全文获取类型

收费全文 |
174篇 |

免费 |
27篇 |

专业分类

化学 |
135篇 |

力学 |
3篇 |

数学 |
11篇 |

物理学 |
52篇 |

出版年

2022年 |
3篇 |

2021年 |
8篇 |

2020年 |
7篇 |

2019年 |
12篇 |

2018年 |
5篇 |

2017年 |
11篇 |

2016年 |
14篇 |

2015年 |
13篇 |

2014年 |
11篇 |

2013年 |
31篇 |

2012年 |
17篇 |

2011年 |
11篇 |

2010年 |
10篇 |

2009年 |
10篇 |

2008年 |
14篇 |

2007年 |
5篇 |

2006年 |
7篇 |

2005年 |
2篇 |

2004年 |
1篇 |

2003年 |
1篇 |

2002年 |
1篇 |

2000年 |
1篇 |

1998年 |
1篇 |

1995年 |
3篇 |

1990年 |
1篇 |

1985年 |
1篇 |

**排序方式：**共有201条查询结果，搜索用时 15 毫秒

1.

A new dirhenium(I) complex

*fac*-[{Re(CO)_{3}(4,7-dinonadecyl-1,10-phenanthro -line)}_{2}(4,4′-bipyridyl)] (trifluoromethanesulfonate)_{2}(denoted as D-Re(I) ) is assembled in MCM-41 and SBA-15 type mesoporous silica support. The emission peaks of D-Re(I) in D-Re(I)/MCM-41 and D-Re(I)/SBA-15 are observed at 522 and 517 nm, respectively. Their long excited lifetimes, which are of the order of microseconds, indicate the presence of phosphorescence emission arising from the metal to ligand charge-transfer (MLCT) transition. The luminescence intensities of D-Re(I)/MCM-41 and D-Re(I)/SBA-15 decrease remarkably with increase in the oxygen concentration, meaning that they can be used as optical oxygen sensing materials based on luminescence quenching. The ratios*I*_{0}/*I*_{100}of D-Re(I)/MCM-41 and D-Re(I)/SBA-15 are estimated to be 5.6 and 20.1, respectively. The obtained Stern-Volmer oxygen quenching plots of the mesoporous sensing materials could be fitted well to the two-site Demas model and Lehrer model. 相似文献2.

A class of piecewise linear paths, as a generalization of Littelmann’s paths, are introduced, and some operators, acting on
the above paths with fixed parametrization, are defined. These operators induce the ordinary Littelmann’s root operators’
action on the equi-alence classes of paths. With these induced operators, an explicit realization of

*B*(∞) is given in terms of equivalence classes of paths, where*B*(∞) is the crystal base of the negative part of a quantum group*U*_{ q }(g). Furthermore, we conjecture that there is a complete set of representatives for the above model by fixing a parametrization, and we prove the case when g is of finite type. 相似文献3.

4.

5.

6.

This paper reports numerical convergence study for simulations of steady shock‐induced combustion problems with high‐resolution shock‐capturing schemes. Five typical schemes are used: the Roe flux‐based monotone upstream‐centered scheme for conservation laws (MUSCL) and weighted essentially non‐oscillatory (WENO) schemes, the Lax–Friedrichs splitting‐based non‐oscillatory no‐free parameter dissipative (NND) and WENO schemes, and the Harten–Yee upwind total variation diminishing (TVD) scheme. These schemes are implemented with the finite volume discretization on structured quadrilateral meshes in dimension‐by‐dimension way and the lower–upper symmetric Gauss–Seidel (LU–SGS) relaxation method for solving the axisymmetric multispecies reactive Navier–Stokes equations. Comparison of iterative convergence between different schemes has been made using supersonic combustion flows around a spherical projectile with Mach numbers

*M*= 3.55 and 6.46 and a ram accelerator with*M*= 6.7. These test cases were regarded as steady combustion problems in literature. Calculations on gradually refined meshes show that the second‐order NND, MUSCL, and TVD schemes can converge well to steady states from coarse through fine meshes for*M*= 3.55 case in which shock and combustion fronts are separate, whereas the (nominally) fifth‐order WENO schemes can only converge to some residual level. More interestingly, the numerical results show that all the schemes do not converge to steady‐state solutions for*M*= 6.46 in the spherical projectile and*M*= 6.7 in the ram accelerator cases on fine meshes although they all converge on coarser meshes or on fine meshes without chemical reactions. The result is based on the particular preconditioner of LU–SGS scheme. Possible reasons for the nonconvergence in reactive flow simulation are discussed.Copyright © 2012 John Wiley & Sons, Ltd. 相似文献7.

