全文获取类型
收费全文 | 2357篇 |
免费 | 69篇 |
国内免费 | 15篇 |
专业分类
化学 | 1729篇 |
晶体学 | 20篇 |
力学 | 23篇 |
数学 | 166篇 |
物理学 | 503篇 |
出版年
2022年 | 18篇 |
2021年 | 23篇 |
2019年 | 41篇 |
2018年 | 31篇 |
2016年 | 27篇 |
2015年 | 53篇 |
2014年 | 46篇 |
2013年 | 132篇 |
2012年 | 122篇 |
2011年 | 124篇 |
2010年 | 80篇 |
2009年 | 79篇 |
2008年 | 121篇 |
2007年 | 137篇 |
2006年 | 131篇 |
2005年 | 133篇 |
2004年 | 111篇 |
2003年 | 87篇 |
2002年 | 101篇 |
2001年 | 32篇 |
2000年 | 36篇 |
1999年 | 32篇 |
1998年 | 25篇 |
1997年 | 24篇 |
1996年 | 34篇 |
1995年 | 16篇 |
1994年 | 24篇 |
1993年 | 27篇 |
1992年 | 34篇 |
1991年 | 22篇 |
1990年 | 21篇 |
1989年 | 23篇 |
1988年 | 21篇 |
1987年 | 17篇 |
1986年 | 22篇 |
1985年 | 30篇 |
1984年 | 35篇 |
1983年 | 21篇 |
1982年 | 27篇 |
1981年 | 26篇 |
1980年 | 24篇 |
1979年 | 24篇 |
1978年 | 14篇 |
1977年 | 26篇 |
1976年 | 23篇 |
1975年 | 28篇 |
1974年 | 21篇 |
1973年 | 26篇 |
1972年 | 18篇 |
1965年 | 12篇 |
排序方式: 共有2441条查询结果,搜索用时 0 毫秒
951.
Yasushi Yokoyama Takahiko Tsuyuki Nobuo Nakamura Takeyoshi Takahashi Steven W. Hanson Kazuhiro Matsushita 《Tetrahedron letters》1980,21(38):3701-3702
The structures of cymbopogone and cymbopogonol were revised to D:A-friedo-18β,19αH-lupan-3-one and D:A-friedo-18β,19αH-lup-4(23)-en-3β-ol, respectively. 相似文献
952.
953.
Yasumitsu Tamura Hironori Hayashi Jun-Ichi Minamikawa Masazumi Ikeda 《Journal of heterocyclic chemistry》1974,11(5):781-786
3-Amino-1-alkylimidazolium and benzimidazolium mesitylenesulfonates were readily prepared in good to high yeilds by treating the parent heterocycles with O-mesitylenesulfonylhydroxylamine. Treatment of the 3-amine salts with acylating agents gave crystalline 3-acylimines, which showed the characteristic ir, uv, nmr, and mass spectral properties. Deuterium exchange of the 3-acylimines occurs at the 2-position. Thermolysis of neat 3-benzoylimino-1-rnethylbenzimidazolium betaine afforded 2-benzamido-1-methylbenzimidazole and products derived from N? N bond cleavage. Irradiation of 3-benzoylimino-1-alkylbenzimidazoliurn betaines resulted in N? N bond cleavage to give 1-alkylbenzimidazoles and benzamide, while the corresponding 3-ethoxycarbonylimines underwent rearrangement to afford ethyl 1-alkyl-2-benzimidazolecarbamates. 相似文献
954.
955.
956.
957.
Koji Yamaguchi Tsutomu Takata Kazuhiro Sakuyama Toshihiko Maeda Naoki Koshizuka H. Yamauchi Shoji Tanaka 《Physica C: Superconductivity and its Applications》1990,170(5-6):486-490
Crystallographic properties of a new lead cuprate superconducting material (Pb, Cu) (Eu, Ce)2(Eu, Sr)2Cu2Oz are examined by electron probe micro-analysis and transmission electron microscopy. It is confirmed that although the sample examined here is not of single-phase, the composition of the superconducting phase is close to the nominal composition. From TEM observations, it follows that the crystal structure of the new phase is similar to that of Tl-1222 which consists of a fluorite type block, a rock salt type layer and a perovskite block. 相似文献
958.
959.
In this paper, the decision problem with multi-objectives is considered, and the nondominated solutions associated with a polyhedral domination cone are discussed. The necessary and sufficient conditions for the solutions are given in the decision space rather than the objective space. The similarity of the solution conditions obtained in this article to the Kuhn-Tucker condition of a convex programming problem is examined. As an application of the solution condition, an algorithm to locate the set of all nondominated solutions is shown for the linear multi-objective decision problem.The author would like to thank the reviewer for his helpful comments. 相似文献
960.
Ken-Ichi Okamoto Kazuhiro Tanaka Hidetoshi Kita Asumaru Nakamura Yoshihiro Kusuki 《Journal of Polymer Science.Polymer Physics》1989,27(6):1221-1233
Sorption and transport of CO2 have been investigated for polyimide films prepared from 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and 4,4′-oxydianilline (ODA) as well as for a chemically identical commercial polyimide film, Upilex-R. The BPDA-ODA polyimide films annealed above the glass transition temperature (270°C) are found to have some degree of ordering owing to molecular aggregation of polymer chains, whereas the films as-cast are amorphous. The solubility, permeability, and diffusion coefficients decrease significantly with increasing density or increasing average degree of molecular aggregation. The influence of morphology on the parameters in the dual-mode sorption and transport model has also been investigated. With an increase in density, the Langmuir capacity constant and the diffusion coefficients for Henry's law and Langmuir populations decrease by a larger factor than the Henry's law solubility constant. These results can be tentatively interpreted by assuming either a one-phase or two-phase structure for these polyimide films. 相似文献