全文获取类型
收费全文 | 604篇 |
免费 | 17篇 |
国内免费 | 1篇 |
专业分类
化学 | 489篇 |
晶体学 | 5篇 |
力学 | 7篇 |
数学 | 25篇 |
物理学 | 96篇 |
出版年
2023年 | 3篇 |
2022年 | 3篇 |
2021年 | 9篇 |
2020年 | 11篇 |
2019年 | 8篇 |
2018年 | 8篇 |
2017年 | 8篇 |
2016年 | 13篇 |
2015年 | 9篇 |
2014年 | 16篇 |
2013年 | 30篇 |
2012年 | 39篇 |
2011年 | 39篇 |
2010年 | 23篇 |
2009年 | 26篇 |
2008年 | 42篇 |
2007年 | 45篇 |
2006年 | 34篇 |
2005年 | 32篇 |
2004年 | 41篇 |
2003年 | 29篇 |
2002年 | 18篇 |
2000年 | 9篇 |
1999年 | 6篇 |
1998年 | 9篇 |
1996年 | 4篇 |
1995年 | 8篇 |
1994年 | 13篇 |
1993年 | 5篇 |
1992年 | 9篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1977年 | 2篇 |
1974年 | 2篇 |
1973年 | 4篇 |
1972年 | 3篇 |
1971年 | 2篇 |
1970年 | 2篇 |
1969年 | 2篇 |
1968年 | 2篇 |
1964年 | 3篇 |
1909年 | 2篇 |
排序方式: 共有622条查询结果,搜索用时 218 毫秒
61.
A new effective copper catalyzed CO coupling reaction using excess amount of strongly coordinating monodentate ligands was successfully developed. Among the DMAP-type monodentate ligands, 4-pyrrolidinopyridine afforded the best results. The developed reaction is widely applicable for the synthesis of various hindered or acyclic secondary alkyl-aryl ethers. In this study, a novel and remarkable acceleration of the coupling reaction using excess amount of monodentate ligands was discovered. 相似文献
62.
The synthesis and properties of the ion exchange polymer 3‐n‐propyl(3‐methylpyridinium)silsesquioxane chloride (SiPy+Cl?) are described. Based on the Langmuir model, the equilibrium constant at the solid‐solution interface for the reaction, SiPy+Cl?+NO ?SiPy+NO , was calculated for nitrite adsorption. The value found, β=8.7×103 L mol?1, indicates good affinity of the anion for the solid phase. A carbon paste electrode of the material was tested for NO oxidation and a linear response, in the concentration range between 6.3 and 143.6 μmol L?1, was obtained by amperometry. The analytical applicability of the proposed system was ascertained by the satisfactory results attained in its application to monitoring of nitrite in natural waters. 相似文献
63.
64.
65.
Yoshitaka Nakano Yoshihiro Irokawa Yasunobu Sumida Shuichi Yagi Hiroji Kawai 《固体物理学:研究快报》2010,4(12):374-376
We have investigated electronic deep levels in two AlGaN/GaN hetero‐structures with different current collapses grown at 1150 and 1100 °C by a photo‐capacitance spectroscopy technique, using Schottky barrier diodes. Three specific deep levels located at ~2.07, ~2.80, and ~3.23 eV below the conduction band were found to be significantly enhanced for severe current collapse, being in reasonable agreement with photoluminescence and capacitance–voltage characteristics. These levels probably originate in Ga vacancies and residual C impurities and are probably responsible for the current collapse phenomena of the AlGaN/GaN hetero‐structures. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
66.
Microwave-assisted synthesis method enabled the preparation of the (tris-acetylacetonate)(2,9-dimethyl-4,7-diphenyl-1,10-phenanthrolinate) terbium(III) (Tb(acac)3(dmdpphen)) complex with outstanding high green luminescence. This method is appropriate for green chemistry and energy-saving processes. The Tb(acac)3(dmdpphen) complex has good thermal stability. Emission peaks are assigned to the f-f transitions of the Tb3+. The Tb(acac)3(dmdpphen) complex is expected to be used in functional materials of electronic products. 相似文献
67.
