全文获取类型
收费全文 | 357篇 |
免费 | 9篇 |
国内免费 | 1篇 |
专业分类
化学 | 310篇 |
晶体学 | 1篇 |
力学 | 1篇 |
数学 | 16篇 |
物理学 | 39篇 |
出版年
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 3篇 |
2020年 | 7篇 |
2019年 | 5篇 |
2018年 | 2篇 |
2017年 | 3篇 |
2016年 | 4篇 |
2015年 | 7篇 |
2014年 | 11篇 |
2013年 | 22篇 |
2012年 | 26篇 |
2011年 | 33篇 |
2010年 | 19篇 |
2009年 | 9篇 |
2008年 | 27篇 |
2007年 | 30篇 |
2006年 | 23篇 |
2005年 | 20篇 |
2004年 | 19篇 |
2003年 | 21篇 |
2002年 | 26篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 4篇 |
1995年 | 1篇 |
1994年 | 3篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1990年 | 1篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1935年 | 1篇 |
排序方式: 共有367条查询结果,搜索用时 15 毫秒
61.
We have found that the use of the PhI(OAc)2/Et4N+Br− combination in water can significantly enhance its oxidation ability and oxidize a wide range of alcohols 1 to carbonyl compounds 2 in good to excellent yields. This clean aqueous oxidation method shows no detectable racemization processes, and even an enolizable ketone 2m could be obtained in an optically pure form from the corresponding chiral alcohol 1m. Utilization of the recyclable reagent 3 as a more practical alternative to PhI(OAc)2 is also successful in these reactions. 相似文献
62.
Kohzuma T Kikuchi M Horikoshi N Nagatomo S Kitagawa T Czernuszewicz RS 《Inorganic chemistry》2006,45(21):8474-8476
A copper-containing nitrite reductase from Alcaligenes xylosoxidans NCIMB 11015 has its own unique blue or type 1 copper protein resonance Raman spectrum in the usual Cu-S(Cys) stretching region, nu(Cu-S(Cys)), with a pair of strong peaks at 412 and 420 cm(-1) and a weak peak at 364 cm(-1). The predominantly nu(Cu-S(Cys)) Raman bands at 412, 420, and 364 cm(-1) of the type 1 copper site all shifted to higher frequencies upon binding of nitrite to the type 2 copper site, and the resonance Raman difference spectra progressively intensified with the increments of nitrite ion concentration. Positive support for substrate binding to the type 2 copper is provided by the nu(Cu-S(Cys)) bands in the resonance Raman spectrum of a type 2 copper-depleted enzyme, which is insensitive to the presence of NO2-. The shift to higher frequency of the Raman bands of the type 1 copper center with the addition of nitrite ions suggests a stronger Cu-S(Cys) interaction in the substrate-bound A. xylosoxidans nitrite reductase. 相似文献
63.
In the present study, all-trans retinoic acid (RA) gels formulated with various compositions of polyethylene oxide (Emulgen?) and iota-carrageenan (ι-CG) were prepared and their physicochemical properties were evaluated. The compression energy, which is the work required to compress the product through a fixed distance, increased with increasing amount of ι-CG or Emulgen?. The adhesion energy and displacement decreased with increasing amount of ι-CG or Emulgen? due to the progression of gel formation. From the results of the sensory tests, the properties of RA gels such as adhesiveness, gel strength and spreadability seemed to be adjustable depending on the condition of skin by varying the components of RA gels. Through photostability study, the expiration date and storage conditions of RA gels were determined as "4°C for 28?d with no exposure to light." 相似文献
64.
Yoshimi Ohmae Natsuko I. Kobayashi Keitaro Tanoi Atsushi Hirose Takayuki Saito Akihiko Noda Naoko Iwata Akimasa Nakano Satoru Nakamura Tomoko M. Nakanishi 《Journal of Radioanalytical and Nuclear Chemistry》2012,291(1):241-244
The mineral composition of frozen food of taro [Colocasia esculenta (L.) Schott] was analyzed to categorize the geographical production place of taro. The concentrations of Co and H2PO4
− were found to be useful to separate the producing place between Japan and China. The analysis was performed by instrumental
neutron activation analysis (INAA) and ion chromatography (IC). In the case of INAA, the samples were dried and sealed in
a vinyl bag and irradiated with thermal neutrons from JRR3M, installed at Japan Atomic Energy Agency (JAEA). The activated
samples were cooled down for a few weeks and the elements (Co, Cr, Fe, Rb, Zn) were determined. Cobalt concentration of frozen
taro from China was higher than that from Japan. The tendency was the same in the fresh sample of taro. When concentration
of H2PO4
− of frozen sample was measured, taro from Japanese product was higher than that of Chinese one, contrary to fresh sample.
