全文获取类型
收费全文 | 231篇 |
免费 | 6篇 |
专业分类
化学 | 183篇 |
晶体学 | 14篇 |
力学 | 5篇 |
数学 | 5篇 |
物理学 | 30篇 |
出版年
2023年 | 1篇 |
2022年 | 10篇 |
2021年 | 7篇 |
2020年 | 9篇 |
2019年 | 1篇 |
2018年 | 8篇 |
2017年 | 5篇 |
2016年 | 6篇 |
2015年 | 4篇 |
2014年 | 9篇 |
2013年 | 14篇 |
2012年 | 15篇 |
2011年 | 13篇 |
2010年 | 7篇 |
2009年 | 5篇 |
2008年 | 16篇 |
2007年 | 16篇 |
2006年 | 16篇 |
2005年 | 17篇 |
2004年 | 16篇 |
2003年 | 15篇 |
2002年 | 4篇 |
1999年 | 1篇 |
1998年 | 2篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1975年 | 1篇 |
排序方式: 共有237条查询结果,搜索用时 93 毫秒
21.
Theoretical insight of nitric oxide adsorption on neutral and charged Pdn (n = 1–5) clusters
下载免费PDF全文
![点击此处可从《International journal of quantum chemistry》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Pakiza Begum Pranjal Gogoi Bhupesh Kumar Mishra Ramesh Chandra Deka 《International journal of quantum chemistry》2015,115(13):837-845
Density functional theory (DFT) calculations within the framework of generalized gradient approximation have been used to systematically investigate the adsorption of nitric oxide (NO) molecule on neutral, cationic, and anionic Pdn (n = 1–5) clusters. NO coordinate to one Pd atom of the cluster by the end‐on mode, where the tilted end‐on structure is more favorable due to the additional electron in the π* orbital. On the contrary, in the neutral and cationic Pd2 system, NO coordinates to the bridge site of cluster preferably by the side‐on mode. Charge transfer between Pd clusters and NO molecule and the corresponding weakening of N? O bond is an essential factor for the adsorption. The N? O stretching frequency follow the order of cationic > neutral > anionic. Binding energy of NO on anionic clusters is found to be greater than those of neutral and cationic clusters. © 2015 Wiley Periodicals, Inc. 相似文献
22.
BinaS. Siddiqui Tahsin Gulzar Sabira Begum Farhana Afshan FouziaA. Sattar 《Helvetica chimica acta》2004,87(3):660-666
The methanolic extract of dried ground seeds of Piper nigrum Linn . afforded fourteen compounds, of which thirteen were amides, including two new isomeric insecticidal amides, pipsaeedine ( 1 ) and pipbinine ( 2 ), along with eleven known amides and piptaline; (this is the first report of isolation of these compounds from this plant). The structures of 1 and 2 have been elucidated as (E,E)‐1‐[(E)‐5‐(7‐{6‐[5‐(piperidin‐1‐yl)‐5‐oxopent‐3‐enyl]‐1,3‐benzodioxol‐4‐yl}‐1,3‐benzodioxol‐5‐yl)‐1‐oxopenta‐2,4‐dienyl]piperidine and (E,E)‐1‐[(E)‐5‐(4‐{6‐[5(piperidin‐1‐yl)‐5‐oxopent‐3‐enyl]‐1,3‐benzodioxol‐4‐yl}‐1,3‐benzodioxol‐5‐yl)‐1‐oxopenta‐2,4‐dienyl]piperidine, respectively, through extensive 1D‐ and 2D‐NMR spectral studies, while the known constituents have been identified through comparison of their spectral data with those reported in the literature. Compounds 1 and 2 exhibited toxicities of 45.0 and 40.0 ppm, respectively, against fourth instar larvae of Aedes aegypti Liston. 相似文献
23.
24.
Tatsuya Kinjo Yoshinori Namihira Kazuya Arakaki Shubi F. Kaijage S. M. Abdur Razzak Feroza Begum Hiroki Higa Shinya Nozaki Nianyu Zou 《Optical Review》2010,17(2):66-73
In this paper we present the design of a modified hexagonal photonic crystal fiber (PCF) having high birefringence and a near-zero
flattened dispersion. Using the finite-difference method (FDM), it is shown that the proposed multiple Gedoped core hexagonal
PCF exhibits a high birefringence of order 10−3 and a nearly zero flattened dispersion in the optical coherence tomography (OCT) waveband. In addition, the proposed PCF
has a confinement loss of less than 10−8 dB/m at 1.06 μm. PCFs with such properties are considered suitable for both endoscopic OCT and other experimental setups
employing 1.06 μm lasers. 相似文献
25.
