全文获取类型
收费全文 | 225篇 |
免费 | 7篇 |
国内免费 | 1篇 |
专业分类
化学 | 148篇 |
晶体学 | 1篇 |
力学 | 15篇 |
数学 | 49篇 |
物理学 | 20篇 |
出版年
2022年 | 2篇 |
2021年 | 5篇 |
2020年 | 1篇 |
2019年 | 5篇 |
2017年 | 6篇 |
2016年 | 3篇 |
2015年 | 8篇 |
2014年 | 6篇 |
2013年 | 17篇 |
2012年 | 13篇 |
2011年 | 13篇 |
2010年 | 3篇 |
2009年 | 8篇 |
2008年 | 13篇 |
2007年 | 17篇 |
2006年 | 15篇 |
2005年 | 11篇 |
2004年 | 12篇 |
2003年 | 11篇 |
2002年 | 16篇 |
2001年 | 5篇 |
2000年 | 10篇 |
1999年 | 6篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1975年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有233条查询结果,搜索用时 562 毫秒
121.
Shingo Kimura Satoshi Kobayashi Takuya Kumamoto Aki Akagi Naomi Sato Tsutomu Ishikawa 《Helvetica chimica acta》2011,94(4):578-591
Towards total synthesis of a series of kinamycin and related antibiotics via common synthetic intermediates, total synthesis of prekinamycin was achieved via Suzuki coupling of naphthaleneboronic acid and bromobenzene derivative, intramolecular Friedel? Crafts reaction of 2‐(naphthalen‐2‐yl)benzoic acid, and diazotization in ten steps from 3,5‐dimethylphenol. Synthetic studies towards kinamycin antibiotics was also examined, and the tetracyclic quinone core for kinamycins was synthesized. Palladium‐catalyzed site‐selective hydroxylation of a benzoic acid derivative with the AB‐D ring part was successfully applied to the selective D‐ring functionalizations. 相似文献
122.
P. Surya Mohan Tanja Tarvainen Martin Schweiger Aki Pulkkinen Simon R. Arridge 《Journal of computational physics》2011,230(19):7364-7383
We propose the PN approximation based on a finite element framework for solving the radiative transport equation with optical tomography as the primary application area. The key idea is to employ a variable order spherical harmonic expansion for angular discretization based on the proximity to the source and the local scattering coefficient. The proposed scheme is shown to be computationally efficient compared to employing homogeneously high orders of expansion everywhere in the domain. In addition the numerical method is shown to accurately describe the void regions encountered in the forward modeling of real-life specimens such as infant brains. The accuracy of the method is demonstrated over three model problems where the PN approximation is compared against Monte Carlo simulations and other state-of-the-art methods. 相似文献
123.
Takayoshi Kimura Satoshi Fujie Takashi Yukiyama Masao Fujisawa Tadashi Kamiyama Hatsumi Aki 《Journal of inclusion phenomena and macrocyclic chemistry》2011,70(3-4):269-278
In order to investigate the contribution of the hydrophilic parts of guest molecules of aliphatic compounds to the inclusion reaction, the thermodynamic properties of inclusion compounds of cyclodextrin (??-CD) with eight pentane derivatives into the cavity of ??-CD in dilute aqueous solutions were measured by micro-calorimeter at 298.15 K. The thermodynamic properties of the inclusion reactions of pentane derivatives into ??-CD were compared to the hydrophobicity and polarizability of guest molecules and discussed. The interaction energies of inclusion compounds of ??-CD and pentane derivatives were determined by DFT calculation (B3LYP/6-31G (d,p)) in water and compared with the experimental results. 相似文献
124.
Aki Tsuruhara Hirohiko Kaneko So Kanazawa Yumiko Otsuka Nobu Shirai Masami K. Yamaguchi 《Optical Review》2013,20(3):277-281
Both horizontal and vertical binocular disparities produce depth perception in adults. In developmental studies, infants aged around 4 to 6 months were shown to perceive depth from horizontal disparity. However, infants’ sensitivity to vertical disparity has not been shown clearly. To examine the sensitivity in infants, this study measured preferential looking behavior of infants aged 20 to 27 weeks. Results showed a significant preference for the stimulus with vertical disparity, providing the first evidence of infants’ sensitivity to vertical disparity. The infants in the same age group did not show preference for stimulus with horizontal disparity when the stimulus were comparable to the stimulus with vertical disparity, while their sensitivity to horizontal disparity was confirmed with the stimuli used in a previous study. Our results would suggest that properties in processing horizontal and vertical disparities are different in infancy, and that the sensitivity to horizontal disparity are still premature in 27 weeks after birth. 相似文献
125.
