全文获取类型
收费全文 | 1944篇 |
免费 | 50篇 |
国内免费 | 10篇 |
专业分类
化学 | 1460篇 |
晶体学 | 23篇 |
力学 | 32篇 |
数学 | 116篇 |
物理学 | 373篇 |
出版年
2021年 | 11篇 |
2020年 | 22篇 |
2019年 | 21篇 |
2018年 | 15篇 |
2017年 | 12篇 |
2016年 | 31篇 |
2015年 | 32篇 |
2014年 | 42篇 |
2013年 | 76篇 |
2012年 | 83篇 |
2011年 | 89篇 |
2010年 | 70篇 |
2009年 | 53篇 |
2008年 | 121篇 |
2007年 | 96篇 |
2006年 | 119篇 |
2005年 | 95篇 |
2004年 | 85篇 |
2003年 | 94篇 |
2002年 | 98篇 |
2001年 | 50篇 |
2000年 | 39篇 |
1999年 | 32篇 |
1998年 | 21篇 |
1997年 | 21篇 |
1996年 | 17篇 |
1995年 | 29篇 |
1994年 | 37篇 |
1993年 | 25篇 |
1992年 | 31篇 |
1991年 | 27篇 |
1990年 | 20篇 |
1989年 | 22篇 |
1988年 | 18篇 |
1987年 | 18篇 |
1986年 | 22篇 |
1985年 | 29篇 |
1984年 | 23篇 |
1983年 | 14篇 |
1982年 | 16篇 |
1981年 | 20篇 |
1980年 | 19篇 |
1979年 | 17篇 |
1978年 | 13篇 |
1977年 | 20篇 |
1976年 | 20篇 |
1975年 | 17篇 |
1973年 | 14篇 |
1968年 | 13篇 |
1966年 | 11篇 |
排序方式: 共有2004条查询结果,搜索用时 265 毫秒
61.
62.
In order to interpret abrupt changes of distributions of orientations andmagnitudes of hyperfine fields in Mössbauer measurements of57Fe in YFeMnO4, a model is proposed. The origin is assumed to be not static but dynamic. Fluctuating fields are caused by spins in a fully frustrated spin system, namely, a Heisenberg spin system on a triangular lattice in a two-dimensional antiferromagnet. Extending the stochastic theory for the fluctuation between two states to that among many states with a Gaussian distribution, we fit the spectra with three parameters, hyperfine fieldH
hf, correlation time c, andwidth of fluctuating field , within a limited condition of =c=1. Obtained results represent the characteristic features of Mössbauer spectra well, in spite of a simplified model. 相似文献
63.
64.
Crawford G Daubenmier CM Fulton R Fujino D Gan KK Honscheid K Kagan H Kass R Lee J Malchow R Morrow F Skovpen Y Sung M White C Whitmore J Wilson P Butler F Fu X Kalbfleisch G Lambrecht M Ross WR Skubic P Snow J Wang PL Wood M Bortoletto D Brown DN Fast J McIlwain RL Miao T Miller DH Modesitt M Schaffner SF Shibata EI Shipsey IP Wang PN Battle M Ernst J Kroha H Roberts S Sparks K Thorndike EH Wang CH Dominick J Sanghera S Skwarnicki T Stoynowski R Artuso M He D Goldberg M Horwitz N Kennett R 《Physical review letters》1993,71(20):3259-3262
65.
