全文获取类型
收费全文 | 359篇 |
免费 | 7篇 |
专业分类
化学 | 294篇 |
晶体学 | 4篇 |
力学 | 1篇 |
数学 | 18篇 |
物理学 | 49篇 |
出版年
2023年 | 3篇 |
2021年 | 2篇 |
2020年 | 4篇 |
2019年 | 4篇 |
2018年 | 6篇 |
2017年 | 1篇 |
2016年 | 2篇 |
2015年 | 6篇 |
2014年 | 6篇 |
2013年 | 21篇 |
2012年 | 26篇 |
2011年 | 16篇 |
2010年 | 7篇 |
2009年 | 16篇 |
2008年 | 17篇 |
2007年 | 21篇 |
2006年 | 29篇 |
2005年 | 24篇 |
2004年 | 21篇 |
2003年 | 23篇 |
2002年 | 17篇 |
2001年 | 4篇 |
2000年 | 5篇 |
1999年 | 4篇 |
1998年 | 2篇 |
1997年 | 5篇 |
1996年 | 7篇 |
1995年 | 2篇 |
1994年 | 5篇 |
1993年 | 6篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1972年 | 3篇 |
1966年 | 2篇 |
排序方式: 共有366条查询结果,搜索用时 15 毫秒
41.
Selective solvation can be crucial in phase separation in polar binary mixtures (water–oil) with a small amount of hydrophilic ions or hydrophobic particles. They are preferentially attracted to one of the solvent components, leading to a number of intriguing effects coupled to phase separation. For example, if cations and anions interact differently with the two components, an electric double layer emerges at a liquid–liquid interface. The main aim of this paper is to show that a strongly hydrophilic (hydrophobic) solute induces precipitation of water-rich (oil-rich) domains above a critical solute density np outside the solvent coexistence curve. 相似文献
42.
B 2-groups are special (torsion-free) abelian Butler groups. The interest in this class of groups comes from representation theory. A particular functor, also called Butler functor, connects algebraic properties of the category of free abelian groups with (a few) distinguished subgroups with these Butler groups. This helps to understand Butler groups and caused lots of activities on Butler groups. Butler groups were originally defined for finite rank, however a homological connection discovered by Bican and Salce opened the investigation of Butler groups of infinite rank. Despite the fact that classifications of Butler groups are possible under restriction even for infinite rank (see a forthcoming paper by Files and Göbel [Mathematische Zeitschrift]), general structure theorems are impossible. This is supported by the following very special case of the Main Theorem of this paper, showing that any ring with a free additive group is an endomorphism ring of a Butler group. The result implies the existence of large indecomposable or of large superdecomposable Butler groups as well as the existence of counter-examples for Kaplansky’s test problems. 相似文献
43.
44.
Kanehiro Nakamura Ryuichi Endo Masatami Takeda 《Journal of Polymer Science.Polymer Physics》1977,15(12):2095-2101
Molecular motions of hydrophobic–hydrophilic water-soluble block copolymers in solution were investigated by high-resolution proton magnetic resonance (NMR). Samples studied include block copolymers of polystyrene–poly(ethylene oxide), polybutadiene–poly(ethylene oxide), and poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide). NMR measurements were carried out varying molecular weight, temperature, and solvent composition. For AB copolymers of polystyrene and poly(ethylene oxide), two peaks caused by the phenyl protons of low-molecular-weight (M?n = 3,300) copolymer were clearly resolved in D2O at 100°C, but the phenyl proton peaks of high-molecular-weight (M?n = 13,500 and 36,000) copolymers were too broad to observe in the same solvent, even at 100°C. It is concluded that polystyrene blocks are more mobile in low-molecular-weight copolymer in water than in high-molecular-weight copolymer in the same solvent because the molecular weight of the polystyrene block of the low-molecular-weight copolymer is itself small. In the mixed solvent D2O and deuterated tetrahydrofuran (THF-d8), two peaks caused by the phenyl protons of the high-molecular-weight (M?n = 36,000) copolymer were clearly resolved at 67°C. It is thought that the molecular motions of the polystyrene blocks are activated by the interaction between these blocks and THF in the mixed solvent. 相似文献
45.
Tetsuo Tsutsui Ryuichi Tanaka Takehide Tanaka 《Journal of Polymer Science.Polymer Physics》1976,14(12):2273-2284
Six 6,10-ionenes with different counterions were prepared by ion exchange reactions in aqueous solutions. The counterions were Br, I, CIO4, BF4, SCN, and B(C6H5)4. The dynamic mechanical properties of these polymers were investigated by use of a torsional braid analyser. Three relaxations α (25–140°C), β (?30–0°C), and γ (?140–120°C) were observed at the frequencies of 0.3–0.8 Hz. The temperature of the α and β relaxations were largely dependent on the size of counterions, but those of the γ relaxations had little variation. The effects of electrostatic forces in the polymers on each relaxation was discussed. The influence of absorbed water on the α, β, and γ relaxations was examined. The absorbed water in the polymers greatly depressed the temperature of the α relaxations and this phenomenon was interpreted to be the result of the specific hydration on ionic portions. 相似文献
46.
