全文获取类型
收费全文 | 436篇 |
免费 | 17篇 |
国内免费 | 1篇 |
专业分类
化学 | 345篇 |
力学 | 21篇 |
数学 | 28篇 |
物理学 | 60篇 |
出版年
2022年 | 6篇 |
2021年 | 3篇 |
2020年 | 6篇 |
2019年 | 3篇 |
2018年 | 3篇 |
2017年 | 4篇 |
2016年 | 11篇 |
2015年 | 9篇 |
2014年 | 15篇 |
2013年 | 21篇 |
2012年 | 18篇 |
2011年 | 40篇 |
2010年 | 23篇 |
2009年 | 15篇 |
2008年 | 30篇 |
2007年 | 22篇 |
2006年 | 24篇 |
2005年 | 31篇 |
2004年 | 17篇 |
2003年 | 13篇 |
2002年 | 14篇 |
2001年 | 5篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1998年 | 6篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 9篇 |
1991年 | 5篇 |
1990年 | 8篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 6篇 |
1983年 | 8篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1972年 | 2篇 |
1971年 | 2篇 |
1955年 | 2篇 |
1948年 | 6篇 |
排序方式: 共有454条查询结果,搜索用时 31 毫秒
91.
92.
Gerrit L'abb Maria Bruynseels Pieter Delbeke Suzanne Toppet 《Journal of heterocyclic chemistry》1990,27(7):2021-2027
The two structural isomers, 4 and 5 , of 1-substituted-4-iminomethyl-1,2,3-triazoles are interconvertible when heated in dimethyl sulfoxide at 80°. The equilibrium position depends on the electronic properties of the R-substituent, favoring 5 for R = alkyl, benzyl and anisyl, and 4 for p-chlorophenyl and p-nitrophenyl. An interesting application is the synthesis of 1-alkyl-1,2,3-triazole-4-carbaldehydes from 1-phenyl-1,2,3-triazole-4-carbaldehyde by Scheme I. The hydrazones 4ij and the oxime 4k do not rearrange due to an unfavorable Z-configuration around the C ? N bond, whereas the acyloximino derivative 4m is converted into the nitrile 11 . The structures of the products have been fully characterized by 13C nmr spectroscopy and the mechanistic details of the rearrangement are discussed. 相似文献
93.
94.
Juan F. Vega Denka G. Hristova Gerrit W. M. Peters 《Journal of Thermal Analysis and Calorimetry》2009,98(3):655-666
We investigated the effect of flow in combination with molecular architecture on crystallization for linear and branched polypropylenes
by means of dynamical mechanical spectroscopy. Compared to the linear polymer, the branched one exhibits much slower relaxation
after deformation, causing higher levels of molecular orientation and molecular stretch for the same flow conditions. Different
regimes of flow-induced crystallization are observed as a function of an increased level of molecular orientation and stretch.
These regime changes cause the structure development in the material to vary from 3-dimensional spherulitical growth to nearly
1-dimensional fiber-like growth. Intermediate behavior is observed when the flow is strong (for the linear polymer) or weak
enough (for the branched polymer), or in time when the effect of flow is exhausting. It is important to note that dynamical
mechanical measurements can be used to probe different aspects of the (flow induced) crystallization process, such as a relative
level of crystallinity and timescales of the evolution, but do not give absolute values. A correlation is found with the level
of crystallinity obtained from real-time WAXS measurements and the kinetics of linear viscoelastic properties, but this correlation
is not unique and depends on the pre-shear conditions applied. 相似文献
95.
96.
Ohne Zusammenfassung 相似文献
97.
98.
99.
The electron transport properties of hybrid ferromagnetic|normal metal structures such as multilayers and spin valves depend on the relative orientation of the magnetization direction of the ferromagnetic elements. Whereas the contrast in the resistance for parallel and antiparallel magnetizations, the so-called giant magnetoresistance, is relatively well understood for quite some time, a coherent picture for non-collinear magnetoelectronic circuits and devices has evolved only recently. We review here such a theory for electron charge and spin transport with general magnetization directions that is based on the semiclassical concept of a vector spin accumulation. In conjunction with first-principles calculations of scattering matrices many phenomena, e.g. the current-induced spin-transfer torque, can be understood and predicted quantitatively for different material combinations. 相似文献
100.
Kim H Dooley KS Groenenboom GC North SW 《Physical chemistry chemical physics : PCCP》2006,8(25):2964-2971
We have studied the v'-dependent predissociation dynamics of the ClO A (2)Pi(3/2) state using velocity-map ion-imaging. Experimental final correlated state branching ratios, i.e. Cl((2)P(J=3/2,1/2)) + O((3)P(J=2,1,0)) channels, have been measured for v' = 6-11. We find that the branching ratios are highly variable and depend strongly on v', providing a window into the v'-dependent predissociation mechanism. A comparison of the experimental results with the recent model of Lane et al. (I. C. Lane, W. H. Howie and A. J. Orr-Ewing, Phys. Chem. Chem. Phys., 1999, 1, 3087) in both the diabatic and adiabatic limits suggests that the dynamics are closer to the diabatic limit. The overall Cl((2)P(J)) branching ratios are in good agreement with the diabatic model results. There are significant differences, however, between theory and experiment at the correlated state level, demonstrating the sensitivity of correlated measurements to the role of the exit channel coupling in the predissociation dynamics. The results highlight the need for more sophisticated quantum dynamical calculations to describe the correlated fine structure branching ratios in this system. 相似文献