全文获取类型
收费全文 | 1709篇 |
免费 | 30篇 |
国内免费 | 5篇 |
专业分类
化学 | 1356篇 |
晶体学 | 31篇 |
力学 | 18篇 |
综合类 | 1篇 |
数学 | 80篇 |
物理学 | 258篇 |
出版年
2021年 | 13篇 |
2020年 | 18篇 |
2019年 | 10篇 |
2018年 | 14篇 |
2017年 | 9篇 |
2016年 | 13篇 |
2015年 | 27篇 |
2014年 | 27篇 |
2013年 | 69篇 |
2012年 | 63篇 |
2011年 | 79篇 |
2010年 | 57篇 |
2009年 | 38篇 |
2008年 | 88篇 |
2007年 | 120篇 |
2006年 | 99篇 |
2005年 | 93篇 |
2004年 | 89篇 |
2003年 | 85篇 |
2002年 | 77篇 |
2001年 | 32篇 |
2000年 | 37篇 |
1999年 | 32篇 |
1998年 | 21篇 |
1997年 | 40篇 |
1996年 | 22篇 |
1995年 | 22篇 |
1994年 | 16篇 |
1993年 | 20篇 |
1992年 | 22篇 |
1991年 | 18篇 |
1990年 | 19篇 |
1989年 | 14篇 |
1988年 | 11篇 |
1987年 | 15篇 |
1986年 | 10篇 |
1985年 | 35篇 |
1984年 | 21篇 |
1983年 | 17篇 |
1982年 | 11篇 |
1981年 | 21篇 |
1980年 | 26篇 |
1979年 | 20篇 |
1978年 | 18篇 |
1977年 | 16篇 |
1976年 | 25篇 |
1975年 | 21篇 |
1974年 | 12篇 |
1973年 | 11篇 |
1968年 | 9篇 |
排序方式: 共有1744条查询结果,搜索用时 15 毫秒
91.
Mitsunori Fukaya Shota Nagamine Dr. Taro Ozaki Yaping Liu Miina Ozeki Taro Matsuyama Dr. Kazunori Miyamoto Prof. Dr. Hirokazu Kawagishi Prof. Dr. Masanobu Uchiyama Prof. Dr. Hideaki Oikawa Dr. Atsushi Minami 《Angewandte Chemie (International ed. in English)》2023,62(44):e202308881
Mushroom terpenoids are biologically and chemically diverse fungal metabolites. Among them, melleolides are representative sesquiterpenoids with a characteristic protoilludane skeleton. In this study, we applied a recently established hot spot knock-in method to elucidate the biosynthetic pathway leading to 1α-hydroxymelleolide. The biosynthesis of the sesquiterpene core involves the cytochrome P450 catalyzing stepwise hydroxylation of the Δ6-protoilludene framework and a stereochemical inversion process at the C5 position catalyzed by short-chain dehydrogenase/reductase family proteins. The highlight of the biosynthesis is that the flavoprotein Mld7 catalyzes an oxidation-triggered double-bond shift accompanying dehydration and acyl-group-assisted substitution with two different nucleophiles at the C6 position to afford the Δ7-protoilludene derivatives, such as melleolide and armillarivin. The complex reaction mechanism was proposed by DFT calculations. Of particular importance is that product distribution is regulated by interaction with the cell membrane. 相似文献
92.
N Kubodera K Miyamoto M Akiyama M Matsumoto T Mori 《Chemical & pharmaceutical bulletin》1991,39(12):3221-3224
Three vitamin D3 analogues, 1 alpha,25-dihydroxy-23-oxavitamin D3 (3), 1 alpha,25-dihydroxy-23-thiavitamin D3 (4) and 1 alpha,25-dihydroxy-23-azavitamin D3 (5) were synthesized. In the differentiation-inducing activity of human myeloid leukemia cells into macrophages in vitro, the 23-aza analogue (5) showed the least activity, while no remarkable differences were observed between the 23-oxa analogue (3) and the 23-thia analogue (4), which were less active than 1 alpha,25-dihydroxyvitamin D3 (1). 相似文献
93.
A Kamizono N Inotsume K Miyamoto K Ueda T Miyakawa H Arimoto M Nakano 《Journal of chromatography. A》1991,567(1):113-120
A sensitive and selective method has been developed for the determination of sultopride and tiapride in serum using gas chromatography with a surface ionisation detector. No interfering peaks from endogenous substances were observed. The method showed good reproducibility and accuracy, and the standard curve was linear up to 2 micrograms/ml with a correlation coefficient of 0.999. This method is applicable to pharmacokinetic studies and therapeutic drug monitoring of sultopride and tiapride. 相似文献
94.
95.
