全文获取类型
收费全文 | 1716篇 |
免费 | 46篇 |
国内免费 | 7篇 |
专业分类
化学 | 1223篇 |
晶体学 | 18篇 |
力学 | 19篇 |
数学 | 46篇 |
物理学 | 463篇 |
出版年
2023年 | 9篇 |
2021年 | 13篇 |
2020年 | 18篇 |
2019年 | 20篇 |
2018年 | 20篇 |
2016年 | 21篇 |
2015年 | 32篇 |
2014年 | 48篇 |
2013年 | 66篇 |
2012年 | 89篇 |
2011年 | 94篇 |
2010年 | 47篇 |
2009年 | 61篇 |
2008年 | 78篇 |
2007年 | 103篇 |
2006年 | 90篇 |
2005年 | 89篇 |
2004年 | 58篇 |
2003年 | 60篇 |
2002年 | 68篇 |
2001年 | 51篇 |
2000年 | 27篇 |
1999年 | 14篇 |
1998年 | 12篇 |
1997年 | 19篇 |
1996年 | 23篇 |
1995年 | 14篇 |
1994年 | 17篇 |
1993年 | 22篇 |
1992年 | 32篇 |
1991年 | 24篇 |
1990年 | 31篇 |
1989年 | 21篇 |
1988年 | 30篇 |
1987年 | 33篇 |
1986年 | 34篇 |
1985年 | 32篇 |
1984年 | 20篇 |
1983年 | 11篇 |
1982年 | 18篇 |
1981年 | 19篇 |
1980年 | 17篇 |
1979年 | 26篇 |
1978年 | 14篇 |
1977年 | 19篇 |
1976年 | 13篇 |
1975年 | 22篇 |
1974年 | 24篇 |
1973年 | 10篇 |
1971年 | 6篇 |
排序方式: 共有1769条查询结果,搜索用时 281 毫秒
91.
92.
Kakehi A Suga H Kako T Fujii T Tanaka N Kobayashi T 《Chemical & pharmaceutical bulletin》2003,51(11):1246-1252
Some thieno[3,4-b]indolizine derivatives having a 1-naphthylmethylthio, 2-methyl-1-naphthylmethylthio, 2-naphthylmethylthio, or 9-anthrylmethylthio group at the 3-position were prepared and their intramolecular arene-arene interactions were investigated. In comparison with 3-(methylthio)thieno[3,4-b]indolizines which have no such interactions, the (1)H-NMR spectra of title compounds showed large high-field shifts (delta 0.06-0.89 ppm) for the protons of the pyridine ring in the thieno[3,4-b]indolizine, and these values were considerably larger than those (delta <0.3 ppm) in 3-(benzylthio)thieno[3,4-b]indolizines. The UV spectra also exhibited a characteristic absorption band near 425 nm attributable to the arene-arene interaction. In the X-ray analyses of some compounds, however, the presence of both the gauche and the anti conformers at the sulfide spacer were confirmed. 相似文献
93.
Chip-to-world interface is a major issue in the field of microfluidics and its applications. We developed a plug and play microfluidic device composed of a fluid driving unit and a polymer chip containing microfluidic channels and reservoirs. The one and only connection of the device to the external world is a set of electric control lines for the driving unit. Just putting the reagents and samples onto the reservoirs, the chip can be operated for chemical or biochemical reaction and analysis. We demonstrate here that silicon-based micropumps embedded in the present device allow us to achieve flexible fluidic manipulations with minimum time delay and dead volume. 相似文献
94.
Nakamura K Suzuki T Hasegawa M Kato Y Sasaki H Inouye K 《Journal of chromatography. A》2003,1009(1-2):133-139
An affinity sorbent, hydrophilic polymer-based carrier of different pore size (Toyopearl) with immobilized p-aminobenzamidine (ABA), has been prepared. Its basic properties and some applications for protein purification were studied. ABA, which is a synthetic inhibitor for trypsin-like proteases, was covalently immobilized to Toyopearl by reductive amination. The ligand density and binding capacity for porcine trypsin varied depending on the pore size of Toyopearl. The maximum binding capacity of the immobilized p-aminobenzamidine Toyopearl (ABA-Toyopearl) for trypsin was more than 40 mg/ml gel. ABA-Toyopearl thus obtained was very stable below pH 8 and was successfully used for high-performance affinity chromatography of trypsin-like proteases such as trypsin, thrombin, tissue-type plasminogen activator or urokinase in a single step at 25 degrees C. 相似文献
95.
