全文获取类型
收费全文 | 1682篇 |
免费 | 62篇 |
国内免费 | 6篇 |
专业分类
化学 | 1414篇 |
晶体学 | 24篇 |
力学 | 14篇 |
数学 | 68篇 |
物理学 | 230篇 |
出版年
2022年 | 13篇 |
2021年 | 14篇 |
2020年 | 18篇 |
2019年 | 36篇 |
2018年 | 15篇 |
2017年 | 9篇 |
2016年 | 43篇 |
2015年 | 32篇 |
2014年 | 55篇 |
2013年 | 68篇 |
2012年 | 100篇 |
2011年 | 113篇 |
2010年 | 74篇 |
2009年 | 50篇 |
2008年 | 115篇 |
2007年 | 108篇 |
2006年 | 112篇 |
2005年 | 126篇 |
2004年 | 113篇 |
2003年 | 94篇 |
2002年 | 71篇 |
2001年 | 18篇 |
2000年 | 21篇 |
1999年 | 17篇 |
1998年 | 28篇 |
1997年 | 21篇 |
1996年 | 16篇 |
1995年 | 11篇 |
1994年 | 7篇 |
1993年 | 5篇 |
1992年 | 17篇 |
1991年 | 10篇 |
1990年 | 8篇 |
1988年 | 7篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 17篇 |
1984年 | 14篇 |
1983年 | 9篇 |
1982年 | 16篇 |
1981年 | 18篇 |
1980年 | 12篇 |
1979年 | 22篇 |
1978年 | 11篇 |
1977年 | 11篇 |
1976年 | 8篇 |
1975年 | 7篇 |
1974年 | 9篇 |
1973年 | 9篇 |
1972年 | 3篇 |
排序方式: 共有1750条查询结果,搜索用时 15 毫秒
101.
Four new aromatic constituents, rhododendroketoside, (-)-sakuraresinoside, acernikol, and nikoenoside, were isolated from a Japanese folk medicine, the stem bark of Acer nikoense MAXIM. The structures of the new constituents were determined on the basis of chemical and physicochemical evidence. The principle cyclic diarylheptanoids were found to show inhibitory effects on the release of beta-hexosaminidase in RBL-2H3 cells. 相似文献
102.
Hatano T Bae AH Sugiyasu K Fujita N Takeuchi M Ikeda A Shinkai S 《Organic & biomolecular chemistry》2003,1(13):2343-2347
It was found that [60]fullerene encapsulated in p-sulfonatocalix[8]arene and single-walled carbon nanotubes (SWNTs) solubilized by sodium dodecylsulfate can be readily deposited on the ITO electrode by electrochemical oxidative polymerization of ethylenedioxythiophene (EDOT) without chemical modification of these carbon clusters. The driving force for the deposition is an electrostatic interaction between the anionic complexes and the cationic charges of poly(EDOT) formed in the oxidative polymerization process. The surface morphology was thoroughly characterized by scanning electron micrograph: the [60]fullerene/poly(EDOT) film is covered by nano-particles with 20-100 nm diameters whereas the SWNTs/poly(EDOT) film is covered by nanorods with several microm length and ca. 100 nm diameter. The results indicate that the anionic complexes act as nuclei for the polymer growth in the oxidation polymerization. Interestingly, when these modified ITO electrodes were photoirradiated, the appearance of a photocurrent wave was observed. The action spectra showed that the photoexcited energy of [60]fullerene or SWNTs is efficiently collected by the electroconductive poly(EDOT) film and transferred to the ITO electrode. 相似文献
103.
Masayuki Inoue 《Tetrahedron》2003,59(30):5645-5659
Ladder-shaped polyether natural products show diverse biological activities with extreme potency. As the initial phase of detailed SAR studies of bioactive polyethers, we set out to construct structurally simple mimics. This paper details the divergent synthesis of 6-X-7-6 tetracycles (X=7, 8, or 9) starting from a simple 6-membered ether. Key reactions in the synthesis include (i) the direct formation of an O,S-acetal by the coupling of an alcohol with an α-chlorosulfide, (ii) the construction of a 7-membered ring by radical cyclization, and (iii) cyclization to the 7, 8 or 9-membered ring via a ring-closing metathesis reaction. The neutral reaction conditions of our strategy enable the synthesis of a wide variety of substrates. The results of this study can be applied for the rapid construction of artificial polyether compounds with diversified molecular shapes and sizes. 相似文献
104.