This result might be caused by the leakage of H2PO4
− during freezing process, indicating that we should be careful to apply the discrimination indicators. In addition to Co,
there was a significant difference of Rb and Fe concentrations between frozen taro from Japan and China. 相似文献
65.
Naoko Asakuma Toshimi Fukui Mamoru Aizawa Motoyuki Toki Hiroaki Imai Hiroshi Hirashima 《Journal of Sol-Gel Science and Technology》2000,19(1-3):333-336
Structural changes stimulated by ultraviolet (UV) laser irradiations of sol-gel derived inorganic oxide films were investigated. Dried gel films of TiO2, Nb2O5, Ta2O5, SrTiO3 and Pb(Zr
x
Ti1–x
)O3 (PZT) were found to be crystallized by the laser irradiation. On the other hand, the photo-induced change in gel films of BaTiO3, LiNbO3 and LiTaO3 was not observed although the laser beams were absorbed in the films. These sol-gel films were thermally crystallized at almost the same temperature around 600–700°C except TiO2. Thus, the UV-laser-induced crystallization is not directly ascribed to a simple thermal effect with the irradiation. Photochemical properties of the cations are assumed to be important for the change in sol-gel films. 相似文献
66.
Akira Abe Naoko Aoyama Satoshi Sumiya Noriyoshi Kakuta Kiyohide Yoshida 《Reaction Kinetics and Catalysis Letters》1998,65(1):139-144
The influence of SO2 (200 ppm) on the durability of a Ag/Al2O3 catalyst for the reduction of NOx with ethyl alcohol was examined. The results strongly suggest that H2O in diesel engine exhaust is essential for the high durability of Ag/Al2O3 catalyst in the presence of SO2. 相似文献
67.
Naoko Yoshie Mariko Watanabe Hitomi Araki Kazuki Ishida 《Polymer Degradation and Stability》2010,95(5):826-6079
Remending properties of a network polymer with reversible reactivity are described. The network structure is constructed by a Diels-Alder (DA) reaction between furyl-telechelic poly(ethylene adipate) (PEAF2) and a tris-maleimide, M3. When a film sample was cut into two pieces and the cut surfaces were kept in contact with each other at 60 °C, rejoining of the cut pieces was observed. This mending was induced by the reversible cross-linking reaction bridging the cut surfaces. At the cut front, the “weak” DA adducts are selectively dissociated sacrificially to release the stress so as to protect the chemical structure of the prepolymer and the linker against the scission or degradation. The dissociated furan and maleimide readily reconnect by forward DA reaction to mend the material. The remending was also observed for the samples kept at room temperature after melting at 60 °C. So, the PEAF2 network polymer is a thermo-responsive mendable material in which crack healing is induced by a prompt thermal stimulus. 相似文献
68.
Polyelectrolyte complex films were prepared with polyethyleneoxide-maleic acid copolymer and chitosan using a casting/solvent evaporation method. The films were examined in terms of their IR spectra, surface and cross-section morphologies, cytotoxicity, and swelling behavior at different pH levels. To assess the potential of these films as a biomedical device, the profiles of the release of model drug from the CS/PEOMA films were examined at pH 4.8. The surface morphology of the films was quite smooth and uniform, and the cross-sectional morphology was dense and homogeneous. The swelling behaviors of CS/PEOMA films were found to depend on the pH of the solution as well as on the CS/PEOMA composition. Drug release from different CS/PEOMA films at pH 4.8 was found to be dependent on film composition. The results showed the potential applicability of CS/PEOMA film as a drug delivery vehicle. 相似文献
69.
Negi N Jinguji Y Ushijima K Ikeda S Takemura Y Ju-ichi M Wu TS Ito C Furukawa H 《Chemical & pharmaceutical bulletin》2004,52(3):362-364
Two new acridone dimers, glycobismines-F (1) and -G (2), were isolated from the roots of Glycosmis citrifolia collected in Taiwan. The structures of the new compounds were determined based on spectral analysis. 相似文献
70.
Nakanishi T Miyashita N Michinobu T Wakayama Y Tsuruoka T Ariga K Kurth DG 《Journal of the American Chemical Society》2006,128(19):6328-6329
Fullerene derivatives bearing long alkyl chains epitaxially adsorb on the basal plane of graphite forming well-ordered one-dimensional lamellae. Within the lamellae, the C60 moieties are organized in a zigzag-type fashion. The ordering is mainly governed by the substitution pattern and chain length of the alkyl chains. The electrochemical activity of the C60 groups is fully maintained in the surface-confined assemblies. 相似文献