全文获取类型
收费全文 | 321篇 |
免费 | 17篇 |
专业分类
化学 | 209篇 |
晶体学 | 5篇 |
力学 | 9篇 |
数学 | 46篇 |
物理学 | 69篇 |
出版年
2023年 | 1篇 |
2022年 | 6篇 |
2021年 | 9篇 |
2020年 | 10篇 |
2019年 | 18篇 |
2018年 | 10篇 |
2017年 | 11篇 |
2016年 | 19篇 |
2015年 | 13篇 |
2014年 | 18篇 |
2013年 | 41篇 |
2012年 | 22篇 |
2011年 | 32篇 |
2010年 | 17篇 |
2009年 | 13篇 |
2008年 | 18篇 |
2007年 | 13篇 |
2006年 | 15篇 |
2005年 | 6篇 |
2004年 | 7篇 |
2003年 | 3篇 |
2002年 | 5篇 |
2001年 | 3篇 |
1999年 | 2篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1987年 | 1篇 |
1985年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1969年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有338条查询结果,搜索用时 15 毫秒
91.
Bozkir Cem Deniz Caglar Kundakcioglu O. Erhun Henry Andrea C. 《Journal of Global Optimization》2022,83(3):565-584
Journal of Global Optimization - In this study, we consider a health network that faces uncertain supply disruptions in the form of regional, nationwide, or worldwide drug shortages. Each hospital... 相似文献
92.
93.
Aslihan Argun Melek Pamuk Algi Deniz C. Tuncaboylu Oguz Okay 《Colloid and polymer science》2014,292(2):511-517
Different reversible molecular interactions have been used in the past few years to generate self-healing in synthetic hydrogels. However, self-healing hydrogels synthesized so far suffer from low mechanical strength which may limit their use in any stress-bearing applications. Here, we present a simple technique to heal mechanically strong polyacrylamide hydrogels formed via hydrophobic interactions between stearyl groups. A complete healing in the hydrogels was achieved by the treatment of the damaged areas with an aqueous solution of wormlike sodium dodecyl sulfate micelles. The micelles in the healing agent solubilize the hydrophobes in the cut surfaces, so that they easily find their partners in the other cut surface due to the hydrophobic interactions. Surfactant-induced healing produces high toughness (~1 MPa) gels withstanding 150 kPa of stress at a deformation ratio of 1,100 %. The healing technique developed here is generally applicable to the physical gels formed by hydrophobic associations. 相似文献
94.
Spatio-spectral analyses of electromagnetic wave energy absorption and heating effect 总被引:1,自引:0,他引:1
This study presents a theoretical analysis method to calculate electromagnetic (EM) wave power absorption spectrum of materials by using attenuation coefficients. The heating effect of EM waves is modeled to analyze spectral distribution of temperature rises inside material body as a result of EM wave power absorption. These analyses are very useful for the investigation of electromagnetic wave-material interaction on the bases of electro-physical material parameters (permittivity, permeability and conductivity). An illustrative analysis of spatio-spectral distribution of EM wave energy absorption and resulting heating effect were conducted for muscle tissues and the results are discussed. 相似文献
95.
Deniz Gunes Okan Sirkecioglu Niyazi Bicak 《Phosphorus, sulfur, and silicon and the related elements》2013,188(8):1685-1690
A simple and convenient one-pot procedure is described for the synthesis of thioethers via boron esters. This procedure involves in-situ generation of alkyl sulfates by reaction of trialkyl borates with concentrated sulfuric acid and subsequent reaction with thiols in the presence of pyridine. The reactions with boron esters of primary or secondary alcohols proceed cleanly at 100°C and afford aliphatic thioethers in reasonable yields (59–93%) within 24 h. Interestingly, the 1H NMR spectra of the products showed no sign of positional isomerisms. The method fails however with thiophenol and does not yield aromatic thioethers, due to electrophilic substitution at the phenyl ring. 相似文献
96.
