全文获取类型
收费全文 | 1296篇 |
免费 | 59篇 |
国内免费 | 4篇 |
专业分类
化学 | 1057篇 |
晶体学 | 13篇 |
力学 | 25篇 |
数学 | 30篇 |
物理学 | 234篇 |
出版年
2023年 | 8篇 |
2021年 | 13篇 |
2020年 | 26篇 |
2019年 | 35篇 |
2018年 | 14篇 |
2017年 | 11篇 |
2016年 | 27篇 |
2015年 | 23篇 |
2014年 | 25篇 |
2013年 | 79篇 |
2012年 | 58篇 |
2011年 | 62篇 |
2010年 | 30篇 |
2009年 | 36篇 |
2008年 | 56篇 |
2007年 | 47篇 |
2006年 | 58篇 |
2005年 | 44篇 |
2004年 | 46篇 |
2003年 | 43篇 |
2002年 | 31篇 |
2001年 | 50篇 |
2000年 | 29篇 |
1999年 | 32篇 |
1998年 | 11篇 |
1997年 | 13篇 |
1996年 | 22篇 |
1995年 | 7篇 |
1994年 | 23篇 |
1993年 | 16篇 |
1992年 | 42篇 |
1991年 | 21篇 |
1990年 | 24篇 |
1989年 | 23篇 |
1988年 | 26篇 |
1987年 | 24篇 |
1986年 | 18篇 |
1985年 | 22篇 |
1984年 | 25篇 |
1983年 | 15篇 |
1982年 | 12篇 |
1981年 | 7篇 |
1979年 | 9篇 |
1977年 | 10篇 |
1975年 | 10篇 |
1974年 | 8篇 |
1973年 | 8篇 |
1964年 | 9篇 |
1962年 | 7篇 |
1960年 | 7篇 |
排序方式: 共有1359条查询结果,搜索用时 687 毫秒
111.
112.
The equations of state of CeCu2Si2 and CeCu2Ge2 to about 60 GPa, as well as that of CeNi2Ge2 to 22 GPa and the valence state of Ce in CeCu2Ge2 to 20 GPa have been studied at room temperature in a diamond-anvil cell using synchrotron radiation sources. In each compound, the ambient-pressure phase (tetragonal ThCr2Si2-type structure) persisted to the highest pressure studied. The unit cell volumes of CeNi2Ge2 at ∼5 GPa and CeCu2Ge2 at ∼7 GPa, respectively, approached that of CeCu2Si2 taken at ambient pressure. From the equation-of-state data, the bulk modulus was derived to be 112.0±5.1 GPa for CeCu2Si2, 125.6±4.3 GPa for CeCu2Ge2, and 178.4±14.3 GPa for CeNi2Ge2. The valence state of Ce in CeCu2Ge2 remained trivalent throughout the pressure range investigated. 相似文献
113.
K. Asayama Y. Kitaoka G. -Q. Zheng K. Ishida Y. Tokunaga H. Mukuda T. Ohno 《Applied magnetic resonance》2000,19(3-4):305-319
This paper introduces nuclear magnetic resonance works in the strongly correlated super-conductors: heavy-Fermion, high-T C superconductors and Sr2RuO4. The analyses strongly support the spin-fluctuation-mediated superconductivity model in a high-T C superconductor. 相似文献
114.
Nonlinear resonances and self-excited oscillations of a rotor caused by radial clearance and collision 总被引:1,自引:0,他引:1
This paper investigates oscillations in a flexible rotor system with radial clearance between an outer ring of the bearing
and a casing by experiments and numerical simulations. The mathematical model considers the collisions of the bearing with
the casing. The following phenomena are found: (1) Nonlinear resonances of subharmonic, super-subharmonic and combination
oscillation occur. (2) Self-excited oscillation of a forward whirling mode occurs in a wide range above the major critical
speed. (3) Entrainment phenomena from self-excited oscillation to nonlinear forced oscillation occur at these nonlinear resonance
ranges. Moreover, this study analyzes periodic solutions of the mathematical model by the Harmonic Balance Method (HBM). As
the results, the nonlinear resonances of subharmonic oscillation and its entrainment phenomenon can be explained theoretically
by investigating the stability of the periodic solutions. The influence of the static force and the bearing damping on these
oscillation are also clarified. 相似文献
115.
We designed bisnitroxide compounds where the radical sites are located close to each other in a molecule. Two new pincer-type bisnitroxide compounds have been synthesized, involving xanthene-4,5-diyl as a spacer and tert-butyl phenyl nitroxides as arms. From the X-ray crystal structure analysis, the shortest intramolecular interatomic N?O and O?O distances respectively are 5.074(6) and 5.258(6) Å for the m,m′-derivative and 3.624(3) and 3.771(3) Å for the p,p′-derivative. The N?O distance in the latter satisfies the empirical criterion for possible dimerization/degradation reaction accompanied by dia-/paramagnetic transition. However, the magnetic study clarified paramagnetic behavior in all the temperature range. According to a singlet-triplet model, antiferromagnetic couplings were characterized with 2J/kB = ?7.71(2) and ?8.83(4) K for the m,m′ and p,p′-derivatives, respectively. The present result suggests that a more flexible spacer is required for realization of possible dia-/paramagnetic transition. 相似文献
116.
