全文获取类型
收费全文 | 514篇 |
免费 | 21篇 |
国内免费 | 1篇 |
专业分类
化学 | 394篇 |
晶体学 | 10篇 |
力学 | 12篇 |
数学 | 16篇 |
物理学 | 104篇 |
出版年
2021年 | 7篇 |
2020年 | 5篇 |
2019年 | 9篇 |
2017年 | 3篇 |
2016年 | 9篇 |
2015年 | 6篇 |
2014年 | 23篇 |
2013年 | 17篇 |
2012年 | 21篇 |
2011年 | 20篇 |
2010年 | 27篇 |
2009年 | 12篇 |
2008年 | 17篇 |
2007年 | 18篇 |
2006年 | 22篇 |
2005年 | 19篇 |
2004年 | 31篇 |
2003年 | 21篇 |
2002年 | 17篇 |
2001年 | 13篇 |
2000年 | 10篇 |
1999年 | 7篇 |
1997年 | 6篇 |
1996年 | 13篇 |
1995年 | 8篇 |
1994年 | 6篇 |
1993年 | 4篇 |
1992年 | 8篇 |
1991年 | 13篇 |
1990年 | 7篇 |
1989年 | 12篇 |
1988年 | 11篇 |
1987年 | 10篇 |
1986年 | 11篇 |
1985年 | 10篇 |
1984年 | 14篇 |
1983年 | 6篇 |
1982年 | 2篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1979年 | 10篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1968年 | 3篇 |
1963年 | 2篇 |
排序方式: 共有536条查询结果,搜索用时 31 毫秒
81.
Dianjie Ma Yasuaki Okamoto Takahiro Kumamaru Etsuro Iwamoto 《Analytica chimica acta》1999,390(1-3):201-206
Tungsten-coated non-pyrolytic graphite (NPG), pyrolytic graphite (PG) and pyrolytic L'vov platform graphite (PPG) tubes were prepared, and their analytical performances were compared. The coating process simply involved injecting 100 μl of a sodium tungstate solution (0.01 mol l−1) into each graphite tube, followed by heating according to a temperature programme similar to an atomisation cycle for the determination of gallium. This procedure for coating was repeated at least 12, 25, and 7 times towards NPG, PG, and PPG tubes, respectively. Among these tubes, the tungsten-coated PPG tube showed excellent performance for the determination of gallium. By combined use of a chemical modifier such as aluminium(III) or nickel(II) a detection limit (3σ) of 6 pg and sensitivity (1% absorption) of 3–4 pg were achieved. The practical potential of the proposed technique was demonstrated for the determination of gallium in several samples of alloys and fresh water. 相似文献
82.
The present paper aims to understand the surface freezing occurring on the interface between liquid normal alkane and air. After proposing a simple microscopic model, it reveals that the model can describe the surface freezing of normal alkanes. Subsequently, surface freezing is immediately proved to be a first order phase transition, which has been illustrated by numerous experiments. Moreover, our calculation predicts a new first order phase transition on the interface. These two transitions correspond to the liquid to monolayer and monolayer to perfect solid transitions, respectively. A phase diagram is obtained directly from the calculations as well. The model indicates that both van der Waals interaction and the entropy influenced by the surface are essential for explaining the surface phase transition. 相似文献
83.
Harada T Narazaki R Nagira S Ohwaki T Aoki S Iwamoto K 《Chemical & pharmaceutical bulletin》2006,54(8):1072-1075
The purpose of this study was to demonstrate the usefulness and broad-applicability of a simple disintegration test method for orally disintegrating tablets (ODT). Eight types of commercial famotidine 20 mg orally disintegrating tablets with different physical properties (formulation, manufacturing method, tablet weight, shape, diameter, thickness, etc.), were used. Disintegration times of these tablets were evaluated employing human sensory test, conventional disintegration test, and the new proposed disintegration test. The human sensory test was performed in 5 healthy volunteers. In the conventional disintegration test, the disintegration apparatus described in the Japanese Pharmacopeia (JP 1(st)) was used. Our proposed new test which is characterized by a rotating shaft with a low weight (10, 15 g) and rotation speed (10, 25, 50 rpm) was evaluated using tablets with and without storage under severe conditions (60 degrees C/75%RH for 1 week). The disintegration times of famotidine 20 mg orally disintegrating tablets in human sensory test varied from 9 to 32 s. In contrast, disintegration times in the conventional test were prolonged to over 300 s. Disintegration times in the new proposed test were close to those in human sensory test. Especially, when the new test was conducted with 15 or 10 g weight and 25 rpm, the slope (human sensory test vs. new proposed test) was almost 1. We were able to demonstrate that the new proposed test was useful to estimate the actual human disintegration time. 相似文献
84.
