全文获取类型
收费全文 | 5009篇 |
免费 | 297篇 |
国内免费 | 21篇 |
专业分类
化学 | 3875篇 |
晶体学 | 13篇 |
力学 | 111篇 |
数学 | 665篇 |
物理学 | 663篇 |
出版年
2023年 | 55篇 |
2022年 | 47篇 |
2021年 | 89篇 |
2020年 | 110篇 |
2019年 | 112篇 |
2018年 | 68篇 |
2017年 | 62篇 |
2016年 | 226篇 |
2015年 | 196篇 |
2014年 | 190篇 |
2013年 | 286篇 |
2012年 | 366篇 |
2011年 | 387篇 |
2010年 | 241篇 |
2009年 | 217篇 |
2008年 | 313篇 |
2007年 | 267篇 |
2006年 | 281篇 |
2005年 | 279篇 |
2004年 | 241篇 |
2003年 | 173篇 |
2002年 | 188篇 |
2001年 | 95篇 |
2000年 | 82篇 |
1999年 | 77篇 |
1998年 | 61篇 |
1997年 | 87篇 |
1996年 | 69篇 |
1995年 | 66篇 |
1994年 | 45篇 |
1993年 | 50篇 |
1992年 | 32篇 |
1991年 | 24篇 |
1990年 | 22篇 |
1989年 | 21篇 |
1988年 | 14篇 |
1987年 | 15篇 |
1986年 | 13篇 |
1985年 | 10篇 |
1984年 | 10篇 |
1983年 | 8篇 |
1982年 | 10篇 |
1981年 | 11篇 |
1979年 | 7篇 |
1978年 | 12篇 |
1977年 | 8篇 |
1976年 | 7篇 |
1975年 | 8篇 |
1974年 | 13篇 |
1973年 | 14篇 |
排序方式: 共有5327条查询结果,搜索用时 30 毫秒
141.
Markus Neuenschwander Peter Bigler Klaus Christen Rudolf Iseli Rolf Kyburz Hansueli Mühle 《Helvetica chimica acta》1978,61(6):2047-2058
Chloroacylation and bromoacylation of carbonyl compounds: A forgotten carbonyl reaction. I. Scope of the reaction Aliphatic, α,β-unsaturated and aromatic aldehydes as well as aliphatic ketones react with acyl halides to (α-haloalkyl)esters. These bifunctional derivates contain two leaving groups of different reactivity. The scope of this scarcely of this scarcely known carbonyl reaction is discussed. 相似文献
142.
Constable EC Housecroft CE Neuburger M Schaffner S Shardlow EJ 《Dalton transactions (Cambridge, England : 2003)》2005,(2):234-235
Reaction of 4'-(2-propyn-1-oxy)-2,2':6',2'-terpyridine (HC triple bond CCH2Oterpy) with trans-[PtI2(PEt3)2] regioselectively metallates the alkyne to give trans-[Pt(C triple bond CCH2Oterpy)2(PEt3)2] which, when treated with Fe(II), gives a [2 + 2]-metallocycle. 相似文献
143.
Fabian Gerson Axel Lamprecht Markus Scholz Heinz Troxler Dieter Lenoir 《Helvetica chimica acta》1996,79(1):307-318
The radical anions of 5H-dibenzo[a,d]cycloheptene ( 9 ), 5 H-dibenzo[c,f][1,2]diazepine ( 10 ), 5,6-dihydrodibenzo[a,e]cyclooctene ( 11 ), 5,6-dihydrodibenzo[c,g][1,2]diazocine ( 12 ), and (E)-2,2,5,5-tetramethyl-3,4-diphenylhex-3-ene ( 13 ) were characterized by ESR and ENDOR spectroscopy. Their hyperfine data were compared with those previously reported for radical anions also containing the stilbene or the azobenzene π-system. Whereas the π-spin distribution in the radical anions of the stilbene series is only moderately sensitive to deviations of the π-system from planarity, the radical anions of the azobenzene series respond to steric strain by shifting the π-spin population from the benzene rings to the azo group. This finding is impressively demonstrated by the similar hyperfine data for 9 · ? and 11 · ? which contrast with the strongly highly hindered 13 · ?. A. plausible interpretation is readily provided by the electron affinities of the constituent π-moieties in stilbene and azobenzene. While those of benzene and ethene are both comparatively low, the azo group has a considerably higher electron affinity. 相似文献
144.
Reactions of MoNCl3 and WNCl3 with Elemental Fluorine. Crystal Structures of [MoO2F2(THF)2] and [WF4(NCl)(CH3CN)] The nitrido chlorides MoNCl3 and WNCl3 as well as WCl4(NCl) react with elemental fluorine forming the N-chloro imido complexes MoF4(NCl) and WF4(NCl), which were characterized by IR spectroscopy. With tetrahydrofurane MoF4(NCl) reacts to give [MoF4(NCl)(THF)], which in THF solution slowly converts into [MoO2F2(THF)2]. From WF4(NCl) with acetonitrile the complex [WF4(NCl)(CH3CN)] is obtained. Both donor acceptor complexes were characterized by crystal structure determinations. [MoO2F2(THF)2] : Space group P21/n, Z = 4, structure solution with 1823 unique reflections, R = 0.033 for reflections with I > 2σ(I). Lattice dimensions at ?40°C: a = 636.2, b = 1119.5, c = 1625.2 pm; β = 93.92(1)º. The compound has a monomeric molecular structure with the fluorine atoms in trans-position to one another and with the oxygen atoms of the THF molecules in trans to the oxo ligands. [WF4(NCl)(CH3CN)] : Space group P21/m, Z = 2, structure solution with 1119 unique reflections, R = 0.038 for reflections with I > 2σ(I). Lattice dimensions at 20°C: a = 511.7, b = 714.9, c = 1002.5 pm; β = 102.59(10)º. The compound has a monomeric molecular structure in which the nitrogen atom of the acetonitrile molecule coordinates in trans-position to the N-chloro imido group W?N? Cl. The structural parameters of this group are WN = 172.2 pm, NCl = 161.1 pm, WNCl = 178.6º. 相似文献
145.
146.
Markus Follmann Nils Griebenow Michael G. Hahn Ingo Hartung Franz‐Josef Mais Joachim Mittendorf Martina Schfer Hartmut Schirok Johannes‐Peter Stasch Friederike Stoll Alexander Straub Peter Jeschke Ralf Nauen Michael Edmund Beck Hans‐Wilhelm Engels Hans‐Georg Pirkl Reinhard Albers Rolf W. Albach Jens Krause Andreas Hoffmann Holger Casselmann Jeff Dormish 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2013,125(36):9503-9503
147.
148.
149.
150.
An alternative pathway for the biosynthesis of the fungal alkaloid necatorone has been studied using fluorine-labeled 3-(2-carboxyphenylamino)-l-tyrosine. Although no incorporation of this compound could be detected in feeding experiments with young specimens of Lactarius necator, an analogous 3-aminotyrosine derivative could be converted synthetically into the oxopyridoacridine core structure of necatorone. In experiments aimed at the synthesis of aaptamine-type alkaloids, an unprecedented cyclization of a 3-aminotyrosine-methyl propiolate adduct to a methyl isoquinoline-3-carboxylate was observed. A mechanism is proposed, in which C3 of the propiolate delivers C1 of the isoquinoline nucleus. 相似文献