全文获取类型
收费全文 | 1854篇 |
免费 | 360篇 |
国内免费 | 606篇 |
专业分类
化学 | 2436篇 |
晶体学 | 14篇 |
力学 | 7篇 |
综合类 | 8篇 |
数学 | 210篇 |
物理学 | 145篇 |
出版年
2024年 | 5篇 |
2023年 | 17篇 |
2022年 | 39篇 |
2021年 | 86篇 |
2020年 | 117篇 |
2019年 | 97篇 |
2018年 | 82篇 |
2017年 | 85篇 |
2016年 | 104篇 |
2015年 | 169篇 |
2014年 | 142篇 |
2013年 | 228篇 |
2012年 | 193篇 |
2011年 | 165篇 |
2010年 | 164篇 |
2009年 | 175篇 |
2008年 | 154篇 |
2007年 | 145篇 |
2006年 | 127篇 |
2005年 | 120篇 |
2004年 | 86篇 |
2003年 | 80篇 |
2002年 | 46篇 |
2001年 | 50篇 |
2000年 | 38篇 |
1999年 | 34篇 |
1998年 | 19篇 |
1997年 | 13篇 |
1996年 | 12篇 |
1995年 | 3篇 |
1994年 | 6篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1987年 | 3篇 |
1985年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有2820条查询结果,搜索用时 500 毫秒
91.
W.O. Rosa L.G. Vivas K.R. Pirota A. Asenjo M. Vázquez 《Journal of magnetism and magnetic materials》2012
The size effects on magnetic properties of nanowires arrays were studied varying the nanowires diameter and maintaining the same periodicity among them, for two different nominal compositions of Co and Ni in the alloy form. The competition among magnetocrystalline and shape anisotropies changes drastically from smallest to biggest diameters altering the easy axis direction. In the case of 75% of Co in alloy, experimental values of the effective anisotropy constant (Keff) vary from positive to negative depending on the diameter, which means a reversal of the easy axis direction. For 50% of Co the shape anisotropy dominates over the magnetocrystalline for all studied diameters. 相似文献
92.
Jing Wu Ying Qu Kun Shi Bingyang Chu Yanpeng Jia Xue Xiao Qianjun He Zhiyong Qian 《中国化学快报》2018,29(12):1819-1823
The CPT was loaded into the HMSNs with the high loading capacity. Then the CPT@HMSNs were loaded into the PLEL thermosensitive hydrogels for local therapy to prevent the recurrence of breast cancer after the tumor was resected. 相似文献
93.
94.
Facile Fabrication of Well‐Dispersed Pt Nanoparticles in Mesoporous Silica with Large Open Spaces and Their Catalytic Applications 下载免费PDF全文
Xianchun Liu Dashu Chen Lin Chen Renxi Jin Dr. Shuangxi Xing Dr. Hongzhu Xing Prof. Yan Xing Prof. Zhongmin Su 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(27):9293-9298
In this paper, a facile strategy is reported for the preparation of well‐dispersed Pt nanoparticles in ordered mesoporous silica (Pt@OMS) by using a hybrid mesoporous phenolic resin‐silica nanocomposite as the parent material. The phenolic resin polymer is proposed herein to be the key in preventing the aggregation of Pt nanoparticles during their formation process and making contributions both to enhance the surface area and enlarge the pore size of the support. The Pt@OMS proves to be a highly active and stable catalyst for both gas‐phase oxidation of CO and liquid‐phase hydrogenation of 4‐nitrophenol. This work might open new avenues for the preparation of noble metal nanoparticles in mesoporous silica with unique structures for catalytic applications. 相似文献
95.
