全文获取类型
收费全文 | 309篇 |
免费 | 4篇 |
国内免费 | 2篇 |
专业分类
化学 | 210篇 |
晶体学 | 6篇 |
力学 | 5篇 |
数学 | 13篇 |
物理学 | 81篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 4篇 |
2020年 | 2篇 |
2019年 | 1篇 |
2018年 | 1篇 |
2017年 | 2篇 |
2016年 | 3篇 |
2015年 | 4篇 |
2014年 | 13篇 |
2013年 | 6篇 |
2012年 | 23篇 |
2011年 | 23篇 |
2010年 | 10篇 |
2009年 | 12篇 |
2008年 | 23篇 |
2007年 | 20篇 |
2006年 | 14篇 |
2005年 | 17篇 |
2004年 | 17篇 |
2003年 | 9篇 |
2002年 | 14篇 |
2001年 | 12篇 |
2000年 | 6篇 |
1999年 | 1篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 4篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1988年 | 6篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 10篇 |
1984年 | 6篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 9篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有315条查询结果,搜索用时 15 毫秒
131.
Fukuji Higashi Toshiharu Nishi 《Journal of polymer science. Part A, Polymer chemistry》1988,26(12):3235-3240
The direct polycondensation of terephthalic acid and p-phenylenediamine hydrochloride (PPD.2HCl) with thionyl chloride was found to be significantly promoted in N-methylpyrrolidone (NMP) by dissolved CaCl2 and tertiary amines. The inherent viscosity of the polymer obtained varied with the amount of CaCl2 and tertiary amines added. The reaction, when effectively promoted by CaCl2, proceeded homogeneously in the early state of polycondensation, and then resulted in a highly swollen gel. CaCl2 had to be present in the PPD.2HCl/tertiary amines/NMP solution as well as in the TPA/SOCl2/NMP mixture for the polycondensation to proceed to high molecular weight. Complexes of CaCl2, PPD.2HCl, and tertiary amines in NMP similar to the well known complex, CaCl2 · nNH3 (n = 2, 4, 8) was proposed to facilitate the polycondensation. 相似文献
132.
Newly designed phosphino-phenol 1c was found to be an efficient chiral auxiliary for copper-mediated asymmetric conjugate addition of diethylzinc to acyclic enones. High enantioselectivity up to >99% ee was achieved in the reaction of acyclic α,β-enones. 相似文献
133.
Teranishi T Wachi A Kanehara M Shoji T Sakuma N Nakaya M 《Journal of the American Chemical Society》2008,130(13):4210-4211
Exchange-coupled fct-FePd/alpha-Fe nanocomposite magnets were fabricated by converting anisotropically phase-segregated Pd/gamma-Fe2O3 nanoparticles via the interfacial atom diffusion. The magnetically hard fct-FePd phases formed by the interdiffusion between alpha-Fe and fcc-Pd phases nearly preserve their sizes at the nanometer scale because they are surrounded by the alpha-Fe matrix. The VSM measurements reveal that the exchange coupling between the soft and hard phases has been realized. 相似文献
134.
135.
136.
A series of double-chained phosphatidylcholines (PCs), 1,2-dioctadec-9′-ynoyl-sn-glycero-3-phosphocholine analogs containing perfluoroalkyl moieties (CF3, C2F5, n-C4F9 or n-C8F17) as the terminal segment in two hydrophobic chains, 1a-d, were synthesized. Equilibrium spreading pressures of these fluorinated PCs at the air-water interface were measured as an indication of monolayer stability, in order to obtain the minimal fluorine content in PC molecule efficient to exhibit monolayer stabilizing effect. The monolayer stability sigmoidally increased with the fluorine content in PC molecule and subsequently leveled off above a certain fluorine content, i.e., n-C4F9 moiety, at 25 °C. Under this condition, the replacement of at least five hydrogen atoms at the terminal hydrophobic segment in double-chained PC molecule by fluorine atoms, i.e., CF3CF2 moiety, is required to exhibit the monolayer stabilizing effect, whereas further fluorination of double-chained PC (F(CF2)n; n > 4) has a minor effect on the monolayer stability. 相似文献
137.
Shimizu H Onitsuka S Egami H Katsuki T 《Journal of the American Chemical Society》2005,127(15):5396-5413
Chiral (nitrosyl)ruthenium(salen) complexes were found to be efficient catalysts for aerobic oxidative desymmetrization of meso-diols under photoirradiation to give optically active lactols. The scope of the applicability of this reaction ranges widely from acyclic diols to mono-cyclic diols, although fine ligand-tuning of the ruthenium(salen) complexes was required to attain high enantioselectivity (up to 93% ee). In particular, the nature of the apical ligand was found to affect not only enantioselectivity but also kinetics of the desymmetrization reaction. Spectroscopic analysis of the oxidation disclosed that irradiation of visible light is indispensable not only for dissociation of the nitrosyl ligand but also for single electron transfer from the alcohol-bound ruthenium ion to dioxygen. 相似文献
138.
Antifluorite type solid electrolytes, Li2+x-y-z[(NH)1-x-y-zNxClyHz] have been synthesized from Li3N, LiCl and LiCl·H2O or ]. Either of the last two compounds introduces NH2- ions into the product and is indispensable to form the antifluorite type structure. The lattice parameter decreases with increasing amount of NH2- ions in the compound, reflecting the difference of anion sizes between Cl- and NH2- ions. Activation energies of Li+ diffusive motion, derived from both conductivity and NMR measurements, increase with concentration of NH2- ions, although the values differ by a factor of ≈2 netween the both methods. 相似文献
139.
Mössbauer studies of potassium borate glasses containing a small amount of iron were performed at dry ice and liquid nitrogen temperatures in order to investigate the physical properties of non-bridging oxygens in the glasses. The Mössbauer spectra at the temperature of dry ice were almost the same as those at room temperature. On the other hand, the spectra at the temperature of liquid nitrogen consisted of quadrupole doublet and hyperfine structure due to Fe3+ ions with tetrahedral symmetry. Magnetic suceptibility measurements revealed that the hyperfine structure was observed because of a paramagnetic relaxation effect. Isomer shift values for both the quadrupole doublet and the hyperfine structure were constant in the alkali region below 20 mol.%, and continuously decreased when the alkali content of the glasses was in the region ? 20 mol.%. The absorption areas for the hyperfine structure were also constant in the alkali region below 20 mol.%, and linearly decreased with alkali content in the region ? 20 mol.%. The internal magnetic field for the hyperfine structure also showed the same tendency as the absorption area. These results were attributed to the formation of non-bridging oxygen at the site adjacent to the iron, and the decrease of the absorption area for the hyperfine structure seemed to be directly related to the fraction of non-bridging oxygen in the oxygens constituting FeO4 tetrahedra. 相似文献
140.
The ionic conductivity of evaporated Li2OB2O3 thin films has been studied. These thin films were found to show a considerably high ionic conductivity of 1 × 10?7 Ω?1 cm?1 at room temperature. The conductivity increases with increasing Li content and exhibits a maximum value near 3Li2O·B2O3. The structure of these films was determined using infrared absorption and laser Raman scattering spectroscopy. Using the results, the correlation between structure and conductivity is also discussed. 相似文献