全文获取类型
收费全文 | 288篇 |
免费 | 16篇 |
国内免费 | 2篇 |
专业分类
化学 | 220篇 |
晶体学 | 1篇 |
力学 | 5篇 |
数学 | 9篇 |
物理学 | 71篇 |
出版年
2023年 | 5篇 |
2022年 | 6篇 |
2021年 | 7篇 |
2020年 | 16篇 |
2019年 | 15篇 |
2018年 | 10篇 |
2017年 | 8篇 |
2016年 | 6篇 |
2015年 | 8篇 |
2014年 | 11篇 |
2013年 | 18篇 |
2012年 | 12篇 |
2011年 | 20篇 |
2010年 | 10篇 |
2009年 | 8篇 |
2008年 | 16篇 |
2007年 | 15篇 |
2006年 | 9篇 |
2005年 | 13篇 |
2004年 | 6篇 |
2003年 | 16篇 |
2002年 | 6篇 |
2001年 | 1篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1995年 | 1篇 |
1994年 | 3篇 |
1993年 | 5篇 |
1992年 | 5篇 |
1991年 | 7篇 |
1989年 | 5篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1973年 | 3篇 |
1972年 | 1篇 |
排序方式: 共有306条查询结果,搜索用时 31 毫秒
51.
[Eu(pda)2]? and [Eu(bda)2]? (pda=1,10‐phenanthroline‐2, 9‐dicarboxylic acid; bda=2,2′ bipyridine 5,5′‐dicarboxylic acid) have an achiral D2d structure in crystals. These complexes exhibit circularly polarized luminescence (CPL) in water containing chiral amino acids. In this work, induced CPL of [Eu(pda)2]? and [Eu(bda)2]? in water solutions containing a mixture of d ‐ and l ‐ amino acids were examined. Plots of glum values of the induced CPL as a function of mol‐fraction of l ‐ and d ‐ arginine reveal that [Eu(pda)2]? favors homo‐association ([Eu(pda)2]?‐(l ‐arginine)2 or [Eu(pda)2]?‐(d ‐arginine)2) over hetero‐association {[Eu(pda)2]?‐(l ‐arginine)?(d ‐arginine)}. This suggests that association of an arginine molecule induces a structural change in [Eu(pda)2]? to promote chiral selective association to another arginine, i.e., homo‐allosteric association. On the other hand, the system of [Eu(pda)2]? with histidine favors hetero‐allosteric association over homo‐association. No allosteric effect is recognized in CPL from [Eu(bda)2]?. 相似文献
52.
Masao Takahashi Takeru Shishido Hitoo Iwasa Hikaru Kobayashi 《Central European Journal of Physics》2009,7(2):227-231
The local photovoltage of the pn-junction single-crystalline silicon solar cells observed by spot light scanning gradually
decreases in the vicinity of edges. The energy conversion efficiency is increased by shadowing the edge regions where the
local photovoltage is lower, showing that the defect density is high in the edge regions. From the analysis of the local photovoltage,
the spacial distribution of defect states is obtained. The cyanide method, i. e., immersion of solar cells in HCN solutions at room temperature, increases the local photovoltage and increases the energy
conversion efficiency.
相似文献
53.
Peter Bury Hikaru Kobayashi Masao Takahashi Kentaro Imamura Peter Sidor Franti??ek ??ernobila 《Central European Journal of Physics》2009,7(2):237-241
Ultrathin silicon dioxide (SiO2) layers formed on Si substrate with nitric acid have been investigated using both acoustic deep-level transient spectroscopy
(A-DLTS) and electrical methods to characterize the interface states. The set of SiO2/Si structures formed in different conditions (reaction time, concentrations of nitric acid (HNO3), and SiO2 thickness [3–9 nm]) was prepared. The leakage current density was decreased by post-oxidation annealing (POA) treatment at
250°C in pure nitrogen for 1 h and/or post-metallization annealing (PMA) treatment at 250°C in a hydrogen atmosphere for 1
h. All structures of the set, except electrical investigation, current-voltage (I - V), and capacitance — voltage (C - V) measurements, were investigated using A-DLTS to find both the interface states distribution and the role of POA and/or PMA
treatment on the interface-state occurrence and distribution. The evident decreases of interface states and shift of their
activation energies in the structures with PMA treatment in comparison with POA treatment were observed in most of the investigated
structures. The results are analyzed and discussed.
相似文献
54.
Keisuke Kato Hideaki Nouchi Satoshi Takaishi Hikaru Tanaka Tomoyuki Mochida Koki Shigenobu 《Tetrahedron》2006,62(11):2545-2554
The oxidative cyclization-carbonylation of propargylic esters mediated by Pd(II) afforded cyclic orthoesters, which were hydrolyzed into γ-acetoxy-β-ketoesters. Based on the NMR experiments, it was presumed that the cyclization reaction was initiated by a nucleophilic attack of carbonyl oxygen to the alkyne carbon coordinated to palladium(II). When the γ-acetoxy-β-ketoesters were treated with a basic condition, Knoevenagel-Claisen type condensation took place, and spiro furanone derivatives were obtained in good yields. We applied these reactions to steroid derivatives, and steroid derivatives having a spiro furanone fragment were synthesized. Among them, the spiro furanone 4j had vasorelaxant and bradycardiac activities. Compounds 2i-4k had inhibitory effect on CYP3A. 相似文献
55.