Synthesis and healing properties of poly(arylether sulfone)–poly(alkylthioether) multiblock copolymers containing disulfide bonds 下载免费PDF全文
Takayoshi Akiyama Akira Ushio Yoshitaka Itoh Yuya Kawaguchi Kazuya Matsumoto Mitsutoshi Jikei 《Journal of polymer science. Part A, Polymer chemistry》2017,55(21):3545-3553
Thermoplastic elastomers composed of soft and hard segments are important elastic and processable synthetic polymers. The microphase‐separated soft domains show low glass transition temperature and possess sufficient chain mobility at room temperature. In this study, we report the synthesis and healing properties of multiblock copolymers containing disulfide bonds as dynamic covalent bonds. The multiblock copolymers composed of poly(arylether sulfone) and poly(alkylthioether) segments were synthesized by oxidative coupling polymerization of the corresponding thiol‐terminated oligomers. Atomic force microscopy phase images, differential scanning calorimetry, and dynamic mechanical analysis curves indicated the microphase‐separated morphology of the multiblock copolymer. Self‐healing properties of the polymer were evaluated by changes in the elongation at break of the cut/adhered samples. The elongation recovery increased with UV irradiation time, and the multiblock copolymer showed a 93% recovery after UV irradiation for 5 h. The healing efficiency induced by UV irradiation, determined by subtracting the recovery without UV irradiation, was calculated to be 51%. According to the UV spectra and solubility changes after UV irradiation, the main healing factor in this study was the crosslinking reactions caused by thiyl radicals generated from UV irradiation instead of disulfide exchange reactions. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3545–3553 相似文献
68.
Mitsuhiro T. Nakao Yoshitaka Watanabe 《Journal of Computational and Applied Mathematics》1994,50(1-3):401-410
This paper is an extension of the preceding study (Nakao, this journal, 1991) in which we described a numerical verification method of the solution for one-space dimensional parabolic problems, to the several-space dimensional case. Here, numerical verification means the automatic proof of the existence of solutions to the problems by some numerical techniques on a computer. We reformulate the verification condition for nonlinear parabolic initial boundary value problems using the fixed-point problem of a compact operator on certain function spaces. As in the preceding study based upon a simple C0 finite-element approximation and its constructive a priori error estimates, a numerical verification procedure is presented with some numerical examples. 相似文献
69.
Lars Lauterbach Hongxin Wang Marius Horch Leland B. Gee Yoshitaka Yoda Yoshihito Tanaka Ingo Zebger Oliver Lenz Stephen P. Cramer 《Chemical science》2015,6(2):1055-1060
Hydrogenases are complex metalloenzymes that catalyze the reversible splitting of molecular hydrogen into protons and electrons essentially without overpotential. The NAD+-reducing soluble hydrogenase (SH) from Ralstonia eutropha is capable of H2 conversion even in the presence of usually toxic dioxygen. The molecular details of the underlying reactions are largely unknown, mainly because of limited knowledge of the structure and function of the various metal cofactors present in the enzyme. Here, all iron-containing cofactors of the SH were investigated by 57Fe specific nuclear resonance vibrational spectroscopy (NRVS). Our data provide experimental evidence for one [2Fe2S] center and four [4Fe4S] clusters, which is consistent with the amino acid sequence composition. Only the [2Fe2S] cluster and one of the four [4Fe4S] clusters were reduced upon incubation of the SH with NADH. This finding explains the discrepancy between the large number of FeS clusters and the small amount of FeS cluster-related signals as detected by electron paramagnetic resonance spectroscopic analysis of several NAD+-reducing hydrogenases. For the first time, Fe–CO and Fe–CN modes derived from the [NiFe] active site could be distinguished by NRVS through selective 13C labeling of the CO ligand. This strategy also revealed the molecular coordinates that dominate the individual Fe–CO modes. The present approach explores the complex vibrational signature of the Fe–S clusters and the hydrogenase active site, thereby showing that NRVS represents a powerful tool for the elucidation of complex biocatalysts containing multiple cofactors. 相似文献
70.
Dr. Masahito Yoshida Yoshitaka Ishida Kenta Adachi Hayato Murase Dr. Hiroshi Nakagawa Prof.Dr. Takayuki Doi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(50):18417-18430
The solid‐phase combinatorial synthesis of cyclodepsipeptide destruxin E has been demonstrated. The combinatorial synthesis of cyclization precursors 8 was achieved by using a split and pool method on SynPhase Lanterns. The products were successfully macrolactonized in parallel in the solution phase by using 2‐methyl‐6‐nitrobenzoic anhydride and 4‐(dimethylamino)pyridine N‐oxide to afford macrolactones 9 , and the subsequent formation of an epoxide in the side chain gave 18 member destruxin E analogues 6 . Biological evaluation of analogues 6 indicated that the N‐MeAla residue was crucial to the induction of morphological changes in osteoclast‐like multinuclear cells (OCLs). Based on structure–activity relationships, azido‐containing analogues 15 were then designed for use as a molecular probe. The synthesis and biological evaluation of analogues 15 revealed that 15 b , in which the Ile residue was replaced with a Lys(N3) residue, induced morphological changes in OCLs at a sufficient concentration, and modification around the Ile residue would be tolerated for attachment of a chemical tag toward the target identification of destruxin E ( 1 ). 相似文献