Kazuya Miyagi Yoshinori Namihira S. M. Abdur Razzak Shubi F. Kaijage Feroza Begum 《Optical Review》2010,17(4):388-392
We have demonstrated that the correction factor k
n
= A
eff/(πw
2), where ω = MFD/2 (MFD: mode field diameter), is above 1.20 for photonic crystal fibers (PCFs) with structural parameters in the range
of d/Λ ≅ 0.40 to 0.90 (d/Λ ratio of hole diameter d and pitch Λ). By using the far-field scanning (FFS) technique and the finite difference method, the results of experimental
measurements and numerical simulations differed by only 0.9 to 3.0% for two types of PCFs. The finding that k
n
≠ 1.0 for PCFs indicates that their electrical field distribution is non-Gaussian and cannot be determined by assuming a
conventional step-index distribution for PCFs. It was also found that the ITU-T Petermann II definition is the most suitable
for MFD measurements of PCFs with non-Gaussian distribution. 相似文献
26.
Studies on the chemical constituents of the stem of Morinda citrifolia, Linn. have led to the isolation of two new compounds, morindicinone (=2-hydroxy-1,8-dimethoxy-7-methoxymethylanthraquinone, 1) and morindicininone (=4-hydroxymethyl-1,3-dimethoxyanthraquinone, 2), as well as two known constituents, 2-hydroxyanthraquinone (3) and 2-methoxyanthraquinone (4). Their structures were elucidated by spectral analysis including 2D-NMR techniques. 相似文献
27.
Jiling Cao Teh Raihana Nazirah Roslan Wenjun Zhang 《Methodology and Computing in Applied Probability》2018,20(4):1359-1379
In this paper, we consider the problem of pricing discretely-sampled variance swaps based on a hybrid model of stochastic volatility and stochastic interest rate with regime-switching. Our modeling framework extends the Heston stochastic volatility model by including the Cox-Ingersoll-Ross (CIR) stochastic interest rate model. In addition, certain model parameters in our model switch according to a continuous-time observable Markov chain process. This enables our model to capture several macroeconomic issues such as alternating business cycles. A semi-closed form pricing formula for variance swaps is derived. The pricing formula is assessed through numerical implementation, where we validate our pricing formula against the Monte Carlo simulation. The impact of incorporating regime-switching for pricing variance swaps is also discussed, where variance swaps prices with and without regime-switching effects are examined in our model. We also explore the economic consequence for the prices of variance swaps by allowing the Heston-CIR model to switch across three different regimes. 相似文献
28.
29.
Silver nanoparticles loaded into shell of poly (styrene-N-isopropylmethacrylamide-co-acrylic acid) core shell [P (SNA-CS)] gel particles were synthesized and analyzed by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), ultraviolet–visible spectroscopy (UV–vis) and dynamic light scattering (DLS). Catalytic activity of Ag@P (SNA-CS) particles was investigated by reducing p-nitroaniline (p-NA) into p-aminoaniline (p-AA) in the presence of sodium borohydride (NaBH4) reductant. Molecules of the substrate adsorbed on the surface of silver nanoparticles interact with borohydride ions (BH4−) to form p-AA. Other nitroarenes like o-nitroaniline (o-NA), p-nitrophenol (p-NP) o-nitrophenol (o-NP), 2,4-dinitrophenol(2,4-DNP) were also reduced into their corresponding aryl amines using Ag@P (SNA-CS) composite microgels as catalyst. Reported catalyst efficiently reduced the nitro aromatic compounds individually as well as simultaneously at ambient temperature. Effect of different reaction conditions (catalyst dose, concentration of NaBH4 and concentration of p-NA) on reaction completion time, value of apparent rate constant (kapp) and reduction efficiency of the catalyst for reduction of p-NA was also demonstrated. Ag@P (SNA-CS) catalyst was found to be able to retain activity up to four cycles. 相似文献
30.
Russian Journal of Organic Chemistry - The present work describes the synthesis of 4-amino-6-(2-benzylidenehydrazinyl)-pyrimidine-5-carbonitrile derivatives,... 相似文献