全文获取类型
收费全文 | 4468篇 |
免费 | 172篇 |
国内免费 | 14篇 |
专业分类
化学 | 3532篇 |
晶体学 | 46篇 |
力学 | 35篇 |
数学 | 269篇 |
物理学 | 772篇 |
出版年
2023年 | 30篇 |
2021年 | 50篇 |
2020年 | 83篇 |
2019年 | 69篇 |
2018年 | 35篇 |
2017年 | 22篇 |
2016年 | 97篇 |
2015年 | 102篇 |
2014年 | 114篇 |
2013年 | 194篇 |
2012年 | 245篇 |
2011年 | 279篇 |
2010年 | 159篇 |
2009年 | 133篇 |
2008年 | 288篇 |
2007年 | 292篇 |
2006年 | 271篇 |
2005年 | 274篇 |
2004年 | 279篇 |
2003年 | 218篇 |
2002年 | 218篇 |
2001年 | 89篇 |
2000年 | 86篇 |
1999年 | 64篇 |
1998年 | 62篇 |
1997年 | 51篇 |
1996年 | 49篇 |
1995年 | 43篇 |
1994年 | 41篇 |
1993年 | 30篇 |
1992年 | 35篇 |
1991年 | 39篇 |
1990年 | 32篇 |
1989年 | 34篇 |
1988年 | 28篇 |
1987年 | 19篇 |
1986年 | 29篇 |
1985年 | 46篇 |
1984年 | 46篇 |
1983年 | 28篇 |
1982年 | 38篇 |
1981年 | 39篇 |
1980年 | 39篇 |
1979年 | 26篇 |
1978年 | 23篇 |
1977年 | 35篇 |
1976年 | 19篇 |
1975年 | 19篇 |
1974年 | 17篇 |
1973年 | 22篇 |
排序方式: 共有4654条查询结果,搜索用时 427 毫秒
81.
82.
Synthesis of two naturally occurring 3-methyl-2,5-dihydro-1-benzoxepin carboxylic acids 总被引:1,自引:0,他引:1
[structures: see text] Two naturally occurring 3-methyl-2,5-dihydro-1-benzoxepin carboxylic acids, 6-hydroxy-3-methyl-8-(phenylethyl)-2,5-dihydro-1-benzoxepin-9-carboxylic acid (radulanin E) (1) and 9-hydroxy-3-methyl-2,5-dihydro-1-benzoxepin-7-carboxylic acid (2), were synthesized using Stille coupling followed by Mitsunobu cyclization. 相似文献
83.
The induced circular dichroism (ICD) spectra of the inclusion complexes of maleimide, phthalimide, and naphthalene‐2,3‐dicarboximide with β‐ or γ‐cyclodextrin (CDx) have been measured. The structure of the CDx inclusion complexes are interpreted by the signs and shapes of ICD spectra compared with the results of PPP calculations. In maleimide and naphthalene‐2,3‐dicarboximide, the ICD spectra of the β‐CDx inclusion complex are very similar to those of the γ‐CDx inclusion complex in spite of the differences in dimensions between the cavity of β‐CDx and that of γ‐CDx. In phthalimide, the ICD spectra of the β‐CDx inclusion complex are very different from those of the γ‐CDx inclusion complex. The split‐type ICD bands at 220–235 nm show that the dimer of phthalimide is formed in the presence of β‐CDx. 相似文献
84.
Novel Lewis-base ionic liquids replacing typical anions 总被引:1,自引:0,他引:1
Masahiro Yoshizawa-Fujita Katarina Johansson Douglas R. MacFarlane 《Tetrahedron letters》2006,47(16):2755-2758
We have synthesized two kinds of new Lewis-base ionic liquids (ILs); one is based on the relatively strong Lewis basic acetate anion, and the other is a salt composed of a mono-alkylated diamine such that the Lewis base site is incorporated in the cation. 1-Octyl-4-aza-1-azonia-bicyclo[2.2.2]octane bis(trifluoromethanesulfonyl)amide, [C8dabco]TFSA, and N-butyl-N-methylpyrrolidinium acetate, [p1,4]OAc, melted into fluid liquids at 26 and 81 °C, respectively. The thermal decomposition of [p1,4]OAc started at around 150 °C, whereas the thermal stability of [C8dabco]TFSA was almost equal to that of typical TFSA-based ILs in spite of the Lewis base site. This suggests that if the Lewis base site is incorporated into the cation the IL can maintain higher thermal stability. In addition, as a further result of the presence of the basic nitrogen, [C8dabco]TFSA can dissolve hydrated Cu(NO3)2 whereas the other TFSA-based ILs cannot. 相似文献
85.
86.
N. Takahashi T. Shimoda Y. Fujita T. Itahashi H. Miyatake 《Zeitschrift für Physik B Condensed Matter》1995,98(3):347-351
Short-lived ions12B (beta-radioactive, T1/2=20.3 ms) sustaining nuclear spin polarization were introduced into superfluid helium at 1.7 K. It was found that the12B ions were transported as charged entities under a static electric field and that the nuclear polarization was maintained throughout the lifetime of12B nuclei. Polarization of12B was determined through beta-NMR method. Snowball, a singly charged microcluster of helium atoms formed around an impurity ion, is responsible for the behaviour and thus constitutes a suitable environment for preserving nuclear polarization of the core ions12B. In a separate experiment snowballs were produced by implanting8Li (T1/2=830 ms) into liquid helium and detected by means of alpha particles from the core ions to guarantee that the snowballs survive longer than the lifetime of12B. 相似文献
87.
The equations for a barotropic viscous gas in one space dimensiondν=(μ(?νε)ε?p ε)dt+dG,? t +?2νε=0,p=?γ with a perturbationdG are considered under the assumption thatG is only a function of bounded variation inL 2(Θ) orH 0 1 (Θ) (Θ=]0, α[) and the esistence and the uniqueness of the global solution in a class of solutions of «strong type» as well as in a class of solutions of «weak type» are proved. This result constitutes a generalization of the result of Kazhikhov [8] and that of Shelukhin [10] and contains preliminary considerations for the corrisponding stochastic equations. 相似文献
88.
89.
Katsunori Wakabayashi Mitsutaka Fujita Koichi Kusakabe Kyoka Nakada 《Czechoslovak Journal of Physics》1996,46(4):1865-1866
Anoble mechanism of spin polarization is proposed for finite graphite sheet with edge. For graphite ribbon with zigzag edge, there appear peculiar ‘edge states’. These localized states comprise nearly flat band at the Fermi level, which easily causes magnetic instability. Magnetic structure is suggested from Hartree-Fock analysis of the Hubbard model, where huge magnetic moments are induced at around both of edges by weak HubbardU and are coupled antiferromagnetically with each other. 相似文献
90.
Changes in the fluorescence intensity of polyanions bearing 4-acryloylbenzo-18-crown-6 units on the addition of cations were studied in a mixed solvent of methanol and water at 30°C. The sensitivity of the change in fluorescence intensities of the polymers toward cations was strongly enhanced compared to that of the corresponding model compound. When alkali metal cations were added, the fluorescence intensity of the polymers decreased in the orders Li+>Na+>Cs+>Rb+>K+ in a methanol-water (19) mixture and Li+>Na+>Rb+>K+Cs+ in a methanol-water (91) mixture. Alkaline earth metal cations and alkylamine hydrochlorides decreased the fluorescence intensity of the polymers in a methanol-water (19) mixture. The cation-dependent decrease in the fluorescence intensity of the polymers was affected by the water fraction in a mixed solvent of methanol and water. 相似文献