全文获取类型
收费全文 | 1456篇 |
免费 | 59篇 |
国内免费 | 8篇 |
专业分类
化学 | 1142篇 |
晶体学 | 24篇 |
力学 | 17篇 |
数学 | 84篇 |
物理学 | 256篇 |
出版年
2023年 | 13篇 |
2022年 | 11篇 |
2021年 | 24篇 |
2020年 | 18篇 |
2019年 | 36篇 |
2018年 | 28篇 |
2017年 | 13篇 |
2016年 | 36篇 |
2015年 | 26篇 |
2014年 | 58篇 |
2013年 | 69篇 |
2012年 | 81篇 |
2011年 | 95篇 |
2010年 | 66篇 |
2009年 | 66篇 |
2008年 | 88篇 |
2007年 | 78篇 |
2006年 | 93篇 |
2005年 | 70篇 |
2004年 | 54篇 |
2003年 | 78篇 |
2002年 | 66篇 |
2001年 | 38篇 |
2000年 | 22篇 |
1999年 | 15篇 |
1998年 | 14篇 |
1997年 | 13篇 |
1996年 | 10篇 |
1995年 | 8篇 |
1994年 | 6篇 |
1993年 | 9篇 |
1992年 | 11篇 |
1991年 | 13篇 |
1990年 | 7篇 |
1989年 | 5篇 |
1988年 | 12篇 |
1987年 | 9篇 |
1986年 | 9篇 |
1985年 | 20篇 |
1984年 | 13篇 |
1983年 | 9篇 |
1982年 | 12篇 |
1981年 | 13篇 |
1980年 | 8篇 |
1979年 | 17篇 |
1978年 | 13篇 |
1977年 | 12篇 |
1974年 | 6篇 |
1968年 | 4篇 |
1961年 | 5篇 |
排序方式: 共有1523条查询结果,搜索用时 46 毫秒
1.
Dr. Nozomi Mihara Dr. Yasuyuki Yamada Dr. Hikaru Takaya Prof. Yasutaka Kitagawa Dr. Kazunobu Igawa Prof. Katsuhiko Tomooka Prof. Hiroshi Fujii Prof. Kentaro Tanaka 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(13):3369-3375
Development of supramolecular methods to further activate a highly reactive intermediate is a fascinating strategy to create novel potent catalysts for activation of inert chemicals. Herein, a supramolecular approach to enhance the oxidizing ability of a high-valent oxo species of a nitrido-bridged iron porphyrinoid dimer that is a known potent molecular catalyst for light alkane oxidation is reported. For this purpose, a nitrido-bridged dinuclear iron complex of porphyrin-phthalocyanine heterodimer 3 5+, which is connected through a fourfold rotaxane, was prepared. Heterodimer 3 5+ catalyzed ethane oxidation in the presence of H2O2 at a relatively low temperature. The site-selective complexation of 3 5+ with an additional anionic porphyrin (TPPS4−) through π–π stacking and electrostatic interactions afforded a stable 1:1 complex. It was demonstrated that the supramolecular post-synthetic modification of 3 5+ enhances its catalytic activity efficiently. Moreover, supramolecular conjugates achieved higher catalytic ethane oxidation activity than nitrido-bridged iron phthalocyanine dimer, which is the most potent iron-oxo-based molecular catalyst for light-alkane oxidation reported so far. Electrochemical measurements proved that the electronic perturbation from TPPS4− to 3 5+ enhanced the catalytic activity. 相似文献
2.
3.
Miyuki Harada Kentaro Aoyama Mitsukazu Ochi 《Journal of Polymer Science.Polymer Physics》2004,42(22):4044-4052
A liquid‐crystalline epoxy resin was cured at two different temperatures. The phases of the cured systems clearly showed isotropic and nematic polydomain structures, which depended on the curing temperature. The fracture toughness of the systems was measured, and the fracture mechanism was investigated with polarized IR measurements. The nematic polydomain structure system showed considerably higher fracture toughness than the isotropic structure. Moreover, both systems exhibited a reorientation of the network chains near the fracture surface during the fracture process, and the region of the network reorientation in the nematic polydomain structure system was larger than that in the isotropic structure system. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4044–4052, 2004 相似文献
4.
Interface properties of BCN/GaN metal-insulator-semiconductor (MIS) structures are investigated by X-ray photoelectron spectroscopy (XPS) and capacitance versus voltage (C-V) characteristics measurements. The BCN/GaN samples are fabricated by in situ process consisting of plasma treatment and deposition of BCN film in the plasma-assisted chemical vapor deposition (PACVD) apparatus. XPS measurement shows that the oxide formation at the BCN/GaN interface is suppressed by nitrogen (N2) and hydrogen (H2) plasma treatment. The interface state density is estimated from C-V characteristics measured at 1 MHz using Terman method. The minimum interface state density appears from 0.2 to 0.7 eV below the conduction band edge of GaN. The minimum value of the interface state density is estimated to be 3.0 × 1010 eV−1 cm−2 for the BCN/GaN structure with mixed N2 and H2 plasma treatment for 25 min. Even after annealing at 430 °C for 10 min, the interface state density as low as 6.0 × 1010 eV−1 cm−2 is maintained. 相似文献
5.
