全文获取类型
收费全文 | 470篇 |
免费 | 13篇 |
国内免费 | 1篇 |
专业分类
化学 | 345篇 |
晶体学 | 3篇 |
力学 | 17篇 |
数学 | 56篇 |
物理学 | 63篇 |
出版年
2021年 | 2篇 |
2020年 | 7篇 |
2019年 | 5篇 |
2018年 | 2篇 |
2017年 | 6篇 |
2016年 | 6篇 |
2015年 | 9篇 |
2014年 | 14篇 |
2013年 | 20篇 |
2012年 | 26篇 |
2011年 | 28篇 |
2010年 | 13篇 |
2009年 | 14篇 |
2008年 | 27篇 |
2007年 | 34篇 |
2006年 | 33篇 |
2005年 | 22篇 |
2004年 | 25篇 |
2003年 | 14篇 |
2002年 | 25篇 |
2001年 | 5篇 |
2000年 | 2篇 |
1999年 | 4篇 |
1998年 | 7篇 |
1997年 | 2篇 |
1996年 | 5篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1992年 | 10篇 |
1991年 | 6篇 |
1990年 | 2篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1985年 | 10篇 |
1984年 | 11篇 |
1982年 | 10篇 |
1981年 | 8篇 |
1980年 | 2篇 |
1979年 | 5篇 |
1978年 | 7篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1974年 | 7篇 |
1973年 | 4篇 |
1968年 | 2篇 |
1964年 | 2篇 |
1959年 | 1篇 |
排序方式: 共有484条查询结果,搜索用时 125 毫秒
441.
[reaction: see text] The enantioselective [2 + 2 + 2] cycloaddition of 1,6-enynes and alkynes using chiral rhodium catalysts gave cycloadducts containing quaternary carbon stereocenters. Both symmetrical and unsymmetrical alkynes and acetylene could be used as coupling partners, and the corresponding bicyclic cyclohexa-1,3-dienes were obtained in good to excellent ee. 相似文献
442.
Hata M Tanaka Y Fujii Y Neya S Hoshino T 《The journal of physical chemistry. B》2005,109(33):16153-16160
The whole reaction of the deacylation of class C beta-lactamase was investigated by performing quantum chemical calculations under physiological conditions. In this study, the X-ray crystallographic structure of the inhibitor moxalactam-bound class C beta-lactamase (Patera et al. J. Am. Chem. Soc. 2000, 122, 10504-10512.) was utilized and moxalactam was changed into the substrate cefaclor. A model for quantum chemical calculations was constructed using an energy-minimized structure of the substrate-bound enzyme obtained by molecular mechanics calculation, in which the enzyme was soaked in thousands of TIP3P water molecules. It was found that the deacylation reaction consisted of two elementary processes. The first process was formation of a tetrahedral intermediate, which was initiated by the activation of catalytic water by Tyr150, and the second process was detachment of the hydroxylated substrate from the enzyme, which associated with proton transfer from the side chain of Lys67 to Ser64O(gamma). The first process is a rate-determining process, and the activation energy was estimated to be 30.47 kcal/mol from density functional theory calculations considering electron correlation (B3LYP/6-31G**). The side chain of Tyr150 was initially in a deprotonated state and was stably present in the active site of the acyl-enzyme complex, being held by Lys67 and Lys315 cooperatively. 相似文献
443.
Our theory is useful for establishing the convergence of a crystalline algorithm as well as for justifying the crystalline
flow as a limit of anisotropic curvature flow with smooth interfacial energy.
Accepted March 29, 2001?Published online September 3, 2001 相似文献
444.
Takanori Shibata Shiho Yoshida Yoshikazu Arai Maiko Otsuka Kohei Endo 《Tetrahedron》2008,64(5):821-830
A chiral iridium complex catalyzed a consecutive and enantioselective [2+2+2] cycloaddition of polyynes to give axially chiral compounds. Intermolecular reaction of tetraynes, possessing aryl groups on their termini, with protected but-2-yne-1,4-diols gave C2-symmetrical quateraryl compounds. Intramolecular reaction of hexaynes, possessing aryl or alkyl groups on their termini gave C2-symmetrical biaryl compounds. The catalytic synthesis of a pentacene derivative with axial chiralities is also discussed. 相似文献
445.
Mugio Nishizawa Tomoaki Iyenaga Hirofumi Yamamoto Kosuke Namba Yoshikazu Shizuri Yoshihide Matsuo 《Tetrahedron letters》2007,48(24):4229-4233
Total synthesis of (±)-thallusin was achieved using Hg(OTf)2·PhNMe2-induced olefin cyclization, and Suzuki coupling with a pyridylboronic acid derivative. Hg(OTf)2 also acted as a catalyst to isomerize the double bond into the more thermodynamically stable isomer when treated in toluene. Synthetic (±)-thallusin as well as an analogue showed morphogenesis-inducing activity. 相似文献
446.
Yoshikazu Kobayashi Toshitaka Matsumoto Naoki Tanaka 《Journal of Mathematical Analysis and Applications》2007,330(2):1042-1067
In this paper we introduce the notion of semigroups of locally Lipschitz operators which provide us with mild solutions to the Cauchy problem for semilinear evolution equations, and characterize such semigroups of locally Lipschitz operators. This notion of the semigroups is derived from the well-posedness concept of the initial-boundary value problem for differential equations whose solution operators are not quasi-contractive even in a local sense but locally Lipschitz continuous with respect to their initial data. The result obtained is applied to the initial-boundary value problem for the complex Ginzburg–Landau equation. 相似文献
447.
Hideki Jona Jun Shibata Masanori Asai Yasuhiro Goto Sachie Arai Shigeru Nakajima Osamu Okamoto Hiroshi Kawamoto Yoshikazu Iwasawa 《Tetrahedron: Asymmetry》2009,20(21):2439-2446
An efficient and practical asymmetric synthesis of 1-tert-butyl 3-methyl (3R,4R)-4-(2-oxo-2,3-dihydro-1H-benzimidazol-1-yl)piperidine-1,3-dicarboxylate 1, a useful intermediate for the synthesis of nociceptin antagonists, has been developed. This method includes the following key steps: (1) diastereoselective reduction of a chiral enaminoester 3 having (R)-1-phenylethylamine as a chiral pool constituent with the use of a combined TFA–NaBH4 reduction system and (2) efficient isomerization from 3,4-cis-substituted piperidine 8 to 3,4-trans-substituted piperidine 1 under basic conditions. The above methods proved to be applicable for large-scale operation and hundred grams of enantiomerically pure compound 1 (>98% ee) was obtained. 相似文献
448.
449.
Yoshikazu Kobayashi 《Journal of Mathematical Analysis and Applications》2008,338(2):852-872
A generation theorem of semigroups of locally Lipschitz operators on a subset of a real Banach space is given and applied to the problem of the well-posedness of the Carrier equation utt−κ(‖u‖2)Δu+γ|ut|p−1ut=0 in Ω×(0,∞) with acoustic boundary condition, where p>2 and Ω is a bounded domain in an arbitrary dimensional space. 相似文献
450.
We study simple cases of crystalline driven curvature flow with spatially nonuniform driving force term. We assume special
monotonicity properties of the driving term, which are motivated by our previous work on Berg’s effect. We show that initially
flat facets may begin to bend, provided, loosely speaking, they are too large.
相似文献