全文获取类型
收费全文 | 181篇 |
免费 | 6篇 |
专业分类
化学 | 120篇 |
晶体学 | 1篇 |
力学 | 4篇 |
数学 | 27篇 |
物理学 | 35篇 |
出版年
2023年 | 4篇 |
2022年 | 2篇 |
2021年 | 2篇 |
2020年 | 3篇 |
2019年 | 6篇 |
2017年 | 2篇 |
2016年 | 2篇 |
2015年 | 9篇 |
2014年 | 2篇 |
2013年 | 3篇 |
2012年 | 8篇 |
2011年 | 12篇 |
2010年 | 6篇 |
2009年 | 10篇 |
2008年 | 9篇 |
2007年 | 9篇 |
2006年 | 4篇 |
2005年 | 8篇 |
2004年 | 5篇 |
2003年 | 6篇 |
2002年 | 8篇 |
2001年 | 8篇 |
1999年 | 1篇 |
1998年 | 6篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 5篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 5篇 |
1988年 | 9篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1969年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有187条查询结果,搜索用时 250 毫秒
61.
62.
Nagatsu A Sugitani T Mori Y Okuyama H Sakakibara J Mizukami H 《Natural product research》2004,18(3):231-239
A simple but novel compound, S-1-methoxy-1-(3,5-dimethoxy-4-hydroxyphenyl)ethane, was isolated as a moderately antioxidative compound from rape (Brassica campestris L. subsp. napus) oil cake together with 5 known compounds. Three of these compounds, indolacetonitrile, 4-hydroxyindolacetonitrile, and 4-hydroxyphenylacetonitrile, showed strong antioxidative activity evaluated by the ferric thiocyanate method. 相似文献
63.
Hirakawa K Yoshida M Nagatsu A Mizukami H Rana V Rawat MS Oikawa S Kawanishi S 《Photochemistry and photobiology》2005,81(2):314-319
Photosensitized DNA damage participates in solar-UV carcinogenesis, photogenotoxicity and phototoxicity. A chemoprevention of photosensitized DNA damage is one of the most important methods for the above phototoxic effects. In this study, the chemopreventive action of xanthone (XAN) derivatives (bellidifolin [BEL], gentiacaulein [GEN], norswertianin [NOR] and swerchirin [SWE]) on DNA damage photosensitized by riboflavin was demonstrated using [32P]-5'-end-labeled DNA fragments obtained from genes relevant to human cancer. GEN and NOR effectively inhibited the formation of piperidine-labile products at consecutive G residues by photoexcited riboflavin, whereas BEL and SWE did not show significant inhibition of DNA damage. The four XAN derivatives decrease the formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo), an oxidative product of G, by photoexcited riboflavin. The preventive action for the 8-oxodGuo formation of these XAN derivatives increased in the following order: GEN>NOR>BEL>SWE. A fluorescence spectroscopic study and ab initio molecular orbital calculations suggested that the prevention of DNA photodamage is because of the quenching of the triplet excited state of riboflavin by XAN derivatives through electron transfer. This chemoprevention is based on neither antioxidation nor a physical sunscreen effect; rather, it is based on the quenching of a photosensitizer. In conclusion, XAN derivatives, especially GEN, may act as novel chemopreventive agents by the quenching mechanism of an excited photosensitizer. 相似文献
64.
