全文获取类型
收费全文 | 254篇 |
免费 | 41篇 |
国内免费 | 4篇 |
专业分类
化学 | 162篇 |
晶体学 | 2篇 |
力学 | 39篇 |
综合类 | 6篇 |
数学 | 31篇 |
物理学 | 59篇 |
出版年
2024年 | 1篇 |
2023年 | 5篇 |
2021年 | 3篇 |
2020年 | 5篇 |
2019年 | 6篇 |
2018年 | 4篇 |
2017年 | 1篇 |
2016年 | 5篇 |
2015年 | 11篇 |
2014年 | 10篇 |
2013年 | 17篇 |
2012年 | 13篇 |
2011年 | 14篇 |
2010年 | 15篇 |
2009年 | 12篇 |
2008年 | 5篇 |
2007年 | 7篇 |
2006年 | 5篇 |
2005年 | 8篇 |
2004年 | 8篇 |
2003年 | 23篇 |
2002年 | 30篇 |
2001年 | 32篇 |
2000年 | 13篇 |
1999年 | 10篇 |
1998年 | 5篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 2篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1970年 | 2篇 |
排序方式: 共有299条查询结果,搜索用时 15 毫秒
71.
In this paper, we prove that the modified implicit iteration sequence for a finite family of relatively weak quasi-nonexpansive mappings converges strongly to a common fixed point of the family in the framework of Banach spaces. Our results improve and extend the results announced by many others. 相似文献
72.
73.
74.
75.
Clinical laboratory tests provide critical information at every stage of the medical decision‐making process, and measurement of the activity levels of enzymes such as alkaline phosphatase, lactate dehydrogenase, etc. provide information regarding various body functions such as the liver and gastrointestinal tract. The uncertainty associated with these enzyme measurement processes describes the quality of the measurement process, and therefore methods to improve the quality of the measurement process require minimizing the measurement uncertainty of the enzyme assay. In this study, we develop a mathematical model of the lactate dehydrogenase measurement process, with uncertainty introduced into its parameters that represent the sources of variation in the different components and stages of the measurement process. The Monte Carlo method is then utilized to estimate the uncertainty associated with the model, and therefore the measurement process. An empirical function used to generate estimates of uncertainty for patient samples with unknown activity levels is constructed using the model. The model is then used to quantify the contributions of the individual sources of uncertainty to the net measurement uncertainty and also quantify the effect of uncertainty within the calibration process on the distribution of the measurement result. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
76.
In this study, the microwave dielectric properties of (1‐x)La(Mg0.5Sn0.5)O3‐x(Sr0.8Ca0.2)3Ti2O7 ceramic system prepared by the conventional solid‐state method have been investigated for application in mobile communication. It was found that the diffraction peaks of (1‐x)La(Mg0.5Sn0.5)O3‐x(Sr0.8Ca0.2)3Ti2O7 ceramic system shift to higher angles as x increases from 0.2 to 0.4. It was also found that the X‐ray diffraction patterns of the 0.8La(Mg0.5Sn0.5)O3‐0.2(Sr0.8Ca0.2)3Ti2O7 ceramics exhibited no significant phase difference at different sintering temperatures. The average grain size of the (1‐x)La(Mg0.5Sn0.5)O3‐x(Sr0.8Ca0.2)3Ti2O7 ceramic system decreased from 6.4 to 4.3 μm as the value of x increased from 0.2 to 0.4 sintered at 1550 °C for 4 h. The dielectric constant increased from 26.6 to 35.9 and the quality factor (Q×f) decreased from 31,600 to 23,300 GHz for (1‐x)La(Mg0.5Sn0.5)O3‐x(Sr0.8Ca0.2)3Ti2O7 ceramic system as the x value increases from 0.2 to 0.4 sintered at 1550 °C for 4 h. The average value of temperature coefficient of resonant frequency (τf) increased from ‐18 to +8 ppm/ K as the x value increases from 0.2 to 0.4. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
77.
