全文获取类型
收费全文 | 913篇 |
免费 | 31篇 |
国内免费 | 21篇 |
专业分类
化学 | 569篇 |
晶体学 | 1篇 |
力学 | 77篇 |
数学 | 129篇 |
物理学 | 189篇 |
出版年
2024年 | 3篇 |
2023年 | 1篇 |
2022年 | 16篇 |
2021年 | 42篇 |
2020年 | 41篇 |
2019年 | 42篇 |
2018年 | 44篇 |
2017年 | 51篇 |
2016年 | 59篇 |
2015年 | 33篇 |
2014年 | 66篇 |
2013年 | 149篇 |
2012年 | 83篇 |
2011年 | 72篇 |
2010年 | 56篇 |
2009年 | 38篇 |
2008年 | 35篇 |
2007年 | 30篇 |
2006年 | 14篇 |
2005年 | 14篇 |
2004年 | 7篇 |
2003年 | 11篇 |
2002年 | 5篇 |
2001年 | 5篇 |
2000年 | 3篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1977年 | 6篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1972年 | 1篇 |
排序方式: 共有965条查询结果,搜索用时 4 毫秒
31.
32.
Ali Ahmadi Peyghan Mohammad Bigdeli Tabar Sirous Yourdkhani 《Journal of Cluster Science》2013,24(4):1011-1020
By using density functional theory calculations, we have investigated the adsorption of OH and OCH3 free radicals on a BC2N nanotube based on the energetic, electronic and geometric properties. The adsorption of radicals on the top of a B atom is more favorable than that on the other sites and reaction energies have been calculated to be in the range of ?0.57 to ?1.48 eV for OH and ?0.27 to ?1.19 eV for OCH3. It was found that the adsorption of radicals may facilitate the electron emission from the BC2N nanotube surface by decreasing the work function due to the charge transfer which occurs between the tube and radicals. Also, HOMO/LUMO gap of the tube is significantly decreased, which may result in the increase of the electrical conductivity of the tube. 相似文献
33.
34.
35.
36.
37.
This paper presents the design principles of a novel optimized microring-based uni-traveling carrier photodiode (MR-UTC-PD), for wavelength division multiplexing (WDM) optical systems. The fundamental parameters for output characteristics such as quantum efficiency and 3-dB bandwidth of MR-UTC-PD are discussed. We analyze the effects of basic parameters as effective ring radius, definite coupling condition and the suitable cross section on the MR-UTC-PD main characteristics for high performance of the device. It is shown that the maximum quantum efficiency and most efficient performance of the device can be obtained at critical coupling condition. We show that the maximum 3-dB bandwidth and an efficient approach for high bandwidth-efficiency product can be achieved at overcoupling condition. In this regard, some design curves are presented for the optimized MR-UTC-PD. 相似文献
38.
Farhad Shirini Manouchehr Mamaghani Seyyed Vahid Atghia 《Journal of the Iranian Chemical Society》2013,10(3):415-420
Nanoporous Na+-montmorillonite sulfonic acid was found to be an efficient and green catalyst for the synthesis of various 14-aryl-14H-dibenzo[a,j]xanthenes and 1,8-dioxo-dodecahydroxanthene derivatives by the reaction of aldehydes with 2-naphthol and 1,3-cyclohexanedione, respectively. This novel synthetic method has the advantages of high yields, short reaction times and recyclability of the catalyst, simplicity and easy workup compared to the conventional methods reported in the literature. 相似文献
39.
F. Ahmadi M. Saberkari R. Abiri H. Mohammadi Motlagh H. Saberkari 《Applied biochemistry and biotechnology》2013,170(4):988-1009
A tetrahedral Zn(II) complex with the second generation fluoroquinolone, norfloxacin, was prepared and characterized (NOR–Zn complex, NZC). The antibacterial efficiency of the NZC was tested on two Gram-positive and four Gram-negative bacteria by minimum inhibitory concentration method. The cytotoxic potential of NZC on MDA (human breast adenocarcinoma), Caco-2 (human colon adenocarcinoma), and Hela (human cervix carcinoma) cell lines was studied. The DNA interaction property of the NZC has been investigated using UV–vis, fluorescence, Fourier transform infrared, as well as cyclic voltammetry methods. Intrinsic binding constant (K b ), thermodynamic, and other spectroscopic and voltammetric data indicate that the NZC has more affinity for DNA than for norfloxacin and interacted with DNA via two modes: electrostatic and outside hydrogen binding. The proposed DNA binding mode supports the large enhancement in the cytotoxicity and antibacterial activity of NZC. 相似文献
40.
Ali Ramazani Nahid Shajari Amir Tofangchi Mahyari Mehdi Khoobi Yavar Ahmadi Ali Souldozi 《Phosphorus, sulfur, and silicon and the related elements》2013,188(12):2496-2502
Reactions of (N-isocyanimino)triphenylphosphorane with 1,1,1-trifluoroacetone in the presence of aromatic (or heteroaromatic) carboxylic acids (3-methylbenzoic acid, 1-naphthalenecarboxylic acid, 2-naphthalenecarboxylic acid, 2-furancarboxylic acid, and 2-thiophenecarboxylic acid) proceed smoothly at room temperature and in neutral conditions to afford sterically congested 1,1,1-trifluoro-2-(5-aryl-1,3,4-oxadiazol-2-yl)-2-propanol derivatives in high yields. The reaction proceeds smoothly and cleanly under mild conditions, and no side reactions were observed. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file. 相似文献