Mesoporous chitosan‐immobilized iron tetrakis(4‐carboxyphenyl)porphyrin as a model of cytochrome P‐450 enzyme for oxidation of ethylbenzene 下载免费PDF全文
Mesoporous chitosan‐grafted iron tetra (4‐carboxyphenyl) porphyrin catalyst (Fe TCPP/mesp‐CTS) was prepared and investigated as a practical model for the nano‐cavity and coordinate regulation‐catalysis(CRC) function in cytochrome P‐450 enzyme. Fe TCPP/mesp‐CTS was characterized by X‐ray Diffraction (XRD), Thermogravimetry (TG), Ultraviolet–visible spectroscopy(UV‐Vis), Ultraviolet–visible– Diffuse reflectance spectroscopy (UV‐DRS), Scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT‐IR), and X‐ray photoelectron spectroscopy (XPS) techniques. The catalytic activity of Fe TCPP/mesp‐CTS for ethylbenzene oxidation was investigated and it was proved to be a better catalyst than Fe TCPP/macp‐CTS based on the ethylbenzene conversion, turnover numbers(TON), and the reusability. These results are attributed to the mesocavity and CRC of amino group in Fe TCPP/mesp‐CTS. The highest ethylbenzene conversion and yields of ketone and alcohol were 24.4% and 18.2%, respectively. 相似文献
96.
A fast and efficient eco‐friendly two‐step preparation of a palladium‐containing mesoporous carbon catalyst ( C1 ) from green and readily available carbon precursors (phloroglucinol and glyoxal), a porogen template (pluronic F‐127) and PdCl2 is described. Catalyst C1 contains ultra‐small Pd nanoparticles (1.2 nm) uniformly dispersed in the carbon network and shows an outstanding activity for Suzuki‐Miyaura reactions in pure water: extremely low amounts of palladium (10 μequiv. in most cases) are sufficient to afford almost palladium‐free products (containing <0.25 ppm of precious metal without further purification steps). 相似文献
97.
This work presents a scalable approach for preparing spherical hollow mesoporous silica with high surface area/pore volume, serving as outstanding support for supported phosphotungstic acid catalyst with much superior catalytic performance to the one on previously reported spherical mesoporous silica toward diverse transformations, ascribed to the strengthened mass transfer and the enlarged exposure degree of acidic sites to reactants those resulting from unique hollow and mesoporous morphology. 相似文献
98.
Cu(II) immobilized on mesoporous organosilica as an efficient and reusable nanocatalyst for one‐pot Biginelli reaction under solvent‐free conditions 下载免费PDF全文
Cu(II) immobilized on mesoporous organosilica nanoparticles (Cu2+@MSNs‐(CO2?)2) has been synthesized, as a inorganic–organic nanohybrid catalyst, through a post‐grafting approach. Its characterization is carried out by Fourier transform infrared spectroscopy (FT‐IR), X‐ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Energy dispersive X‐ray (EDX), Thermogravimetric/differential thermal analyses (TGA‐DTA), and Nitrogen adsorption–desorption analysis. Cu2+@MSNs‐(CO2?)2 exhibits high catalytic activity in the Biginelli reaction for the synthesis of a diverse range of 3, 4‐dihydropyrimidin‐2(1H)‐ones, under mild conditions. The anchored Cu(II) could not leach out from the surface of the mesoporous catalyst during the reaction and it has been reused several times without appreciable loss in its catalytic activity. 相似文献
99.
FTIR photothermal beam deflection spectroscopy (PBDS) was used to record infrared spectra of medium-temperature carbons before and after they had been subjected to treatments with aqueous HNO3 or H2O2 solution. Changes in the functional groups present on the carbon surfaces can be clearly observed. 相似文献
100.
Razieh Fazaeli Hamid Aliyan Elham Naderi 《Phosphorus, sulfur, and silicon and the related elements》2013,188(6):745-754
Abstract The immobilization of heteropoly acids (HPAs) into the Al-functionalized KIT-6 mesoporous molecular sieve has been carried out to see the effect of Al-KIT-6 as a host matrix on the HPA activities. These modified mesoporous molecular sieves are effective catalysts for the Hosomi–Sakurai three-component coupling reaction via condensation of aldehydes, silyl ethers, and allylsilanes. Supplemental materials are available for this paper. 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