Akio Maeda Jun Sasaki Jean-Marc Pfefferl Yoshinori Shichida Tru Yoshizawa 《Photochemistry and photobiology》1991,54(6):911-921
Abstract– Difference Fourier transform infrared spectra were recorded for bacteriorhodopsin upon irradiation at 230, 170 or 77 K, which gave, respectively, the spectrum of the M, L or K intermediate minus unphotolyzed all-trans bacteriorhodopsin (denoted as BR). By replacement of the Schiff base nitrogen with 15N, or of either its hydrogen at N or C15 with deuterium, the vibrational bands related to the Schiff base were identified and the isotope-shifts evaluated for BR, K and L. The 1348 cm?l band of BR and K and the 1400 cm?1 band of L were sensitive to each of these isotope substitutions. The 1254 cm?1 band of BR, the 1245 cm?1 band of K and the 1301 cm?1 band of L were sensitive to either N- or C15-deuteration but not to 15N-substitution. The N—D in-plane bending vibration of K and L appeared at 969 and 997 cm?1, respectively, upon substitution with D2O. All the results show that L is larger in frequencies related to the N—H in-plane bending vibration than K or BR and suggest that L has the strongest interaction with the protein. Among the bands containing an N—H bending vibration, the 1348 cm?1 band of K was more intense than the corresponding band of L at 1400 cm?1. The C15-deuteration-induced upshift of the 1245 cm?1 band of K was unobservable for the 1301 cm?1 band of L. Such differences between L and K might be brought about by a distortion in the retinal moiety close to the protonated Schiff base of the 13-cis chromophore. 相似文献
96.
97.
Sorbitol was readily converted by heating in hydrophobic ionic liquids by the presence of ion exchange resins. Chemoseletivity of the dehydration depended on the choice of ion exchange resin; Nafion selectively produced isosorbide while Amberlite gave 1,5-anhydrosorbitol along with unreacted sorbitol. Ionic liquids used in the reaction were readily recovered by simple extraction procedure. With these procedures, we succeeded to prepare isosorbide in pure form, not contaminated with either ionic liquids or acid catalyst, by simple experimental procedure. 相似文献
98.
A. Koiwai H. Miyaji T. Asahi K. Asai Y. Miyamoto 《Journal of inclusion phenomena and macrocyclic chemistry》1986,4(3):255-264
The decomposition of urea adducts with hydrocarbons is treated as a first-order phase transition and the pressure dependence is studied up to 0.7 GPa for several kinds of adducts. The thermodynamic quantities at the decomposition of the adduct can be analysed as a sum of those quantities of the component materials. The transition from the orthorhombic to the hexagonal form of the adduct with polyethylene is also investigated by X-ray diffraction and the pressure dependence of the lattice parameters is measured for the adducts. The results are compared with the phase transition in the pure paraffin. 相似文献
99.
Akio Tanizaki Mitsuo Sawamoto Toshinobu Higashimura 《Journal of polymer science. Part A, Polymer chemistry》1986,24(1):87-96
The cationic polymerization of p-methylstyrene initiated by acetyl perchlorate at ?78°C led to long-lived (living-like) polymers with a narrow molecular weight distribution (M?w/M?n = 1.1–1.4) in methylene chloride containing a common ion salt (n-Bu4NClO4) or in a less polar solvent (CH2Cl2/toluene, 1/4v/v). Under these conditions, the number-average molecular weight (M?n) of the polymers increased in proportion to monomer conversion and was regulated by the monomer-to-initiator ratio. When fresh feeds of the monomer were repeatedly added to a completely polymerized solution, the polymerization ensued at the same rate as before and the linear increase in M?n with monomer conversion continued. The effects of solvent polarity and the common ion salt on the polymerization showed the suppression of the ionic dissociation of the propagating species, resulting in a “nondissociated species,” to be the key factor for the formation of the long-lived polymers. 相似文献
100.
正相高效液相色谱法分离检测壬基酚和短链壬基酚聚氧乙烯醚 总被引:4,自引:0,他引:4
建立了一种以正相高效液相色谱等强度洗脱分离检测壬基酚和短链壬基酚聚氧乙烯醚的新方法。采用Cosmosil5SL-Ⅱ(250mm×4.6mmi.d,5μm)色谱柱,以乙酸乙酯-乙醇为流动相,流速1.0mL/min,281nmUV检测,在10min内可分离检测p-壬基酚以及短链壬基酚聚氧乙烯醚混合物的3种主要组分。运用本方法对NP,NPnEO(n=1~3)进行测定的相对标准偏差分别为1.4%、1.6%、2.5%和1.4%;检出限分别为0.1mg/L(NP)和0.5mg/L(NPnEO),重复性好且灵敏度高。 相似文献