全文获取类型
收费全文 | 361篇 |
免费 | 9篇 |
国内免费 | 6篇 |
专业分类
化学 | 213篇 |
晶体学 | 5篇 |
力学 | 17篇 |
数学 | 48篇 |
物理学 | 93篇 |
出版年
2024年 | 2篇 |
2023年 | 1篇 |
2022年 | 8篇 |
2021年 | 15篇 |
2020年 | 12篇 |
2019年 | 8篇 |
2018年 | 15篇 |
2017年 | 4篇 |
2016年 | 9篇 |
2015年 | 13篇 |
2014年 | 14篇 |
2013年 | 39篇 |
2012年 | 27篇 |
2011年 | 29篇 |
2010年 | 25篇 |
2009年 | 34篇 |
2008年 | 27篇 |
2007年 | 17篇 |
2006年 | 6篇 |
2005年 | 4篇 |
2004年 | 6篇 |
2003年 | 4篇 |
2002年 | 6篇 |
2001年 | 7篇 |
2000年 | 4篇 |
1999年 | 2篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1995年 | 3篇 |
1992年 | 1篇 |
1990年 | 1篇 |
1987年 | 1篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1976年 | 3篇 |
1963年 | 1篇 |
排序方式: 共有376条查询结果,搜索用时 15 毫秒
371.
Rahim Hekmatshoar Ghodsieh Nanva Kenary Sodeh Sadjadi Yahya S. Beheshtiha 《合成通讯》2013,43(13):2007-2013
An efficient method for the synthesis of 4-amino-5-pyrimidinecarbonitriles by three-component reaction of malononitrile, aldehydes, and N-unsubstituted amidines, under aqueous conditions, using ZnO nanoparticles as catalyst is reported. The catalyst exhibited remarkable activity and is recyclable. 相似文献
372.
Ultrasonic assisted extraction-dispersive liquid-liquid microextraction (UAE-DLLME) coupled with gas chromatography (GC) was applied for extraction and determination of essential oil constituents of the plant Oliveria decumbens Vent. Scanning electron microscopy (SEM) was used to see the effect of ultrasonic radiation on the extraction efficiency. By comparison with hydrodistillation, UAE-DLLME is fast, low cost, simple, efficient and consuming small amount of plant materials (~1.0 g). The effects of various parameters such as temperature, ultrasonication time, volume of disperser and extraction solvents were investigated by a full factorial design to identify significant variables and their interactions. The results demonstrated that temperature and ultrasonication time had no considerable effect on the results. In the next step, a central composite design (CCD) was performed to obtain the optimum levels of significant parameters. The obtained optimal conditions were: 0.45 mL for disperser solvent (acetonitrile) and 94.84 μL for extraction solvent (chlorobenzene). The limits of detection (LODs), linear dynamic range and determination coefficients (R(2)) were 0.2-29 ng mL(-1), 1-2100 ng mL(-1) and 0.995-0.998, respectively. The main components of the essential oil were: thymol (47.06%), carvacrol (23.31%), gamma-terpinene (18.94%), p-cymene (8.71%), limonene (0.76%) and myristicin (0.63%). 相似文献
373.
Y. Köseoğlu M. Bay M. Tan A. Baykal H. Sözeri R. Topkaya N. Akdoğan 《Journal of nanoparticle research》2011,13(5):2235-2244
We present a systematic investigation on the structural and magnetic properties of Mn0.2Ni0.8Fe2O4 nanoparticles synthesized by a polyethylene glycol (PEG)-assisted hydrothermal route. XRD, FT-IR, TEM and VSM were used for
the structural, morphological, dielectric properties and magnetic investigation of the products, respectively. Average crystallite
size of product was estimated using Line profile fitting as 6 ± 1 nm and particle size as 6.5 ± 1.0 nm from TEM micrographs.
Magnetization measurements have shown that the particles have a blocking temperature of 134 K. Magnetization and the coercive
field of the sample increase by decreasing the temperature. The conductivity measurements reveal the semiconducting behaviour
for the sample. Temperature-dependent dielectric properties: dielectric permittivity (ε) and ac conductivity (σac) for the sample were studied as a function of applied frequency in the range from 1 Hz to 3 MHz. These studies indicated
that the dielectric dispersion curve for the sample showed usual dielectric dispersion which can be explained on the basis
of Koop’s theory, which is based on the Maxwell–Wagner model for the interfacial polarization of homogeneous double structure. 相似文献
374.
H. T. Eyyuboğlu E. Sermutlu Y. Baykal Y. Cai O. Korotkova 《Applied physics. B, Lasers and optics》2008,93(2-3):605-611
The scintillation index of a J n -Bessel–Gaussian beam of any order propagating in turbulent atmosphere is derived and numerically evaluated at transverse cross-sections with the aid of a specially designed triple integral routine. The graphical outputs indicate that, just like the previously investigated J 0-Bessel–Gaussian beam, higher-order members of the family also offer favorable scintillation characteristics at large source sizes. This advantage is maintained against rising beam orders. Viewed along the propagation axis, beams with lower orders and smaller widths exhibit smaller values of the scintillation index at shorter propagation distances and large values at longer propagation distances. Further, it is shown that the scintillation index of the J n -Bessel–Gaussian beams (n>0) is larger than that of the fundamental Gaussian and the J 0-Bessel–Gaussian beams only near the on-axis points, while remaining smaller towards the edges of the beam. 相似文献
375.
C. Naceur Abouloula M. Rizwan V. Selvanathan C. I. Abdullah A. Hassan R. Yahya A. Oueriagli 《Ionics》2018,24(12):3827-3836
Biopolymer-based materials from renewable sources are the core target of the researchers in modern time. Following this motivation, we have developed solid polymer electrolytes (SPEs) from empty fruit branch (EFB) of oil palm. The cellulose was extracted from EFB and modified to carboxymethyl cellulose (CMC) by its reaction with monochloroacetic acid in a strongly alkaline medium. The samples were characterized by FTIR, 13C NMR, and XRD to confirm the presence of different functional groups, new connectivity, and crystalline/amorphous nature of the materials, respectively. The CMC-based SPEs were fabricated by blending it with different quantities of lithium iodide (LiI) as dopant. The existence of polymer-salt interactions was revealed by FTIR analysis. The maximum ionic conductivity of 5.58?×?10?3 S cm?1 was observed on sample containing 65 wt% LiI with the lowest activation energy of 0.249 eV. 相似文献
376.
The electronic absorption spectra as well as molecular orbital (MO) calculations at the ab initio level of some 1,2‐benzoquinone diazides have been studied. The results of spectral study support the open isomer over the closed one (1,2,3‐oxadiazole derivative) and indicate the contribution of both the benzenoid and quinonoid structures to the molecule. Spectral results were confirmed by MO calculations. The results of the latter gave a lower total energy for a benzoquinone diazide than for 1,2,3‐benzoxadiazole structure. Bond length and charge density indicate the contribution of both quinonoid and benzenoid structures for the studied compounds. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 78: 52–62, 2000 相似文献