全文获取类型
收费全文 | 246篇 |
免费 | 17篇 |
国内免费 | 24篇 |
专业分类
化学 | 26篇 |
晶体学 | 1篇 |
力学 | 10篇 |
综合类 | 6篇 |
数学 | 210篇 |
物理学 | 34篇 |
出版年
2023年 | 3篇 |
2022年 | 3篇 |
2021年 | 2篇 |
2020年 | 3篇 |
2019年 | 5篇 |
2018年 | 3篇 |
2017年 | 4篇 |
2016年 | 6篇 |
2015年 | 5篇 |
2014年 | 9篇 |
2013年 | 13篇 |
2012年 | 4篇 |
2011年 | 9篇 |
2010年 | 8篇 |
2009年 | 8篇 |
2008年 | 22篇 |
2007年 | 18篇 |
2006年 | 19篇 |
2005年 | 16篇 |
2004年 | 10篇 |
2003年 | 13篇 |
2002年 | 19篇 |
2001年 | 17篇 |
2000年 | 8篇 |
1999年 | 7篇 |
1998年 | 4篇 |
1997年 | 11篇 |
1996年 | 6篇 |
1995年 | 3篇 |
1994年 | 6篇 |
1993年 | 4篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1976年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有287条查询结果,搜索用时 375 毫秒
281.
Financial instruments traded in the market are usually subject to mutually dependent default risks, and a default does not always make a zero return for the concerned risky asset. This paper revisits the portfolio selection problem with assets exposed to dependent default risks. To better model the default mechanism, we generalize the threshold default model and the independence default model due to Cheung and Yang (2004) by introducing a smaller nonzero realizable return for a default risky asset. By utilizing stochastic arrangement increasing techniques, we develop sufficient conditions to enable actuaries to order the amount allocated to each asset in the two generalized models. Also, some examples of dependence structures fulfilling the sufficient conditions are presented as illustrations. 相似文献
282.
Intense photoluminescence at room temperature was observed in amorphous cadmium aluminum silicate doped with europium prepared by the sol-gel method. The structure of the 3CdO-Al2O3-3SiO2:Eu3+ system (CAS:Eu3+) has been determined by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The excitation and the emission spectra indicated that the red characteristic emission (611 nm) of CAS:Eu3+ under UV excitation due to 5D0→7F2 electric dipole transition is the strongest. Both XRD data and the emission ratio of (5D0→7F2)/(5D0→7F1) reveal that the Eu3+ is in a site without inversion symmetry. The maximum photoluminescence intensity has been obtained for 25 mol% concentration of Eu3+ in CAS, and the intensity enhancement and lifetime increase of Eu3+ with increasing sintering temperature were observed due to the less OH-content in the samples. 相似文献
283.
Banach空间中一类非单调算子方程解的存在性定理 总被引:3,自引:0,他引:3
运用锥理论与非对称迭代方法,得到了Banach空间不具有单调性、连续性和紧性条件的一类算子的不动点的存在唯一性,并给出了迭代序列收敛于解的误差估计,所得结果改进和推广了增(减)算子方程的某些已知结果. 相似文献
284.
Application of Almost Increasing Sequence for Absolute Riesz $|\overline{N}, p_n^{\alpha, \beta}; \delta|_k$ Summable Factor 下载免费PDF全文
Smita Sonker Rozy Jindal Lakshmi Narayan Mishra 《Journal of Nonlinear Modeling and Analysis》2021,3(3):377-384
In this paper, we generate an extended result by Bor and Seyhan concerning absolute Riesz summability factors. Further, we develop some well-known results from our main result. 相似文献
285.
Xin-Hai Meng Dr. Xu-Dong Zhang Dr. Hang Sheng Dr. Min Fan Ting Lin Dr. Dongdong Xiao Jianxin Tian Prof. Rui Wen Wen-Zhe Liu Prof. Ji-Lei Shi Prof. Li-Jun Wan Prof. Yu-Guo Guo 《Angewandte Chemie (International ed. in English)》2023,62(22):e202302170
Layered transition metal oxide cathodes have been one of the dominant cathodes for lithium-ion batteries with efficient Li+ intercalation chemistry. However, limited by the weak layered interaction and unstable surface, mechanical and chemical failure plagues their electrochemical performance, especially for Ni-rich cathodes. Here, adopting a simultaneous elemental-structural atomic arrangement control based on the intrinsic Ni−Co−Mn system, the surface role is intensively investigated. Within the invariant oxygen sublattice of the crystal, a robust surface with the synergistic concentration gradient and layered-spinel intertwined structure is constructed on the model single-crystalline Ni-rich cathode. With mechanical strain dissipation and chemical erosion suppression, the cathode exhibits an impressive capacity retention of 82 % even at the harsh 60 °C after 150 cycles at 1 C. This work highlights the coupling effect of structure and composition on the chemical-mechanical properties, and the concept will spur more researches on the cathodes that share the same sublattice. 相似文献
286.
《Particuology》2023
The structure of the gas distributor is closely related to the production efficiency of organosilicon monomers. To improve the production efficiency of organosilicon monomers, this study uses Eulerian-Eulerian two fluid model and proposes a design formula for the gas distributor to optimize the gas distributor. It is proposed that the pressure drop of the gas distributor, the velocity nonuniformity coefficient, the relative standard deviation of the solid holdup, and the solid particle dispersion coefficient are used to evaluate the performance of the gas distributor. The results show that the performance of the gas distributor is significantly improved when the opening ratio Φ = 0.53% is optimized to Φ = 0.18%, in which the relative standard deviation of the solid holdup is reduced by 22%, and the solid particle dispersion coefficient is reduced by 40%. On this basis, this article studies the influence of different arrangements of vent holes on gas-solid fluidization characteristics. The results show that the circular arrangement of vent holes is helpful to the mixing of gas and solid. 相似文献
287.
The COVID −19 pandemic reminded us that we need better contingency plans to prevent the spread of infectious agents and the occurrence of epidemics or pandemics. Although the transmissibility of SARS-CoV-2 in water has not been confirmed, there are studies that have reported on the presence of infectious coronaviruses in water and wastewater samples. Since standard water treatments are not designed to eliminate viruses, it is of utmost importance to explore advanced treatment processes that can improve water treatment and help inactivate viruses when needed. This is the first study to investigate the effects of hydrodynamic cavitation on the inactivation of bacteriophage phi6, an enveloped virus used as a SARS-CoV-2 surrogate in many studies. In two series of experiments with increasing and constant sample temperature, virus reduction of up to 6.3 logs was achieved. Inactivation of phi6 at temperatures of 10 and 20 °C occurs predominantly by the mechanical effect of cavitation and results in a reduction of up to 4.5 logs. At 30 °C, the reduction increases to up to 6 logs, where the temperature-induced increased susceptibility of the viral lipid envelope makes the virus more prone to inactivation. Furthermore, the control experiments without cavitation showed that the increased temperature alone is not sufficient to cause inactivation, but that additional mechanical stress is still required. The RNA degradation results confirmed that virus inactivation was due to the disrupted lipid bilayer and not to RNA damage. Hydrodynamic cavitation, therefore, has the potential to inactivate current and potentially emerging enveloped pathogenic viruses in water at lower, environmentally relevant temperatures. 相似文献