全文获取类型
| 收费全文 | 534篇 |
| 免费 | 1篇 |
| 国内免费 | 5篇 |
专业分类
| 化学 | 331篇 |
| 晶体学 | 13篇 |
| 力学 | 13篇 |
| 数学 | 61篇 |
| 物理学 | 122篇 |
出版年
| 2021年 | 8篇 |
| 2020年 | 7篇 |
| 2019年 | 7篇 |
| 2017年 | 3篇 |
| 2016年 | 12篇 |
| 2015年 | 6篇 |
| 2014年 | 16篇 |
| 2013年 | 13篇 |
| 2012年 | 27篇 |
| 2011年 | 28篇 |
| 2010年 | 11篇 |
| 2009年 | 11篇 |
| 2008年 | 22篇 |
| 2007年 | 18篇 |
| 2006年 | 27篇 |
| 2005年 | 31篇 |
| 2004年 | 22篇 |
| 2003年 | 22篇 |
| 2002年 | 22篇 |
| 2001年 | 12篇 |
| 2000年 | 17篇 |
| 1999年 | 18篇 |
| 1998年 | 11篇 |
| 1997年 | 4篇 |
| 1996年 | 8篇 |
| 1995年 | 3篇 |
| 1994年 | 3篇 |
| 1993年 | 9篇 |
| 1992年 | 10篇 |
| 1991年 | 6篇 |
| 1990年 | 7篇 |
| 1989年 | 5篇 |
| 1988年 | 8篇 |
| 1986年 | 11篇 |
| 1985年 | 6篇 |
| 1984年 | 8篇 |
| 1983年 | 5篇 |
| 1982年 | 8篇 |
| 1981年 | 9篇 |
| 1980年 | 5篇 |
| 1979年 | 4篇 |
| 1978年 | 5篇 |
| 1977年 | 3篇 |
| 1976年 | 5篇 |
| 1975年 | 9篇 |
| 1974年 | 3篇 |
| 1973年 | 7篇 |
| 1971年 | 4篇 |
| 1969年 | 2篇 |
| 1968年 | 3篇 |
排序方式： 共有540条查询结果，搜索用时 0 毫秒
91.
Steen Hildebrandt 《European Journal of Operational Research》1981,8(2):123-129
The article deals with information in the OR process. The value of an ‘optimal’ model solution which is not implemented is not very high. Many errors are due to a too narrow formulation of the problem, often a formulation which has focused on purely technical and economic aspects, or a formulation which has been adapted for a standard model. The concepts and models treated in the article take their point of departure in the actual problem. The models can be used as a frame of reference by various individuals and groups which are involved in OR work. 相似文献
92.
Thin films of poly(methyl methacrylate) (PMMA) (25 nm) deposited on gold coated glass substrates have been locally modified by exposure to biased atomic force microscopy (AFM) tips. Constant exposure currents in the range of 0.5–0.65 nA leads to removal of PMMA both by direct ablation and enhanced solubility in a developer solution. Possible mechanisms causing such modifications have been discussed. Submicron Au structures were formed by combining AFM lithography, involving localized removal of PMMA, with sputter deposition of gold and a lift-off process. 相似文献
93.
94.
Mössbauer spectroscopy has been widely used for determining the ferric/ferrous ratio in amorphous rock samples to reveal the oxygen pressure in the melt. In the present investigation, Mössbauer spectroscopy in conjunction with melting experiments at controlled oxygen pressures was used to determine the rates of redox reactions in basaltic melts at 1300°C. The samples were kept at a fixed oxygen pressure long enough to reach equilibrium at a well established ferric/ferrous ratio. Then, the oxygen fugacity in the furnace was changed abruptly and the samples were kept for different lengths of time, from 15 min, to 4 hrs, at the new condition. At the end of each run the samples were quenched and the ferric/ferrous ratio analyzed by Mössbauer spectroscopy. A geological corollary of our results is that natural volcanic glasses, representing quenched melts, retain and reflect the oxidation state in the melt immediately prior to eruption, and hence the oxygen fugacity in the magma. 相似文献
95.