A composition spread metal thin film fabrication technique based on ion beam sputter deposition method was developed. The technique enables us to fabricate any desired part or a complete binary/ternary composition spread metal thin films onto a single substrate by sequentially sputtering different target materials. Composition spread metal thin films can be deposited directly on a dielectric film in patterned electrode shape for C-V and I-V measurements. The system could be especially useful in the search for new multi-component metal gate materials. 相似文献
6.
A binary alloy Schottky barrier diode on zinc oxide (ZnO) was developed using the combinatorial ion beam-assisted deposition system. The compositional fraction of the binary alloy was continuously varied using the composition-spread technique, to control the Schottky barrier height. After metal deposition, patterned Schottky diodes were fabricated on a ZnO single-crystal substrate. Pt-Ru alloy was selected from the work function viewpoint. Our experiments showed that the compositional fraction of the Schottky binary alloys changed continuously as designed and the Schottky barrier heights measured by current-voltage (I-V) measurements increased with increasing Pt content. Maximum barrier height difference for ZnO was 137 meV. Using ion beam deposition in parallel with the combinatorial system showed that the Schottky barrier heights for ZnO can be controlled by binary metal alloying. 相似文献
7.
The peroxyoxalate chemiluminescence(CL) detection method for the evaluation of the CL intensity of malondialdehyde(MDA) condensates with seven 2-thiobarbituric acid derivatives is described. The method consists of a flow injection technique together with a CL detection system using bis(2,4,6-trichlorophenyl) oxalate(TCPO) and hydrogen peroxide as chemiluminogenic reagents. Linear correlations between CL intensity and concentration are obtained for pmol levels of condensates. Among the condensates, 1,3-diethyl-2-thiobarbituric acid(DETBA)-MDA shows the largest CL intensity. High performance liquid chromatography (HPLC)/CL detection of DETBA-MDA and 1,3-diphenyl-2-thiobarbituric acid(DPTBA)-MDA using a mixture of TCPO and hydrogen peroxide in acetonitrile as a postcolumn reagent solution is also described. The detection limits for DETBA-MDA and DPTBA-MDA are 20 and 200 fmol, respectively, per 20 microL injection at a signal-to-noise ratio of 2. This HPLC/CL detection system was applied to the determination of MDA in rat brains by using DETBA as a fluorescent derivatizing reagent. 相似文献
8.
Kentaro Suzuya Tomoaki Kamiyama Takemi Yamamura Kiyohito Okamura Kenji Suzuki 《Journal of Non》1992,150(1-3):167-171
A small-angle X-ray scattering (SAXS) study was performed to reveal the nanometer scale hybrid structure of Si---Ti---C---O fibers prepared by the pyrolysis of polytitanocarbosilane. The SAXS profile for Si---Ti---C---O fibers is attributed to two different types of scattering entities: an anisotropic contribution from long filaments with diameters hundreds to thousands of Ångströms and an isotropic contribution from β-SiC fine clusters of about a nanometer in diameter. A drastic degradation in the tensile strength of the fibers is correlated to the characteristic variations in their long-and medium-range structure. 相似文献
9.
Sebastiaan van Dijken Xavier Fain Steven M. Watts Kentaro Nakajima J. M. D. Coey 《Journal of magnetism and magnetic materials》2004,280(2-3):322-326
A detailed study of the in-plane magnetotransport properties of spin valves with one and two Fe3O4 electrodes is presented. Fe3O4/Au/Fe3O4 spin valves exhibit a clear anisotropic magnetoresistance in small magnetic fields but no giant magnetoresistance (GMR). The absence of GMR in these structures is due to simultaneous magnetization reversal in the two Fe3O4 layers. By contrast, a negative GMR effect is measured on Fe3O4/Au/Fe spin valves. The negative GMR is attributed to an electron spin scattering asymmetry at the Fe3O4/Au interface or an induced spin scattering asymmetry in the Au interfacial layers. 相似文献
10.
Kentaro Suzuki Taro Toyota Katsuhiko Sato Masakazu Iwasaka Shoogo Ueno Tadashi Sugawara 《Chemical physics letters》2007,440(4-6):286-290
Collagen-containing tubular giant vesicles (Col–tGVs) under a high static magnetic field were found to constitute characteristic curved structures (e.g. circular, 8-figure, and hairpin-loop), which were sustained by polymerization of collagen units inside the tGV. We ascribed the formation of these structures to the elasticity of the tGV and to the competing diamagnetic anisotropies between collagen and the tGV. These curved structures can be well expressed by the equation of elastica. 相似文献