全文获取类型
收费全文 | 2001篇 |
免费 | 80篇 |
国内免费 | 12篇 |
专业分类
化学 | 1611篇 |
晶体学 | 9篇 |
力学 | 43篇 |
综合类 | 1篇 |
数学 | 147篇 |
物理学 | 282篇 |
出版年
2022年 | 20篇 |
2021年 | 23篇 |
2020年 | 34篇 |
2019年 | 30篇 |
2018年 | 31篇 |
2017年 | 25篇 |
2016年 | 58篇 |
2015年 | 49篇 |
2014年 | 51篇 |
2013年 | 87篇 |
2012年 | 124篇 |
2011年 | 103篇 |
2010年 | 74篇 |
2009年 | 61篇 |
2008年 | 130篇 |
2007年 | 129篇 |
2006年 | 123篇 |
2005年 | 137篇 |
2004年 | 109篇 |
2003年 | 88篇 |
2002年 | 79篇 |
2001年 | 35篇 |
2000年 | 29篇 |
1999年 | 30篇 |
1998年 | 25篇 |
1997年 | 17篇 |
1996年 | 26篇 |
1995年 | 18篇 |
1993年 | 12篇 |
1992年 | 9篇 |
1991年 | 11篇 |
1989年 | 7篇 |
1988年 | 11篇 |
1985年 | 24篇 |
1984年 | 21篇 |
1982年 | 24篇 |
1981年 | 21篇 |
1980年 | 16篇 |
1979年 | 29篇 |
1978年 | 15篇 |
1977年 | 21篇 |
1976年 | 16篇 |
1975年 | 13篇 |
1974年 | 8篇 |
1973年 | 7篇 |
1972年 | 7篇 |
1970年 | 9篇 |
1969年 | 10篇 |
1968年 | 9篇 |
1967年 | 8篇 |
排序方式: 共有2093条查询结果,搜索用时 359 毫秒
71.
Takuji Hirahara Takaaki Sugimura Yuji Minoura 《Journal of polymer science. Part A, Polymer chemistry》1970,8(10):2827-2837
Diphenylsulfone (DPSO2) was found to react with an equimolar amount of potassium in tetrahydrofuran (THF), dimethoxyethane (DME), or diglyme (DG) at reflux or an elevated temperature to yield a reddish-black solution, giving an electron spin resonance (ESR) signal. The signal was attributed to the formation of relatively labile DPSO2 anion radical. The apparent effects of solvents on the reactivity of DPSO2 with potassium depended on the polarities and the solvation powers: benzene ? toluene ? dioxane ? tetrahydrofuran < monoglyme < diglyme. The monopotassium complex was found to react further with another molecular amount of the metal to yield a dark blue solution giving no ESR signal. The monopotassium complex initiated the polymerization of acrylonitrile (AN). It did not, however, initiate the polymerization of methyl methacrylate (MMA), styrene (St), or isoprene (IP). The active species of the monopotassium complex that initiated the polymerization of AN was found from analyses of the reaction products and the infrared spectrum of oily oligomer of AN obtained by the complex to be potassium benzenesulfinate. The dipotassium complex was found to initiate the polymerization of MMA, St, IP and AN. The active species of the dipotassium complex that initiated the polymerization of MMA, St, or IP was found from analyses of the reaction products and the infrared spectrum of the oily oligomer of MMA obtained by the complex to be phenyl potassium. 相似文献
72.
Tetsuo Yamasaki Yuji Yoshihara Yoshinari Okamoto Tadashi Okawara Mitsuru Furukawa 《Journal of heterocyclic chemistry》1992,29(5):1313-1316
The reaction of 5-hydrazinopyridazin-3(2H)-ones 1 with α-keto diester 2 in acetic acid afforded the corresponding 4,6-dihydropyridazino[4,5-c]pyridazin-5(1H)-ones 3 and pyrrolo[2,3-d)pyridazin-4(5H)-ones 4 . Compounds 3 were also obtained from 4-bromo-5-hydrazinopyridazin-3(2H)-ones 8 and 2 under milder conditions. 5-Bromo-4-hydrazinopyridazin-3(2H)-one 9 , the regioisomer of 8b , also reacted readily with 2a to give 4,7-dihydropyridazino[4,5-c]pyridazin-8(1H)-one 10b , the regioisomer of 3b . 相似文献
73.
Yamanaka N Kawano R Kubo W Kitamura T Wada Y Watanabe M Yanagida S 《Chemical communications (Cambridge, England)》2005,(6):740-742
Use of a new ionic liquid crystal, 1-dodecyl-3-methylimidazolium iodide, and iodine as an electrolyte of dye-sensitized solar cells leads to a high short circuit photocurrent density and a high light-to-electricity conversion efficiency, due to a self-assembled structure of the imidazolium cations, resulting in high conductivity of the electrolyte. 相似文献
74.
75.
Yuji Hanzawa Kei-ichi Kawagoe Naomi Tanahashi Yoshiro Kobayashi 《Tetrahedron letters》1984,25(42):4749-4752
The hydrometallation of trifluoromethylated propargyl alcohol derivatives with metal hydride reagents proceeds smoothly to give cis- and trans-olefins on H2O quenching. The halodemetallation of intermediate formed in the reaction process was also examined. 相似文献
76.
