全文获取类型
收费全文 | 415篇 |
免费 | 22篇 |
国内免费 | 1篇 |
专业分类
化学 | 280篇 |
晶体学 | 6篇 |
力学 | 10篇 |
数学 | 43篇 |
物理学 | 99篇 |
出版年
2021年 | 7篇 |
2020年 | 4篇 |
2019年 | 7篇 |
2018年 | 3篇 |
2017年 | 3篇 |
2016年 | 14篇 |
2015年 | 11篇 |
2014年 | 15篇 |
2013年 | 18篇 |
2012年 | 17篇 |
2011年 | 26篇 |
2010年 | 15篇 |
2009年 | 14篇 |
2008年 | 29篇 |
2007年 | 20篇 |
2006年 | 23篇 |
2005年 | 18篇 |
2004年 | 28篇 |
2003年 | 20篇 |
2002年 | 19篇 |
2001年 | 13篇 |
2000年 | 6篇 |
1998年 | 8篇 |
1997年 | 8篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 7篇 |
1992年 | 10篇 |
1991年 | 2篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 7篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 10篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1975年 | 5篇 |
1974年 | 4篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1967年 | 2篇 |
1964年 | 1篇 |
1963年 | 2篇 |
排序方式: 共有438条查询结果,搜索用时 15 毫秒
381.
When a Hg/NH3 mixture is irradiated at 260 nm or longer wavelengths luminescence appears around 340 nm. The luminescence originates from an excited HgNH3 complex formed through a bound—free transition. Both the luminescence excitation spectrum and the dispersed spectrum have been analysed in terms of postulated potentials for the ground and excited-state HgNH3 complexes. 相似文献
382.
Yuu Maezawa Toshiki Maruyama Naoyuki Itagaki Tetsuo Hatsuda 《Acta Physica Hungarica A》2005,22(1-2):61-68
The problem of the long life time of the pentaquark Θ+ is investigated on the basis of the color molecular dynamics simulation. We find that it takes a long time (typically of 50–100 fm/c) for the initial pentaquark state to rearrange its color and spatial positions to decay into the nucleon+kaon final state. Structure of the potential surface in the color and position spaces also supports this picture. Pentaquark wanders on the potential surface to find a narrow channel to decay. 相似文献
383.
The synthesis of side chain-type polyurethanes is described. Their thermal properties were investigated by differential scanning calorimetry and polarizing microscopy and are discussed in terms of the dependence of the polymer backbone on temperature as shown by FT-infrared spectroscopy. The hydrogen bonding which arises from the rather flexible polymer backbone plays a more important role in determining the thermal stability than does the rigid polymer backbone. 相似文献
384.
385.
Naoyuki Kotoku 《Tetrahedron》2005,61(30):7211-7218
An efficient total synthesis of bastadin 6 (1), a cyclic tetramer of brominated tyrosine derivatives from the marine sponge, Ianthella basta, with selective anti-angiogenic activity, was accomplished. We developed a novel Ce(IV)-mediated oxidative coupling reaction of 2,6-dibromophenols to give the diaryl ether derivatives, the characteristic segment of 1. Condensation of two segments and subsequent intramolecular macrocyclization gave bastadin 6 (1) in nine steps, 26% overall yield. 相似文献
386.
Imamura S Ishihara Y Hattori T Kurasawa O Matsushita Y Sugihara Y Kanzaki N Iizawa Y Baba M Hashiguchi S 《Chemical & pharmaceutical bulletin》2004,52(1):63-73
A novel lead compound, N-(3-[4-(4-fluorobenzoyl)piperidin-1-yl]propyl)-1-methyl-5-oxo-N-phenylpyrrolidine-3-carboxamide (1), was identified as a CCR5 antagonist by high-throughput screening using [(125)I]RANTES and CCR5-expressing CHO cells. The IC(50) value of 1 was 1.9 microM. In an effort to improve the binding affinity of 1, a series of 5-oxopyrrolidine-3-carboxamides was synthesized. Introduction of 3,4-dichloro substituents to the central phenyl ring (10i, IC(50)=0.057 microM; 11b, IC(50)=0.050 microM) or replacing the 1-methyl group of the 5-oxopyrrolidine moiety with a 1-benzyl group (12e, IC(50)=0.038 microM) was found to be effective for improving CCR5 affinity. Compound 10i, 11b, and 12e also inhibited CCR5-using HIV-1 envelope-mediated membrane fusion with IC(50) values of 0.44, 0.19, and 0.49 microM, respectively. 相似文献
387.
