全文获取类型
收费全文 | 456篇 |
免费 | 8篇 |
国内免费 | 1篇 |
专业分类
化学 | 356篇 |
晶体学 | 8篇 |
力学 | 6篇 |
数学 | 26篇 |
物理学 | 69篇 |
出版年
2021年 | 4篇 |
2020年 | 8篇 |
2019年 | 2篇 |
2018年 | 6篇 |
2017年 | 5篇 |
2016年 | 6篇 |
2015年 | 7篇 |
2014年 | 6篇 |
2013年 | 23篇 |
2012年 | 24篇 |
2011年 | 20篇 |
2010年 | 10篇 |
2009年 | 21篇 |
2008年 | 24篇 |
2007年 | 25篇 |
2006年 | 21篇 |
2005年 | 18篇 |
2004年 | 17篇 |
2003年 | 23篇 |
2002年 | 27篇 |
2001年 | 10篇 |
2000年 | 9篇 |
1999年 | 3篇 |
1998年 | 10篇 |
1997年 | 8篇 |
1996年 | 10篇 |
1995年 | 6篇 |
1994年 | 6篇 |
1993年 | 5篇 |
1992年 | 5篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 10篇 |
1984年 | 14篇 |
1983年 | 2篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1976年 | 2篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1973年 | 2篇 |
1968年 | 1篇 |
排序方式: 共有465条查询结果,搜索用时 15 毫秒
51.
Yoshihiko Ito Hiroshi Imai Takaharu Matsuura Takeo Saegusa 《Tetrahedron letters》1984,25(29):3091-3094
This paper describes the finding that BF3 etherate effectuates the conjugate additions of copper(I) aldimines, generated in situ from lithium aldimines and Cu(I) halide, to α,β-unsaturated carbonyl compounds to produce 4-(N-alkylimino)-ketones, which give on acid hydrolysis 1,4-diketone derivatives. 相似文献
52.
Katsuo Ohkata Yoshihiko Ohyama Yuko Watanabe Kin-ya Akiba 《Tetrahedron letters》1984,25(40):4561-4564
Substituents at 5-position of 5-amino-3-methyl- and 3-p-chlorophenyl-5-methylisothiazoles (7 and 8) were silylated and then lithiated to couple with aromatic nitriles in order to afford the adducts (4 and 5) via 1,3-silyl group shift. Desilylation of 5 with TBAF gave solely non-ring-transformed product (3-α-form). By using the pure sample of 3-α-form, the reversible ring-trans- formation (bond switch) was observed for the first time. 相似文献
53.
Shosuke Yamamura Masatoki Ito Masatake Niwa Izumi Hasegawa Shigeru Ohba Yoshihiko Saito 《Tetrahedron letters》1981,22(8):739-740
Tricyclosolidagolactone has been isolated from the leaves of L., and its structure also been elucidated on the basis of its spectral data coupled with an X-ray crystallographic analysis of the corresponding trihydroxy compound produced on LiAlH4 reduction. 相似文献
54.
55.
Three novel 22-beta-O-spirostanol oligoglycosides, torvosides J (1), K (2) and L (3) have been isolated from the fruits of Solanum torvum SWARTZ and their chemical structures have been characterized based on the spectroscopic means. They are worth of note as rare 22-beta-O-spirostanol glycosides. 相似文献
56.
Hiroharu Suzuki Hidehiko Yashima Toshiyuki Hirose Mitsuru Takahashi Yoshihiko Moro-Oka Tsuneo Ikawa 《Tetrahedron letters》1980,21(51):4927-4930
Trans-tetrahydrofuran-3-carbaldehydes are prepared by ruthenium-catalyzed isomerization of 4,7-dihydro-1,3-dioxepines and subsequent Lewis acid-catalyzed 1,3-alkyl migration. 相似文献
57.
58.
We observed self-formations of multiple lasing channels and two-dimensional lasing patterns consisting of composite local modes having different lasing frequencies in a laser-diode-pumped wide-aperture thin-slice solid-state laser with imperfect reflective end surfaces. Global patterns resembling higher-order Hermite-Gaussian modes or possessing N-fold rotational symmetries were experimentally shown to appear due to the standard polished surface roughness of closely spaced reflective ends and nonlinear modal interactions. 相似文献
59.
The reactivity of neurotransmitters toward hydrogen abstraction by an active oxygen species (the cumylperoxyl radical) is comparable to that of a strong antioxidant such as catechin due to the strong intramolecular hydrogen bonding, which has been successfully detected by ESR. 相似文献
60.
Hiromitsu Terao Yoshihiko Kai Kazuyo Kita Yoshihiro Furukawa 《Hyperfine Interactions》2010,198(1-3):93-101
The crystals of 4-NH2PyHSbI4 (Py = C5H4N) have been investigated by means of 127I NQR, 1H NMR T 1 and DTA. The crystals can exist in two modifications of β and α(I) at room temperatures. The α(I)-phase is a metastable state which is obtained when the stable β form is heated. The α(I)-phase undergoes a first-order type phase transition of α(I) $\leftrightarrow \alpha $ (II) at 272 K (on heating), while the β-phase is stable down to 77 K. Four and two 127I (m = ±1/2 $\leftrightarrow \pm $ 3/2) NQR lines have been found for the β- and α(II)-phases, respectively. One half of them is assignable to the terminal I atom(s) and the other to the bridging I atom(s) in each phase. All the resonance lines of the α(II)-phase underwent a disappearance above ca. 240 K and no resonance line was observed in the α(I)-phase. The second moment M 2 value of 1H NMR spectra with 8 G2 at 290 K shows that the 4-NH2PyH?+? cations reside in the rigid lattice in the β-phase. In contrast, in the α(I)-phase the cation rotates about an axis more symmetric than pseudo threefold axis. The activation energy of 21 kJ mol???1 was estimated for the reorientational motion in the α(I)-phase from the 1H NMR T 1 measurements. The nature of phase transitions in the 4-NH2PyHSbI4 is discussed in comparison with that in 4-NH2PyHSbBr4. 相似文献