |
1978年 | 5738篇 |
1977年 | 5639篇 |
1976年 | 5655篇 |
1975年 | 5346篇 |
1974年 | 5347篇 |
1973年 | 5347篇 |
1972年 | 3730篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
971.
O. S. Filipenko S. M. Aldoshin G. V. Shilov N. I. Makarova V. A. Kharlanov M. I. Knyazhanskii 《Russian Chemical Bulletin》1995,44(2):287-292
The molecular structures of the initial compounds and the products of photocyclization involving amino and azomethine groups in perchlorates ofN-amino (1) andN-azomethine (2) derivatives of 2,4,6-triphenylpyridinium cations were studied. Cations1 and2 have an essentially non-coplanar arrangement of the -Ph rings, and the product of photocyclization of2, cation3, is characterized by a flattened structure. It was found that the orientation of the lone electron pair of the N atom with respect to one of the planes of the -Ph rings in molecule1 is more favorable for monocyclization involving the amino group. The structure of molecule2 allows two routes of the photoreaction,viz., O N proton transfer and monocyclization with an -Ph ring. However, the structural features of molecule2 are more favorable for photocyclization.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 296–301, February, 1995. 相似文献
972.
973.
974.
It is shown that it is possible to increase the yield of liquid hydrocarbons of the benzene fraction in the Mobil process by use of a catalyst modified by treatment with CO2 of the Zn form of the TsVK zeolite. It is established that on treatment with CO2 of the Zn-TzVK zeolite the concentration of strongly acidic -centers is increased. As a result of alkylation of C2-C4 olefins by methanol at these sites more of the high molecular C5-C8 aliphatic hydrocarbons are formed. Selectivity of conversion of methanol to liquid C5-C10 hydrocarbons of the benzene fraction is increased, but selectivity with respect to the light C2-C4 fractions is decreased. 相似文献
975.
Cs. Vértes I. Czakó-Nagy W. Meisel M. Kolonits F. Horkai A. Vértes 《Journal of Radioanalytical and Nuclear Chemistry》1990,144(3):179-187
A stacking Mössbauer technique, MMS has been applied for studying thin surface layers. The surface layers formed on the57Fe film in aqueous solutions of corrosion inhibitors, such as zinc phosphate and barium metaborate, and in distilled water was studied by this method. It has been found that the corrosion is much slower in the presence of zinc phosphate and barium metaborate. XPS analysis suggests the formation of a mixed iron zinc phosphate on the surface of the57Fe film after corrosion in a zinc phosphate solution. 相似文献
976.
977.
A. T. Lebedev P. A. Sharbatyan A. M. Sipyagin V. G. Kartsev V. S. Petrosyan 《Chemistry of Heterocyclic Compounds》1982,18(7):697-703
A comparison of the mass spectra of 1-diazo-4-sulfonylamino-butan-2-ones and N-sulfonylpyrrolidin-3-ones makes it possible to conclude that under the conditions of electron impact and chemical ionization the molecular ions of the investigated diazo ketones lose a molecule of nitrogen and undergo partial cyclization to the corresponding pyrrolidinones without undergoing the Wolff rearrangement.See [1] for Communication 1.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 919–925, July, 1982. 相似文献
978.
979.
980.
Bagdasaryan G. B. Sarkisova E. A. Pogosyan P. S. Indzhikyan M. G. 《Russian Journal of General Chemistry》2002,72(12):1951-1951
Russian Journal of General Chemistry - 相似文献