To deal with the radiation from an axially symmetric pillbox resonator embedded in LiNbO3 substrate, an eigenvalue equation is derived from the expression of the finite-element beam propagation method in a cylindrical coordinate system. By solving the eigenvalue equation iteratively, the field distributions and the angular phase constants of the pillbox resonator are evaluated. The iterative scheme of solving the eigenvalue equation is an extension of our previous direct solution method which was described for a lossless case. The results obtained by this method are compared with those obtained analytically, and excellent agreement is found. 相似文献
47.
Tetsuo Mori Yutaka Kuchihara Ryuichi Tanaka Takehide Tanaka 《Journal of Polymer Science.Polymer Physics》1974,12(3):501-513
Heterogeneous network polymers composed of rigid polypeptide chains and flexible polyether chains were synthesized. That is, poly(L -glutamic acid) (PLGA) was crosslinked with poly(oxyethylene glycol) (PEG) at various carboxy/hydroxyl mole ratios K. The solubility tests and hydrolysis of heterogeneous network polymers suggest that the crosslinking reaction proceeds by esterification. The dynamic mechanical properties of these polymers(100 Hz, ?100–200°C) are greatly influenced by the presence of a trace of water and the weight per cent of PLGA. In addition, some of these polymers show only one maximum in the temperature dispersion of dynamic loss modulus E″ and tan δ, although their shape is rather broad. The x-ray photographs of these polymers show an amorphous halo or weak Debye-Sherrer rings. These findings suggest that these polymers are not simple adducts; neverthless PLGA and/or PEG domains exist. 相似文献
48.
49.
Yamada K Wada N Onaka H Matsubara R Isobe R Inagaki M Higuchi R 《Chemical & pharmaceutical bulletin》2005,53(7):788-791
An ante-iso type regio-isomer on the long chain base moiety of a glucocerebroside, HLC-2-A, has been isolated from its parent glucocerebroside molecular species HLC-2 composed of iso and ante-iso isomers, from the less polar lipid fraction of a chloroform/methanol extract of the sea cucumber Holothuria leucospilota. Reverse-phase HPLC that included a recycling system was effective in separating the regio-isomer from its counterpart, revealing a very close resemblance in structure. Other typical glucocerebroside molecular species HLC-1 and HLC-3 were obtained together with HLC-2. The structures of these glucocerebrosides were determined on the basis of chemical and spectroscopic evidence. 相似文献
50.
Tetrathiafulvalen (TTF) and tetraselenafulvalen (TSF) salts with diorganochloro-stannate anions, [TTF][SnEt2Cl3] (1), [TTF]2[SnPh2Cl4] (2), [TTF]3[SnEt2Cl4] (3), [TTF]3.3[SnPh2Cl4] (4), [TSF]2[SnPh2Cl4] (5) and [TSF]3.3[SnPh2Cl4] (6), were prepared by the reactions of [TTF or TSF]3[BF4]2 with SnR2Cl2 (R = Et or Ph) in the presence of [Ph3PCH2Ph]Cl and by electrocrystallization of TTF or TSF in acetonitrile containing SnR2Cl2 and [Ph3PCH2Ph]Cl. All the salts behave as semiconductors with electrical resistivities of the order of 10–108 Ω cm as compacted samples at 25°C. Electronic reflectance spectra of the simple salts 1, 2 and 5, show a band due to the dimeric(TTF+)2 or (TSF+)2 unit in the 12,200–12,800-cm?1 region. The complex salt 3 exhibits a TTF+/TTF° charge-transfer (CT) band at 8700 cm?1, and the remaining complex salts, 4 and 6, both display CT bands between the radical cations and between the radical cation and the neutral donor molecule. The crystal structure of 3 was determined by a single-crystal X-ray diffraction. The tetragonal crystal, space group I4cm, has cell dimensions a = 11.710(3) Å, c = 25.242(7) Å, and Z = 4. The structure was solved by the heavy-atom method and refined to a final R value of 0.082 for 479 independent reflections with >F° > 3σ(F). TTF molecules exist as trimers, in which a slight lateral shift from the eclipsed TTF overlap occurs, although TTF molecules are arranged with equal spacing between them. The trimer units are located perpendicularly to each other, forming a two-dimensional layer. The [SnEt2Cl4]2? anion is disordered with respect to the two SnEt and two SnCl bonds. 相似文献