Wang CR Kai T Tomiyama T Yoshida T Kobayashi Y Nishibori E Takata M Sakata M Shinohara H 《Angewandte Chemie (International ed. in English)》2001,40(2):265
The cover picture shows a section of the electron charge density of the first metal carbide endohedral metallofullerene (Sc(2)C(2))@C(84) obtained from a synchrotron X-ray powder diffraction study by the maximum entropy method (MEM). The several density maxima, which correspond to scandium and carbon atoms, are clearly seen inside the C(84) carbon cage. The MEM charge density distribution also reveals that the C(84) cage has D(2d) symmetry (no. 23) and that the C(2) axis is parallel to the <100> face-centered cubic (fcc) direction of the unit cell. As a consequence of the site symmetry being 4mm, the C(2) axis of (Sc(2)C(2))@C(84) is oriented to six equivalent <100> directions and shows a merohedral disorder. The resultant Sc small middle dot small middle dot small middle dotSc distances and C-C bond lengths of the Sc(2)C(2) cluster are 0.429(2) and 0.142(6) nm, respectively. The observed C-C bond length is between that of a typical single and a double bond, and is very close to that of the C-C bond (0.143 nm) combining two pentagons in a C(60) molecule. More about this fascinating structure can be found in the contribution by Shinohara and co-workers on p. 397 ff. 相似文献
77.
Makoto Karakawa Yuji Mikawa Hiroshi Kamitakahara Fumiaki Nakatsubo 《Journal of polymer science. Part A, Polymer chemistry》2002,40(23):4167-4179
Seven possible regioselectively methylated cellulose acetates (RS‐MCAs)—2,3,6‐tri‐O‐methyl cellulose acetate, 3,6‐di‐O‐methyl cellulose acetate, 2,6‐di‐O‐methyl cellulose acetate, 2,3‐di‐O‐methyl cellulose acetate, 6‐O‐methyl cellulose acetate, 3‐O‐methyl cellulose acetate, and 2‐O‐methyl cellulose acetate—were prepared for the first time from chemically synthesized cellulose derivatives obtained by cationic ring‐opening polymerization and then were analyzed by 1H and 13C NMR spectroscopy. The chemical shifts of ring protons and carbons were influenced by substituent groups (methyl or acetyl) and clearly reflected the pattern of substituent distribution in anhydroglucose units. These data may conveniently be used for the determination of the substituent distribution of methyl cellulose. The synthesized RS‐MCAs also may be used for the elucidation of the structure–property relationship. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4167–4179, 2002 相似文献
78.
A method of free energy calculation is proposed, which enables to cover a wide range of pressure and temperature. The free energies of proton-disordered hexagonal ice (ice Ih) and liquid water are calculated for the TIP4P [J. Chem. Phys. 79, 926 (1983)] model and the TIP5P [J. Chem. Phys. 112, 8910 (2000)] model. From the calculated free energy curves, we determine the melting point of the proton-disordered hexagonal ice at 0.1 MPa (atmospheric pressure), 50 MPa, 100 MPa, and 200 MPa. The melting temperatures at atmospheric pressure for the TIP4P ice and the TIP5P ice are found to be about T(m)=229 K and T(m)=268 K, respectively. The melting temperatures decrease as the pressure is increased, a feature consistent with the pressure dependence of the melting point for realistic proton-disordered hexagonal ice. We also calculate the thermal expansivity of the model ices. Negative thermal expansivity is observed at the low temperature region for the TIP4P ice, but not for the TIP5P ice at the ambient pressure. 相似文献
79.
Gas mixtures of methane and ethane form structure II clathrate hydrates despite the fact that each of pure methane and pure ethane gases forms the structure I hydrate. Optimization of the interaction potential parameters for methane and ethane is attempted so as to reproduce the dissociation pressures of each simple hydrate containing either methane or ethane alone. An account for the structural transitions between type I and type II hydrates upon changing the mole fraction of the gas mixture is given on the basis of the van der Waals and Platteeuw theory with these optimized potentials. Cage occupancies of the two kinds of hydrates are also calculated as functions of the mole fraction at the dissociation pressure and at a fixed pressure well above the dissociation pressure. 相似文献
80.
Yuji Minoura Hisashi Hironaka Toshiyuki Kasabo Yukio Ueno 《Journal of polymer science. Part A, Polymer chemistry》1969,7(11):3245-3255
Reaction of poly(vinyl chloride) with magnesium under various conditions was attempted, but poly(vinyl chloride) did not react with magnesium. The reactions of poly(vinyl chloride) with benzylmagnesium chloride and allylmagnesium chloride as Grignard reagents were carried out in tetrahydrofuran at reflux temperature. It was found that the chlorine atoms in the poly(vinyl chloride) were replaced by benzyl and allyl groups by the coupling reaction, and a small amount of Grignard reagent of poly(vinyl chloride) was formed by the magnesium–halogen exchange reaction. The extent of the substitution increased with increasing reaction time and concentration of the Grignard reagent. 相似文献