全文获取类型
收费全文 | 1456篇 |
免费 | 31篇 |
国内免费 | 3篇 |
专业分类
化学 | 1244篇 |
晶体学 | 16篇 |
力学 | 14篇 |
数学 | 15篇 |
物理学 | 201篇 |
出版年
2020年 | 9篇 |
2019年 | 10篇 |
2018年 | 12篇 |
2017年 | 10篇 |
2016年 | 18篇 |
2015年 | 24篇 |
2014年 | 28篇 |
2013年 | 79篇 |
2012年 | 59篇 |
2011年 | 70篇 |
2010年 | 52篇 |
2009年 | 29篇 |
2008年 | 65篇 |
2007年 | 78篇 |
2006年 | 90篇 |
2005年 | 102篇 |
2004年 | 82篇 |
2003年 | 75篇 |
2002年 | 71篇 |
2001年 | 22篇 |
2000年 | 28篇 |
1999年 | 20篇 |
1998年 | 14篇 |
1997年 | 20篇 |
1996年 | 26篇 |
1995年 | 9篇 |
1994年 | 15篇 |
1993年 | 9篇 |
1992年 | 15篇 |
1991年 | 11篇 |
1990年 | 11篇 |
1989年 | 12篇 |
1988年 | 17篇 |
1987年 | 10篇 |
1986年 | 11篇 |
1985年 | 12篇 |
1984年 | 25篇 |
1983年 | 11篇 |
1982年 | 25篇 |
1981年 | 28篇 |
1980年 | 35篇 |
1979年 | 15篇 |
1978年 | 10篇 |
1976年 | 14篇 |
1975年 | 8篇 |
1974年 | 10篇 |
1973年 | 12篇 |
1969年 | 8篇 |
1968年 | 15篇 |
1967年 | 12篇 |
排序方式: 共有1490条查询结果,搜索用时 0 毫秒
91.
Novel aryl-β-C-glucosidation method using glucal boronate was developed. This protocol can offer several advantages including use of non-toxic, easily handling glucal boronate as a crystalline solid and storable at room temperature for several months. Tri-O-methylnorbergenin (8,10-di-O-methylbergenin), an anti-HIV active bergenin derivative, was concisely synthesized by application of the aryl-β-C-glucosidation method. 相似文献
92.
Kazuyuki Kubo Hiroshi Nakazawa Hiroyasu Inagaki Tomoyuki Miyake Tsutomu Mizuta Katsuhiko Miyoshi 《Phosphorus, sulfur, and silicon and the related elements》2013,188(8-9):2159-2160
Treatment of [Cp*(CO) 2 M{P(NHPh)(OMe) 2 }]PF 6 (M = Fe and Ru) with NaNH 2 gives metallaiminophosphoranes, Cp*(CO) 2 M{P(NPh)(OMe) 2 }. The x-ray structures and reactivity of the complexes are reported. 相似文献
93.
Tatsuro Ouchi Kazuhiro Nomoto Yoshifumi Hosaka Minoru Imoto Tadao Nakaya Tsutomu Iwamoto 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(6-7):859-866
Abstract Three kinds of betaine-type polymers, which are macromolecular amphoteric electrolytes, were found to be able to polymerize vinyl monomers in aqueous solution through a radical mechanism without any further initiator. Betain-type polymers form hydrophobic areas (HA) in water. Vinyl polymerization commenced in the HA. The effect of the pH of the aqueous solution on polymerization was investigated. 相似文献
94.
A new type of optically active N-(L-menthylcarboxylatomethyl)maleimide (MGMI) was synthesized from maleic anhydride, glycine, and L-menthol. Radical homopolymerization of MGMI was performed at 50°C for 24 h to give optically active polymer having [α]D = -57°. Radical copolymerizations of MGMI (M 1) were performed with styrene (ST, M 2), methyl methacrylate (MMA, M 2) in benzene at 50°C. From the results, the monomer reactivity ratios (r 1, r 2) and the Alfrey-Price Q, e values were determined as follows: r 1 = 0.16, r 2 = 0.006 for the MGMI-ST system; r 1 = 0.15, r 2 = 1.65 for the MGMI-MMA system, and Q 1 = 0.72, e 1 = 1.59 calculated from the MGMI-MMA system. Anionic homopolymerizations of MGMI were also carried out. Chiroptical properties of the polymers were investigated. 相似文献
95.
