全文获取类型
收费全文 | 9383篇 |
免费 | 1429篇 |
国内免费 | 1544篇 |
专业分类
化学 | 10461篇 |
晶体学 | 380篇 |
力学 | 36篇 |
综合类 | 47篇 |
数学 | 11篇 |
物理学 | 1421篇 |
出版年
2024年 | 25篇 |
2023年 | 139篇 |
2022年 | 238篇 |
2021年 | 371篇 |
2020年 | 533篇 |
2019年 | 417篇 |
2018年 | 364篇 |
2017年 | 340篇 |
2016年 | 535篇 |
2015年 | 550篇 |
2014年 | 570篇 |
2013年 | 961篇 |
2012年 | 597篇 |
2011年 | 505篇 |
2010年 | 486篇 |
2009年 | 536篇 |
2008年 | 579篇 |
2007年 | 655篇 |
2006年 | 581篇 |
2005年 | 568篇 |
2004年 | 514篇 |
2003年 | 430篇 |
2002年 | 278篇 |
2001年 | 199篇 |
2000年 | 206篇 |
1999年 | 167篇 |
1998年 | 155篇 |
1997年 | 142篇 |
1996年 | 143篇 |
1995年 | 134篇 |
1994年 | 74篇 |
1993年 | 64篇 |
1992年 | 55篇 |
1991年 | 26篇 |
1990年 | 27篇 |
1989年 | 22篇 |
1988年 | 26篇 |
1987年 | 25篇 |
1986年 | 21篇 |
1985年 | 22篇 |
1984年 | 10篇 |
1983年 | 5篇 |
1982年 | 8篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1977年 | 8篇 |
1976年 | 7篇 |
1975年 | 7篇 |
1974年 | 6篇 |
1973年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 421 毫秒
41.
Praveen K. Tandon Gayatri Sumita Sahgal Manish Srivastava Santosh B. Singh 《应用有机金属化学》2007,21(3):135-138
Catalytic activities of three transition metals, as iridium (III) chloride, rhodium (III) chloride and palladium (II) chloride, were compared in the oxidation of six aromatic aldehydes (benzaldehyde, p‐chloro benzaldehyde, p‐nitro benzaldehyde, m‐nitro benzaldehyde, p‐methoxy benzaldehyde and cinnamaldehyde), two hydrocarbons (viz. (anthracene and phenanthrene)) and one aromatic and one cyclic alcohol (cyclohexanol and benzyl alcohol) by 50% H2O2. The presence of traces (substrate: catalyst ratio equal to 1:62500 to 1:1961) of the chlorides of iridium(III), rhodium(III) and palladium(II) catalyze these oxidations, resulting in good to excellent yields. It was observed that in most of the cases palladium(II) chloride is the most efficient catalyst. Conditions for the highest and most economical yields were obtained. Deviation from the optimum conditions decreases the yields. Oxidation in aromatic aldehydes is selective at the aldehydeic group only and other groups remain unaffected. This new, simple and economical method, which is environmentally safe, also requires less time. Reactive species of catalysts, existing in the reaction mixture are also discussed. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
42.
Mössbauer spectroscopy was used to investigate the influence of dissolved hydrogen on the interatomic bonds in austenitic steels. It was carried out to prove the decohesion mechanism of hydrogen embrittlement (HE). It is shown that hydrogen increases Debye temperature, i.e., the interatomic bonds in hydrogenated austenitic steel becomes stronger. 相似文献
43.
44.
J. P. S. Farinha J. M. G. Martinho H. Xu M. A. Winnik R. P. Quirk 《Journal of Polymer Science.Polymer Physics》1994,32(9):1635-1642
Cyclization of a polystyrene chain (Mn = 10,600; Mw/Mn = 1.09) both ends labeled with 4-(1-pyrenyl)butanoamide groups was studied in cyclohexane between 25 and 95°C. The amide groups (peptide bonds) at both ends can form an intrachain hydrogen bond between the amide hydrogen at one chain end and the carbonyl oxygen at the other. The presence of two sets of conformers, random coils, and chains cyclized through hydrogen bonding, complicates the data analysis. The pyrene excimer kinetics of this polymer is well described by a model composed of two monomers (hydrogen bonded and nonbonded chains) and one excimer, in equilibrium. The cyclization rate constant for hydrogen-bonded chains is larger than the one for nonhydrogen-bonded chains. The pyrene excimer binding energy (ca. 1.6 kcal/mol) is lower than the published value for nonhydrogen-bonded chains (~ 9 kcal/mol), suggesting that intrachain hydrogen bonding hinders the stabilization of the excimer. © 1994 John Wiley & Sons, Inc. 相似文献
45.
46.
47.
Reactions of 1,4-dilithio-1,3-dienes with dimethyl oxalates afforded multiply substituted o-benzoquinones or stereodefined 2,6-dioxabicyclo[3.3.0]-octa-3,7-dienes in good yields. 相似文献
48.
49.
The central zinc(II) atom in the title complex is tetrahedrally coordinated by four nitrogen atoms derived from 4‐methyl‐5‐imidazolecarboxyaldehyde ligands with Zn? N in the range 2.007(3) to 2.026(4) Å. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
50.
Michael C. W. Chan Dr. 《化学:亚洲杂志》2008,3(1):18-27
The notion of weak attractive ligand–polymer interactions is introduced, and its potential application, importance, and conceptual links with “cooperative” ligand–substrate interactions are discussed. Synthetic models of weak attractive ligand–polymer interactions are described, in which intramolecular weak C? H???F? C interactions (the existence of which remains contentious) have been detected by NMR spectroscopy and neutron and X‐ray diffraction experiments. These C? H???F? C interactions carry important implications for the design of catalysts for olefin polymerization, because they provide support for the practical feasibility of ortho‐F???Hβ ligand–polymer contacts proposed for living Group 4 fluorinated phenoxyimine catalysts. The notion of weak attractive noncovalent interactions between an “active” ligand and the growing polymer chain is a novel concept in polyolefin catalysis. 相似文献