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排序方式: 共有235条查询结果,搜索用时 250 毫秒
131.
Masaki Yoshida Dr. Shigeyuki Masaoka Prof. Dr. Jiro Abe Prof. Dr. Ken Sakai 《化学:亚洲杂志》2010,5(11):2369-2378
The mechanism of O2 evolution from water catalyzed by a series of mononuclear aquaruthenium complexes, [Ru(terpy)(bpy)(OH2)]2+, [Ru(tmtacn)(R2bpy)(OH2)]2+ (R=H, Me, and OMe; R2bpy=4,4′‐disubstituted‐2,2′‐bipyridines), and [Ru(tpzm)(R2bpy)(OH2)]2+ (R=H, Me, and OMe), is investigated, where terpy=2,2′:6′,2′′‐terpyridine, bpy=2,2′‐bipyridine, tmtacn=1,4,7‐trimethyl‐1,4,7‐triazacyclononane, and tpzm=tris(1‐pyrazolyl)methane. The kinetics of O2 evolution is investigated as a function of either the catalyst concentration or the oxidant concentration by employing Ce(NH4)2(NO3)6 as an oxidant; these catalysts can be classified into two groups that have different rate laws for O2 evolution. In one class, the rate of O2 evolution is linear to both the catalyst and Ce4+ concentrations, as briefly reported for [Ru(terpy)(bpy)(OH2)]2+ (S. Masaoka, K. Sakai, Chem. Lett. 2009 , 38, 182). For the other class, [Ru(tmtacn)(R2bpy)(OH2)]2+, the rate of O2 evolution is quadratic to the catalyst concentration and independent of the Ce4+ concentration. Moreover, the singlet biradical character of the hydroxocerium(IV) ion was realized by experimental and DFT investigations. These results indicate that the radical coupling between the oxygen atoms of a RuV?O species and a hydroxocerium(IV) ion is the key step for the catalysis of [Ru(terpy)(bpy)(OH2)]2+ and [Ru(tpzm)(R2bpy)(OH2)]2+, while the well‐known oxo‐oxo radical coupling among two RuV?O species proceeds in the catalysis of [Ru(tmtacn)(R2bpy)(OH2)]2+. This is the first report demonstrating that the radical character provided by the hydroxocerium(IV) ion plays a crucial role in the catalysis of such ruthenium complexes in the evolution of O2 from water. 相似文献
132.
Tono Y Kojima C Haba Y Takahashi T Harada A Yagi S Kono K 《Langmuir : the ACS journal of surfaces and colloids》2006,22(11):4920-4922
Dendrimers are unique polymers with globular shapes and well-defined structures. We previously prepared poly(amidoamine) (PAMAM) dendrimers having phenylalanine (Phe) residues at every chain end of the dendrimer as efficient gene carriers. In this study, we found that Phe-derivatized PAMAM dendrimers change their water solubility depending on temperature. The dendrimers were soluble in aqueous solutions at low temperatures, but they became water-insoluble at temperatures above a specific threshold, which is termed the lower critical solution temperature (LCST). Although the LCST of Phe-modified dendrimers decreased with increasing dendrimer generation, these dendrimers exhibited an LCST of 20-30 degrees C under physiological conditions. In addition, the LCST of the dendrimers was controlled by introducing isoleucine (Ile) residues at chain ends of dendrimers at varying ratios with respect to Phe residues. The PAMAM dendrimers are known to encapsulate various drug molecules. For these reasons, temperature-sensitive dendrimers might be useful as efficient drug carriers with controlled size and temperature-responsive properties. 相似文献
133.
Renguo Lu Shigeyuki Mori Kimihiro Kobayashi Hidetaka Nanao 《Applied Surface Science》2009,255(22):8965-8971
Tribological properties and the decomposition process of ionic liquids (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide and 1-dodecyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide) on a nascent surface of bearing steel 52100 were investigated by a ball-on-disk friction tester in a vacuum chamber equipped with a quadrupole mass spectrometer (Q-MS). Ionic liquids exhibited better tribological properties than synthetic hydrocarbon oil (multialkylated cyclopentane (MAC)) in high vacuum conditions. The induction period for decomposition of MAC was about 10 km, while no obvious gaseous products were observed for ionic liquids even after a sliding distance of 22 km under the same mechanical conditions. The mass spectra indicated that both the anionic and cationic moieties of ionic liquids decomposed on the nascent steel surface during friction processes. The cationic moiety with a longer alkyl chain was more difficult to decompose on the nascent steel surface than that with a shorter alkyl chain. XPS analysis revealed that the tribofilm formed by ionic liquid was mainly composed of FeF2 and FeS, which deactivated the nascent surface. As a result, desorption rate of gaseous products decreased appreciably comparing with MAC. The critical load for the mechanical activation of the decomposition correspondingly increased from 1.1 N of MAC to 8 N of ionic liquids. 相似文献
134.
