全文获取类型
收费全文 | 89篇 |
免费 | 1篇 |
国内免费 | 16篇 |
专业分类
化学 | 68篇 |
晶体学 | 1篇 |
力学 | 16篇 |
数学 | 11篇 |
物理学 | 10篇 |
出版年
2021年 | 2篇 |
2020年 | 1篇 |
2018年 | 1篇 |
2017年 | 1篇 |
2015年 | 2篇 |
2014年 | 3篇 |
2013年 | 2篇 |
2012年 | 7篇 |
2011年 | 6篇 |
2010年 | 8篇 |
2009年 | 15篇 |
2008年 | 8篇 |
2007年 | 4篇 |
2006年 | 1篇 |
2005年 | 4篇 |
2004年 | 1篇 |
2003年 | 6篇 |
2002年 | 5篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1999年 | 4篇 |
1998年 | 1篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1987年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有106条查询结果,搜索用时 46 毫秒
1.
煤炭液化复合铁系催化剂的研究 总被引:1,自引:0,他引:1
用微型高压釜,以杂酚油为溶剂,在反应温度400℃,氢初压6.08MPa,反应时间30分钟的条件下,研究了多种含铁矿物质、复合铁系催化剂对煤炭液化的催化效果。并用高压DTA技术进一步证实了复合铁系催化剂的良好液化加氢活性。 相似文献
2.
Fifteen isomers of [Si,N,C,O]2+ system are obtained at UB3LYP/6-311G(d) and UCCSD(T)/6-311+G(2df) (single-point) levels. The analyses are made for predicting the structures of optimized isomers, while ionic fragments with lower energies are suggested. The calculated results indicate that linear isomer SiNCO2+(2Π) is thermodynamically the most stable species in [Si,N,C,O]2+ system, followed by linear SiOCN2+ (2Π), SiCNO2+ (2Π), and SiC(NO) (2A) with NCO three-membered ring. The order of stability of several kinetically stable isomers is SiNCO2> SiCNO2+ (2Π)>SiOCN2+>SiC(NO)2+>OSiNC2+ (2Π). The obtained results by analyzing the isomerizations and ionic fragment patterns show that the signal peaks of [Si,N,C,O]2+ are attributed to the contribution of linear SiNCO2+ species, which is metastable and can dissociate to the ionic fragments in the mass spectrometry experiments. 相似文献
3.
Zhang Wenfan Liu Yan Cao Shengli Chen Jiahui Zhang Zexia Zhang Jiazhong 《Nonlinear dynamics》2017,90(3):1841-1850
Nonlinear Dynamics - The flow-induced vibration of two-dimensional wing coupled with two nonlinear energy sinks (NESs) under freestream is studied by numerical methods, and the relationship between... 相似文献
4.
Jiazhong Zhang Haiping Xia Yongzhang Jiang Shuo Yang Xuemei Gu Jianli Zhang Haochuan Jiang Baojiu Chen 《Crystal Research and Technology》2015,50(7):574-579
Downconversion (DC) luminescence with emission at about 1000 nm under excitation of 448‐nm light in Ho3+/Yb3+ codoped α‐NaYF4 single crystal is realized. The crystal was grown by the Bridgman method using KF as an assisting flux in a NaF‐YF3 system. The energy‐transfer process and quantum cutting (QC) mechanisms are presented through the analysis of the spectra. The energy‐transfer processes of first‐ and second‐order cooperative DC are responsible for the increase of the emission intensity at 1000 nm, and it is the first‐order cooperative DC that is dominant for the DC process. When the Ho3+ concentration is fixed at about 0.8 mol%, the optimal concentration for ∼1000 nm emission is 3.02 mol% Yb3+ in the current research. The energy‐transfer efficiency and the total quantum efficiency are analyzed through the luminescence decay curves. The maximum quantum cutting efficiency approaches to 184.4% in α‐NaYF4 single crystals of 0.799 mol% Ho3+ and 15.15 mol% Yb3+. However, the emission intensity at 1000 nm decreases while the energy‐transfer efficiency from Ho3+ to Yb3+ increases, which may result from the fluorescence quenching between Ho3+ and Yb3+ ions, Yb3+ and Yb3+ ions. 相似文献
5.
采用不可约张量法,分析了KTbP4O12晶体荧光光谱,拟合了五个晶场参量和八个相对论参量,结果与实验吻合。 相似文献
6.
7.
In this Note, we study the unfolding of a vector field that possesses a degenerate homoclinic (of inclination-flip type) to a hyperbolic equilibrium point where its linear part possesses a resonance. For the unperturbed system, the resonant term associated with the resonance vanishes. After suitable rescaling, the Poincaré return map is a cubic Hénon-like map. We deduce the existence of a strange attractor which persists in the Lebesgue measure sense. We also show the presence of an attractor with topological entropy close to . To cite this article: M. Martens et al., C. R. Acad. Sci. Paris, Ser. I 340 (2005). 相似文献
8.
Jiazhong Yang 《Proceedings of the American Mathematical Society》2003,131(9):2715-2720
We prove that on , except for those germs of vector fields whose linear parts are conjugated to , any two Poincaré type vector fields are at least conjugated to each other provided their linear approximations have the same eigenvalues and the nonlinear parts are generic.
9.
A theoretical approach to polycondensation reaction of Aa-Bb type Involving intramolecular cycllzatlon has been proposed by Tang Au-chin et al.. In this paper, the theoretical sol-gel distribution is tested by polycondensation of adipic acid with trimethylol propane in a sto-ichiometric ratio of 0. 8, and the effect of intramolecular cyclization is discussed in detail. 相似文献
10.
Yan LiuKailun Li Jiazhong Zhang Hang WangLiguang Liu 《Communications in Nonlinear Science & Numerical Simulation》2012,17(8):3427-3434
By the finite element method combined with Arbitrary-Lagrangian-Eulerian (ALE) frame and explicit Characteristic Based Split Scheme (CBS), the complex flows around stationary and sinusoidal pitching airfoil are studied numerically. In particular, the static and dynamic stalls are analyzed in detail, and the natures of the static stall of NACA0012 airfoil are given from viewpoint of bifurcations. Following the bifurcation in Map, the static stall is proved to be the result from saddle-node bifurcation which involves both the hysteresis and jumping phenomena, by introducing a Map and its Floquet multiplier, which is constructed in the numerical simulation of flow field and related to the lift of the airfoil. Further, because the saddle-node bifurcation is sensitive to imperfection or perturbation, the airfoil is then subjected to a perturbation which is a kind of sinusoidal pitching oscillation, and the flow structure and aerodynamic performance are studied numerically. The results show that the large-scale flow separation at the static stall on the airfoil surface can be removed or delayed feasibly, and the ensuing lift could be enhanced significantly and also the stalling incidence could be delayed effectively. As a conclusion, it can be drawn that the proper external excitation can be considered as a powerful control strategy for the stall. As an unsteady aerodynamic behavior of high angle of attack, the dynamic stall can be investigated from viewpoint of nonlinear dynamics, and there exists a rich variety of nonlinear phenomena, which are related to the lift enhancement and drag reduction. 相似文献