全文获取类型
收费全文 | 320篇 |
免费 | 9篇 |
国内免费 | 5篇 |
专业分类
化学 | 177篇 |
晶体学 | 4篇 |
力学 | 5篇 |
数学 | 60篇 |
物理学 | 88篇 |
出版年
2024年 | 1篇 |
2023年 | 5篇 |
2022年 | 2篇 |
2021年 | 10篇 |
2020年 | 10篇 |
2019年 | 7篇 |
2018年 | 6篇 |
2017年 | 5篇 |
2016年 | 4篇 |
2015年 | 11篇 |
2014年 | 11篇 |
2013年 | 24篇 |
2012年 | 19篇 |
2011年 | 11篇 |
2010年 | 13篇 |
2009年 | 9篇 |
2008年 | 15篇 |
2007年 | 23篇 |
2006年 | 9篇 |
2005年 | 17篇 |
2004年 | 17篇 |
2003年 | 12篇 |
2002年 | 17篇 |
2001年 | 4篇 |
2000年 | 11篇 |
1999年 | 6篇 |
1998年 | 3篇 |
1997年 | 4篇 |
1996年 | 9篇 |
1995年 | 10篇 |
1994年 | 6篇 |
1993年 | 4篇 |
1992年 | 7篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1980年 | 1篇 |
1887年 | 1篇 |
1886年 | 1篇 |
排序方式: 共有334条查询结果,搜索用时 177 毫秒
101.
102.
We establish global W 1, p(·)-estimates for second order elliptic equations in divergence form under the natural assumption that p(·) is log-Hölder continuous. To this end, we assume that the coefficients are measurable in one variable and have small BMO semi-norms in the other variables and the boundary of the domain is Reifenberg flat. Our work is an optimal and natural extension of W 1,p -regularity for such equations with merely measurable coefficients beyond Lipschitz domains. 相似文献
103.
Jaewoo Lee Jooyoung Chung Sang Moon Byun B. Moon Kim Chulbom Lee 《Tetrahedron》2013,69(27-28):5660-5664
The direct C–H arylation of a heteroarene with aryl bromides has been achieved under the catalysis of magnetic nanoparticles. In the presence of bimetallic Pd–Fe3O4 heterodimer nanocrystals (1 mol % in palladium), the reaction of imidazo[1,2-a]pyridine with various aryl bromides gives the corresponding arylated products with exclusive C3-selectivity. The highly regioselective method is applicable to a wide range of aryl bromides with varying electronic and steric properties. The Pd–Fe3O4 nanocrystals can be recoverable by simple magnetic separation and have been recycled ten times without loss of catalytic activity. 相似文献
104.
Jooyoung Chung Jinju Kim Youngjin Jang Sangmoon Byun Taeghwan Hyeon B. Moon Kim 《Tetrahedron letters》2013
We have developed a convenient Pd–Fe3O4 heterodimeric nanocrystal catalyst system for Heck and Sonogashira reactions. This catalyst offers an environment-friendly, atom-efficient, and robust catalytic system for both reactions. Furthermore the nanocrystal catalyst could be easily separated by an external magnet and recycled six times without losing its catalytic activity. 相似文献
105.
Conductivity stability at thermal environment of conductive polyaniline‐complexes/polyimide (PANI‐complexes/PI) blends, which were doped by camphorsulfonic acid (CSA) and dodecylbenzenesulfonic acid (DBSA), respectively, were investigated by conductivity measurements, electron spin resonance (ESR) spectra, differential and scanning thermometer (DSC). In the conversion process of PANI/Polyamic acid (PAA) to PANI/PI, the blend endeavored some kinds of alteration such as decomplexation of moisture and solvent, dissociation of dopant, crosslinking of PANI chain, and the imidization of PAA chain. PANI‐DBSA/PI showed higher thermal stability of conductivity than PANI‐CSA/PI, and both samples showed nearly linear decay of conductivity with increasing temperature showing greatly enhancement of conductivity stability. When they were exposed at near or over glass transition temperature, the conductivity decay became faster. The conductivity stability at base environment was also higher for PANI‐DBSA/PI due to difficulty in accessing of hydroxyl ion to PANI, which were resulted from dopant. DBSA‐doped blends showed increased polaron mobility and concentration at relatively high temperature, which led to extremely higher conductivity and its stability at high temperature. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
106.
