全文获取类型
收费全文 | 1456篇 |
免费 | 78篇 |
国内免费 | 10篇 |
专业分类
化学 | 1224篇 |
晶体学 | 16篇 |
力学 | 10篇 |
数学 | 100篇 |
物理学 | 194篇 |
出版年
2023年 | 11篇 |
2022年 | 8篇 |
2021年 | 10篇 |
2020年 | 29篇 |
2019年 | 31篇 |
2018年 | 15篇 |
2017年 | 15篇 |
2016年 | 50篇 |
2015年 | 37篇 |
2014年 | 27篇 |
2013年 | 72篇 |
2012年 | 70篇 |
2011年 | 96篇 |
2010年 | 56篇 |
2009年 | 62篇 |
2008年 | 107篇 |
2007年 | 98篇 |
2006年 | 93篇 |
2005年 | 89篇 |
2004年 | 75篇 |
2003年 | 63篇 |
2002年 | 64篇 |
2001年 | 26篇 |
2000年 | 31篇 |
1999年 | 11篇 |
1998年 | 17篇 |
1997年 | 9篇 |
1996年 | 15篇 |
1995年 | 15篇 |
1994年 | 10篇 |
1993年 | 11篇 |
1992年 | 12篇 |
1991年 | 10篇 |
1990年 | 14篇 |
1989年 | 6篇 |
1988年 | 14篇 |
1987年 | 9篇 |
1986年 | 6篇 |
1985年 | 14篇 |
1984年 | 21篇 |
1983年 | 8篇 |
1982年 | 18篇 |
1981年 | 20篇 |
1980年 | 10篇 |
1979年 | 10篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1974年 | 5篇 |
1973年 | 8篇 |
1972年 | 6篇 |
排序方式: 共有1544条查询结果,搜索用时 15 毫秒
991.
Dr. Hajime Hirao Pratanphorn Chuanprasit Ying Yi Cheong Dr. Xiaoqing Wang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(23):7361-7369
A precise understanding of the mechanism‐based inactivation of cytochrome P450 enzymes (P450s) at the quantum mechanical level should allow more reliable predictions of drug–drug interactions than those currently available. Hydrazines are among the molecules that act as mechanism‐based inactivators to terminate the function of P450s, which are essential heme enzymes responsible for drug metabolism in the human body. Despite its importance, the mechanism explaining how a metabolic intermediate (MI) is formed from hydrazine is not fully understood. We used density functional theory (DFT) calculations to compare four possible mechanisms underlying the reaction between 1,1‐dimethylhydrazine (or unsymmetrical dimethylhydrazine, UDMH) and the reactive compound I (Cpd I) intermediate of P450. Our DFT calculations provided a clear view on how an aminonitrene‐type MI is formed from UDMH. In the most favorable pathway, hydrogen is spontaneously abstracted from the N2 atom of UDMH by Cpd I, followed by a second hydrogen abstraction from the N2 atom by Cpd II. Nitrogen oxidation of nitrogen atoms and hydrogen abstraction from the C? H bond of the methyl group were found to be less favorable than the hydrogen abstraction from the N? H bond. We also found that the reaction of protonated UDMH with Cpd I is rather sluggish. The aminonitrene‐type MI binds to the ferric heme more strongly than a water molecule. This is consistent with the notion that the catalytic cycle of P450 is impeded when such an MI is produced through the P450‐catalyzed reaction. 相似文献
992.
Hajime Yasuda Eiji Ihara Toshiyuki Hayakawa Takamaro Kakehi 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(10):1929-1944
Abstract Organolanthanide(III) initiated polymerization of methyl methacryate gave both syndiotactic and isotactic living polymers of high molecular weight. Organolanthanide(III) initiated polymerization of alkyl acrylates also gave high molecular weight poly(alkyl acrylate)s with very narrow molecular weight distribuion in high yield. Molecular weights of the resulting polymers increased linearly with the conversion. Random and block copolymerizations of alkyl acrylates with methyl methacrylate were realized successfully. For the sake of development of the olefin polymerization catalyst, bulky substituents were introduced into Me2Si bridged Cp rings and they were used as ligands for the lanthanide complexes. Tri- and divalent lanthanide complexes with such ligands showed high activity for olefin polymerization and gave high molecular weight polyolefins. 相似文献
993.
Mitsuo Sawamoto Hajime Shohi Hiroe Sawamoto Hiroji Fukui Toshinobu Higashimura 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(11):1609-1618
A series of multiarmed polymers with terminal functional groups have been synthesized on the basis of living cationic polymerizations of vinyl ethers and p-alkoxystyrenes. The syntheses were performed by two methods, one via living polymerizations with new multifunctional initiating systems followed by endcapping of the resultant multifunctional living polymers, and the other using designed silyl enol ethers as multifunctional terminators (coupling agents) that combine two to four end- functionalized linear living polymers. These two methodologies thus led to telechelic and 3- or 4-arm star polymers and macromonomers with hydroxyl, acetate, methacrylate, and styryl end functionalities. 相似文献
994.