Tatsuro Ouchi Hiroshi Sakamoto Yoshifumi Hosaka Minoru Imoto Tsutomu Iwamoto 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(8):1025-1038
Abstract The polymerization of some kinds of vinyl monomer was found to occur without an ordinary initiator in aqueous solutions of AB-type block or random copolymers of sodium methacrylate with styrene as a so-called “uncatalyzed polymerization.” Although the spin trapping technique showed that the initiation mechanism by the block copolymer was the same as that by the random copolymer, the initiating ability of the block copolymer was lower than that of the random copolymer. Such results are attributable to the difference in the incorporating ability of monomer into the micelles formed by the block copolymer and into the hydrophobic areas formed by the random copolymer. 相似文献
96.
Copolymerization of an optically active N-(1-menthyl carboxylatomethyl)citraconimide (MCMCI) was carried out with methyl methacrylate (MMA) with azobisisobutyronitrile as the initiator in benzene at 50°C. All the copolymers obtained were optically active. After the removal of the optically active menthyl group, the hydrolyzed poly(MCMCI-co-MMA)'s still showed optical activity. The asymmetric induction to the copolymer main chain and the mechanism are discussed based on the measurements of optical rotatory dispersion and circular dichroism of the original and hydrolyzed copolymers. 相似文献
97.
Tatsuro Ouchi Kazuo Hagita Hiroshi Sakamoto Minoru Imoto Tsutomu Iwamoto 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(12):1651-1665
Abstract The polymerization of some kinds of vinyl monomer was found to occur in aqueous solutions of poly(ethylene glycol) diglycolic acid (PEG Acid) or sodium poly(ethylene glycol) diglycolate (PEG Acid Na) through radical mechanisms without any further initiator, as a so-called “uncatalyzed polymerization.” Although the initiating radical species for PEG Acid was determined to be the same as that for PEG Acid Na by means of the spin-trapping technique, the initiating ability of PEG Acid was higher than that of PEG Acid Na. These results are assumed to be attributable to the difference in the initiation mechanisms of the two systems and in the incorporating abilities of monomer into the hydrophobic areas formed by PEG Acid and PEG Acid Na. 相似文献
98.
Atsunori Morigaki Kazuki Tsukade Satoru Arimitsu Tsutomu Konno Toshio Kubota 《Tetrahedron》2013,69(5):1521-1525
The reaction of β-fluoroalkylated α,β-unsaturated ketones with various enamines gave 4-fluoroalkylated 3,4-dihydro-2H-pyrans as a major product in good yields by a one-pot operation, and these products display the high diastereoselection just after single recrystallization. This unexpected result is rationalized by the unique reactivity of β-fluoroalkylated α,β-unsaturated ketones. As the synthetic application, 4-trifluoromethyl tetrahydropyran was synthesized in moderate isolated yield with high diastereoselectivity. 相似文献
99.
In this paper, we report the preparation and red-light-emitting behavior of benzothiadiazole–tris(alkyloxy)phenylethene dyes. In solution, we observed an efficient red light emission with high fluorescence quantum yields (up to 0.78). With increase in solvent polarity, the emission bands shifted to longer wavelengths accompanied by a large Stokes shift of up to 152 nm. A moderate fluorescence quantum yield of 0.52 could be achieved even in the polar solvent dimethylformamide. Red light emission with good fluorescence quantum yields (up to 0.50) was also observed in the bulk solid, liquid, and film state. 相似文献
100.
Little is known of the biosynthesis of sesquarterpenes and the synthesis of unnatural terpenoids by sesquarterpene biosynthetic enzymes has not yet been reported. In this study, the enzymatic cyclization of head-to-tail acyclic triterpene β-hexaprene—a natural product isolated from Bacillus clausii—using tetraprenyl-β-curcumene cyclase (TC) from Bacillus subtilis resulted in the formation of two unnatural pentacyclic triterpenes. It was revealed that B. subtilis TC, which forms tetracyclic terpenoid scaffold from tetraprenyl-β-curcumene in vivo, could be used to construct the 6/6/6/6/6-fused pentacyclic scaffold in vitro, suggesting that the active site cavity of TC has sufficient space to accommodate this unnatural pentacyclic scaffold. This is the first report demonstrating the utility of a sesquarterpene cyclase toward the synthesis of unnatural terpenoids. 相似文献