135.
Masako Akimitsu Tadashi Mizoguchi Jun Akimitsu Shigeyuki Kimura 《Journal of Physics and Chemistry of Solids》1983,44(6):497-505
The magnetic structure of non-stoichiometric Fe1?xO was investigated by neutron scattering measurements on a quenched single crystal of Fe0.91O below the Néel temperature. In each defect cluster, there exist ferromagnetic moments and they are arranged antiferromagnetically with the periodicity of twice that of the atomic superstructure. Relation between the defect structure and the magnetic properties for a wide range of compositions was discussed. 相似文献
136.
137.
Takaoka Y Endo Y Yamanobe S Kakinuma H Okubo T Shimazaki Y Ota T Sumiya S Yoshikawa K 《Journal of chemical information and computer sciences》2003,43(4):1269-1275
The concept of drug-likeness, an important characteristic for any compound in a screening library, is nevertheless difficult to pin down. Based on our belief that this concept is implicit within the collective experience of working chemists, we devised a data set to capture an intuitive human understanding of both this characteristic and ease of synthesis, a second key characteristic. Five chemists assigned a pair of scores to each of 3980 diverse compounds, with the component scores of each pair corresponding to drug-likeness and ease of synthesis, respectively. Using this data set, we devised binary classifiers with an artificial neural network and a support vector machine. These models were found to efficiently eliminate compounds that are not drug-like and/or hard-to-synthesize derivatives, demonstrating the suitability of these models for use as compound acquisition filters. 相似文献
138.
In this study, we synthesized a series of fluorinated and non-fluorinated tolanes, in which one or more fluorine atoms were systematically introduced into one aromatic ring of a tolane scaffold, and systematically evaluated their photophysical properties. All the tolanes with or without fluorine substituents were found to have poor photoluminescence (PL) in tetrahydrofuran (THF) solutions. On the other hand, in the crystalline state, non-fluorinated and fluorinated tolanes with one or four fluorine atoms were less emissive, whereas fluorinated tolanes with three or five fluorine atoms exhibited high PL efficiencies (ФPL) up to 0.51. X-ray crystallographic analyses of the emissive fluorinated tolanes revealed that the position of the fluorine substituent played a key role in achieving a high ФPL. Fluorine substituents at the ortho (2/6) and para (4) positions led to tight and rigid packing due to plural π–π stacking and/or hydrogen bonding interactions, resulting in enhanced ФPL caused by the suppression of non-radiative deactivation. Additionally, fluorinated tolanes with three fluorine atoms exhibited notable aggregation-induced PL emission enhancement in THF/water mixed solvents. This demonstrates that the PL characteristics of small PL materials can be tuned depending on the usage requirements. 相似文献
139.
Yoshiaki Hidaka Tetsuo Higashihara Natsuhiko Ninomiya Hiromitsu Masaoka Takuji Nakamura Hiroyuki Kawano 《国际化学动力学杂志》1996,28(2):137-151
1,3-Butadiene (1,3-C4H6) was heated behind reflected shock waves over the temperature range of 1200–1700 K and the total density range of 1.3 × 10−5 −2.9 × 10−5 mol/cm3. Reaction products were analyzed by gas-chromatography. The concentration change of 1,3-butadiene was followed by UV kinetic absorption spectroscopy at 230 nm and by quadrupole mass spectrometry. The major products were C2H2, C2H4, C4H4, and CH4. The yield of CH4 for a 0.5% 1,3-C4H6 in Ar mixture was more than 10% of the initial 1.3-C4H6 concentration above 1500 K. In order to interpret the formation of CH4 successfully, it was necessary to include the isomerization of 1,3-C4H6 to 1,2-butadiene (1,2-C4H6) and to include subsequent decomposition of the 1,2-C4H6 to C3H3 and CH3. The present data and other shock tube data reported over a wide pressure range were qualitatively modeled with a 89 reaction mechanism, which included the isomerizations of 1,3-C4H6 to 1,2-C4H6 and 2-butyne (2-C4H6). © 1996 John Wiley & Sons, Inc. 相似文献
140.