全文获取类型
收费全文 | 352801篇 |
免费 | 2412篇 |
国内免费 | 636篇 |
专业分类
化学 | 168430篇 |
晶体学 | 4337篇 |
力学 | 18442篇 |
综合类 | 9篇 |
数学 | 52484篇 |
物理学 | 112147篇 |
出版年
2019年 | 2295篇 |
2018年 | 11090篇 |
2017年 | 11870篇 |
2016年 | 8215篇 |
2015年 | 3416篇 |
2014年 | 4392篇 |
2013年 | 10788篇 |
2012年 | 12039篇 |
2011年 | 21186篇 |
2010年 | 13575篇 |
2009年 | 13466篇 |
2008年 | 18874篇 |
2007年 | 22230篇 |
2006年 | 9065篇 |
2005年 | 13936篇 |
2004年 | 10459篇 |
2003年 | 9889篇 |
2002年 | 7946篇 |
2001年 | 7475篇 |
2000年 | 5967篇 |
1999年 | 4067篇 |
1998年 | 3612篇 |
1997年 | 3611篇 |
1996年 | 3487篇 |
1995年 | 3338篇 |
1994年 | 3474篇 |
1993年 | 3157篇 |
1992年 | 3627篇 |
1991年 | 3637篇 |
1990年 | 3576篇 |
1989年 | 3460篇 |
1988年 | 3546篇 |
1987年 | 3475篇 |
1986年 | 3267篇 |
1985年 | 4367篇 |
1984年 | 4672篇 |
1983年 | 3888篇 |
1982年 | 4021篇 |
1981年 | 3938篇 |
1980年 | 3910篇 |
1979年 | 3906篇 |
1978年 | 4239篇 |
1977年 | 4092篇 |
1976年 | 4183篇 |
1975年 | 3844篇 |
1974年 | 3906篇 |
1973年 | 4081篇 |
1972年 | 2854篇 |
1971年 | 2370篇 |
1970年 | 2194篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
63.
L. G. Kuz'mina I. I. Konstantinov A. V. Churakov 《Molecular Crystals and Liquid Crystals》2018,664(1):95-100
4-methoxyphenyl-4′-n-nonyloxybenzoate have been investigated by single crystal X-ray structural analysis. Crystal packing of the compounds does not represent a precursor of the mesophse although the typical for liquid crystal compounds separation of crystal packing on aromatic and aliphatic areas is observed here. Possible reason for monotropic properties are discussed. 相似文献
64.
65.
M. Kroon E. Andreasson E. Persson Jutemar V. Petersson L. Persson M. Dorn P.A.T. Olsson 《Experimental Mechanics》2018,58(1):75-86
Injection-moulding is one of the most common manufacturing processes used for polymers. In many applications, the mechanical properties of the product is of great importance. Injection-moulding of thin-walled polymer products tends to leave the polymer structure in a state where the mechanical properties are anisotropic, due to alignment of polymer chains along the melt flow direction. The anisotropic elastic-viscoplastic properties of low-density polyethylene, that has undergone an injection-moulding process, are therefore examined in the present work. Test specimens were punched out from injection-moulded plates and tested in uniaxial tension. Three in-plane material directions were investigated. Because of the small thickness of the plates, only the in-plane properties could be determined. Tensile tests with both monotonic and cyclic loading were performed, and the local strains on the surface of the test specimens were measured using image analysis. True stress vs. true strain diagrams were constructed, and the material response was evaluated using an elastic-viscoplasticity law. The components of the anisotropic compliance matrix were determined together with the direction-specific plastic hardening parameters. 相似文献
66.
I. Pop 《应用数学和力学(英文版)》2018,39(7):1057-1058
The present comment concerns some doubtful results included in the above paper. 相似文献
67.
Dr. Silvia Castro-Fernández Carlos M. Cruz Dr. Inês F. A. Mariz Dr. Irene R. Márquez Vicente G. Jiménez Lucía Palomino-Ruiz Prof. Juan M. Cuerva Dr. Ermelinda Maçôas Dr. Araceli G. Campaña 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(18):7205-7211
A new family of distorted ribbon-shaped nanographenes was designed, synthesized, and their optical and electrochemical properties were evaluated, pointing out an unprecedented correlation between their structural characteristics and the two-photon absorption (TPA) responses and electrochemical band gaps. Three nanographene ribbons have been prepared: a seven-membered-ring-containing nanographene presenting a tropone moiety at the edge, its full-carbon analogue, and a purely hexagonal one. We have found that the TPA cross-sections and the electrochemical band gaps of the seven-membered-ring-containing compounds are higher and lower, respectively, than those of the fully hexagonal polycyclic aromatic hydrocarbon (PAH). Interestingly, the inclusion of additional curvature has a positive effect in terms of non-linear optical properties of those ribbons. 相似文献
68.
Carvalho Patricia R. Munita Casimiro S. Neves Eduardo G. Zimpel Carlos A. 《Journal of Radioanalytical and Nuclear Chemistry》2020,324(3):1053-1058
Journal of Radioanalytical and Nuclear Chemistry - This research aims to contribute to the discussion of ceramic objects found at the Monte Castelo shellmound, an archaeological site located at... 相似文献
69.
70.
Vanessa R. Machado Louis P. Sandjo Giovanni L. Pinheiro Milene H. Moraes Mario Steindel Moacir G. Pizzolatti 《Natural product research》2018,32(3):275-281
The natural product lupeol 1 was isolated from aerial parts of Vernonia scorpioides with satisfactory yield, which made it viable to be used as starting material in semisynthetic approach. Ten lupeol derivatives 2–11 were prepared by classical procedures. Including, five new esters derivatives 7–11, which were obtained by structural modifications in the isopropylidene fragment. All semisynthetic compounds and lupeol 1–11 were confirmed by 1H NMR, 13C NMR and HRMS. Their antiprotozoal activity was evaluated in vitro against L. amazonensis and T. cruzi. Derivative 6 showed the best antitrypanosomal activity (IC50 = 12.48 μg/mL) and the lowest cytotoxic derivative (CC50 = 161.50 μg/mL). The mechanism of action of the most active derivatives (4, 6 and 11) is not dependent from the enzyme trypanothione reductase. 相似文献