Cemil Ibis Nahide Gulsah Deniz 《Phosphorus, sulfur, and silicon and the related elements》2013,188(11):2324-2332
New S-,O-substituted naphthoquinone compounds (3a, 4b, 6, 7c, 9d, 10, 12, 13c, 14d, 15) were synthesized via vinilic substitution. 2,3-Dichloro-1,4-naphthoquinone gave 3a and 4b with 4,4′-thiobisbenzenethiol, respectively. Compounds 6 and 7c were obtained from the reaction of 2,3-dichloro-1,4-naphthoquinone with cyclohexylmercaptane. The compounds 9d and 10 were prepared from the reaction of 2,3-dichloro-1,4-naphthoquinone with 6-mercapto-1-hexanol. Compounds 12, 13c, 14d, and 15 were synthesized from the reaction of 2,3-dichloro-1,4-naphthoquinone with 1,6-hexanedithiol. Their structures were characterized by micro analysis, FT-IR, 1H NMR, 13C NMR, MS, UV-Vis, and fluorescence spectroscopy. 相似文献
97.
Deniz Zengel Pirmin Koch Bentolhoda Torkashvand Jan‐Dierk Grunwaldt Maria Casapu Olaf Deutschmann 《Angewandte Chemie (International ed. in English)》2020,59(34):14423-14428
Reducing greenhouse gas and pollutant emissions is one of the most stringent priorities of our society to minimize their dramatic effects on health and environment. Natural gas (NG) engines, in particular at lean conditions, emit less CO2 in comparison to combustion engines operated with liquid fuels but NG engines still require emission control devices for NOx removal. Using state‐of‐the‐art technologies for selective catalytic reduction (SCR) of NOx with NH3, we evaluated the interplay of the reducing agent NH3 and formaldehyde, which is always present in the exhaust of NG engines. Our results show that a significant amount of highly toxic hydrogen cyanide (HCN) is formed. All catalysts tested partially convert formaldehyde to HCOOH and CO. Additionally, they form secondary emissions of HCN due to catalytic reactions of formaldehyde and its oxidation intermediates with NH3. With the present components of the exhaust gas aftertreatment system the HCN emissions are not efficiently converted to non‐polluting gases. The development of more advanced catalyst formulations with improved oxidation activity is mandatory to solve this novel critical issue. 相似文献
98.
Proton spin-lattice relaxation times,T
1, have been measured in the smectic phases, S
G
2
, S
G
1
and SA, and in the nematic phase of HxBPA, in the temperature range, 220K<T<360 K. In the S
G
1
and S
G
2
phases,T
1 has been measured at 15 and 40 MHz. The (S
G
1
→S
G
2
) and (S
G
2
→S
G
1
) transitions are clearly seen as discontinuities inT
1. The former transition is seen to be due to possible freezing or change of hydrocarbon chain motions of the molecule. Our
data in the S
G
1
phase have been fitted to a model in which anisotropic rotational diffusion of the end hydrocarbon chains as also that of
the rigid part of the molecule are considered. In the nematic phase, at 351 K, the observed behaviour ofT
1, measured in the frequency range, 5 to 40 MHz, agrees well with the theoretical predictions of Uklejaet al and Freed, who take into account long range collective order fluctuations and local reorientations. Using these theories,
the correlation time for short range reorientations has been calculated from our results to be 4.3 × 10−10 and 1.1 × 10−9 s respectively. 相似文献
99.
100.
An approach to find transition pathways in complex systems is presented. The method, which is related to the string method in collective variables of Maragliano et al. (J. Chem. Phys. 2006, 125, 024106), is conceptually simple and straightforward to implement. It consists of refining a putative transition path in the multidimensional space supported by a set of collective variables using the average dynamic drift of those variables. This drift is estimated on-the-fly via swarms of short unbiased trajectories started at different points along the path. Successive iterations of this algorithm, which can be naturally distributed over many computer nodes with negligible interprocessor communication, refine an initial trial path toward the most probable transition path (MPTP) between two stable basins. The method is first tested by determining the pathway for the C7eq to C7ax transition in an all-atom model of the alanine dipeptide in vacuum, which has been studied previously with the string method in collective variables. A transition path is found with a committor distribution peaked at 1/2 near the free energy maximum, in accord with previous results. Last, the method is applied to the allosteric conformational change in the nitrogen regulatory protein C (NtrC), represented here with a two-state elastic network model. Even though more than 550 collective variables are used to describe the conformational change, the path converges rapidly. Again, the committor distribution is found to be peaked around 1/2 near the free energy maximum between the two stable states, confirming that a genuine transition state has been localized in this complex multidimensional system. 相似文献