全文获取类型
收费全文 | 3203篇 |
免费 | 102篇 |
国内免费 | 177篇 |
专业分类
化学 | 3356篇 |
晶体学 | 33篇 |
综合类 | 2篇 |
数学 | 7篇 |
物理学 | 84篇 |
出版年
2024年 | 1篇 |
2023年 | 36篇 |
2022年 | 23篇 |
2021年 | 31篇 |
2020年 | 55篇 |
2019年 | 89篇 |
2018年 | 89篇 |
2017年 | 103篇 |
2016年 | 96篇 |
2015年 | 73篇 |
2014年 | 147篇 |
2013年 | 425篇 |
2012年 | 121篇 |
2011年 | 157篇 |
2010年 | 179篇 |
2009年 | 172篇 |
2008年 | 218篇 |
2007年 | 228篇 |
2006年 | 193篇 |
2005年 | 187篇 |
2004年 | 160篇 |
2003年 | 160篇 |
2002年 | 84篇 |
2001年 | 56篇 |
2000年 | 40篇 |
1999年 | 25篇 |
1998年 | 27篇 |
1997年 | 24篇 |
1996年 | 30篇 |
1995年 | 40篇 |
1994年 | 47篇 |
1993年 | 29篇 |
1992年 | 31篇 |
1991年 | 17篇 |
1990年 | 9篇 |
1989年 | 11篇 |
1988年 | 7篇 |
1987年 | 8篇 |
1986年 | 5篇 |
1985年 | 8篇 |
1984年 | 8篇 |
1983年 | 1篇 |
1982年 | 5篇 |
1981年 | 14篇 |
1980年 | 6篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1974年 | 1篇 |
排序方式: 共有3482条查询结果,搜索用时 15 毫秒
51.
A larger quantity of a β-keto ester that is 1.5–1.7 equiv more than the base (t-BuOK, NaH) was found to be essential in securing sufficient yields of the products in the palladium-catalyzed allylic substitution of the monoacetate of 4-cyclopentene-1,3-diol with β-keto esters. This requirement also works well for substitutions with the TBS ether of the monoacetate and the monoacetate of 2-cyclohexene-1,4-diol. As an application, the coronafacic acid ethyl ester was synthesized as an optically active form. 相似文献
52.
The synthesis of the first series of 5-alkoxy-1,3-thiazole-based liquid crystals is reported. The aforementioned liquid crystals were synthesised through a Lawesson's reagent-mediated cyclisation of appropriate α-benzamido esters. This methodology was found to be highly efficient, even on a large scale, and the resulting 5-alkoxy-1,3-thiazoles could be purified without the use of column chromatography. The synthesis and mesomorphic properties of a family of 5-alkoxy-2-(4-cyanophenyl)-1,3-thiazole liquid crystals prepared via this approach are discussed and compared with their thiophene and phenyl analogues. 相似文献
53.
54.
Shigekazu Ito Hiroki Sugiyama Masaaki Yoshifuji 《Phosphorus, sulfur, and silicon and the related elements》2013,188(4-5):785-788
1-(2,4,6-Tri-tert-butylphenyl)-2-phosphaethyne (1) was allowed to react with 0.5 equiv of an alkyllithium and subsequently with an alcohol to afford a bulky 1,3-diphosphacyclobutene, and its structure and coordination properties on transition metals were investigated. On the other hand, 1 was allowed to react with an alkyllithium and iodomethane to form a stable biradical, 1,3-diphosphacyclobutane-2,4-diyl. 相似文献
55.
An extremely short synthesis of 2,2-dimethyl-3-hydroxymethyl cyclopentanone 2 (R1 = R2 = Me), an advanced intermediate in the synthesis of the pheromone planococcyl acetate 3, is described. 相似文献
56.
Chengdong Wang Yingjie Guo Prof. Dr. Xiaoming Wang Dr. Zheng Wang Prof. Kuiling Ding 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(64):15903-15907
An efficient nickel-catalyzed regioselective hydroarylation of 1,3-dienes with aryl halides and a silane has been developed, affording a range of allylic arenes in good to excellent yields under mild conditions. This method exhibits broad substrate scope, and excellent functional group tolerance. Late-stage modification of complex architectures was demonstrated. 相似文献
57.
Hidenori Kinoshita Kazuki Yaguchi Takayuki Tohjima Katsukiyo Miura 《Tetrahedron letters》2017,58(16):1607-1610
The diisobutylaluminum hydride (DIBAL-H)-promoted benzocyclization, recently developed by this group, was adopted for the synthesis of a natural product containing a 9,10-dihydrophenanthrene skeleton to demonstrate its synthetic utility. One of the extracts from the roots of Salvia hydrangea DC. ex Bentham (Lamiaceae), a 20-norabietane derivative, was selected as the target molecule. The key step forming the 9,10-dihydrophenanthrene skeleton was achieved by the DIBAL-H-promoted cyclization of a silylated 1,3-dien-5-yne easily accessible from a substituted α-tetralone. 相似文献
58.
A concise approach for the total synthesis of attenols A and B is described involving MacMillan’s α-aminooxylation, Evan’s asymmetric alkylation, Brown’s allylation, and spiro-ketalization as key steps. This approach has successfully demonstrated the α-aminooxylation protocol for the construction of the anti-1,3-diol unit. 相似文献
59.
A novel synthetic method is introduced to prepare the biologically important montagnetol and erythrin compounds starting from a 1,3-benzodioxin-4-one, synthesized from commercially available orsellinic acid and erythritol. 相似文献
60.
A novel and metal free catalysis of synthesizing 5-substituted 1H-tetrazoles through 1,3-dipolar cycloaddition of boron-azides and nitriles is reported with broad substrate scope and excellent yields. 相似文献