Hikaru Kuramochi Genki Aoyama Hajime Okajima Akira Sakamoto Shinji Kanegawa Osamu Sato Satoshi Takeuchi Tahei Tahara 《Angewandte Chemie (International ed. in English)》2020,59(37):15865-15869
Capability to control macroscopic molecular properties with external stimuli offers the possibility to exploit molecules as switching devices of various types. However, application of such molecular‐level switching has often been limited by its speed and thus efficiency. Herein, we demonstrate ultrafast, photoinduced polarization switching in the crystal of a [CrCo] dinuclear complex by ultrafast pump–probe spectroscopy in the visible and mid‐infrared regions. The photoinduced polarization switching was found to have a time constant of 280 fs, which makes the [CrCo] complex crystal the fastest polarization‐switching material realized using the metastable state. Moreover, the pump–probe data in the visible region reveal the pronounced appearance of coherent nuclear wavepacket motion with a frequency as low as 22 cm?1, which we attribute to a lattice vibrational mode. The pronounced non‐Condon effect for its resonance Raman enhancement implies that this mode couples the relevant electronic states, thereby facilitating the ultrafast polarization switching. 相似文献
995.
Shoi Suzuki Yutaka Ishida Hajime Kameo Shigeyoshi Sakaki Hiroyuki Kawaguchi 《Angewandte Chemie (International ed. in English)》2020,59(32):13444-13450
We report the synthesis of anionic diniobium hydride complexes with a series of alkali metal cations (Li+, Na+, and K+) and the counterion dependence of their reactivity with N2. Exposure of these complexes to N2 initially produces the corresponding side‐on end‐on N2 complexes, the fate of which depends on the nature of countercations. The lithium derivative undergoes stepwise migratory insertion of the hydride ligands onto the aryloxide units, yielding the end‐on bridging N2 complex. For the potassium derivative, the N?N bond cleavage takes place along with H2 elimination to form the nitride complex. Treatment of the side‐on end‐on N2 complex with Me3SiCl results in silylation of the terminal N atom and subsequent N?N bond cleavage along with H2 elimination, giving the nitride‐imide‐bridged diniobium complex. 相似文献
996.
A photoreaction between benzoyl compounds, such as benzoylformate derivatives, and 2-(p-anisyl)-1,3-dimethylbenzimidazoline in the presence of allyl bromide was found to give various allylated alcohols. In the reaction of benzoylformates, α-hydroxy ester enolates, for which the negative charge occurs on the carbonyl carbon of benzoyl (umpolung reactivity), are proposed to be generated as intermediates by electron-transfer from benzimidazolines to the photoexcited benzoylformates; these species react with allyl bromide to produce α-allyl-α-hydroxy esters. 相似文献
997.
Hajime Hoshi 《Liquid crystals》2013,40(7):906-913
The second harmonic generation (SHG) in ferroelectric liquid crystals under oblique incidence was studied by using a numerical band matrix method that uses boundary conditions directly. No approximations were used except for the nondepleted fundamental wave. By matching the edge of the full-pitch band with that of the half-pitch band, the SH intensity increased significantly. The thickness (L) dependence of the SH intensity showed L 6.93–L 7.09 dependence without the limitation of the thickness. 相似文献
998.
Inorganic‐Base‐Mediated Hydroamination of Alkenyl Oximes for the Synthesis of Cyclic Nitrones 下载免费PDF全文
Dr. Xingao Peng Benny Meng Kiat Tong Prof. Hajime Hirao Prof. Shunsuke Chiba 《Angewandte Chemie (International ed. in English)》2014,53(7):1959-1962
A method based on hydroamination mediated by inorganic base was developed for the synthesis of cyclic nitrones from alkenyl oximes. DFT calculations of the reaction pathway suggested that this hydroamination could proceed through an unprecedented nucleophilic amination of the unactivated alkene by the oxime nitrogen atom. The transition state of this reaction is stabilized by an ionic interaction between a metal cation such as K+ and the oxime oxygen and negatively charged alkene moiety. 相似文献
999.
1000.
Ion-exchange chromatography using a high-capacity anion exchanger with UV detection was applied to the determination of nitrate in seawater. Major ions in seawater samples did not affect the peak shape and the retention time of the nitrate when an alkaline metal cation-chloride solution was used as an eluent at high concentrations (0.5-2 mol/l). At a wavelength of 220 nm, the peak of bromide was very small because of low absorption, while its separation from the nitrate peak was good at high concentrations. Among the eluents tested, lithium chloride gave the best separation of nitrate from bromide. It was estimated that the lithium ion had the least potential for ion-pair formation with nitrate, and its retention time was prolonged compared with the retention times when using other cations; with bromide and nitrite, such an effect was not observed. The results of shipboard seawater nitrate determination by our method in the South Pacific Ocean and Antarctic Sea showed good agreement with those by the conventional photometric method using continuous flow. 相似文献