全文获取类型
收费全文 | 330篇 |
免费 | 9篇 |
专业分类
化学 | 190篇 |
晶体学 | 8篇 |
力学 | 6篇 |
数学 | 13篇 |
物理学 | 122篇 |
出版年
2023年 | 4篇 |
2022年 | 8篇 |
2021年 | 6篇 |
2020年 | 15篇 |
2019年 | 8篇 |
2018年 | 12篇 |
2017年 | 10篇 |
2016年 | 13篇 |
2015年 | 6篇 |
2014年 | 13篇 |
2013年 | 17篇 |
2012年 | 23篇 |
2011年 | 18篇 |
2010年 | 16篇 |
2009年 | 14篇 |
2008年 | 13篇 |
2007年 | 20篇 |
2006年 | 13篇 |
2005年 | 8篇 |
2004年 | 9篇 |
2003年 | 2篇 |
2002年 | 5篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1999年 | 4篇 |
1998年 | 6篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1992年 | 4篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1985年 | 9篇 |
1983年 | 1篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1973年 | 2篇 |
1967年 | 2篇 |
1965年 | 1篇 |
1963年 | 2篇 |
1962年 | 3篇 |
1961年 | 2篇 |
1960年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有339条查询结果,搜索用时 15 毫秒
331.
Stijn Claerhout Sweta Sharma Christian Sköld Claudia Cavaluzzo Anja Sandström Mats Larhed Meganathan Thirumal Virinder S. Parmar Erik V. Van der Eycken 《Tetrahedron》2012,68(14):3019-3029
Herein, an efficient synthetic approach to a furopyrazine scaffold with four points of diversity, starting from 2(1H)-pyrazinones, with dipeptomimetic properties, is presented. R-groups corresponding to amino acid side chains were introduced during the 2(1H)-pyrazinone and subsequent furopyrazine formation. The furopyrazine scaffold was further functionalized with an amino- and a carboxy-terminus resulting in a conformationally restricted dipeptidomimetic scaffold. The carboxy-terminus was introduced via a chemoselective vinylation of the 7-position followed by oxidative cleavage, while the amino-terminus was obtained via Buchwald–Hartwig amidation of the 2-position of the scaffold. The versatility of the synthetic method was demonstrated by the synthesis of a small library of diversely substituted furopyrazines having various amino acid side chains on the four points of diversity. Evaluation with an X-ray structure of the scaffold and computational analysis supports the exploitation of the furopyrazine scaffold as a restricted dipeptide mimic, which can mimic the two central residues of a β-turn. 相似文献
332.
Using Vorbrüggen's protocol, reaction of persilylated uracil with xylofuranose derivatives having 3beta-oxy-3alpha-alkyl substitution produced both alpha- and beta-nucleosides. Only the beta-nucleosides were formed from substrates having the reverse stereochemistry at C-3 or lacking the 3-alkyl substituent. Participation of the 3beta-oxy substituent in stabilizing the incipient C-1 carbonium ion (or oxonium ion) intermediate has been suggested from analysis of energy-minimized conformations. 相似文献
333.
Sk Hafijur Rahaman Rajarshi Ghosh Hoong-Kun Fun Barindra K. Ghosh 《Structural chemistry》2006,17(6):553-559
Three new Schiff bases, -(bis(pyridin-2-yl)alkylidene)butane-1,4-diamine [(py)(R)C=N-(CH)N=C(R)(py), L: py = pyridine; R = H, -(bis(pyridin-2-yl)formylidene)butane-1,4-diamine (bpfd); R = Me, -(bis(pyridin-2-yl)methylidene)butane-1,4-diamine (bpmd); R = C, -(bis(pyridin-2-yl)bezylidene)butane-1,4-diamine (bpbd)] were prepared and used to synthesize six dinuclear cadmium(II)azido
complexes of type [Cd(L)(N)](Y) [L = bpfd, Y = ClO (1a); L = bpfd, Y = PF (1b); L = bpmd, Y = ClO (2a); L = bpmd, Y = PF (2b); L = bpbd, Y = ClO (3a); and L = bpbd, Y = PF (3b)]. Two representative members of the series, 3a and 3b, have been characterized by single crystal X-ray diffraction measurements. Structural study reveals that each cadmium center
in both dinuclear compounds is located in a distorted octahedral coordination environment surrounded by six nitrogen atoms—four
(N1, N2, N3, N4) from tetradentate ligand, and the fifth and sixth positions occupied by nitrogen atoms (N5, N5*) of doubly end-on bridging azides. The complexes display intraligand 1
fluorescence and intraligand 3
phosphorescence in glassy solutions (MeOH at 77 K). 相似文献
334.