Aliakbar Dehno Khalaji Gholamhossein Grivani Samaneh Jalali Akerdi Kazuma Gotoh Hiroyuki Ishida Hossein Mighani 《Structural chemistry》2010,21(5):995-1003
Two thiosemicarbazones, (E)-2-(2,4-dimethoxybenzylidene)thiosemicarbazone (24-MBTSC (1)) and (E)-2-(2,5-dimethoxybenzylidene)thiosemicarbazone (25-MBTSC (2)), derived from 2,4-dimethoxybenzaldehyde and 2,5-dimethoxybenzaldehyde, respectively, with thiosemicarbazide have been synthesized and their structures were characterized by elemental analyses, FT-IR, 1H NMR spectroscopy, and X-ray single-crystal diffraction analysis. Molecular orbital calculations have been carried out for 1 and 2 by using an ab initio method (HF) and also density functional method (B3LYP) at 6-31G basis set. Compound 1 crystallizes in the monoclinic system, space group P21/c, with a = 8.1342(5) Å, b = 18.1406(10) Å, c = 8.2847(6) Å, β = 109.7258(17)°, V = 1150.75(12) Å3, and Z = 4, whereas compound 2 crystallizes in the orthorhombic system, space group Pbca, with a = 11.0868(6) Å, b = 13.1332(6) Å, c = 15.9006(8) Å, V = 2315.2(2) Å3, and Z = 8. The compounds 1 and 2 displays a trans-configuration about the C=N double bond. 相似文献
117.
118.
119.
Akira Hasegawa Takao Nagahama Hitoshi Ohki Kenji Hotta Hideharu Ishida Makoto Kiso 《Journal of carbohydrate chemistry》2013,32(3):493-498
Development of an efficient α-glycoside synthesis of sialic acids is critically significant for the syntheses of sialoglycoconjugates, especially gangliosides which carry important biological functions1 in biological systems. Previously, we demonstrated2 a new α-glycosylation of sialic acids by use of dimethyl(methylthio)sulfonium triflate (DMTST)3 as the glycosyl promoter, the suitably protected glycosyl acceptors and the methyl 2-thioglycoside 1 of N-acetylneuraminic acid (Neu5Ac) as the donor in acetonitrile under kinetically controlled conditions, and accomplished4 the syntheses of a variety of gangliosides and their analogs. 相似文献
120.
Yukihiro Isogai Hideharu Ishida Makoto Kiso Akira Hasegawa 《Journal of carbohydrate chemistry》2013,32(9):1119-1137
ABSTRACT 3-O-Sulfo glucuronyl neolactohexanosyl ceramide derivatives (heptasaccharides) have been synthesized. Condensation of 2-(trimethylsilyl)ethyl 2,4,6-tri-O-benzyl-β-D-galactopyranoside (2) with 4-O-acetyl-3,6-di-O-benzyl-2-deoxy-2-phthalimido-β-D-glucopyranosyl trichloroacetimidate (1) gave the desired β-glycoside 3, which was converted into 2-(trimethylsilyl)ethyl O-(2-acetamido-3,6-di-O-benzyl-2-deoxy-β-D-glucopyranosyl)-(1→3)-2,4,6-tri-O-benzyl-β-D-galactopyranoside (4) via removal of the O-acetyl and N-phthaloyl groups, followed by N-acetylation. Glycosylation of 4 with O-(methyl 4-O-acetyl-2-O-benzoyl-3-O-levulinoyl-β-D-glucopyranosyluronate)-(1→3)-2,4,6-tri-O-benzoyl-α-D-galactopyranosyl trichloroacetimidate (5) using trimethylsilyl trifluoromethanesulfonate gave the target tetrasaccharide 6, which was transformed via removal of the benzyl group, O-benzoylation, removal of the 2-(trimethylsilyl)ethyl group and imidate formation into the tetrasaccharide donor 9. Glycosylation of 2-(trimethylsilyl)ethyl O-(2-acetamido-3,6-di-O-benzyl-2-deoxy-β-D-glucopyranosyl)-(1→3)-O-(2,4,6-tri-O-benzyl-β-D-galactopyranosyl)-(1→4)-2,3,6-tri-O-benzyl-β-D-glucopyranoside (10) with the imidate donor 9 using trimethylsilyl trifluoromethanesulfonate gave the desired heptasaccharide 11, which was transformed into the heptasaccharide imidate donor 14. Glycosylation of (2S, 3R, 4E)-2-azido-3-O-benzoyl-4-octadecene-1,3-diol (15) with 14 gave β-glycoside 16, which was transformed into the four target compounds, via reduction of the azido group, coupling with octadecanoic acid or tetracosanoic acid, selective removal of the levulinoyl group, O-sulfation, hydrolysis of the methyl ester group and O-deacylation. 相似文献