Bin Li Haoyu Liu Muhammad Amin Lindsay A. Wegiel Lynne S. Taylor Kevin J. Edgar 《Cellulose (London, England)》2013,20(4):2137-2149

Naringenin (Nar) is an important bioactive flavonoid with poor organic solubility and oral bioavailability. It is highly promising for treatment of conditions including diabetes, hyperlipidemia, and hepatitis C infection. Amorphous solid dispersion (ASD) of Nar is an appealing way to enhance its solubility, and carboxylated cellulose esters are attractive polymers for this purpose because of their ability to stabilize drugs against crystallization in both solid and solution phases, while restricting drug release to the pH of the small intestine (ca. 6.8). We demonstrate that ASDs of Nar can be formed using such carboxylated cellulose derivatives as cellulose acetate adipate propionate (CAAdP), carboxymethylcellulose acetate butyrate (CMCAB) and hydroxypropylmethylcellulose acetate succinate (HPMCAS). We compare Nar solution concentrations and release profiles from these cellulosic ASDs to those from pure crystalline Nar, and to Nar ASD in poly(vinylpyrrolidinone) (PVP). We show that all polymers in this study form ASDs with Nar, that the PVP ASDs release Nar at both gastric (1.2) and small intestine (6.8) pH, and that the cellulosic polymers release Nar selectively at neutral pH. Solution concentrations of Nar are significantly enhanced from these ASDs. These preliminary studies indicate that HPMCAS, CAAdP, and CMCAB are practical ASD polymers for Nar due to their ability to generate and stabilize high solution concentrations, and their pH-triggered drug release. 相似文献

8.

In this paper, we prove the existence and uniqueness of the local mild solution to the Cauchy problem of the

*n*‐dimensional (*n*≥3) Wigner–Poisson–BGK equation in the space of some integrable functions whose inverse Fourier transform are integrable. The main difficulties in establishing mild solution are to derive the boundedness and locally Lipschitz properties of the appropriate nonlinear terms in the Wiener algebra. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献9.

This study presents a tapered zero-thickness finite element model together with its parameter identification method for modelling the spindle–holder taper joint in machine tools. In the presented model, the spindle and the holder are modelled as solid elements and the taper joint is modelled as a tapered zero-thickness finite element with stiffness and damping but without mass or thickness. The proposed model considers not only the coupling of adjacent degrees of freedom but also the radial, tangential and axial effects of the spindle–holder taper joint. Based on the inverse relationship between the dynamic matrix and frequency response function matrix of a multi-degree-of-freedom system, this study proposes a combined analytical–experimental method to identify the stiffness matrix and damping coefficient of the proposed tapered zero-thickness finite element. The method extracts those parameters from FRFs of an entire specimen that contains only the spindle–holder taper joint. The simulated FRF obtained from the proposed model matches the experimental FRF quite well, which indicates that the presented method provides high accuracy and is easy to implement in modelling the spindle–holder taper joint. 相似文献

10.

Yu He Sen Liao Zhipeng Chen Yu Li Yao Xia Wenwei Wu Bin Li 《Journal of Thermal Analysis and Calorimetry》2014,115(1):237-245

The precursor of LiNiPO

_{4}was synthesized by solid-state reaction at low-heating temperature using LiOH·H_{2}O and NH_{4}NiPO_{4}·H_{2}O as raw materials. LiNiPO_{4}was obtained by calcining the precursor. Based on the advanced isoconversional procedure and the distributed activation energy model (DAEM), the activation energies calculated indicated that the thermal process involved two stages which stage II was a kinetically complex process, but stage I was single-step process. The most probable mechanism for the stage I is random nucleation and subsequent growth. DAEM and nonlinear model-fitting method were applied to study the stage II of decomposition process of the precursor. The distributions of activation energy,*f*(*E*_{a}) and values of preexponential factor*A*of the stage II of the thermal decomposition of precursor were obtained on the basis of DAEM. The results of nonlinear model-fitting method showed the most probable mechanisms of the parallel reactions for stage II are chemical reaction and nucleation. 相似文献