Several kinds of cyclic silsesquioxane (CSSQ) precursors containing linear siloxane chain were prepared to improve both the mechanical properties of their thin films and the compatibility with heptakis (2,3,6-tri-O-methyl)-β-cyclodextrin (tCD) as a porogen. The precursors were synthesized using a hydrolysis/condensation reaction with 2,4,6,8-tetramethyl-2,4,6,8-tetra (trimethoxysilylethyl) cyclotetrasiloxane (cyclic monomer) and three kinds of linear siloxane monomers. As the linear siloxane chain length increases in the CSSQ precursors, the compatibility between the CSSQ precursor and tCD molecules improved due to the chain flexibility of the precursor. Moreover, the mechanical strength of the CSSQ precursor (4ST37) containing linear tetrasiloxane was the best among the prepared precursors. The enhancement of mechanical property might also be attributed to the content of Si-OH groups as well as the chain flexibility, which could help the crosslinking reaction of Si-OH groups in the film curing process. 相似文献
107.
J. H. Lee In-Woo Chang S. J. Byun T. K. Hong K. Rhie W. Y. Lee Kyung-Ho Shin Chanyong Hwang S. S. Lee B. C. Lee 《Journal of magnetism and magnetic materials》2002,240(1-3):137-139
An unusually large enhancement of TMR at 77 K was observed in double barrier tunnel junctions (DBTJ). This is explained with extended Julliere's model which yields a twice larger TMR value. When the spin coherence length is much smaller at higher temperature, DBTJ is shown to work as a series of two single barrier tunnel junctions. 相似文献
108.
考虑了Kantorovich-Vertesi有理插值型算子L^*n,s(f,X,x)对L^p[-1,1](1≤p≤∞)空间函数逼近的Jackson型估计。并获得了如下逼近阶:‖L^*n,s(f,X,x)-f(x)‖L^p[-1,1]≤Cp,sw(f,1/n 2)L^p[-1,1] (s>2)。 相似文献
109.
The conformational preferences of the Cys dipeptides with thiol and thiolate groups (Ac-Cys-NHMe and Ac-Cys (-)-NHMe, respectively) and the apparent (i.e., macroscopic) p K a value of the Cys dipeptide have been studied at the hybrid density functional B3LYP/6-311++G(d,p)//B3LYP/6-31+G(d) level with the conductor-like polarizable continuum model in the gas phase and in water. The hydrogen bonds and/or favorable interactions between the backbone and the thiol group of the side chain resulted in the different conformational preferences of the Cys and Cys (-) dipeptides from those of the Ala dipeptide in the gas phase and in water, although the preferred conformations of the Cys dipeptide are in part similar to those of the Ala dipeptide. In particular, the interactions between the thiolate group and the backbone amide groups appear to play a role in stabilizing the alpha- or 3 10-helical conformations for the Cys (-) dipeptide in the gas phase and in water. The p K a value of the Cys residue is estimated to be 8.58 at 25 degrees C using the statistically weighted free energies of all feasible conformations for the Cys and Cys (-) dipeptides in the gas phase and solvation free energies, which is consistent with the observed values of 8.3 and 8.22 +/- 0.16. 相似文献
110.
Dr. Doyun Kim Dr. Thien S. Nguyen Hyejeong Lee Bolormaa Bayarkhuu Vepa Rozyyev Dr. Jeehye Byun Prof. Sheng Li Prof. Cafer T. Yavuz 《Angewandte Chemie (International ed. in English)》2023,62(28):e202304378
Porous poly(aryl thioether)s offer stability and electronic tunability by robust sulfur-aryl conjugated architecture, but synthetic access is hindered due to limited control over the nucleophilic nature of sulfides and the air sensitivity of aromatic thiols. Here, we report a simple, one-pot, inexpensive, regioselective synthesis of highly porous poly(aryl thioether)s through polycondensation of perfluoroaromatic compounds with sodium sulfide. The unprecedented temperature-dependent para-directing formation of thioether linkages leads to a stepwise transition of the polymer extension into a network, thereby allowing fine control of the porosity and optical band gaps. The obtained porous organic polymers with ultra-microporosity (<1 nm) and sulfur as the surface functional groups show size-dependent separation of organic micropollutants and selective removal of mercury ions from water. Our findings offer easy access to poly(aryl thioether)s with accessible sulfur functionalities and higher complexity, which will help in realizing advanced synthetic designs in applications such as adsorption, (photo)catalysis, and (opto)electronics. 相似文献