全文获取类型
收费全文 | 308篇 |
免费 | 5篇 |
国内免费 | 1篇 |
专业分类
化学 | 195篇 |
力学 | 17篇 |
数学 | 28篇 |
物理学 | 74篇 |
出版年
2021年 | 2篇 |
2020年 | 4篇 |
2019年 | 4篇 |
2018年 | 4篇 |
2017年 | 2篇 |
2016年 | 6篇 |
2015年 | 2篇 |
2014年 | 4篇 |
2013年 | 12篇 |
2012年 | 13篇 |
2011年 | 13篇 |
2010年 | 10篇 |
2009年 | 9篇 |
2008年 | 8篇 |
2007年 | 10篇 |
2006年 | 17篇 |
2005年 | 7篇 |
2004年 | 9篇 |
2003年 | 11篇 |
2002年 | 8篇 |
2001年 | 4篇 |
2000年 | 5篇 |
1999年 | 5篇 |
1998年 | 7篇 |
1997年 | 2篇 |
1996年 | 4篇 |
1995年 | 5篇 |
1994年 | 5篇 |
1993年 | 2篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 2篇 |
1989年 | 5篇 |
1987年 | 2篇 |
1986年 | 5篇 |
1985年 | 8篇 |
1984年 | 10篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1977年 | 9篇 |
1976年 | 5篇 |
1975年 | 4篇 |
1974年 | 8篇 |
1973年 | 7篇 |
1925年 | 2篇 |
1906年 | 1篇 |
排序方式: 共有314条查询结果,搜索用时 876 毫秒
51.
We study the finite-size effects associated with the appearance of a light, i.e. Goldstone, particle in the Kogut-Susskind lattice gauge theory. We analytically study the order parameter and the two-meson propagator in the strong coupling limit on a finite lattice. We give their explicit interpolations between the broken phase of the infinite-volume limit and the symmetric one of the finite system. We argue that the results obtained in the strong coupling limit are more general. 相似文献
52.
Andrew M. Raim Nagaraj K. Neerchal Jorge G. Morel 《Journal of computational and graphical statistics》2018,27(3):587-601
Finite mixture distributions arise in sampling a heterogeneous population. Data drawn from such a population will exhibit extra variability relative to any single subpopulation. Statistical models based on finite mixtures can assist in the analysis of categorical and count outcomes when standard generalized linear models (GLMs) cannot adequately express variability observed in the data. We propose an extension of GLMs where the response follows a finite mixture distribution and the regression of interest is linked to the mixture’s mean. This approach may be preferred over a finite mixture of regressions when the population mean is of interest; here, only one regression must be specified and interpreted in the analysis. A technical challenge is that the mixture’s mean is a composite parameter that does not appear explicitly in the density. The proposed model maintains its link to the regression through a certain random effects structure and is completely likelihood-based. We consider typical GLM cases where means are either real-valued, constrained to be positive, or constrained to be on the unit interval. The resulting model is applied to two example datasets through Bayesian analysis. Supporting the extra variation is seen to improve residual plots and produce widened prediction intervals reflecting the uncertainty. Supplementary materials for this article are available online. 相似文献
53.
Jean-Claude Jumas Moulay Tahar Sougrati Alexis Perea Laurent Aldon Josette Olivier-Fourcade 《Hyperfine Interactions》2013,217(1-3):107-115
The performances of Li-ion batteries depend on many factors amongst which the important ones are the electrode materials and their structural and electronic evolution upon cycling. For a better understanding of lithium reactivity mechanism of many materials the combination of X-Ray Powder Diffraction (XRPD) and Transmission Mössbauer Spectroscopy (TMS) providing both structural and electronic information during the electrochemical cycling has been carried out. Thanks to the design of a specific electrochemical cell, derived from a conventional Swagelock cell, such measurements have been realised in operando mode. Two examples illustrate the greatness of combining XRPD and TMS for the study of LiFe0.75Mn0.25PO4 as positive electrode and TiSnSb as negative electrode. Different kinds of insertion or conversion reactions have been identified leading to a better optimization and design of performing electrodes. 相似文献
54.
55.
We present in this paper a general decomposition framework to solve exactly adjustable robust linear optimization problems subject to polytope uncertainty. Our approach is based on replacing the polytope by the set of its extreme points and generating the extreme points on the fly within row generation or column-and-row generation algorithms. The novelty of our approach lies in formulating the separation problem as a feasibility problem instead of a max–min problem as done in recent works. Applying the Farkas lemma, we can reformulate the separation problem as a bilinear program, which is then linearized to obtained a mixed-integer linear programming formulation. We compare the two algorithms on a robust telecommunications network design under demand uncertainty and budgeted uncertainty polytope. Our results show that the relative performance of the algorithms depend on whether the budget is integer or fractional. 相似文献
56.
57.
Reactions of α‐thioxothioamides ( 1 ) with diisothiocyanates were carried out in the hope of generating the N,N′‐bis(1,3‐thiazoline‐2‐thiones) ( A ). Although that purpose could not be achieved, we succeeded in preparing the monocycloadducts 7 from the phenylene‐1,2‐diisothiocyanate ( 4 ). The benzimidazole derivatives 8 and 9 were also characterized and a mechanism was assumed to account for this intramolecular process. On the other hand, the regioselective synthesis of the N,N′‐biimidazole ( 13 ) containing the phenylene bridge was performed by the treatment of the 5‐aminothiazolium chloride ( 2 ) with the diisothiocyanate ( 4 ) in a basic medium. The mesoionic derivative 13 probably arises from the monoimidazolium‐4‐thiolate ( 12 ) which was shown to react with the salt 2 under similar conditions to give the primary cycloadduct 14 as an intermediate towards the bis(imidazolium) ( 13 ). © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:617–624, 2001 相似文献
58.
A number of 2‐(dialkylamino)‐5‐(methylthio)imidazoles 2 are obtained by treating the formamidinium iodides 1a,b with isocyanides R3 NC under mild conditions. Reduction of these species can occur in the reaction medium to furnish the corresponding imidazoles 3 . In some cases, double cycloaddition across the imine bond of starting salts 1 also provides the (azetidin‐1‐yl‐methylene)ammonium iodides 4 . Reactions with tert‐butyl and isopropyl isocyanides in refluxing acetonitrile convert the acetamidinium iodide 1c into the 3,5‐diamino‐2H‐pyrrolium salts 7 . Mechanisms are suggested to account for these ring‐closure processes. © 2000 John Wiley & Sons, Inc. Heteroatom Chem 11:370–376, 2000 相似文献
59.
60.
In the nuclear fuel cycle, fluorine is currently not recycled. In this paper, we have examined the possible routes to implement such a cycle. Because UF6 deconversion requires an excess of water, aqueous HF is produced. Two alternatives are then possible: either separate HF from H2O or recycle the HF-H2O in the deconversion process. Alternative UF6 deconversion could also be implemented to resorb the high UF6 inventory. 相似文献