Shimono S Tamura R Ikuma N Takimoto T Kawame N Tamada O Sakai N Matsuura H Yamauchi J 《The Journal of organic chemistry》2004,69(2):475-481
A synthetic procedure for optically active and racemic alpha-nitronyl nitroxides (alpha-NNs) having a stereogenic center at the 4-position of the imidazolyl ring is described. This procedure consists of (1) the synthesis of a dissymmetric vic-dinitro compound by Kornblum reaction, (2) the enantiomeric resolution of the racemate by a diastereomer method for obtaining the optically active sample, (3) the quick reduction of the optically active or racemic vic-dinitro compound to the bis(hydroxyamino) derivative with Al/Hg, (4) the solvent-free condensation of the bis(hydroxyamino) compound with an aldehyde to give the 1,3-dihydroxyimidazolidine, and (5) the final oxidation of the alpha-NN precursor with aqueous NaIO(4). The absolute configuration of the optically active alpha-NNs was assigned by correlating with the X-ray crystal structure of the (-)-(1S,4R)-camphanic acid ester derivative of the optically active vic-dinitro compound. The molecular conformation of the optically active alpha-NNs was found to be folded both in solution and in the solid state by CD spectroscopy and energy minimization with the Monte Carlo method. The magnetic properties of both optically active and racemic alpha-NNs in solution and in the solid state were characterized by EPR spectroscopy and magnetic susceptibility measurement, respectively. 相似文献
388.
Seto M Aramaki Y Okawa T Miyamoto N Aikawa K Kanzaki N Niwa S Iizawa Y Baba M Shiraishi M 《Chemical & pharmaceutical bulletin》2004,52(5):577-590
The search for orally active CCR5 antagonists was performed by chemical modification of the 1-benzothiepine 1,1-dioxide 3 and 1-benzazepine 4 lead compounds containing a tertiary amine moiety. Replacement of methyl group with a 2-(C(2-4) alkoxy)ethoxy group at the 4-position on the 7-phenyl group of the 1-benzothiepine ring resulted in both enhanced activity and significant improvement in the pharmacokinetic properties upon oral administration in rats. Introduction of C(2-4) alkyl, phenyl or (hetero)arylmethyl groups as the 1-substituent on the 1-benzazepine ring together with the 2-(butoxy)ethoxy group led to further increase of activity. Among the 1-benzazepine derivatives, the isobutyl (6i), benzyl (6o) or 1-methylpyrazol-4-ylmethyl (6s) compounds were found to exhibit highly potent inhibitory effects, equivalent to the injectable CCR5 antagonist 1, in the HIV-1 envelope-mediated membrane fusion assay. In particular, compound 6s showed the most potent CCR5 antagonistic activity (IC(50)=2.7 nM) and inhibitory effect (IC(50)=1.2 nM) on membrane fusion, together with good pharmacokinetic properties in rats. The synthesis of 1-benzothiepine 1,1-dioxide and 1-benzazepine derivatives and their biological activity are described. 相似文献
389.
Horiguchi T Rithner CD Croteau R Williams RM 《The Journal of organic chemistry》2002,67(14):4901-4903
Taxa-4(20),11(12)-dien-5 alpha-acetoxy-10 beta-ol 6 has been identified as an early stage intermediate involved in the biosynthesis of taxol (Paclitaxel). This compound has been efficiently prepared by Barton deoxygenation of the C-2- and C-14-hydroxyl groups on a derivative semisynthetically prepared from taxa-4(20),11(12)-dien-2 alpha,5 alpha,10 beta-triacetoxy-14 beta-(2-methyl)butyrate (7), a major taxoid metabolite isolated from Japanese yew heart wood. The synthetic methodology is amenable for the preparation of isotopically labeled congeners that will be useful to probe further intermediate steps in the biosynthesis of taxol. 相似文献
390.
Xiuyun Wang Hiroaki Watanabe Naoyuki Sekioka Hiroshi Hamana Shunichi Uchiyama 《Electroanalysis》2007,19(12):1300-1306
A large oxidation current can be observed when ammonium carbamate aqueous solution is electrolyzed using a glassy carbon electrode (GCE) at a potential exceeding 1.0 V vs. Ag/AgCl and amino groups are introduced at the surface of the GCE. Aminated GCE exhibits the electrocatalytic activity of the oxidation of ammonium carbamate that is produced from urea as an intermediate product of urease reaction, and a distinct oxidation current is observed when the aminated GCE is used to oxidize the urea in the urease solution. A novel amperometric determination method to detect urea has been developed. This method is based on the electrooxidation of carbamic acid produced during urease reactions. Urease is immobilized to polymaleimidostyrene (PMS) coated on the insulated amorphous carbon sheet set on the aminated GCE surface. A good linear relationship is observed between urea concentration and the electrolytic current of the urease‐immobilized electrode in the concentration range from 0.5 mM to 21.0 mM. The proposed urea biosensor has an effective merit in that the interference resulting from ammonia and pH change caused by the urease reaction can be eliminated, differing from conventional urea biosensors. 相似文献