全文获取类型
收费全文 | 637篇 |
免费 | 29篇 |
国内免费 | 3篇 |
专业分类
化学 | 436篇 |
晶体学 | 3篇 |
力学 | 41篇 |
数学 | 106篇 |
物理学 | 83篇 |
出版年
2023年 | 4篇 |
2022年 | 9篇 |
2021年 | 13篇 |
2020年 | 22篇 |
2019年 | 28篇 |
2018年 | 43篇 |
2017年 | 27篇 |
2016年 | 41篇 |
2015年 | 29篇 |
2014年 | 42篇 |
2013年 | 85篇 |
2012年 | 49篇 |
2011年 | 58篇 |
2010年 | 48篇 |
2009年 | 27篇 |
2008年 | 30篇 |
2007年 | 31篇 |
2006年 | 17篇 |
2005年 | 16篇 |
2004年 | 4篇 |
2003年 | 8篇 |
2002年 | 7篇 |
2001年 | 2篇 |
2000年 | 5篇 |
1998年 | 4篇 |
1997年 | 4篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1988年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有669条查询结果,搜索用时 15 毫秒
51.
Mohammad Reza R. Moghaddam 《Monatshefte für Mathematik》1984,97(3):191-206
The present paper is devoted to calculation of the Baer-invariants of the dihedral and the quaternion groups of order 8, and also a certain class ofp-groups with respect to the variety of nilpotent groups. 相似文献
52.
53.
54.
Chemical imaging systems help to solve many challenges in various scientific fields. Able to deliver rapid spatial and chemical information, modern infrared spectrometers using Focal Plane Array detectors (FPA) are of great interest. Considering conventional infrared spectrometers with a single element detector, we can consider that the diffraction-limited spatial resolution is more or less equal to the wavelength of the light (i.e. 2.5-25 μm). Unfortunately, the spatial resolution of FPA spectroscopic setup is even lower due to the detector pixel size. This becomes a real constraint when micron-sized samples are analysed. New chemometrics methods are thus of great interest to overcome such resolution drawback, while keeping our far-field infrared imaging spectrometers. The aim of the present work is to evaluate the super-resolution concept in order to increase the spatial resolution of infrared imaging spectrometers using FPA detectors. The main idea of super-resolution is the fusion of several low-resolution images of the same sample to obtain a higher-resolution image. Applying the super-resolution concept on a relatively low number of FPA acquisitions, it was possible to observe a 30% decrease in spatial resolution. 相似文献
55.
Firouz Matloubi Moghaddam Mostafa Kiamehr Salman Taheri Zohreh Mirjafary 《Helvetica chimica acta》2010,93(5):964-973
An efficient synthesis of polycyclic indole derivatives is achieved via domino Knoevenagel–hetero‐Diels–Alder reaction of O‐acrylated salicylaldehyde derivatives with dihydroindole‐2‐thiones in H2O as solvent. The products are formed in good‐to‐excellent yields with high regio‐ and stereoselectivity. 相似文献
56.
The synthesis of a series of benzoxazocines has been achieved in good yields by tandem C-alkylation and intramolecular O-alkylation of 1,3-dicarbonyl compounds with quinolinium salts. This is a novel example of the synthesis of eight-membered rings via a tandem process, which provides a method for the synthesis of medium-ring heterocycles. 相似文献
57.
Firouz Matloubi Moghaddam Mostafa Kiamehr 《Monatshefte für Chemie / Chemical Monthly》2010,41(5):1333-1337
Abstract
The site-selectivity and regioselectivity of Diels–Alder reactions of allenyl aryl ethers with cyclopentadiene and acrolein were studied. While cyclopentadiene (as an electron-rich diene) only reacted with the external double bond of allenyl aryl ethers to provide the site-selective normal electron demand Diels–Alder cycloadducts, acrolein (as an electron-deficient diene) reacted with the C1–C2 π bond of allenyl aryl ethers to provide the site- and regioselective hetero-Diels–Alder cycloadducts as exclusive products. 相似文献58.
S. Shahidi A. Rashidi M. Ghoranneviss A. Anvari M. K. Rahimi M. Bameni Moghaddam J. Wiener 《Cellulose (London, England)》2010,17(3):627-634
In this work, the silver particle absorption and antibacterial activity of cotton fabric when modified by low temperature
plasma were investigated. The modification consisted of plasma pre-functionalization followed by one-step wet treatment with
silver nitrate solution. Oxygen and nitrogen were used as the working gases in the system, and the results were compared.
The results showed that nitrogen plasma-treated samples can absorb more silver particles than oxygen-treated samples, and
thus the antibacterial activity of the samples in this case, which was analyzed by the counting bacteria test, was increased
considerably. 相似文献
59.
Mohammad Najafi Hossein Roghani-Mamaqani Mehdi Salami-Kalajahi Vahid Haddadi-Asl 《高分子科学》2010,28(4):483-497
<正>An optimized and high-performance Monte Carlo simulation is developed to take thorough account of four different cases of termination in styrene ATRP.According to the simulation results,the bimolecular termination rate constant sharply drops throughout the polymerization when either chain-length dependency of termination rate constant,gel effect,or both together is applied to the simulation.In addition,as expected,the initiator is quickly decomposed at the early stages of the polymerization.The concentration of the catalyst in lower oxidation state decreases at first and then plateaus at higher conversion;furthermore,the steady concentration of M_t~nY/L in the polymerization is the highest when the chain-length-dependent diffusion-controlled termination rate constant is employed in the simulation.The rates of deactivation and chain end degradation reactions are also smaller in this case.Therefore,the fraction of dormant chains is higher throughout the reaction and consequently the portion of dead polymers decreases.Besides,molecular weight increases linearly with conversion;however,when neither gel effect nor chain-length dependency of termination rate constant is considered,the molecular weight deviates from linearity at the end of the reaction.The peak of chain length distribution shifts toward higher molecular weight too during the reaction.Finally,the molecular weight distribution broadens at higher conversion;however, the chain length distribution of polymers produced under conditions of applying chain-length-dependent diffusion-controlled termination rate constant is narrower. 相似文献
60.
F. Hajiesmaeilbaigi H. Razzaghi M. Mahdizadeh M.R.A. Moghaddam M. Ruzbehani 《Optics & Laser Technology》2011,43(8):1428-1430
In this paper, the design and the construction of a high-power side-diode-pumped Nd:YAG solid-state laser at repetition rates of 6 and 10 kHz has been presented. Second harmonic of the Nd:YAG laser with green light at 532 nm, with an average power of 111.5 W at 10 kHz repetition rate, and with 90 ns pulse duration, has been obtained by the nonlinear crystal of KTP with 59% conversion efficiency and 12% diode-to-green optical–optical efficiency in the linear resonator. Beam spot size and divergence is 4 mm and 8 mrad, respectively. The laser stability is about 97%. As a medical application of this laser, investigation of degree of effectiveness and penetration depth of laser on adenomas of resected prostate after open prostatectomy has been done. 相似文献