Mieko Urano Hitoshi Kagawa Yoshihiro Harigaya Shaoshun Li Masayuki Onda 《Journal of heterocyclic chemistry》1991,28(8):1845-1847
A total synthesis of optically pure (+)-catechin pentaacetate has been established using the (-)-chalcon epoxide (100% ee) derived from 3,4,2′,4′,6′-pentakis(methoxymethoxy)chalcon as the starting material. The optical purity of the product is confirmed by 1H nmr analysis in the presence of a shift reagent. 相似文献
105.
Hamao Watanabe Jun Inose Tsutomu Muraoka Masayuki Saito Yoichiro Nagai 《Journal of organometallic chemistry》1983,244(4):329-341
The reaction of 1,2-dimethoxytetramethyldisilane with styrene and α-methylstyrene in the presence of NaOMe catalyst in tetrahydrofuran (THF) gave the new silacyclopentanes 1,1-dimethyl-2,4-diphenyl-1-silacyclopentane (IIIa) and 1,1,2,4-tetramethyl-2,4-diphenyl-1-silacyclopentane (IIIb), respectively. These silacyclopentanes were found to exist as cis-trans mixtures. The use of sodium metal in place of NaOMe afforded similar results. Reactions of a polysilane mixture, MeO-(SiMe2)nOMe (n ≧ 3), with the styrenes also gave similar results. In some cases, polysilacycloalkanes such as 1,2,3-trisilacyclopentanes (IV) and 1,2,3,4-tetrasilacyclohexanes (V) were obtained as by-products. A mechanism for the formation of the silacyclopentanes and polysilacycloalkanes is presented. It was found that electron impact decomposition of silacyclopentanes IIIa and IIIb, trisilacycloalkane IV and tetrasilacycloalkane V gave molecular ions corresponding to the silacyclopropane, cyclotrisilane and cyclotetrasilane systems. 相似文献
106.
107.
pharaonis phoborhodopsin (ppR, also called pharaonis sensory rhodopsin II [psRII]) is a member of the archaeal rhodopsin family and acts as a repellent phototaxis receptor of Natronobacterium pharaonis. Upon illumination, ppR is excited and undergoes a linear cyclic photoreaction, namely, a photocycle that constitutes photointermediates such as M- and O-intermediates (ppRM and ppRO, respectively). Under a constant background illumination (>600 nm) that irradiates ppRO, the decay rate of the flash-induced ppRO increased with an increase in the background light intensity, indicating the photoreactivity of ppRO. Azide did not influence the light-accelerated ppRO decay, but the time required for the cycle to be completed became shortened in an azide concentration-dependent manner because of acceleration of ppRM decay. Hence, the turnover rate of photocycling increased appreciably in the presence of both the background illumination and the azide. The observation reported previously (Schmies, G. et al. 2000, Biophys. J. 78:967-976) is discussed in connection with the present observations. 相似文献
108.
109.
Masayuki Tomiya Takeshi Fukushima Tadahiro Ogaya Yukiko Sone Shogo Mitsuhashi Toshimasa Toyo'oka 《Biomedical chromatography : BMC》2010,24(6):569-573
The levels of kynurenic acid, an endogenous antagonist of α7 nicotinic acetylcholine and N‐methyl‐D ‐aspartate receptors, were measured in microdialysis samples obtained from the prefrontal cortices of rats using column‐switching high‐performance liquid chromatography with fluorescence detection. When the perfusate was constantly infused at a rate of 1.0 μ/min, the in vitro recovery of kynurenic acid through the dialysis membrane was approximately 20.4%, and the precision was within 1.31%. Endogenous kynurenic acid in the microdialysis sample was clearly detected using column‐switching high‐performance liquid chromatography. As an application study, N‐acetyl‐L ‐aspartic acid, an endogenous metabolite and precursor of N‐acetyl‐L ‐aspartyl‐L ‐glutamic acid, which is an agonist of metabotropic glutamate receptors, was infused for 120 min through the microdialysis probe. The kynurenic acid level significantly increased during the infusion of N‐acetyl‐L ‐aspartic acid, suggesting that kynurenic acid might have some association with N‐acetyl‐L ‐aspartic acid in vivo. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
110.