Kiyoshi Inoue Sigeo Aki Balakrishnan Narayanaswamy 《Methodology and Computing in Applied Probability》2013,15(2):349-362
In this paper, we consider some cover time problems for random walks on graphs in a wide class of waiting time problems. By using generating functions, we present a unified approach for the study of distributions associated with waiting times. In addition, the distributions of the numbers of visits for the random walks on the graphs are also studied. We present the relationship between the distributions of the waiting times and the numbers of visits. We also show that these theoretical results can be easily carried out through some computer algebra systems and present some numerical results for cover times in order to demonstrate the usefulness of the results developed. Finally, the study of cover time problems through generating functions leads to more extensive development. 相似文献
126.
A method of ultrasound-assisted digestion followed by inductively coupled plasma optical emission spectrometry (ICP-OES) used for the determination of trace element (chromium, copper, lead, nickel, vanadium and zinc) concentrations in fly ash samples was developed. All the measurements were performed in robust plasma conditions. Ultrasound-assisted digestion procedures using digestion solutions of aqua regia and hydrofluoric acid (HF) resulted in recovery rates of over 80% for all the analyte elements. Ultrasound-assisted two-step digestion with digestion solutions of 6 mL of HNO3 (Step 1) and 3 mL of HNO3 + 3 mL of HF (Step 2) resulted in recovery rates of over 92% for all the analyte elements with one exception, chromium, which had a recovery of about 85%. The analysis of SRM 1633b showed that the two-step ultrasound-assisted digestion method developed resulted in chromium, copper, nickel and zinc concentrations higher than the microwave digestion method standardized by the United States Environmental Protection Agency (USEPA method 3052). This is the very first time when a digestion method using ultrasound resulted in higher efficiency than microwave (USEPA method 3052) for chromium and nickel in very hard to dissolve samples. The major advantages of the ultrasound-assisted digestion over microwave digestion is the high treatment rate (about 30 samples simultaneously with a sonication time of 18 min) and the possibility to use new sample vessels without a significant increase in costs. 相似文献
127.
在线性压电陶瓷本构关系和裂纹边界绝缘的框架下,用超奇异积分方程的方法对椭圆类片状裂纹问题进行了重新研究.超奇异积分方程中的未知位移间断和电势间断近似地表示为基本密度函数与多项式之积,其中基本密度函数反映了椭圆片状裂纹前沿电弹性场的奇异性,而多项式在均布载荷作用下可用一个常数来表达.引入椭球坐标系后,得到了均布载荷作用下未知位移间断和电势间断的解析解.使用这些解析解和电弹性场强度的定义,得到了裂纹前沿Ⅰ型、Ⅱ型和Ⅲ型应力强度因子以及电位移强度因子的精确表达式.法向均布载荷作用下的结果与现有精确解完全一致,切向均布载荷作用下的结果则尚未见有其它报道. 相似文献
128.
129.
Xu Jian Chen Mengcheng Noda Nao Aki 《Acta Mechanica Solida Sinica》2005,18(4):326-333
According to the constitutive relationship in linear piezoceramics, elliptical crack problems in the impermeable case are reconsidered with the hypersingular integral equation method. Unknown displacement and electric potential jumps in the integral equations are approximated with a product of the fundamental density function and polynomials, in which the fundamental density function reflects the singular behavior of electroelastic fields near the crack front and the polynomials can be reduced to a real constant under uniform loading. Ellipsoidal coordinates are cleverly introduced to solve the unknown displacement and electric potential jumps in the integral equations under uniform loading. With the help of these solutions and definitions of electroelastic field intensity factors, exact expressions for mode Ⅰ, mode Ⅱ and mode Ⅲ stress intensity factors as well as the mode Ⅳ electric displacement intensity factor are obtained. The present results under uniform normal loading are the same as the available exact solutions, but those under uniform shear loading have not been found in the literature as yet. 相似文献
130.
Aki Pulkkinen Katariina Pussi 《The European Physical Journal B - Condensed Matter and Complex Systems》2017,90(10):184
We study atomic oxygen adsorption on a Pb(1 0 0) surface using density functional theory. The structures, binding energies, work function, and charge transfer of on-surface and subsurface adsorption are investigated at a range of coverages from 0.06 to 1.00 ML. The energetically favored adsorption site for on-surface adsorption is found to be a distorted hollow site for the whole coverage range studied. The distorted structures are stabilized by mixing of 6s and 6p states of lead mediated by the 2p states of oxygen. For subsurface adsorption, the sub-bridge site is found to be preferred to the sub-hollow site at low coverages, the two being nearly equal in energy at monolayer coverage. At 0.11 ML coverage, diffusion from an on-surface hollow site to a sub-bridge site is found to be barrierless, suggesting facile subsurface oxidation at low coverages. Combined on-surface and subsurface adsorption leads to the formation of a two-layer oxide structure resembling β-PbO. 相似文献