全文获取类型
收费全文 | 464篇 |
免费 | 14篇 |
专业分类
化学 | 345篇 |
晶体学 | 8篇 |
力学 | 8篇 |
综合类 | 1篇 |
数学 | 19篇 |
物理学 | 97篇 |
出版年
2023年 | 5篇 |
2022年 | 3篇 |
2021年 | 10篇 |
2020年 | 11篇 |
2019年 | 14篇 |
2018年 | 4篇 |
2017年 | 4篇 |
2016年 | 7篇 |
2015年 | 9篇 |
2014年 | 11篇 |
2013年 | 21篇 |
2012年 | 24篇 |
2011年 | 29篇 |
2010年 | 13篇 |
2009年 | 10篇 |
2008年 | 19篇 |
2007年 | 42篇 |
2006年 | 27篇 |
2005年 | 42篇 |
2004年 | 25篇 |
2003年 | 14篇 |
2002年 | 24篇 |
2001年 | 5篇 |
2000年 | 13篇 |
1999年 | 2篇 |
1998年 | 4篇 |
1997年 | 2篇 |
1996年 | 7篇 |
1995年 | 3篇 |
1994年 | 1篇 |
1993年 | 8篇 |
1992年 | 4篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 7篇 |
1983年 | 11篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1980年 | 6篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1975年 | 1篇 |
1974年 | 2篇 |
排序方式: 共有478条查询结果,搜索用时 15 毫秒
121.
Palash Pandit Koji Yamamoto Toshikazu Nakamura Katsuyuki Nishimura Yuki Kurashige Takeshi Yanai Go Nakamura Shigeyuki Masaoka Ko Furukawa Yumi Yakiyama Masaki Kawano Shuhei Higashibayashi 《Chemical science》2015,6(7):4160-4173
Regulation of electron transfer on organic substances by external stimuli is a fundamental issue in science and technology, which affects organic materials, chemical synthesis, and biological metabolism. Nevertheless, acid/base-responsive organic materials that exhibit reversible electron transfer have not been well studied and developed, owing to the difficulty in inventing a mechanism to associate acid/base stimuli and electron transfer. We discovered a new phenomenon in which N–N linked bicarbazole (BC) and tetramethylbiacridine (TBA) derivatives undergo electron transfer disproportionation by acid stimulus, forming their stable radical cations and reduced species. The reaction occurs through a biradical intermediate generated by the acid-triggered N–N bond cleavage reaction of BC or TBA, which acts as a two electron acceptor to undergo electron transfer reactions with two equivalents of BC or TBA. In addition, in the case of TBA the disproportionation reaction is highly reversible through neutralization with NEt3, which recovers TBA through back electron transfer and N–N bond formation reactions. This highly reversible electron transfer reaction is possible due to the association between the acid stimulus and electron transfer via the acid-regulated N–N bond cleavage/formation reactions which provide an efficient switching mechanism, the ability of the organic molecules to act as multi-electron donors and acceptors, the extraordinary stability of the radical species, the highly selective reactivity, and the balance of the redox potentials. This discovery provides new design concepts for acid/base-regulated organic electron transfer systems, chemical reagents, or organic materials. 相似文献
122.
A new mathematical model for finding the optimal harvesting policy of an inland fishery resource under incomplete information is proposed in this paper. The model is based on a stochastic control formalism in a regime‐switching environment. The incompleteness of information is due to uncertainties involved in the body growth rate of the fishery resource: a key biological parameter. Finding the most cost‐effective harvesting policy of the fishery resource ultimately reduces to solving a terminal and boundary value problem of a Hamilton‐Jacobi‐Bellman equation: a nonlinear and degenerate parabolic partial differential equation. A simple finite difference scheme for solving the equation is then presented, which turns out to be convergent and generates numerical solutions that comply with certain theoretical upper and lower bounds. The model is finally applied to the management of Plecoglossus altivelis, a major inland fishery resource in Japan. The regime switching in this case is due to the temporal dynamics of benthic algae, the main food of the fish. Model parameter values are identified from field measurement results in 2017. Our computational results clearly show the dependence of the optimal harvesting policy on the river environmental and biological conditions. The proposed model would serve as a mathematical tool for fishery resource management under uncertainties. 相似文献
123.
Palchunova Kseniya Mino Toshihiro Mihashi Toshifumi Liu Jonathan Tasaki Kuniharu Hasegawa Yumi Hiraoka Takahiro Oshika Tetsuro 《Optical Review》2022,29(3):188-196
Optical Review - To evaluate the repeatability of the optical coherence tomography (OCT) retinal shape measurement with and without alignment correction in children and adults. 62 eyes of the 31... 相似文献
124.
Masashi Kijima Hideki Hasegawa Hideki Shirakawa 《Journal of polymer science. Part A, Polymer chemistry》1998,36(15):2691-2698
Three liquid crystalline N-substituted pyrroles were synthesized from 6-(1-pyrrolyl)hexanol with phenolic derivatives having a mesogenic core of cyclohexylbenzene or biphenyl by Mitsunobu reaction. These pyrroles had two anodic peaks at 1.4 and 1.8 V (vs. SCE). The former was due to an oxidation of the pyrrole moiety and the latter was due to an oxidation of the mesogenic moiety. These pyrrole monomers were polymerized by electrochemical and chemical methods. The potentiostatic method and the chemical method using FeCl3 gave a soluble and fusible polymer, respectively. A polymer having a mesogenic core of cyclohexyl benzene obtained by the chemical method and a polymer having a mesogenic core of biphenylketone obtained by the potentiostatic method had a liquid-crystalline phase. The phase was identified as smectic A by polarizing microscopy and XRD analysis. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2691–2698, 1998 相似文献
125.
