全文获取类型
收费全文 | 421895篇 |
免费 | 7714篇 |
国内免费 | 5603篇 |
专业分类
化学 | 210303篇 |
晶体学 | 5978篇 |
力学 | 23312篇 |
综合类 | 331篇 |
数学 | 70804篇 |
物理学 | 124484篇 |
出版年
2021年 | 3613篇 |
2020年 | 4103篇 |
2019年 | 4455篇 |
2018年 | 15411篇 |
2017年 | 15151篇 |
2016年 | 13165篇 |
2015年 | 5639篇 |
2014年 | 7584篇 |
2013年 | 15287篇 |
2012年 | 16041篇 |
2011年 | 24314篇 |
2010年 | 16057篇 |
2009年 | 16152篇 |
2008年 | 19326篇 |
2007年 | 21220篇 |
2006年 | 12238篇 |
2005年 | 12046篇 |
2004年 | 11285篇 |
2003年 | 10784篇 |
2002年 | 9928篇 |
2001年 | 9586篇 |
2000年 | 7573篇 |
1999年 | 5858篇 |
1998年 | 5329篇 |
1997年 | 5074篇 |
1996年 | 4878篇 |
1995年 | 4359篇 |
1994年 | 4521篇 |
1993年 | 4194篇 |
1992年 | 4568篇 |
1991年 | 4624篇 |
1990年 | 4544篇 |
1989年 | 4314篇 |
1988年 | 4337篇 |
1987年 | 4192篇 |
1986年 | 4020篇 |
1985年 | 5107篇 |
1984年 | 5353篇 |
1983年 | 4507篇 |
1982年 | 4631篇 |
1981年 | 4502篇 |
1980年 | 4417篇 |
1979年 | 4510篇 |
1978年 | 4815篇 |
1977年 | 4726篇 |
1976年 | 4846篇 |
1975年 | 4445篇 |
1974年 | 4527篇 |
1973年 | 4698篇 |
1972年 | 3438篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
V. G. Granik 《Chemistry of Heterocyclic Compounds》1992,28(6):632-647
The review collects the results of investigations on the synthesis of heterocyclic compounds, mainly azaheterocycles, from amide and lactam acetals. The reasons for the high reactivity of these compounds with respect to nucleophilic and electrophilic reagents are considered, as are the principal pathways of heterocyclization of amidine and enamine systems synthesized via amide and lactam acetals.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 762–780, June, 1992. 相似文献
992.
J.C. Gramain N. Simonet G. Vermeersch N. Febvay-Garot S. Caplain A. Lablache-Combier 《Tetrahedron》1982,38(4):539-550
Benzophenone is photoreduced by pthalimidines and dihydro isoquinolones. The hydrogen atom α to the nitrogen atom is abstracted and radical coupling leads to adducts. CIDNP studies of these adducts show inversion of polarisation for the adduct on the N-alkyl chain when the nitrogen is bound to a benzylic methylene. This inversion is explained by considering that the radical on the N-alkyl chain derives from the radical on the ring. 相似文献
993.
994.
M. Grexa G. Hermann G. Lasnitschka A. Scharmann 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1986,2(2):157-158
The hyperfine splittings and isotope shifts of n2PJ-levels in203,205Tl have been measured by high resolution two-photon spectroscopy with a cw dye-laser and an actively stabilized marker cavity for laser frequency scancalibration. 相似文献
995.
V.Yu. Baranovsky L.A. Kazarin A.A. Litmanovich I.M. Papisov 《European Polymer Journal》1984,20(2):191-194
Polycomplex formation between poly(methacrylic acid) and polyacrylamide in aqueous solutions has been studied by means of viscometry, potentionetry and elemental analysis. Stoichiometry of the polycomplex was found to be 1:1 with respect to unit-moles. I.R.-spectroscopic data give evidence of the co-existence of ladder-like regions and loops in the polycomplexes formed by poly(methacrylic acid) with polyacrylamide and poly(ethylene glycol). The reactivities of the same functional groups in ladder-like regions and loops are different. This difference has been shown taking as an example thermochemical reactions in the above polycomplexes. Dehydrocyclization in the poly(methacrylic acid) chain was found to occur in the loops of both polycomplexes. This intramolecular reaction in the polycomplex of poly(methacrylic acid) with polyacrylamide is followed by intermolecular formation of imide bonds in ladder-like regions. 相似文献
996.
997.
998.
999.
1000.
Perea-Carpio R. González-Caballero F. Bruque J. M. Pardo G. 《Colloid and polymer science》1983,261(2):183-187
Colloid and Polymer Science - Data on the surface tension of sodium alkylsulfonate solutions at different temperatures and surfactant concentrations are presented. By applying the thermodynamic... 相似文献