全文获取类型
收费全文 | 1493篇 |
免费 | 30篇 |
国内免费 | 12篇 |
专业分类
化学 | 1125篇 |
晶体学 | 21篇 |
力学 | 20篇 |
数学 | 99篇 |
物理学 | 270篇 |
出版年
2023年 | 6篇 |
2021年 | 5篇 |
2020年 | 14篇 |
2019年 | 25篇 |
2018年 | 18篇 |
2017年 | 13篇 |
2016年 | 25篇 |
2015年 | 30篇 |
2014年 | 36篇 |
2013年 | 89篇 |
2012年 | 86篇 |
2011年 | 93篇 |
2010年 | 52篇 |
2009年 | 68篇 |
2008年 | 82篇 |
2007年 | 85篇 |
2006年 | 81篇 |
2005年 | 83篇 |
2004年 | 96篇 |
2003年 | 84篇 |
2002年 | 70篇 |
2001年 | 26篇 |
2000年 | 18篇 |
1999年 | 15篇 |
1998年 | 20篇 |
1997年 | 21篇 |
1996年 | 23篇 |
1995年 | 11篇 |
1993年 | 7篇 |
1992年 | 17篇 |
1991年 | 17篇 |
1990年 | 13篇 |
1989年 | 13篇 |
1988年 | 9篇 |
1987年 | 19篇 |
1986年 | 6篇 |
1985年 | 20篇 |
1984年 | 10篇 |
1983年 | 10篇 |
1982年 | 7篇 |
1981年 | 12篇 |
1980年 | 9篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1977年 | 11篇 |
1976年 | 9篇 |
1975年 | 7篇 |
1974年 | 8篇 |
1973年 | 11篇 |
1969年 | 5篇 |
排序方式: 共有1535条查询结果,搜索用时 78 毫秒
81.
82.
83.
84.
Akira Mori Hitoshi Takeshita Ryoji Mori Shinji Takematsu Manabu Takemoto Seiji Ujiie 《Liquid crystals》2013,40(2):171-178
Two kinds of monocyclic troponoid mesogens, 2,5-dialkanoyloxytropones (4) and 5-alkanoyloxy2-alkoxytropones (5), were prepared. The former showed monotropic smectic A phases and the virtual isotropic liquid-smectic A transitions of the latter were determined by extrapolation of results in a binary phase diagram. Comparing the mesogenic properties between the tropones 4 and the 2-alkanoyloxy-5-alkoxytropones (1), the alkanoyloxy group at C-5 enhances both the melting points and the transition temperatures of the smectic A phases. From the comparison between 5 and 1, the alkanoyloxy group at C-2 lowers the melting points. 相似文献
85.
86.
87.
Abstract Bacteriochlorophyll d analogues that possessed a series of bulky substituents of OMe, OCOMe, and OCO t Bu at the C71-position were synthesized (Zn-complexes of methyl 71-substituted-3-(1-hydroxy-methyl)pyropheophorbide a). Aggregation behavior of these pigments was examined in comparison with a natural-type compound (C71-H) to elucidate the effects of size of the C71-moiety on self-assembly of the chlorins. These C71-substituted Zn-chlorins formed self-aggregates in 1% THF/hexane. The aggregates gave almost the same visible absorption bands, especially a ca. 2000-cm?1 red-shifted Qy peak; the spectra were essentially similar to those of the natural-type Zn-chlorin (C71-H). All the aggregates of the C71-substituted compounds showed similar exciton-type CD couplets in the red-shifted Qy region, which were different from the feature of the couplet of the C71-H Zn-chlorin aggregate. These spectral data suggested that the C71-moiety did not interrupt the intermolecular linkages between chlorin molecules but altered the supramolecular structure which influences the long-range chirality. 相似文献
88.
Yu Dong Tariq Mosaval Hazim J. Haroosh Rehan Umer Hitoshi Takagi Kin‐Tak Lau 《Journal of Polymer Science.Polymer Physics》2014,52(9):618-623
This pilot study elaborates the development of novel epoxy/electrospun polylactic acid (PLA) nanofiber composites at the fiber contents of 3, 5, and 10 wt % to evaluate their mechanical and thermal properties using flexural tests and differential scanning calorimetry (DSC). The flexural moduli of composites increase remarkably by 50.8 and 24.0% for 5 and 10 wt % fiber contents, respectively, relative to that of neat epoxy. Furthermore, a similar trend is also shown for corresponding flexural strengths being enhanced by 31.6 and 4.8%. Fractured surface morphology with scanning electron microscopy (SEM) confirms a full permeation of cured epoxy matrix into nanofiber structures and existence of nondestructive fibrous networks inside large void cavities. The glass transition temperature (Tg) of composites increases up to 54–60 °C due to embedded electrospun nanofibers compared to 50 °C for that of epoxy, indicating that fibrous networks may further restrict the intermolecular mobility of matrix in thermal effects. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 618–623 相似文献
89.
Enhancement of Light Absorption Ability of Synthetic Chlorophyll Derivatives by Conjugation with a Difluoroboron Diketonate Group 下载免费PDF全文
Dr. Yusuke Kinoshita Dr. Yuichi Kitagawa Prof. Dr. Hitoshi Tamiaki 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(29):9996-10001
The enhancement of the light absorption ability of synthetic chlorophyll derivatives is demonstrated. Chlorophyll derivatives directly conjugated with a difluoroboron 1,3‐diketonate group at the C3 position were synthesized from methyl pyropheophorbide‐d through Barbier acylmethylation of the C3‐formyl moiety, oxidation of the C3‐carbinol, and difluoroboron complexation of the diketonate. Electronic absorption spectra in a diluted solution showed that the synthetic conjugates gave an absorption band at λ=400–500 nm, with a Qy band shifted to a longer wavelength of λ≈700 nm. DFT calculations demonstrated that the absorption bands and redshifts were ascribable to the coupling of the LUMO of chlorin with that of the difluoroboron diketonate moiety. The introduction of a pyrenyl group at the C33‐position of the conjugate afforded an additional charge‐transfer band over λ=500 nm, producing a pigment that bridged the green gap in standard chlorophylls. 相似文献