全文获取类型
收费全文 | 277篇 |
免费 | 24篇 |
专业分类
化学 | 211篇 |
晶体学 | 2篇 |
力学 | 8篇 |
数学 | 13篇 |
物理学 | 67篇 |
出版年
2023年 | 4篇 |
2022年 | 4篇 |
2021年 | 4篇 |
2020年 | 10篇 |
2019年 | 12篇 |
2018年 | 7篇 |
2017年 | 6篇 |
2016年 | 13篇 |
2015年 | 6篇 |
2014年 | 10篇 |
2013年 | 17篇 |
2012年 | 20篇 |
2011年 | 25篇 |
2010年 | 12篇 |
2009年 | 14篇 |
2008年 | 12篇 |
2007年 | 16篇 |
2006年 | 19篇 |
2005年 | 19篇 |
2004年 | 15篇 |
2003年 | 6篇 |
2002年 | 5篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1987年 | 5篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1970年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有301条查询结果,搜索用时 500 毫秒
131.
K. Ichinose K. Fujiwara M. Nakamura M. Oyasato A. Tsujimura 《Journal of magnetism and magnetic materials》1987,70(1-3):154-156
Nuclear magnetic resonances of 59Co nuclei in (Mg1−xRx)Co2 (R = Y, Gd) compounds at 4.2 K have been observed for 0x1. By replacing Mg with R, the 59Co hyperfine field decreases or is nearly constant in the C14 range and increases in the C15 range. These results are explained by the difference of the contribution from R atoms. 相似文献
132.
H. Shinohara M. Iwasaki S. Tsujimura K. Watanabe S. Okazaki 《Journal of polymer science. Part A, Polymer chemistry》1972,10(7):2129-2137
It has been demonstrated that the poly(vinyl fluoride) film can be fluorinated by exposing the polymer to an environment of fluorine under atmospheric pressure and at ambient temperature. Fluorine content, infrared spectra, thermal properties, and solubilities in the polar solvents were investigated for the fluorinated products and the following results were obtained. In the case of films less than 10 μ in thickness, the fluorination appeared to proceed homogeneously. Under any fluorinating conditions applied, i.e., fluorine pressure of up to 800 mm Hg and temperatures of up to 90°C, the fluorine content never exceeded 65% which corresponds to a composition of C2F2.5H1.5. The activation energy of the reaction was calculated to be 6.8 kcal/mole. The polymer reacted with a small amount of oxygen contained in the fluorine to form acyl fluoride groups. The fluorinated films became insoluble in boiling N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide, but colored gradually to a dark brown. The occurrence of some crosslinking in the products was revealed. 相似文献
133.
Hiroyuki Hatayama Taku Swabe Youichi Kurokawa 《Journal of Sol-Gel Science and Technology》1996,7(1-2):13-17
Urease was entrap-immobilized on composite gel fibre of cellulose acetate and TiO2. The immobilization can be easily performed under mild conditions. The gel fibre is stable in high ionic solutions and in phosphate solutions with a range of pH 6–8.The pH and thermal stabilities of immobilized urease were higher than those of the native one. 相似文献
134.
New chiral derivatization reagent for the resolution of amino acids as diastereomers by TLC and HPLC
Summary The applicability of a new chiral reagent to the resolution of amino acid enantiomers has been investigated. The new reagent,
S(-)-N-1-(2-naphthylsulphonyl)-2-pyrrolidinecarbonyl chloride (NSP-C1), was synthesized by the chlorination of S(-)-N-1-(2-naphthylsulphonyl)-2-pyrrolidinecarboxylic
acid which was prepared by the reaction of 2-naphthalene sulphonyl chloride with L-proline. Derivatization of the amino acids
proceeds rapidly at ambient temperature and no racemization takes place during the reaction. The resolution of the diastereomeric
amides was performed by TLC and normal phase HPLC. Complete resolutions were observed for the enantiomers of all amino acids
examined except cysteine, cystine and histidine. The favourable UV absorption of the derivatives enabled the optical antipode
to be determined down to the 0.1% level. 相似文献
135.
Okamoto A Kamei T Tanaka K Saito I 《Journal of the American Chemical Society》2004,126(45):14732-14733
Photostimulated hole transport through DNA duplexes immobilized on gold electrodes has been investigated. By modifying a gold electrode with a DNA duplex containing a photosensitizer, we have observed a sequence-dependent cathodic photocurrent. DNA acts as a good mediator for cathodic photocurrent when appropriate sequences are selected. 相似文献
136.
Takahashi A Kumatani T Usui S Tsujimura R Seki T Morimoto K Ohnishi T 《Photochemistry and photobiology》2005,81(4):1010-1014
Photoreactivation (PR) is an efficient survival mechanism that helps protect cells against the harmful effects of solar-ultraviolet (UV) radiation. The PR mechanism involves photolyase, just one enzyme, and can repair DNA damage, such as cyclobutane-pyrimidine dimers (CPD) induced by near-UV/blue light, a component of sunlight. Although the balance of near-UV/blue light and far-UV light reaching the Earth's surface could be altered by the atmospheric ozone layer's depletion, experiments simulating this environmental change and its possible effects on life have not yet been performed. To quantify the strength of UVB in sunlight reaching the Earth's surface, we measured the number of CPD generated in plasmid DNA after UVB irradiation or exposure to sunlight. To simulate the increase of solar-UV radiation resulting from the ozone layer depletion, Paramecium tetraurelia was exposed to UVB and/or sunlight in clear summer weather. PR recovery after exposure to sunlight was complete at a low dose rate of 0.2 J/m2 x s, but was less efficient when the dose rate was increased by a factor of 2.5 to 0.5 J/m2 x s. It is suggested that solar-UV radiation would not influence the cell growth of P. tetraurelia for the reason of high PR activity even when the ozone concentration was decreased 30% from the present levels. 相似文献
137.
