全文获取类型
收费全文 | 1859篇 |
免费 | 60篇 |
国内免费 | 8篇 |
专业分类
化学 | 1396篇 |
晶体学 | 8篇 |
力学 | 32篇 |
数学 | 196篇 |
物理学 | 295篇 |
出版年
2023年 | 12篇 |
2021年 | 14篇 |
2020年 | 16篇 |
2019年 | 24篇 |
2018年 | 20篇 |
2017年 | 10篇 |
2016年 | 33篇 |
2015年 | 39篇 |
2014年 | 27篇 |
2013年 | 91篇 |
2012年 | 84篇 |
2011年 | 94篇 |
2010年 | 61篇 |
2009年 | 37篇 |
2008年 | 95篇 |
2007年 | 104篇 |
2006年 | 99篇 |
2005年 | 99篇 |
2004年 | 88篇 |
2003年 | 76篇 |
2002年 | 70篇 |
2001年 | 30篇 |
2000年 | 23篇 |
1999年 | 22篇 |
1998年 | 21篇 |
1997年 | 21篇 |
1996年 | 30篇 |
1995年 | 31篇 |
1994年 | 36篇 |
1993年 | 28篇 |
1992年 | 30篇 |
1991年 | 20篇 |
1990年 | 22篇 |
1989年 | 19篇 |
1988年 | 24篇 |
1987年 | 18篇 |
1986年 | 15篇 |
1985年 | 32篇 |
1984年 | 24篇 |
1983年 | 24篇 |
1982年 | 47篇 |
1981年 | 26篇 |
1980年 | 33篇 |
1979年 | 20篇 |
1978年 | 17篇 |
1977年 | 13篇 |
1976年 | 23篇 |
1975年 | 12篇 |
1974年 | 15篇 |
1973年 | 11篇 |
排序方式: 共有1927条查询结果,搜索用时 31 毫秒
1.
Marcelino Maneiro Manuel R. Bermejo M. Isabel Fernndez Ana M. Gonzlez‐Noya Alexei M. Tyryshkin Robin G. Pritchard 《无机化学与普通化学杂志》2003,629(2):285-290
A new MnIII‐Schiff base complex, [MnL(OH2)](ClO4) ( 1 ) (H2L = N, N′‐bis‐(3‐Br‐5‐Cl‐salicylidene)‐1, 2‐diimino‐2‐methylethane), an inorganic model of the catalytic center (OEC, Oxygen Evolving Complex) in photosystem II (PSII), has been synthesized and characterized by elemental analysis, IR and EPR spectroscopy, mass spectrometry, magnetic susceptibility measurement and the study of its redox properties by cyclic and normal pulse voltammetry. This complex mimics reactivity (showing a relevant photolytic activity), and also some structural characteristics (parallel‐mode MnIII EPR signal from partially assembled OEC cluster) of the natural OEC. The complex 1 was found to rearrange in solution into a crystallographically solved square‐pyramidal complex, [MnLL′] ( 2 ) (HL′ = 6‐bromo‐4‐chloro‐2‐cyanophenol), through a process, which probably liberates radical species (detected by EPR), and provokes a C—N bond cleavage in the ligand. A photo‐radical mechanism is discussed to explain this rearrangement. 相似文献
2.
Robert W. Baker Geoffrey R. Pocock Melvyn V. Sargent Edi Twiss 《Tetrahedron: Asymmetry》1993,4(12):2423-2426
Introduction of a 2-isopropoxycarbonyl or 2-NN-dimethylcarbamoyl group into homochiral 1-p-tolyl- or 1-t-butyl-sulfinylnaphthalenes, via directed metalation reaction, followed by ligand coupling reaction with 1-naphthylmagnesium bromide, furnished atropisomeric 1,1′-binaphthyls in 82–95% enantiomeric excess (e.e.). 相似文献
3.
Daria E. Lonsdale Geoffrey Johnston‐Hall Amanda Fawcett Craig A. Bell Carl N. Urbani Michael R. Whittaker Michael J. Monteiro 《Journal of polymer science. Part A, Polymer chemistry》2007,45(16):3620-3625
In this work, we propose that retardation in vinyl acetate polymerization rate in the presence of toluene is due to degradative chain transfer. The transfer constant to toluene (Ctrs) determined using the Mayo method is equal to 3.8 × 10?3, which is remarkably similar to the value calculated from the rate data, assuming degradative chain transfer (2.7 × 10?3). Simulations, including chain‐length‐dependent termination, were carried out to compare our degradative chain transfer model with experimental results. The conversion–time profiles showed excellent agreement between experiment and simulation. Good agreement was found for the Mn data as a function of conversion. The experimental and simulation data strongly support the postulate that degradative chain transfer is the dominant kinetic mechanism. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3620–3625, 2007 相似文献
4.
Maculalactones A, B and C from the marine cyanobacterium Kyrtuthrix maculans are amongst the only compounds based on the tribenzylbutyrolactone skeleton known in nature and (+) maculalactone A from the natural source possesses significant biological activity against various marine herbivores and marine settlers. We now report a concise synthesis of racemic maculalactone A in five steps from inexpensive starting materials. Maculalactones B and C were synthesized by a minor modification to this procedure, and the synthetic design also permitted an asymmetric synthesis of maculalactone A to be achieved in around 85% ee. The (+) and (−) enantiomers of maculalactone A were assigned, respectively, to the S and R configurations on the basis of the chiral selectivity expected for catecholborane reduction of an unsymmetrical ketone in the presence of Corey's oxazoborolidine catalyst. Surprisingly, it appeared that natural (+) maculalactone A was biosynthesized in K. maculans in a partially racemic form, comprising ca. 90-95% of the (S) enantiomer and 5-10% of its (R) enantiomer. Coincidentally therefore, the percentage enantiomeric excess of the product obtained from asymmetric synthesis almost exactly matched that found in nature. 相似文献
5.
6.
7.
8.
9.
Huw O. Pritchard 《国际化学动力学杂志》1994,26(1):61-71
The third-law method is used to assess the authenticity of available equilibrium constants for the thermal dissociation of N2O5 ? NO2 + NO3. © 1994 John Wiley & Sons, Inc. 相似文献
10.