全文获取类型
收费全文 | 1248篇 |
免费 | 44篇 |
国内免费 | 3篇 |
专业分类
化学 | 838篇 |
晶体学 | 17篇 |
力学 | 27篇 |
数学 | 129篇 |
物理学 | 284篇 |
出版年
2023年 | 9篇 |
2022年 | 6篇 |
2021年 | 18篇 |
2020年 | 20篇 |
2019年 | 23篇 |
2018年 | 25篇 |
2017年 | 23篇 |
2016年 | 32篇 |
2015年 | 34篇 |
2014年 | 35篇 |
2013年 | 64篇 |
2012年 | 71篇 |
2011年 | 82篇 |
2010年 | 43篇 |
2009年 | 42篇 |
2008年 | 71篇 |
2007年 | 49篇 |
2006年 | 49篇 |
2005年 | 68篇 |
2004年 | 54篇 |
2003年 | 40篇 |
2002年 | 51篇 |
2001年 | 32篇 |
2000年 | 26篇 |
1999年 | 13篇 |
1998年 | 17篇 |
1997年 | 10篇 |
1996年 | 15篇 |
1995年 | 18篇 |
1994年 | 11篇 |
1993年 | 12篇 |
1992年 | 18篇 |
1991年 | 11篇 |
1990年 | 14篇 |
1989年 | 15篇 |
1988年 | 17篇 |
1987年 | 13篇 |
1986年 | 14篇 |
1985年 | 9篇 |
1984年 | 10篇 |
1983年 | 11篇 |
1982年 | 11篇 |
1981年 | 5篇 |
1980年 | 10篇 |
1979年 | 10篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 11篇 |
1975年 | 10篇 |
1974年 | 6篇 |
排序方式: 共有1295条查询结果,搜索用时 31 毫秒
61.
H. Sano 《Journal of Radioanalytical and Nuclear Chemistry》1977,36(1):105-111
Absorption Mössbauer spectra of high-spin57Fe(acac)3 incorporated in diamagnetic Co(acac)3 and in paramagnetic Mn(acac)3 and of the γ-ray irradiated (57Fe, Co) (acac)3 and (57Fe, Mn) (acac)3 were compared with emission spectra of57Co-labelled Co(acac)3. Magnetic hfs is found in the spectra of (57Fe, Co) (acac)3 at 78 to 195 K, whereas such hfs is observed neither for the spectrum of57Co-labelled Co(acac)3 nor for that of γ-ray irradiated (57Fe, Co) (acac)3). The absence of magnetic hfs in the spectrum of diamagnetic57Co-labelled cobalt(III) compounds was ascribed to the spin-spin interaction due to the radicals produced in the vicinity of the decayed atom. 相似文献
62.
63.
64.
Mari Vellakkaran Taehwan Kim Sungwoo Hong 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2022,134(1):e202113658
The site-selective C?H functionalization of heteroarenes is of considerable importance for streamlining the rapid modification of bioactive molecules. Herein, we report a general strategy for visible-light-induced β-carbonyl alkylation at the C4 position of pyridines with high site selectivity using various cyclopropanols and N-amidopyridinium salts. In this process, hydrogen-atom transfer between the generated sulfonamidyl radicals and O?H bonds of cyclopropanols generates β-carbonyl radicals, providing efficient access to synthetically valuable β-pyridylated (aryl)ketones, aldehydes, and esters with broad functional-group tolerance. In addition, the mild method serves as an effective tool for the site-selective late-stage functionalization of complex and medicinally relevant molecules. 相似文献
65.
