全文获取类型
收费全文 | 313篇 |
免费 | 10篇 |
专业分类
化学 | 205篇 |
晶体学 | 2篇 |
力学 | 6篇 |
数学 | 49篇 |
物理学 | 61篇 |
出版年
2023年 | 3篇 |
2022年 | 2篇 |
2021年 | 6篇 |
2020年 | 4篇 |
2019年 | 3篇 |
2018年 | 4篇 |
2016年 | 8篇 |
2015年 | 4篇 |
2014年 | 5篇 |
2013年 | 15篇 |
2012年 | 14篇 |
2011年 | 11篇 |
2010年 | 9篇 |
2009年 | 12篇 |
2008年 | 15篇 |
2007年 | 17篇 |
2006年 | 16篇 |
2005年 | 12篇 |
2004年 | 20篇 |
2003年 | 10篇 |
2002年 | 7篇 |
2001年 | 16篇 |
2000年 | 12篇 |
1999年 | 3篇 |
1998年 | 4篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1989年 | 6篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1984年 | 4篇 |
1983年 | 7篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1974年 | 6篇 |
1972年 | 4篇 |
1971年 | 2篇 |
1970年 | 2篇 |
1969年 | 3篇 |
1940年 | 2篇 |
1927年 | 2篇 |
1913年 | 2篇 |
排序方式: 共有323条查询结果,搜索用时 31 毫秒
81.
82.
I. T. Vieira R. C. H. Cheng P. R. Harper V. de Senna 《Annals of Operations Research》2010,178(1):173-200
It has long been recognised that the structure of social networks plays an important role in the dynamics of disease propagation.
The spread of HIV results from a complex network of social interactions and other factors related to culture, sexual behaviour,
demography, geography and disease characteristics, as well as the availability, accessibility and delivery of healthcare.
The small world phenomenon has recently been used for representing social network interactions. It states that, given some
random connections, the degrees of separation between any two individuals within a population can be very small. In this paper
we present a discrete event simulation model which uses a variant of the small world network model to represent social interactions
and the sexual transmission of HIV within a population. We use the model to demonstrate the importance of the choice of topology
and initial distribution of infection, and capture the direct and non-linear relationship between the probability of a casual
partnership (small world randomness parameter) and the spread of HIV. Finally, we illustrate the use of our model for the
evaluation of interventions such as the promotion of safer sex and introduction of a vaccine. 相似文献
83.
Lu Z Van Wagoner RM Harper MK Hooper JN Ireland CM 《Natural product communications》2010,5(10):1571-1574
Two ring-A-aromatized bile acids, 1 and 2, were isolated from the sponge Sollasella moretonensis, collected from the seabed of northern Queensland. Structures were assigned on the basis of extensive 1D and 2D NMR studies, as well as analysis by HRESIMS. Compound 2 has previously been produced synthetically, though this marks its first isolation from a natural source. 相似文献
84.
The fluorinated natural products 总被引:5,自引:0,他引:5
85.
86.
87.
Si Jia Chan Andrew G. Howe James M. Hook Jason B. Harper 《Magnetic resonance in chemistry : MRC》2009,47(4):342-347
79Br NMR spectroscopy has been used to monitor a series of reactions in which the bromide ion is produced, including the Menschutkin reaction of pyridine with a range of substituted benzyl bromides and a Heck coupling process. In cases where the process could also be monitored using 1H NMR spectroscopy, the kinetic analyses using heteronuclear magnetic resonance spectroscopy were shown to be completely consistent. Both the utility of the process in following reactions which may be difficult to analyse using other techniques and the practical limitations associated with solvent choice are discussed. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
88.
89.
90.
J.L. Duncan J. Harper E. Hamilton G.D. Nivellini 《Journal of Molecular Spectroscopy》1983,102(2):416-440
A total of 114 spectroscopic data accumulated from 6 isotopic species of diborane have been used to permit a precise determination of the empirical harmonic potential function to be made for the first time. Of the 33 independent force constants, 30 can be determined with numerical significance. The physical significance of the values is probably best demonstrated by the rather close correspondence throughout with scaled ab initio force constants from two sources, only one rather large disagreement in magnitude being found. The potential function reproduces all known frequency, isotopic frequency shift, Coriolis ζ, and centrifugal distortion Δ data to high accuracy. It is used to calculate parameters which will be of value to further spectroscopic and structural studies, to enable accurate analyses to be made of a number of major Fermi resonance interactions present in the spectra, and to explain the anomalously small Coriolis interaction between the infrared active rocking and wagging fundamentals. The advantages of alternative symmetry coordinate definitions are considered, particularly in relation to making comparisons between diborane and ethylene. 相似文献