1H NMR, (13)C NMR, and EPR spectra of six-coordinate ferric porphyrin complexes [Fe(Por)L2]ClO4 with different porphyrin structures are presented, where porphyrins (Por) are planar 5,10,15,20-tetraphenylporphyrin (TPP), ruffled 5,10,15,20-tetraisopropylporphyrin (TiPrP), and saddled 2,3,7,8,12,13,17,18-octaethyl-5,10,15,20-tetraphenylporphyrin (OETPP), and axial ligands (L) are weak oxygen ligands such as pyridine-N-oxide, substituted pyridine-N-oxide, DMSO, DMF, MeOH, THF, 2-MeTHF, and dioxane. These complexes exhibit the spin states ranging from an essentially pure high-spin (S = 5/2) to an essentially pure intermediate-spin (S = 3/2) state depending on the field strength of the axial ligands and the structure of the porphyrin rings. Reed and Guiset reported that the pyrrole-H chemical shift is a good probe to determine the spin state in the spin admixed S = 5/2,3/2 complexes (Reed, C. A.; Guiset, F. J. Am. Chem. Soc. 1996, 118, 3281-3282). In this paper, we report that the chemical shifts of the alpha- and beta-pyrrole carbons can also be good probes to determine the spin state because they have shown good correlation with those of the pyrrole-H or pyrrole-C(alpha). By putting the observed or assumed pyrrole-H or pyrrole-C(alpha) chemical shifts of the pure high-spin and pure intermediate-spin complexes into the correlation equations, we have estimated the carbon chemical shits of the corresponding complexes. The orbital interactions between iron(III) and porphyrin have been examined on the basis of these chemical shifts, from which we have found that both the d(xy)-a(2u) interaction in the ruffled Fe(T(i)PrP)L2+ and d(xy)-a(1u) interaction in the saddled Fe(OETPP)L2+ are quite weak in the high-spin and probably in the intermediate-spin complexes as well. Close inspection of the correlation lines has suggested that the electron configuration of an essentially pure intermediate-spin Fe(T(i)PrP)L2+ changes from (d(xy), d(yz))3(d(xy))1(d(z)2)1 to (d(xy))2(d(xz), d(yz))2(d(z)2)1 as the axial ligand (L) changes from DMF to MeOH, THF, 2-MeTHF, and then to dioxane. Although the DFT calculation has indicated that the highly saddled intermediate-spin Fe(OETPP)(THF)2+ should adopt (d(xy), d(yz))3(d(xy))1(d(z)2)1 rather than (d(xy))2(d(xz), d(yz))2(d(z)2)1 because of the strong d(xy)-a(1u) interaction (Cheng, R.-J.; Wang, Y.-K.; Chen, P.-Y.; Han, Y.-P.; Chang, C.-C. Chem. Commun. 2005, 1312-1314), our 13C NMR study again suggests that Fe(OETPP)(THF)2+ should be represented as (d(xy))2(d(xz), d(yz))2(d(z)2)1 because of the weak d(xy)-a(1u) interaction. The contribution of the S = 3/2 state in all types of the spin admixed S = 5/2,3/2 six-coordinate complexes has been determined on the basis of the (13)C NMR chemical shifts. 相似文献
65.
Akito Tsuboi 《Mathematical Logic Quarterly》2001,47(1):45-50
Let T1 and T2 be two simple complete theories in disjoint languages. We prove that there is a simple complete theory which extends T1 ∪ T2 if T2 has a certain condition. 相似文献
66.
We investigate stationarity of types over models in simple theories. In particular, we show that in simple theories with finite SU‐rank, any complete type over a model having Cantor‐Bendixson rank is stationary. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
67.
The magnetic hyperfine structure of atoms is studied. A new compact expression is introduced for the magnetic hyperfine anomaly. A theoretical foundation is given for an empirical formula discovered by Moskowitz and Lombardi. The effects of core polarization and mesonic exchange currents are discussed. There are two kinds of core polarization, Δl = 0 and Δl = 2. The latter is shown to be important to explain certain isotope shifts, though it is smaller than the former Δl = 0 effect. 相似文献
68.
A simple method to synthesize (+/-)-2-O-(4-coumaroyl)-3-(4-hydroxyphenyl)lactic acid (1), a key intermediate in rosmarinic acid biosynthesis in higher plant cells, was established by condensation of protected 4-coumaric acid and (+/-)-3-(4-hydroxyphenyl)lactic acid followed by deprotection. A stable supply of 1 thus attained will lead to biochemical and molecular biological characterization of later steps of rosmarinic acid biosynthesis. 相似文献
69.
70.
Science China Mathematics - Motivated by the study of coupled Kähler-Einstein metrics by Hultgren and Witt Nyström (2018) and coupled Kähler-Ricci solitons by Hultgren (2017), we... 相似文献