Eiji Shirakawa Yoshiaki Nakao Yasubumi Murota Tamejiro Hiyama 《Journal of organometallic chemistry》2003,670(1-2):132-136
A palladium–iminophosphine complex was found to catalyze the homocoupling reaction of alkynylstannanes using allyl acetate as an oxidant, whereas aryl- and alkenylstannanes were oxidatively homocoupled with air. 相似文献
126.
Nanoparticles formed during the initial period of film growth can migrate, coalesce, and may also melt. Nanoparticles of Au, Ag, Cu, and GaAs ranging from 1 to 15nm in diameter were sputter-deposited on amorphous SiO2 (a-SiO2). Transmission electron microscopy was used to analyze the time-dependent change of the dispersion of particles on a thin film. The number density of nanoparticles was nearly constant during the deposition of Ag. For Au, Cu, and GaAs, however, the number density decreased with time during the early deposition period. For example, for Au the number density decreased from 2.8×1016m–2 (surface coverage ratio of 0.08) to 1.8×1016m–2 (surface coverage ratio of 0.14). The surface coverage increased because the particle size increased as the number density decreased. This decrease suggests that migration followed by coalescence occurred. For Au, although we found evidence of migration of 2-nm particles at 500°C, the migration rate was too slow to account for the results from the deposition experiments. These observations indicate an autocatalytic mechanism that migration followed by coalescence liberates energy by the formation of chemical bonds, heats the coalesced particles, and enhances further migration. The strong dependence of the structure of nanoparticle dispersions on the deposition rate is a direct consequence of the deposition mechanism, which is a nonlinear, kinetically-controlled process. 相似文献
127.
Microbial transformation of (+)-cedrol was investigated by using Staphylococcus epidermidis and found that stereospecific hydroxylation of (+)-cedrol occurred at the C-3 position to form (+)-(3S)-3-hydroxycedrol. 相似文献
128.
[reaction: see text] Mechanistic studies of one-electron reduction in water using samarium were carried out. Unexpected disproportionation in water was observed via UV-vis spectroscopic analysis. This fact indicates that low-valent samarium species can exist in water. Furthermore, the SmCl(3)-Sm and SmCl(3)-Mg systems were found to act as good one-electron reducing agents in water. 相似文献
129.
Takeo Ito Hideki Shirakawa Sakuji Ikeda 《Journal of polymer science. Part A, Polymer chemistry》1975,13(8):1943-1950
Thermal cis-trans isomerization and decomposition of polyacetylene film prepared with a Ti(OC4H9)4–Al(C2H5)3 (Al/Ti = 4) system were investigated under inert gas or in vacuum by means of thermal analysis and infrared spectroscopy. Thermograms of differential thermal analysis of cis-polyacetylene revealed the existence of two exothermic peaks at 145 and 325°C and one endothermic peak at 420°C which were assigned to cis-trans isomerization, hydrogen migration accompanied with crosslinking reaction, and thermal decomposition, respectively. The isomerization was followed by infrared spectroscopy over the temperature range 75–115°C. The reaction did not obey simple kinetics. The apparent activation energy for the cis-trans isomerization was 17.0 kcal/mole for the polymer containing 88% cis configuration and increased with increasing trans content up to 38.8 kcal/mole for 80% trans content. 相似文献
130.
Shirakawa M Kawano S Fujita N Sada K Shinkai S 《The Journal of organic chemistry》2003,68(13):5037-5044
To obtain insights into a correlation relationship between the structure and the aggregation mode in an organogel system, we synthesized gelators 2a-4a bearing a porphyrin moiety as a one-dimensional aggregation unit and amide groups as peripheral hydrogen-bonding sites. Gelators 3a and 3b bearing the amide groups at the 4-position of the meso-phenyl groups are classified as versatile gelators, gelating 10 and 14 solvents, respectively, among 23 solvents tested herein. In contrast, gelators 2a and 4a bearing the amide groups at the 3,5-positions and 3-position, respectively, are classified as poor gelators. Examination by spectroscopic methods (UV-vis, ATR-FTIR, XRD, etc.) revealed that in the organogel phase porphyrins in 3a adopt the H aggregation mode whereas those in 2a and 4a adopt the J aggregation mode. X-ray analysis of the single crystals established that in fact 3b features a columnar stack of porphyrin moieties that can be classified as the H-aggregate, whereas 2a results in a two-dimensional a-b plane, in which porphyrin moieties are arranged in the J-aggregate. Very interestingly, the difference in the H versus J aggregation mode is well-reflected by the difference in the macroscopic aggregate morphology observed by SEM: 3a + cyclohexane gel results in a one-dimensionally aggregated fibrillar structure, whereas 2a + cyclohexane gel results in a two-dimensional sheetlike structure. These findings indicate that the H versus J aggregation mode of porphyrin stacks can be controlled by the peripheral hydrogen-bonding interactions and the microscopic hydrogen-bonding network structure is well-reflected by the macroscopic SEM-observed structure. 相似文献