Yuki Kobayashi Shinsuke Matsuda Kentaro Imamura Hikaru Kobayashi 《Journal of nanoparticle research》2017,19(5):176
Si and its oxide are nonpoisonous materials, and thus, it can be taken for medical effects. We have developed a method of generation of hydrogen by use of reactions of Si nanopowder with water in the neutral pH region. Si nanopowder is fabricated by the simple bead milling method. Si nanopowder reacts with water to generate hydrogen even in cases where pH is set at the neutral region between 7.0 and 8.6. The hydrogen generation rate strongly depends on pH and in the case of pH 8.0, ~55 ml/g hydrogen which corresponds to that contained in approximately 3 L saturated hydrogen-rich water is generated in 1 h. The reaction rate for hydrogen generation greatly increases with pH, indicating that the reacting species is hydroxide ions. The change of pH after the hydrogen generation reaction is negligibly low compared with that estimated assuming that hydroxide ions are consumed by the reaction. From these results, we conclude the following reaction mechanism: Si nanopowder reacts with hydroxide ions in the rate-determining reaction to form hydrogen molecules, SiO2, and electrons in the conduction band. Then, generated electrons are accepted by water molecules, resulting in production of hydrogen molecules and hydroxide ions. The hydrogen generation rate strongly depends on the crystallite size of Si nanopowder, but not on the size of aggregates of Si nanopowder. The present study shows a possibility to use Si nanopowder for hydrogen generation in the body in order to eliminate hydroxyl radicals which cause various diseases. 相似文献
56.
Murata Y Itoh S Morio K Sasaki T Mizobuchi H Shimizu K Yoshida S 《Magnetic resonance imaging》2004,22(3):435-439
We report a case of multiple hemorrhagic cerebral metastases from papillary thyroid cancer, with reference to T(2)*-weighted gradient echo (GRE) magnetic resonance imaging (MRI). Small metastatic nodules were recognized as round nodules with signal loss on T(2)*-weighted GRE MRI, and were more pronounced compared with other sequences. Lesions were later confirmed as hemorrhagic on T(1)- and T(2)-weighted MRI. T(2)*-weighted GRE MRI was a sensitive tool for early detection of metastases displaying hemorrhagic changes. 相似文献
57.
(Z)-Selective olefination of several lactones with ketene silyl acetals was achieved by the catalysis of carbon acids (C-H acids) having a bis(triflyl)methyl group as an acidic functionality; in particular, the triple carbon acid having three bis(triflyl)methyl groups in phloroglucinol shows an excellent catalytic performance. 相似文献
58.
Seki M Tsuruta O Aoyama Y Soejima A Shimada H Nonaka H 《Chemical & pharmaceutical bulletin》2012,60(4):488-498
In investigating potent sodium (Na(+)) channel blockers for the treatment of ischemic stroke, we synthesized a novel series of 3-amino-1-(5-indanyloxy)-2-propanol derivatives and evaluated their inhibitory effects on neuronal Na(+) channels. The 3-amino-1-(5-indanyloxy)-2-propanol derivatives exhibited potent blocking activity for Na(+) channels and a significantly low affinity for dopamine D(2) receptors, which demonstrates a minimal clinical risk for extrapyramidal side effects. In particular, compound 4b, a 3-amino-1-(5-indanyloxy)-2-propanol derivative bearing a benzimidazole moiety, showed desirable neuroprotective activity in a rat transient middle cerebral artery occlusion model. Furthermore, compound 4b displayed a high binding affinity for neurotoxin receptor site 2 of the Na(+) channels, which suggests that 4b would act as a use-dependent Na(+) channel blocker in sustained depolarization during ischemic stroke. 相似文献
59.
Akio Saito Manabu Tojo Hikaru Yanai Fukiko Wada Muga Nakagawa Midori Okada Azusa Sato Rieko Okatani Takeo Taguchi 《Journal of fluorine chemistry》2012
CrCl2/Mn-mediated transformation of various dibromofluoromethylcarbinyl esters including carboxylates, carbonates and carbamates provided 1-fluoro-1-alkenyl esters via [2,3]-sigmatropic rearrangement of ester group. Reaction proceeded by using CrCl2/Mn system under mild conditions (in THF at room temperature) to give 1-fluoro-1-alkenyl esters in good yield with an excellent Z selective manner. 1-Fluoro-1-alkenyl ester thus obtained acts as a double acyl donor in the reaction with necleophiles such as amine, thiol, alcohol as well as bifunctional necleophiles such as ethylene diamine derivative. 相似文献
60.
We consider the heat equation with a superlinear absorption term in and study the existence of nonnegative solutions with an m-dimensional time-dependent singular set, where . We prove that if , then there are two types of singular solutions. Moreover, we show the uniqueness of the solutions and specify the exact behavior of the solutions near the singular set. 相似文献