The chitosan‐Schiff base supported palladium and cobalt bimetallic complex was synthesized in a simple method and characterized by Fourier‐transform infrared spectroscopy (FT‐IR), powder X‐ray diffraction (XRD), and X‐ray photoelectron spectra (XPS). It was found that the catalyst has great activity and stability in the coupling of acrylamide (AA) with the phenyl halide. The influence of various bimetallic catalysts, the different molar ratio of Co/Pd, the bases, the amount of the catalyst and base, and the molar ratio of iodobenzene/AA on the reaction were investigated. The results showed that the catalytic activity of the molar ratio of Co/Pd (3/1) was the best when the iodobenzene was used as a substrate. The yield of the cinnamamide did not change significantly after ten runs. It has been revealed that the catalyst was efficient for the reaction. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
78.
Kuang‐Hway Yih Hsiao‐Fen Wang Keh‐Feng Huang Chang‐Chi Kwan Gene‐Hsiang Lee 《中国化学会会志》2009,56(4):718-724
Treatment of Pd(PPh3)4 with 2‐bromo‐3‐hydroxypyridine [C5H3N(OH)Br] and 3‐amino‐2‐bromopyridine [C5H3N(NH2)Br] in dichloromethane at ambient temperature cause the oxidative addition reaction to produce the palladium complex [Pd(PPh3)2{η1‐C5H3N(OH)}(Br)], 2 and [Pd(PPh3)2{η1‐C5H3N(NH2)}(Br)], 3 , by substituting two triphenylphosphine ligands, respectively. In dichloromethane solution of complexes 2 and 3 at ambient temperature for 3 days, it undergo displacement of the triphenylphosphine ligand to form the dipalladium complexes [Pd(PPh3)Br]2{μ,η2‐C5H3N(OH)}2, 4 and [Pd(PPh3)Br]2{μ,η2‐C5H3N(NH2)}2, 5 , in which the two 3‐hydroxypyridine and 3‐aminopyridine ligands coordinated through carbon to one metal center and bridging the other metal through nitrogen atom, respectively. Complexes 4 and 5 are characterized by X‐ray diffraction analyses. 相似文献
79.
Through the study of photodissociation events in the CS(2) molecule that originate in various selected vibrational modes, but terminate in the same final predissociation state, we looked for the evidence that photodissociation processes can depend on the initial conditions. Such dependence would not occur within RRKM theory, because of its statistical assumptions. The experimental results were compared with trajectory calculations in normal mode coordinates, in which initial conditions were given in terms of coordinates and momenta. We have found that the photodissociation rate for events originating in the combination nu(1), nu(2) mode is higher than that for events from the pure nu(2) mode, and shows a large variation along the vibrational progression. The experimental observations agree with the trajectory calculations. In addition, the trajectory calculations predict that photodissociation events initiated at small values of the vibrational coordinates result in larger dissociation rates at low excess energy above the dissociation limit, while events from large values of the coordinates result in larger dissociation rates at high excess energies. 相似文献
80.
Using a scanning probe lithography method known as nanografting in conjunction with knowledge of self-assembly chemistry, regulation of the heterogeneity of self-assembled monolayers (SAMs) is demonstrated. While nanografting in single-component thiols produces areas of SAMs with designed geometry and size, nanofabrication in mixed thiol solution yields segregated domains. The reaction mechanism in nanografting differs significantly from self-assembly in mix-and-grow methods, as proven in systematic studies reported in this article and a companion paper of theoretical calculations of the nanografting process. Knowledge of the reaction pathways enables development of methods for shifting the interplay between the kinetics and thermodynamics in SAM formation, and thus the heterogeneity of mixed SAMs. By varying fabrication parameters, such as shaving speed, and reaction conditions, such as concentration and ratio of the components, the lateral heterogeneity can be adjusted ranging from near molecular mixing to segregated domains of several to tens of nanometers. 相似文献