Enyo T Arai N Nakane N Nicolaides A Tomioka H 《The Journal of organic chemistry》2005,70(19):7744-7754
[reaction: see text] Computations find that o-phenylene(halo)carbenonitrenes 2-XN, X = F, Cl, Br, have quinoidal singlet biradical ground states such as the parent o-phenylenecarbenonitrene (2-HN). Compared to the parent 2-HN, halogen substitution stabilizes the A' states relative to the A' ones. Halogen substitution also affects the barrier and exothermicity of the ring-opening reaction (to form unsaturated nitriles 4-XN, X = F, Cl, Br), but it has a smaller effect on the ring-closing reaction (to form benzo(aza)cyclobutadiene 3-XN, X = F, Cl, Br). Attempts to generate and observe the o-phenylene(halo)carbenonitrenes 2-XN, X = F, Cl, Br, using matrix isolation spectroscopy under conditions similar to those of the successful observation of 2-HN failed. Instead, the observed photoproducts were a mixture of 3-XN and 4-XN. In each case, the major product of the mixture appears to be the thermodynamically more stable one. In the case of X = Br, the observed mixture contains an additional component that is postulated to be Z-6-BrN. o-Phenylenechlorocarbenocarbene is also computed to have a quinoidal singlet biradical ground state and relatively stabilized A' excited states. Attempts to generate the biscarbene under matrix isolation conditions led to the detection of benzochlorocyclobutadiene (3-ClC), small amounts of the ring-open product (dienediyne 4-ClC), and cycloalkyne 5-ClC. Computations suggest that the formation of 5-ClC implies the generation of Z-6-ClC, which is analogous to the formation of Z-6-BrN from 2-BrN. 相似文献
66.
Beltrami I Bylsma BG DeBonte R Gan KK Koltick D Loeffler FJ Low EH McIlwain RL Miller DH Ng CR Ong PP Rangan LK Shibata EI Wilson RJ Derrick M Fernandez E Fries R Hyman L Kooijman P Loos JS Musgrave B Price LE Schlereth J Sugano K Weiss JM Wood DE Baranko G Baringer P Blockus D Brabson B Forden GE Gray SW Jung C Neal H Ogren H Rust DR Valdata-Nappi M Akerlof C Bonvicini G Chapman J Errede D Harnew N Kesten P Kooijman S Meyer DI Nitz D Rubin D Seidl AA Thun R Trinko T Willutzky W Cork B Keller L 《Physical review letters》1985,54(16):1775-1778
67.
The proposed structures of patellamides B and C, cytotoxic lipophilic cyclic peptides from a marine tunicate, have been revised on the basis of the spectral data of their partial hydrolysates, and their revised structures have been synthetically confirmed by the use of diphenyl phosphorazidate(DPPA) and diethyl phosphorocyanidate(DEPC). 相似文献
68.
69.
Tokuda N Sasaki N Watanabe H Miki K Yamasaki S Hasunuma R Yamabe K 《The journal of physical chemistry. B》2005,109(26):12655-12657
Electroless deposition of Ag on atomically flat H-terminated Si(111) surfaces in aqueous alkaline solutions containing Ag ions produced two different sizes of Ag nanowires along atomic step edges: (1) a narrow nanowire of 10 nm in width and 0.5 nm in height and (2) a wide nanowire of 35 nm in width and 11 nm in height. The narrow and wide nanowires were formed by immersion in the solutions containing less than 1 ppb and 8 ppm dissolved-oxygen concentrations, respectively. This result indicates that the dissolved oxygen initiates the formation of Ag nucleation sites and that the fabrication method has a possibility of controlling the size of Ag nanowires. 相似文献
70.
Takashi Hayashita Akiyo Yamauchi Ai-Jun Tong Jong Chan Lee Bradley D. Smith Norio Teramae 《Journal of inclusion phenomena and macrocyclic chemistry》2004,50(1-2):87-94
The design and function of novel supramolecular fluoroionophore/cyclodextrin (CyD) complex sensors for ion and molecule recognition in water are reviewed. For the crown ether fluoroionophore/-CyD complex, the dimerization of the fluoroionophore inside the -CyD is found to be selectively promoted by alkali metal ion binding, thereby resulting in metal-ion-selective pyrene dimer emission in water. This supramolecular function is successfully utilized in the design of a podand fluoroionophore/-CyD complex for sensing toxic lead ion in water. The boronic acid fluoroionophore/-CyD complex binds sugars and produces increased fluorescence emission in water. The response mechanism appears to be due to the suppression of the photoinduced electron transfer (PET) from pyrene donor to trigonal phenylboronic acid acceptor. This is a novel emission function provided by the boronic acid fluoroionophore/-CyD complex sensors in water. 相似文献