Metal-ion-assisted hydrolysis of dipeptides involving a serine residue in a neutral aqueous solution
Yashiro M Sonobe Y Yamamura A Takarada T Komiyama M Fujii Y 《Organic & biomolecular chemistry》2003,1(4):629-632
Dipeptides having a serine residue at the C-terminus, X-Ser, where X is an appropriate amino acid residue, were efficiently hydrolyzed in the presence of ZnCl2 at pH 7.0. The rapid hydrolysis of X-Ser is due to an autocatalysis of the hydroxy group in the serine residue, and is found to be accelerated by a metal ion, in particular by ZnCl2. Roles of the metal ion in the hydrolysis of peptides involving a serine residue, in relation to the recently reported protein cleavages, are discussed. 相似文献
96.
T. Fujii H. Yamana K. Takamiya M. Watanabe H. Moriyama 《Journal of Radioanalytical and Nuclear Chemistry》2002,253(2):199-204
Adsorption behavior of fission products in nitric acid solution on various alloys and metals was studied by using a multitracer produced by neutron irradiation of UO2. The adsorption behavior of the fission products 99Mo, 131I, 132Te, 140La, and 143Ce, and 239Np was simultaneously studied. Some chemical decontamination tests were also examined. Clear adsorption of 99Mo, 131I, and 132Te was observed, whereas adsorption of 140La, 143Ce, and 239Np was not. The adsorption characteristics were discussed by considering anion-exchange reaction and surface complexation. 相似文献
97.
A biosynthetic gene cluster containing five genes, alt1-5, was cloned from Alternaria solani, a causal fungus of early blight disease to tomato and potato. Homology searching indicated that the alt1, 2, and 3 genes code for cytochrome P450s and the alt4 gene for a FAD-dependent oxygenase/oxidase. The alt5 gene encodes a polyketide synthase (PKS), named PKSN, that was found to be an iterative type I complex reduced-type PKS with a C-methyltransferase domain. To identify the PKSN function, the alt5 gene was introduced into the fungal host Aspergillus oryzae under an alpha-amylase promoter. The transformant produced a polyketide compound, named alternapyrone, whose structure is shown to be 3,5-dimethyl-4-hydroxy-6-(1,3,5,7,11,13-hexamethyl-3,5,11-pentadecatrienyl)-pyran-2-one. Labeling experiments confirmed that alternapyrone is a decaketide with octa-methylation from methionine on every C(2) unit except the third unit. 相似文献
98.
This study shows the ESR spectra of oxoiron(IV) porphyrin pi-cation radicals of 1-8 in dichloromethane-methanol (5:1) mixture. We reported in a previous paper that oxoiron(IV) porphyrin pi-cation radicals of 1-4 are in an a(1u) radical state while those of 5-8 are in an a(2u) radical. The ESR spectra (g( perpendicular)(eff) approximately 3.1 and g( parallel)(eff) approximately 2.0) for the a(1u) radical complexes, 1-4, appear quite different from those reported previously for the oxoiron(IV) porphyrin pi-cation radical of 5 (g(y) = 4.5, g(x) = 3.6, and g(z) = 1.99). The unique ESR spectra of the a(1u) radical complexes rather resemble those of compound I from Micrococcus lysodeikticus catalase (CAT) and ascorbate peroxidase (ASP). This is the first examples to mimic the ESR spectra of compound I in the enzymes. From spectral analysis based on a spin Hamiltonian containing an exchange interaction, the ESR spectra of 1-4 can be explained as a moderate ferromagnetic state (J/D approximately 0.3) between ferryl S = 1 and the porphyrin pi-cation radical S' = (1)/(2). The magnitudes of zero-field splitting (D) for ferryl iron and isotropic J value, estimated from the temperature-dependence of the half-saturation power of the ESR signals, are approximately 28 and approximately +8 cm(-1), respectively. A change in the electronegativity of the beta-pyrrole substituent hardly changes the ESR spectral feature while that of the meso-substituent slightly does owing to the change in the E/D value. On the basis of the present ESR results, we propose the a(1u) radical state for compound I of CAT and ASP. 相似文献
99.
100.