全文获取类型
收费全文 | 819篇 |
免费 | 11篇 |
专业分类
化学 | 610篇 |
晶体学 | 5篇 |
力学 | 9篇 |
数学 | 7篇 |
物理学 | 199篇 |
出版年
2023年 | 5篇 |
2021年 | 4篇 |
2020年 | 8篇 |
2019年 | 10篇 |
2016年 | 5篇 |
2015年 | 12篇 |
2014年 | 17篇 |
2013年 | 33篇 |
2012年 | 41篇 |
2011年 | 37篇 |
2010年 | 15篇 |
2009年 | 27篇 |
2008年 | 59篇 |
2007年 | 48篇 |
2006年 | 47篇 |
2005年 | 36篇 |
2004年 | 37篇 |
2003年 | 22篇 |
2002年 | 36篇 |
2001年 | 20篇 |
2000年 | 17篇 |
1999年 | 6篇 |
1998年 | 9篇 |
1996年 | 11篇 |
1995年 | 7篇 |
1994年 | 10篇 |
1993年 | 10篇 |
1992年 | 13篇 |
1991年 | 13篇 |
1990年 | 12篇 |
1989年 | 9篇 |
1988年 | 15篇 |
1987年 | 20篇 |
1986年 | 7篇 |
1985年 | 11篇 |
1984年 | 10篇 |
1983年 | 6篇 |
1982年 | 7篇 |
1981年 | 13篇 |
1980年 | 8篇 |
1979年 | 10篇 |
1978年 | 14篇 |
1977年 | 9篇 |
1976年 | 11篇 |
1975年 | 4篇 |
1974年 | 8篇 |
1973年 | 11篇 |
1970年 | 4篇 |
1967年 | 3篇 |
1966年 | 4篇 |
排序方式: 共有830条查询结果,搜索用时 78 毫秒
1.
Y Sonoda K Ichinose T Yoshimura Y Sato T Sasaki 《Chemical & pharmaceutical bulletin》1991,39(1):100-103
Lanosterol derivatives with a functional group at C-32 have been synthesized from 3 beta-acetoxylanostan-7 alpha-ol. The key reaction of the synthesis is the hypoiodite reaction of 3 beta-acetoxylanostan-7 alpha-ol. In vitro antitumor activity testing of the lanosterol derivatives revealed that 3 beta-hydroxylanost-7-en-32-oic acid has antineoplastic activity. 相似文献
2.
S. B. Ellis S. J. Kiehl W. S. Hughes K. Schwabe W. C. Gardiner H. L. Sanders H. Yoshimura Hanna Jablezynska-Jedrzewska J. Domański W. A. Dorfman P. Nylén Barbara Stone F. Hovorka W. C. Dearing E. Biilmann W. Kordatzki P. Wulff G. Florence A. Drilhon P. Szigeti O. Tomiček F. Poupě O. Redlich W. Stricks 《Analytical and bioanalytical chemistry》1937,111(2-4):94-104
3.
Etsuro Yoshimura Mariko Akashi Tomonari Umemura Kin-ichi Tsunoda 《Analytical sciences》2004,20(2):373-374
27Al NMR spectra of an equimolar (10 mM) Al(III)-citrate system were obtained at different temperatures. The linewidths of the signals decreased in the spectra recorded at elevated temperatures, which enabled us to unequivocally identify the resonance lines. From the spectrum recorded at 65 approximately C, a mononuclear Al(III)-citrate complex was identified at a solution pH of 3.0 in addition to trinuclear Al(III)-citrate complex, which dominated at pH 4.0. 相似文献
4.
5.
Masaaki Kubota Raul A. Reimer Kuniko Terajima Yuji Yoshimura Akio Nishijima 《Analytica chimica acta》1987
Inductively-coupled plasma/atomic emission spectrometry with a high-resolution vacuum scanning monochromator is described for the determination of sulfur at 180.734 nm. The behavior of the signal-to-background ratio is investigated as functions of RF power, argon gas flow rate and observation height above the load coil. Under the operating conditions selected, the detection limit is 3 μg l?1. The Se I 196.090-nm line is chosen as internal standard, because the S/Se line pair exhibited the least change with carrier gas flow rate and acid concentration of solution. Sulfur in NiMo and CoMo/ Al2O3 catalysts used for coal liquefaction is determined as S(II) and S(VI) species. The total amount of the species agreed well with the sulfur value obtained by the conventinal combustion method. 相似文献
6.
7.