Marién Abreu Jan Goedgebeur Domenico Labbate Giuseppe Mazzuoccolo 《Journal of Graph Theory》2019,92(4):415-444
A -bisection of a bridgeless cubic graph is a -colouring of its vertex set such that the colour classes have the same cardinality and all connected components in the two subgraphs induced by the colour classes ( monochromatic components in what follows) have order at most . Ban and Linial Conjectured that every bridgeless cubic graph admits a -bisection except for the Petersen graph. A similar problem for the edge set of cubic graphs has been studied: Wormald conjectured that every cubic graph with has a -edge colouring such that the two monochromatic subgraphs are isomorphic linear forests (ie, a forest whose components are paths). Finally, Ando conjectured that every cubic graph admits a bisection such that the two induced monochromatic subgraphs are isomorphic. In this paper, we provide evidence of a strong relation of the conjectures of Ban-Linial and Wormald with Ando's Conjecture. Furthermore, we also give computational and theoretical evidence in their support. As a result, we pose some open problems stronger than the above-mentioned conjectures. Moreover, we prove Ban-Linial's Conjecture for cubic-cycle permutation graphs. As a by-product of studying -edge colourings of cubic graphs having linear forests as monochromatic components, we also give a negative answer to a problem posed by Jackson and Wormald about certain decompositions of cubic graphs into linear forests. 相似文献
66.
67.
68.
Charles E. McKenna Boris A. Kashemirov Mari Fujimolo 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4)
Abstract Individual E/Z isomers of the C-methyl ester 1 of α-(hydroxyimino)phosphonoacetic acid (“troika acid”) were recently prepared as dicyclohexylammonium salts and found to be stable at neutral pH.1 On alkaline demethylation followed by pH adjustment to 6–7, E?1 and Z?1 stereospecifically undergo P-Cαand Cα-Cβ cleavage, respectively.1 Herein we report synthesis of the corresponding P-methyl ester from trimethyl phos-phonoacetate 2. The product was isolated as its bis-DCHA+ salt E-3, with stereochemistry assigned by NMR.2 相似文献
69.
Boris A. Kashemirov Mari Fujimoto-posner Charles E. McKenna 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1)
Abstract The (E-oxime of phosphonoglyoxylic acid, or (E-troika acid [(E)-l] undergoe: fragmentation leading to phosphorylation of the aqueous solvent at neutral pH and room temperature.[1] In contrast, the corresponding C-methyl ester (a-2 is stable under these mild conditions. Conversion of the unreactive (E)-2 to (E)-1 requires dewthylation a pH 13–14, generating the polyanion of (E-1, which becomes reactive on protonation.[1] 相似文献
70.
Hirohito Ikeda Yukiko Sano Tomonori Matsubara Mitsunobu Kawahara Miho Yukawa Masao Fujisawa Eiji Yukawa Hatsumi Aki 《Journal of Thermal Analysis and Calorimetry》2013,113(3):1135-1138
Propericiazine (PCZ) is an antipsychotic agent used for the treatment and the prevention of relapse of schizophrenia. We found that when an oral solution containing PCZ was mixed with a green tea drink, the residual content of PCZ was reduced by forming an insoluble complex between PCZ and tea polyphenol. In this study, the mechanism underlying the incompatibility of PCZ with green tea polyphenol (GTP) in the solution was clarified by isothermal titration microcalorimetry (ITC). Both solutions of 27.4 mM PCZ and 2.2 mM (?)-epigallocatechin gallate (EGCg), which is a main ingredient of GTP, were mixed and then PCZ in the filtrate was reduced to approximately 60 %. According to measurement at 298 K by ITC, PCZ formed an insoluble complex with EGCg at an associate constant (K) of 4.75 × 102 M?1 exothermically, ΔH = ?40.0 kJ mol?1. When (?)-epicatechin gallate (ECg) was used as the GTP, PCZ interacted with ECg with K and ΔH values of 3.74 × 102 M?1 and ?22.1 kJ mol?1, respectively. On the other hand, little heat of the reaction between PCZ and (?)-epigallocatechin or (?)-epicatechin was observed. The results indicated that the main reason for this incompatibility was the formation of an insoluble complex by PCZ and a gallate-type GTP such as EGCg and ECg in the aqueous solution. 相似文献