全文获取类型
收费全文 | 3959篇 |
免费 | 123篇 |
国内免费 | 14篇 |
专业分类
化学 | 2703篇 |
晶体学 | 21篇 |
力学 | 123篇 |
数学 | 681篇 |
物理学 | 568篇 |
出版年
2023年 | 17篇 |
2022年 | 59篇 |
2021年 | 87篇 |
2020年 | 36篇 |
2019年 | 74篇 |
2018年 | 48篇 |
2017年 | 69篇 |
2016年 | 136篇 |
2015年 | 126篇 |
2014年 | 135篇 |
2013年 | 236篇 |
2012年 | 217篇 |
2011年 | 268篇 |
2010年 | 175篇 |
2009年 | 157篇 |
2008年 | 247篇 |
2007年 | 214篇 |
2006年 | 237篇 |
2005年 | 219篇 |
2004年 | 159篇 |
2003年 | 164篇 |
2002年 | 89篇 |
2001年 | 50篇 |
2000年 | 43篇 |
1999年 | 46篇 |
1998年 | 32篇 |
1997年 | 34篇 |
1996年 | 45篇 |
1995年 | 39篇 |
1994年 | 36篇 |
1993年 | 41篇 |
1992年 | 30篇 |
1991年 | 20篇 |
1990年 | 22篇 |
1989年 | 20篇 |
1988年 | 19篇 |
1987年 | 22篇 |
1986年 | 17篇 |
1985年 | 42篇 |
1984年 | 35篇 |
1983年 | 41篇 |
1982年 | 29篇 |
1981年 | 23篇 |
1980年 | 31篇 |
1979年 | 24篇 |
1977年 | 24篇 |
1976年 | 18篇 |
1975年 | 18篇 |
1974年 | 13篇 |
1973年 | 15篇 |
排序方式: 共有4096条查询结果,搜索用时 15 毫秒
1.
2.
3.
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
4.
5.
6.
7.
Giuseppe Coppola Andrea Irace Giovanni Breglio Mario Iodice Luigi Zeni Antonello Cutolo Pasqualina M. Sarro 《Optics and Lasers in Engineering》2003,39(3):317-332
In this paper we describe two different kind of optoelectronic devices both based on a three terminals active device and exploit the plasma dispersion effect to achieve the desired working. The first device exploits this effect in order to obtain an optical modulation. The second device is an optoelectronic router based on the mode-mixing principle together with the injection-induced optical phase shift. Both devices are integrated into a Silicon on Silicon optical channel waveguide which can be realized using a standard bipolar process. The possibility of using standard, well-known technology presents several advantages with respect to III–V Optoelectronics. The active three terminal device used is a Bipolar Mode Field Effect Transistor (BMFET). Numerical simulation results are presented on both devices. 相似文献
8.
9.
In this paper we highlighted the synthesis, characterization, and practical exploitation of different types of polyphosphazenes substituted with fluorinated groups. There are several ways in which fluorine atoms can be inserted into polyphosphazenes, all of which leading to different polymers showing a wide range of characteristics. In general it is true that the insertion of fluorine atoms into phosphazene macromolecules leads to an enhancement of the thermal stability, flame resistance, low-temperature elastomericity, and chemical inertness of the phosphazenes obtained. The contribution of Italian research groups to the preparation and exploitation of organic commercial macromolecules grafted onto fluorinated polyphosphazenes is also reviewed. 相似文献
10.