Ali SM 《The Journal of chemical physics》2006,124(14):144504
A scaling law relating the shear viscosity of one and two component liquid mixtures to their excess thermodynamic entropies defined through pair correlation functions is derived by approximating the mode coupling theory expressions of frictions and then combining with the Stokes-Einstein relation. Molecular dynamics simulation has been performed to generate the data of shear viscosity for one and two component liquid mixtures to test the derived scaling law. The derived scaling laws yield numerical results of shear viscosity for one component and two component liquid mixtures, which are in excellent agreement with the molecular dynamics simulation results for a wide range of density and interaction potential. 相似文献
335.
336.
Sahabuddin S Roy A Drew MG Roy BG Achari B Mandal SB 《The Journal of organic chemistry》2006,71(16):5980-5992
The carbohydrate-derived substrate 3-C-allyl-1,2:5,6-di-O-isopropylidene-alpha-D-allofuranose was judiciously manipulated for preparing suitable synthons, which could be converted to a variety of isoxazolidino-spirocycles and -tricycles through the application of ring-closing metathesis (RCM) and intramolecular nitrone cycloaddition (INC) reactions. Cleavage of the isoxazolidine rings of some of these derivatives by transfer hydrogenolysis followed by coupling of the generated amino functionalities with 5-amino-4,6-dichloropyrimidine furnished the corresponding chloropyrimidine nucleosides, which were elaborated to spiroannulated carbanucleosides and conformationally locked bicyclo[2.2.1]heptane/oxa-bicyclo[3.2.1]octane nucleosides. However, use of higher temperature for the cyclization of one of the chloropyrimidines led to the dimethylaminopurine analogue as a sole product, formed via nucleophilic displacement of the chloro group by dimethylamine generated from DMF. 相似文献
337.
Sk Sahabuddin Tsung-Che Chang Chang-Ching Lin Hsuan-Yi Hsiao Jeen-Han Chen Ja-an Annie Ho 《Tetrahedron》2010,66(38):7510-1727
A series of sTn derivative-keyhole limpet hemocyanin (KLH) conjugates were synthesized, and their immunogenicities were evaluated by corresponding IgG production. To achieve a high-throughput screening immunoassay, a glycan microarray with sTn and its analogs was used to detect the production of corresponding antibodies in mouse sera. The immunoassay results revealed that the derived sTn antigens are generally more immunogenic than the parent sTn antigen. The N-propionyl sTn antigen was the most immunogenic among the sTn derivatives investigated, and its antiserum was cross-reactive with natural sTn. These results indicate that N-propionyl sTn may serve as a viable vaccine candidate to produce antibody for detection of sTn antigen. 相似文献
338.
Calculations of the desorption of hydrogen from Pt(110)-(1×2), a surface used to model nanoparticle edge sites, show the activation energy varying strongly with hydrogen coverage, from 0.8 to 0.3?eV. The predicted temperature programed desorption spectra agree well with experiments, but the formation of the hydrogen molecules occurs only at two types of sites on the surface even though three peaks are observed. The lowest and highest temperature peaks result from desorption from the same strong binding sites at the ridge, while desorption from the weakest binding trough sites is insignificant. 相似文献
339.
This article studies the unstructured and structured backward error analysis of specified eigenpairs for matrix polynomials. The structures we discuss include -symmetric, -skew-symmetric, Hermitian, skew Hermitian, -even, -odd, -even, -odd, -palindromic, -anti-palindromic, -palindromic, and -anti-palindromic matrix polynomials. Minimally structured perturbations are constructed with respect to Frobenius norm such that specified eigenpairs become exact eigenpairs of an appropriately perturbed matrix polynomial that also preserves sparsity. Further, we have used our results to solve various quadratic inverse eigenvalue problems that arise from real-life applications. 相似文献