In this work, the usefulness of the inverse Laplace transformation (ILT) in the characterization of diffusion processes in the brain has been investigated. The method has been implemented on both phantom and in vivo cat brain data acquired at high resolution at 9.4 T. The results were compared with monoexponential and biexponential analyses of the same data. It is shown that in the case of diffusion restricted by white matter axonal tracts, the resulting diffusograms are in good agreement with the biexponential model. In gray matter, however, the non-monoexponential decay does not lead to a bimodal distribution in the ILT, even though the data can be fitted to a biexponential. This finding suggests the possibility of a distribution of diffusion coefficients rather than a discrete biexponential behavior. It is shown that this distribution is sensitive, for example, to experimental parameters such as the diffusion time. Thus, the ILT offers the possibility of implementing a unique tool for the analysis of heterogeneous diffusion, that is, the analysis of the diffusion coefficient distribution, which has the yet unexplored potential of being a valuable parameter in the characterization of tissue structure. 相似文献
96.
Steen RG Hunte M Traipe E Hurh P Wu S Bilaniuk L Haselgrove J 《Magnetic resonance imaging》2004,22(3):299-306
Measurement of tissue spin lattice relaxation time (T(1)) has been used to characterize brain development in healthy children. Here we report the first study of brain T(1) in young children with sickle cell disease (SCD). The T(1) in 10 tissue samples was measured by established techniques; 46 SCD patients under the age of 4 years were compared to 267 controls, including 55 well children under the age of 4 years. A model was developed to predict the relationship between age and brain T(1) in controls, then we compared patient T(1) to healthy normal T(1). Most white matter and gray matter tissues in infant patients (<2 years old), had T(1) values significantly higher than normal. For example, 15.0% of patient caudate T(1) values were above the upper bound of the 95% confidence interval for controls, but only 2.5% of normal values are expected to be this high (p = 0.0003). Among infant patients, brain T(1) was significantly higher than normal in every tissue (p < 0.01) except cortical gray matter. However, patient T(1) values declined rapidly to values lower than normal by about age 4. Our findings imply that patients follow an abnormal developmental trajectory beginning early in infancy. 相似文献
97.
A. C. Der Van Steen 《physica status solidi b》1980,100(2):603-611
The luminescence properties of Bi3+-activated Cs2NaYCl6 crystals are presented. The Bi3+ ion (6s2) occupies an Y3+ site which has cubic symmetry. Excitation in the A absorption band yields 3T1u emission. Excitation in the C absorption band, however, yields 3T1u and 3A1u emission, because both levels are populated by nonradiative processes from the 1T1u excited state. The emission and excitation spectra show vibrational structure. The vibronic lines are assigned and discussed. 相似文献
98.
Steen Pedersen 《Proceedings of the American Mathematical Society》2004,132(7):2095-2101
Suppose that where are real numbers such that and The union is not assumed to be disjoint. It is shown that the translates , , tile the real line for some bounded measurable set if and only if the exponentials , , form an orthogonal basis for some bounded measurable set
99.
Malene Steen Nielsen Flagga 《International Journal of Theoretical Physics》1999,38(8):2121-2161
Is time travel possible? While this paper doesnot answer the question, it does put forward a modelthat may one day answer it. The decoherent-historiesapproach to quantum mechanics is used in a nontrivial background provided by a wormhole whose mouthsreside in the same universe, but have a time differencebetween them. A charged scalar particle approaches thewormhole mouth in the present and is decohered spatially through the interaction with theCoulomb field of the wormhole mouth. 相似文献
100.
J.M. Lee K.G. Watkins W.M. Steen 《Applied Physics A: Materials Science & Processing》2000,71(6):671-674
Laser removal of small particles from a metal surface is carried out by changing the incident angle of the laser beam. It
has been found that a dramatic improvement of cleaning efficiency in terms of area and energy is observed when using the laser
at glancing angle of incidence as compared to perpendicular. Furthermore substrate damage is greatly reduced and probably
eliminated at glancing angles. The process mechanism is discussed by considering the adhesion and the laser-induced cleaning
forces for different incident angles. It is shown that there are different laser–matter interactions operating.
Received: 25 April 2000 / Accepted: 9 May 2000 / Published online: 5 October 2000 相似文献