Nahomi Sakaguchi Shuji Matsuo Tsutomu Kurisaki Taku Matsuo Hisanobu Wakita 《Research on Chemical Intermediates》2006,32(2):95-101
The photocatalytic degradation of 2-propanol in D2O solution under UV irradiation was investigated. The conversion yield from 2-propanol to acetone was studied by 1H-NMR measurements. The study was carried out to elucidate effects of O2 in the reaction medium and lanthanide ion modification on the TiO2 surface. Under aerobic conditions, acetone formation was clearly increased in comparison with anaerobic conditions. On the
modification of TiO2 with lanthanide ion, the conversion yield decreased with the increase in the ionic radius. Yb3+ ion modification increased the acetone formation by approx. 5% in comparison with the unmodified case. Appreciably large
effects of the counter ion in lanthanide salts were also observed. The role of OH˙ radical formation in the first step of photocatalysis was emphasized in the experimental results. 相似文献
138.
Imidazole‐Aided Native Chemical Ligation: Imidazole as a One‐Pot Desulfurization‐Amenable Non‐Thiol‐Type Alternative to 4‐Mercaptophenylacetic Acid 下载免费PDF全文
Ken Sakamoto Dr. Shugo Tsuda Dr. Masayoshi Mochizuki Yukie Nohara Dr. Hideki Nishio Dr. Taku Yoshiya 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(50):17940-17944
Various bioactive proteins have been synthesized by native chemical ligation (NCL) and its combination with subsequent desulfurization (e.g., conversion from Cys to Ala). In NCL, excess 4‐mercaptophenylacetic acid (MPAA) is generally added to facilitate the reaction. However, co‐elution of MPAA with the ligation product during preparative high‐performance liquid chromatography sometimes reduces its usefulness. In addition, contamination of MPAA disturbs subsequent desulfurization. Here, we report for the first time that imidazole can be adopted as an alternative to MPAA in NCL using a peptide‐alkylthioester. The efficiency of the imidazole‐aided NCL (Im‐NCL) is similar to that of traditional MPAA‐aided NCL. As model cases, we successfully synthesized adiponectin(19‐107) and [Ser(PO3H2)65]‐ubiquitin using Im‐NCL with a one‐pot desulfurization. 相似文献
139.
Dr. Shunta Nakamura Dr. Hayato Sakai Dr. Masaaki Fuki Rikuto Ooie Dr. Fumitaka Ishiwari Prof. Dr. Akinori Saeki Prof. Dr. Nikolai V. Tkachenko Prof. Dr. Yasuhiro Kobori Prof. Dr. Taku Hasobe 《Angewandte Chemie (International ed. in English)》2023,62(8):e202217704
We newly synthesized a series of homo- and hetero-tetracene (Tc) oligomers to propose a molecular design strategy for the efficient exciton transport in linear oligomers by promoting correlated triplet pair (TT) dissociation and controlling sequential exciton trapping process of individual doubled triplet excitons (T+T) by intramolecular singlet fission. First, entropic gain effects on the number of Tc units are examined by comparing Tc-homo-oligomers [(Tc)n: n=2, 4, 6]. Then, a comparison of (Tc)n and Tc-hetero-oligomer [TcF3-(Tc)4-TcF3] reveals the vibronic coupling effect for entropic gain. Observed entropic effects on the T+T formation indicated that the exciton migration is rationalized by number of possible TT states increased both by increasing the number of Tc units and by the vibronic levels at the terminal TcF3 units. Finally, we successfully observed high-yield exciton trapping process (trapped triplet yield: ΦTrT=176 %). 相似文献
140.
Metabolomics approach for determining growth-specific metabolites based on Fourier transform ion cyclotron resonance mass spectrometry 总被引:2,自引:0,他引:2
Takahashi H Kai K Shinbo Y Tanaka K Ohta D Oshima T Altaf-Ul-Amin M Kurokawa K Ogasawara N Kanaya S 《Analytical and bioanalytical chemistry》2008,391(8):2769-2782
Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR/MS) is the best MS technology for obtaining exact mass
measurements owing to its great resolution and accuracy, and several outstanding FT-ICR/MS-based metabolomics approaches have
been reported. A reliable annotation scheme is needed to deal with direct-infusion FT-ICR/MS metabolic profiling. Correlation
analyses can help us not only uncover relations between the ions but also annotate the ions originated from identical metabolites
(metabolite derivative ions). In the present study, we propose a procedure for metabolite annotation on direct-infusion FT-ICR/MS
by taking into consideration the classification of metabolite-derived ions using correlation analyses. Integrated analysis
based on information of isotope relations, fragmentation patterns by MS/MS analysis, co-occurring metabolites, and database
searches (KNApSAcK and KEGG) can make it possible to annotate ions as metabolites and estimate cellular conditions based on
metabolite composition. A total of 220 detected ions were classified into 174 metabolite derivative groups and 72 ions were
assigned to candidate metabolites in the present work. Finally, metabolic profiling has been able to distinguish between the
growth stages with the aid of PCA. The constructed model using PLS regression for OD600 values as a function of metabolic profiles is very useful for identifying to what degree the ions contribute to the growth
stages. Ten phospholipids which largely influence the constructed model are highly abundant in the cells. Our analyses reveal
that global modification of those phospholipids occurs as E. coli enters the stationary phase. Thus, the integrated approach involving correlation analyses, metabolic profiling, and database
searching is efficient for high-throughput metabolomics.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献