全文获取类型
收费全文 | 2360篇 |
免费 | 77篇 |
国内免费 | 11篇 |
学科分类
数理化 | 2448篇 |
出版年
2022年 | 26篇 |
2021年 | 32篇 |
2020年 | 31篇 |
2019年 | 61篇 |
2018年 | 21篇 |
2017年 | 25篇 |
2016年 | 56篇 |
2015年 | 43篇 |
2014年 | 61篇 |
2013年 | 144篇 |
2012年 | 123篇 |
2011年 | 132篇 |
2010年 | 90篇 |
2009年 | 95篇 |
2008年 | 141篇 |
2007年 | 132篇 |
2006年 | 118篇 |
2005年 | 100篇 |
2004年 | 104篇 |
2003年 | 104篇 |
2002年 | 82篇 |
2001年 | 41篇 |
2000年 | 56篇 |
1999年 | 38篇 |
1998年 | 27篇 |
1997年 | 25篇 |
1996年 | 26篇 |
1995年 | 12篇 |
1994年 | 23篇 |
1993年 | 18篇 |
1992年 | 42篇 |
1991年 | 23篇 |
1990年 | 22篇 |
1989年 | 23篇 |
1988年 | 26篇 |
1987年 | 30篇 |
1986年 | 20篇 |
1985年 | 28篇 |
1984年 | 25篇 |
1983年 | 13篇 |
1982年 | 14篇 |
1981年 | 19篇 |
1980年 | 19篇 |
1979年 | 28篇 |
1978年 | 22篇 |
1977年 | 13篇 |
1976年 | 12篇 |
1975年 | 14篇 |
1974年 | 14篇 |
1973年 | 20篇 |
排序方式: 共有2448条查询结果,搜索用时 109 毫秒
1.
2.
3.
4.
Kohji Masaki Shin-ichi Ohkawara Tomohiro Hirano Makiko Seno Tsuneyuki Sato 《Journal of polymer science. Part A, Polymer chemistry》2004,42(17):4437-4447
The crosslinking reaction of 1,2-polybutadiene (1,2-PB) with dicumyl peroxide (DCPO) in dioxane was kinetically studied by means of Fourier transform near-infrared spectroscopy (FTNIR). The crosslinking reaction was followed in situ by the monitoring of the disappearance of the pendant vinyl group of 1,2-PB with FTNIR. The initial disappearance rate (R0) of the vinyl group was expressed by R0 = k[DCPO]0.8[vinyl group]−0.2 (120 °C). The overall activation energy of the reaction was estimated to be 38.3 kcal/mol. The unusual rate equation was explained in terms of the polymerization of the pendant vinyl group as an allyl monomer involving degradative chain transfer to the monomer. The reaction mixture involved electron spin resonance (ESR)-observable polymer radicals, of which the concentration rapidly increased with time owing to a progress of crosslinking after an induction period of 200 min. The crosslinking reaction of 1,2-PB with DCPO was also examined in the presence of vinyl acetate (VAc), which was regarded as a copolymerization of the vinyl group with VAc. The vinyl group of 1,2-PB was found to show a reactivity much higher than 1-octene and 3-methyl-1-hexene as model compounds in the copolymerization with VAc. This unexpectedly high reactivity of the vinyl group suggested that an intramolecular polymerization process proceeds between the pendant vinyl groups located on the same polymer chain, possibly leading to the formation of block-like polymer. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4437–4447, 2004 相似文献
5.
Yoshio Moriya Shinichi Nakata Hirotaka Morimoto Nobuaki Ogawa 《Analytical sciences》2004,20(11):1533-1536
Analysis by reflection spectrometry was performed to clarify the interfacial adsorption of protonated lipophilic tetraphenylporphyrin derivatives in a dodecane-aqueous sulfuric acid system, and to confirm the utility of partial reflection spectroscopy. Interfacial adsorption was not observed for porphyrins substituted at the 2,6 positions of meso-phenyl groups, suggesting that the substituents prevent porphyrins from forming aggregates by steric hindrance. Polymorphous J-aggregates of acid dications were produced by tetra-p-tolylporphyrin with a saturated interfacial molecular density of 1.0 x 10(-10) mol cm(-2), which could yield 48 degrees as a mean tilting angle of the pyrrole ring plane from the interface normal. Partial-reflection spectrometry can provide sensitive detection and molecular orientation analysis of interfacial adsorbates. 相似文献
6.
Studies on ternary phase diagrams of the Na-Fe-O system have been carried out from the thermodynamic point of view. Thermodynamic data of main ternary Na-Fe oxides Na4FeO3(s), Na3FeO3(s), Na5FeO4(s) and Na8Fe2O7(s) have been assessed. A user database has been created by reviewing literature data together with recent DSC and vapor pressure measurements by the present authors. New ternary phase diagrams of the Na-Fe-O system have been constructed from room temperature to 1000 K. Stable conditions of the ternary oxides at 800 K were presented in predominance diagram as functions of oxygen pressure and sodium pressure. 相似文献
7.
In this paper, we study Schrödinger type operator on a Riemannian manifold. Under some assumptions on a potential function, we characterize the domain of the square root of the Schrödinger type operator on L p space. In the proof, the defective intertwining properties and the Littlewood-Paley inequalities play important roles. 相似文献
8.
9.
Tomohiro Kyotani Sonoko Kakui Takehito Mizuno Naoto Shimotsuma Soushi Inoue Junji Saito 《Analytical sciences》2006,22(7):1031-1034
A zeolite NaA (LTA) membrane supported by an alumina porous support tube for pervaporation (PV) dehydration of ethanol was characterized by transmission electron microscopy (TEM) using a focused ion beam (FIB) thin-layer specimen preparation technique and by Fourier transform infrared attenuated total reflectance method (FTIR-ATR) using a diamond prism as the waveguide. FIB-TEM clearly presented cross-section images up to about 15 microm depth from the membrane surface. FTIR-ATR monitored the Si-O asymmetric stretching vibration spectrum. The Si-O spectrum was compared with the TEM image and their relationships were discussed. By combining the two methods, we could study the thickness of surface LTA crystals, the grain boundary, the LTA/alumina interface structure and the crystallinity and density of materials inside of the alumina porous support. Consequently, fine structure changes of the LTA membrane corresponding to the hydrothermal synthesis condition could be sensitively detected. 相似文献
10.
Haitao Yang Tomoyuki Ogawa Daiji Hasegawa C.N. Chinnasamy Migaku Takahashi 《Journal of magnetism and magnetic materials》2006
Monodisperse bimetallic Pd–Co nanoparticles were prepared via a thermal decomposition of cobalt carbonyl using palladium seeds at the Pd/Co molar ratios 0.5%, 1%, and 5%. The heterogeneously nucleated nanoparticles without any size-selective precipitation are sufficiently uniform to self-assemble into ordered arrays. The as-synthesized nanoparticles are each a single crystal with a complex cubic structure called ε-Co. The presence of Pd seeds seems to improve the stability of Co nanoparticles against oxidation based on the results from time-dependent magnetization measurement. 相似文献