Direct compression is able to produce tablets at a lower cost than wet granulation and tableting method, due to a fewer items of process validation. In this study, acetaminophen was used as a medicine with various granular diameters to formulate tablets by direct compression, thus evaluating their physical properties. Consequently, direct compression was found effective in formulating tablets with excellent physical properties, with the granular diameter taken into account. It was confirmed that tablets produced by direct compression were similar in physical properties in tablets produced by wet granulation and tableting method. Further, it was suggested that use of a dry-type binder would make it possible to provide a tablet having higher content of the medicine with excellent physical properties. 相似文献
8.
Interactions between poly(amidoamine) dendrimer (PAMAM)-gold nanocomposites and alkanethiols and between the former nanocomposites and thiol-modified poly(amidoamine) dendrons in ethyl acetate were investigated by adding alkanethiols, such as 1-propanethiol and 1,3-propanedithiol, and thiol-modified poly(amidoamine) dendrons, generations 0.5 and 2.5 (G0.5-SH and G2.5-SH). The PAMAM dendrimers with surface methyl ester groups used were generations 1.5 and 5.5 (G1.5 and G5.5). The mean particle sizes of PAMAM-gold nanocomposites were about 2.1 for G1.5 and 2.4 nm for G5.5. In both nanocomposite systems where 1-propanethiol and 1,3-propanedithiol were added, the mean particle size was about 4 nm, twice that of the systems where these thiols were not added. Increasing the addition of 1,3-propanedithiol made the average particle size smaller for both nanocomposites systems. To compare with alkanethiol, thiol-modified poly(amidoamine) dendron with a highly branched structure on one side was synthesized. Using G2.5-SH as a protective agent, dendron-gold nanocomposites with mean diameters of 3 to 4 nm were obtained. The difference in particle size was seen only when the combination of PAMAM-gold nanocomposites and thiol-modified dendron was less sterically dense, modified dendron (G0.5-SH). The mechanisms for morphology changes in the dendrimer-gold nanocomposites by the addition of these thiols are discussed. 相似文献
9.
Kunihito Miyake Yasuhiro Masaki Ikuya Miyamoto Shozo Yanagida Takeshi Ohno Akio Yoshimura Chyongjin Pac 《Photochemistry and photobiology》1993,58(5):631-636
We have investigated the photosensitized monomerization of the cis,syn -cyclobutane dimer of 1,3-di-methylthymine using riboflavin tetraacetate and a 5-deazaflavin derivative as photosensitizer. Although little monomerization of the dimer is induced by photoexcitation of the flavins in the absence of any additives, the flavins can function as an efficient photosensitizer in the presence of magnesium perchlorate. Mechanistic studies involving spectroscopic, quantum-yield and flash-photolysis measurements demonstrated that the photosensitized monomerization exclusively proceeds through electron transfer from the dimer to the triplet flavins complexed with Mg2+ . The effects of magnesium perchlorate are compared with those on the chloranil-photosensitized monomerization and also with the effects of HClO4 on the flavin-photosensitized reaction. 相似文献
10.
Optically active o-substituted diphenyl N-substituted sulphilimines are readily synthesised by the reaction of the corresponding sulphides and t-butyl hypochlorite in the presence of l-menthol and amide anions. (−)-N-p-Tolylsulphonylsulphilimines (1, 2) obtained were converted to the corresponding (−)-N-unsubstituted sulphilimines (8, 9) by treating them with concentrated sulphuric acid. When (−)-S-o-anisyl S-phenyl N-(unsubstituted) sulphilimine (8) was treated with acylating agents or acrylonitrile, the corresponding optically active (−)-N-substituted sulphilimines were prepared with complete retention at sulphur. The absolute configuration of (−)-S-o-anisyl S-phenyl N-p-tolylsulphonylsulphilimine (1) was determined by converting it to (+)-S-o-anisyl sulphoxide (17). CD curves of (−)-o-substituted diarylsulphilimines exhibited a negative Cotton effect at around 270–285 nm, which was assigned to (S)-configuration at sulphur by comparing with the analogous sulphoxides. The substituent on the imino group of the sulphilimine gave no appreciable effect on the CD behavior and the lack of substituent effect was considered to be due to the semi-polar character of the S(IV)-N bond. Unusual effect of o-methoxy group on the CD curves was discussed in connection with solvent effect. Mechanism of this asymmetric synthesis has been investigated, and it has become apparent that the diastereomeric menthoxysulphonium chloride was an excess of (RR)-configuration was formed initially and the amide anion attacks the S atom of the salt with net inversion. 相似文献