MS/MS is indispensable for the amino acid sequencing of peptides. However, its use is limited for peptides containing disulfide bonds. We have applied the reducing properties of 1,5-diaminonaphthalene (1,5-DAN) as a MALDI matrix to amino acid sequencing and disulfide bond mapping of human urotensin II possessing one disulfide bond, and human guanylin possessing two disulfide bonds. 1,5-DAN was used in the same manner as the usual MALDI matrices without any pre-treatment of the peptide, and MS/MS was performed using a matrix-assisted laser desorption/ionization quadrupole ion trap time-of-flight mass spectrometer (MALDI QIT TOFMS). The results demonstrated that MS/MS of the molecular ions reduced by 1,5-DAN provided a series of significant b-/y-product ions. All 11 amino acid residues of urotensin II were identified using 1,5-DAN, while only 5 out of 11 residues were identified using 2,5-dihydroxybenzoic acid (DHB); similarly 11 out of 15 amino acid residues of guanylin were identified using 1,5-DAN, while only three were identified using DHB. In addition, comparison of the theoretical and measured values of the mass differences between corresponding MS/MS product ions using 1,5-DAN and DHB narrowed down the possible disulfide bond arrangement candidates. Consequently, 1,5-DAN as a reductive matrix facilitates rapid amino acid sequencing and disulfide mapping for peptides containing disulfide bonds. 相似文献
85.
Hajime Iwamoto 《Tetrahedron letters》2006,47(10):1519-1523
A new chiral carboxylic acid 1 was synthesized for determination of absolute configuration of secondary alcohols. Several chiral alcohols were converted to esters with 1. Their experimental esterification shift changes were successfully reproduced by the chemical shift simulation method combined with molecular dynamic simulation. 相似文献
86.
87.
To investigate the π bonding electron contribution to N-HO[double bond, length as m-dash]C hydrogen-bond (H-bond) formation, we applied IR cavity ringdown spectroscopy to jet-cooled pyrrole-acetone (Py-Ac) binary clusters. The observed NH stretching vibrations were analyzed by density functional theory (DFT), in which the energetically optimized structures, harmonic frequencies, and interaction energies were calculated for various sizes of binary clusters. We observed three NH stretching vibrations, ascribed to binary clusters at 3406, 3388, and 3335 cm(-1). These were assigned to H-bonded NH stretches of the Py(2)-Ac(1), Py(1)-Ac(1), and Py(1)-Ac(2) clusters, respectively. The Py(1)-Ac(1) cluster has a single N-HO[double bond, length as m-dash]C H-bonded structure with C(s) symmetry, while the Py(1)-Ac(2) cluster has a cyclic structure formed by a single N-HO[double bond, length as m-dash]C H-bond, dipole-dipole interactions, and weak CH H-bonds. A natural bond orbital (NBO) analysis was performed to reveal the H-bond strength in Py-Ac binary clusters. For the Py(1)-Ac(2) cluster, we found that the donor-acceptor interactions are not only the n →σ* type (O atom lone pair to the NH anti-bonding orbitals), but also the π→σ* type (the CO π bonding to the NH anti-bonding orbitals). By analyzing the relationship between the frequency shift and the stabilization energy in donor-acceptor interactions, we concluded that larger red-shift of the NH stretching vibration in the Py(1)-Ac(2) can be explained by not only the lone pair and the π electron contributions to the N-HO[double bond, length as m-dash]C H-bond, but also the dipole-interaction between Py and non-H-bonded Ac. We also discussed the structures of Py(2)-Ac(1) clusters. 相似文献
88.
Masahiro Aoyama Tomokatsu Hayakawa Sawao Honda Yuji Iwamoto 《Journal of luminescence》2012,132(10):2603-2607
In this research, zeolite-derived aluminosilicate phosphors were synthesized through the ion exchange route. Red light-emitting property of Eu3+-doped aluminosilicate phosphors were discussed from a view point of the Eu content, heat-treatment condition and the oxidation state of Eu ions. The crystalline phase of the host aluminosilicates could be successfully controlled as designed based on the published NaAlO2–SiO2 binary phase diagram. Orange-red emission peaks derived from the 5D0→7Fj (j=0, 1, 2, 3, 4) transition of Eu3+ were observed around 590–700 nm, and 4f65d→4f7 transition of Eu2+ was observed at around 400–500 nm. The relative intensity I(5D0→7F2) of the dominant emission peak at 612 nm increased consistently with the Eu content. The results of the XANES spectroscopy analysis revealed that Eu2+ ion in the 1400 °C as heat-treated host aluminosilicate were successfully converted to Eu3+ by the additional annealing at 1100 °C. The Eu contents and heat-treatment conditions were determined to exhibit the best performance as a red phosphor, which were 10 wt% and 1500 °C, respectively 相似文献
89.
Copper(II)-acid co-catalyzed intermolecular substitution of electron-rich aromatics with diazoesters
The intermolecular aromatic substitution of N,N-dialkylanilines and alkoxybenzenes with diazoesters is shown to proceed in the presence of catalytic amounts of both copper(II) salt and acid (Lewis or Brønsted). This method is a mild and rare metal-free C-C bond formation reaction between aromatic (sp2) and aliphatic (sp3) carbons. 相似文献
90.
Masamura Shinnosuke Iwamoto Tetsu Sugitani Yoshiki Konishi Keiji Hara Naoyuki 《Nonlinear dynamics》2020,99(4):3155-3168
Nonlinear Dynamics - The present study experimentally investigates amplitude death in delay-coupled double-scroll circuits with a time-varying network topology that randomly changes at a regular... 相似文献