全文获取类型
收费全文 | 1480篇 |
免费 | 18篇 |
国内免费 | 6篇 |
专业分类
化学 | 872篇 |
晶体学 | 9篇 |
力学 | 59篇 |
数学 | 398篇 |
物理学 | 166篇 |
出版年
2019年 | 15篇 |
2017年 | 10篇 |
2016年 | 25篇 |
2015年 | 16篇 |
2014年 | 26篇 |
2013年 | 89篇 |
2012年 | 45篇 |
2011年 | 47篇 |
2010年 | 38篇 |
2009年 | 27篇 |
2008年 | 63篇 |
2007年 | 64篇 |
2006年 | 48篇 |
2005年 | 68篇 |
2004年 | 47篇 |
2003年 | 43篇 |
2002年 | 35篇 |
2001年 | 40篇 |
2000年 | 33篇 |
1999年 | 13篇 |
1998年 | 17篇 |
1997年 | 15篇 |
1996年 | 22篇 |
1995年 | 18篇 |
1994年 | 19篇 |
1993年 | 17篇 |
1992年 | 17篇 |
1991年 | 15篇 |
1990年 | 19篇 |
1989年 | 21篇 |
1988年 | 26篇 |
1987年 | 26篇 |
1986年 | 14篇 |
1985年 | 30篇 |
1984年 | 21篇 |
1983年 | 25篇 |
1982年 | 31篇 |
1981年 | 25篇 |
1980年 | 26篇 |
1979年 | 29篇 |
1978年 | 18篇 |
1977年 | 27篇 |
1976年 | 13篇 |
1975年 | 20篇 |
1974年 | 27篇 |
1973年 | 22篇 |
1972年 | 13篇 |
1971年 | 13篇 |
1969年 | 12篇 |
1965年 | 9篇 |
排序方式: 共有1504条查询结果,搜索用时 359 毫秒
991.
Philippe Flajolet Gilbert Labelle Louise Laforest Bruno Salvy 《Random Structures and Algorithms》1995,7(2):117-144
Several characteristic parameters of randomly grown quadtrees of any dimension are analyzed. Additive parameters have expectations whose generating functions are expressible in terms of generalized hypergeometric functions. A complex asymptotic process based on singularity analysis and integral representations akin to Mellin transforms leads to explicit values for various structure constants related to path length, retrieval costs, and storage occupation. 相似文献
992.
A kinetic scheme is presented to rationalize recent observations of delayed fluorescence ODMR in isotopically mixed naphthalene crystals, in which the sign of the signal changes from negative to positive as the critical concentration for triplet-triplet transport among the perprotonated traps is approached. The effects of chopped optical excitation, prolonged microwave pumping, temperature and light intensity are considered. The observation of positive DF-ODMR in the high concentration case is used to obtain a lower limit for the ratio of the annihilation constantk 2 to the pair dissociation constantk ?1. 相似文献
993.
994.
Gilbert Helmberg 《Monatshefte für Mathematik》1964,68(3):218-223
Ohne Zusammenfassung 相似文献
995.
996.
997.
A. J. Chalk A. R. Gilbert 《Journal of polymer science. Part A, Polymer chemistry》1972,10(7):2033-2043
The monofunctional acetylenes, phenylacetylene and m-ethynyltoluene, were each copolymerized with diethynylbenzene in a 1:1 mole ratio by using TiCl4/3AlEt2Cl as cyclotrimerization catalyst. The aromatic polymers which were produced were polydisperse with a molecular weight of ~10,000. Variation of catalyst concentration had no effect on the molecular weight profile. An excess of bifunctional acetylene produced some insoluble gel but when some of the monofunctional acetylene was withheld and added only after an initial molecular weight build-up by the excess bifunctional acetylene, soluble polymers with molecular weights of approximately 50,000 were obtained in high yield, provided the overall ratio of mono- to bifunctional acetylene was maintained at 1:1. The resulting polyphenylenes were highly soluble in benzene and chlorinated solvents but gave brittle films. This was attributed to a highly branched structure resulting from a lack of specificity by the catalyst. Thermogravimetric analysis showed the polymers to have high thermal stability. 相似文献
998.
The ionisation potentials and the appearance potentials for ions arising from the loss of carbonyl groups as well as certain other low-energy fragmentation ions have been measured for a series of substituted arene chromium tricarbonyls. The values obtained are found to correlate very well, for the loss of one and two carbonyl groups, with both the CO force constant k and the Hammett σp function and substituent on the benzene ring. The appearance potentials of the ions arising by the loss of three carbonyl groups do not exhibit a high correlation. Arene+ ions are found to occur at energies intermediate between those for the loss of two and three carbonyl groups.The various effects observed are discussed in terms of a model which involves definite contributions from both σ- and π- bonding of carbonyl groups in the gaseous cations. 相似文献
999.
1000.
The mass spectrometric study of a series of enolic phosphates of type A leades to fragmentation patterns influenced by the nature of the substituents (R, R′ and R″). It is generally observed that a simple or double hydrogen rearrangement occurs with the loss of the enolic groups. When R and R′ are alkyl groups, the migrating groups are the hydrogen atoms on the alkyl group at position 1. When there is no alkyl group at position 1, the hydrogen atoms of the alkyl group at position 2 induce the rearrangement process. Finally, if R, R′ and R″ are hydrogen atoms, the loss of the enolic chain occurs without any rearrangement. 相似文献