全文获取类型
收费全文 | 1260篇 |
免费 | 72篇 |
国内免费 | 1篇 |
专业分类
化学 | 920篇 |
晶体学 | 2篇 |
力学 | 24篇 |
数学 | 199篇 |
物理学 | 188篇 |
出版年
2024年 | 3篇 |
2023年 | 32篇 |
2022年 | 27篇 |
2021年 | 30篇 |
2020年 | 55篇 |
2019年 | 64篇 |
2018年 | 29篇 |
2017年 | 29篇 |
2016年 | 66篇 |
2015年 | 58篇 |
2014年 | 47篇 |
2013年 | 54篇 |
2012年 | 97篇 |
2011年 | 88篇 |
2010年 | 51篇 |
2009年 | 32篇 |
2008年 | 58篇 |
2007年 | 75篇 |
2006年 | 65篇 |
2005年 | 71篇 |
2004年 | 52篇 |
2003年 | 25篇 |
2002年 | 24篇 |
2001年 | 8篇 |
2000年 | 7篇 |
1999年 | 14篇 |
1998年 | 9篇 |
1997年 | 11篇 |
1996年 | 9篇 |
1994年 | 5篇 |
1993年 | 5篇 |
1992年 | 4篇 |
1990年 | 5篇 |
1989年 | 3篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1986年 | 10篇 |
1985年 | 5篇 |
1983年 | 6篇 |
1981年 | 3篇 |
1980年 | 6篇 |
1979年 | 9篇 |
1976年 | 10篇 |
1975年 | 5篇 |
1973年 | 10篇 |
1969年 | 3篇 |
1968年 | 3篇 |
1934年 | 3篇 |
1932年 | 3篇 |
1922年 | 2篇 |
排序方式: 共有1333条查询结果,搜索用时 453 毫秒
71.
This report establishes that trigonally coordinated "[PhBPiPr3]M" platforms (M = Fe, Co) will support both pi-acidic (N2) and pi-basic (NR) ligands at a fourth binding site. The N2 complexes of iron that are described are the first thoroughly characterized examples to exhibit a 4-coordinate geometry. Methylation of monomeric {Fe0(N2)-} and {Co0(N2)-} species successfully derivatizes the beta-N atom of the coordinated N2 ligand and affords the diazenido products {FeII(N2Me)} and {CoII(N2Me)}, respectively. One-electron oxidation of the mononuclear M0(N2)- species produces dinuclear and synthetically versatile MI(N2)MI complexes. These latter species provide clean access to the chemistry of the "[PhBPiPr3]MI" subunit. For example, addition of RN3 to MI(N2)MI results in oxidative nitrene transfer to generate [PhBPiPr3]MNR with concomitant N2 release. 相似文献
72.
73.
Jonas Enebro Dane Momcilovic Matti Siika-aho Sigbritt Karlsson 《Cellulose (London, England)》2009,16(2):271-280
The benefits of applying cellulose selective enzymes as analytical tools for chemical structure characterization of cellulose
derivatives have been frequently addressed over the years. In a recent study the high selectivity of cellulase Cel45A from
Trichoderma reesei (Tr Cel45A) was utilized for relating the chemical structure to the flow properties of carboxymethyl cellulose (CMC). However,
in order to take full advantage of the enzymatic hydrolysis the enzyme selectivity on the cellulose substrate must be further
investigated. Therefore, the selectivity of Tr Cel45A on CMC was studied by chemical sample preparation of the enzyme products
followed by mass spectrometric chemical structure characterization. The results strongly suggest that, in accordance with
recent studies, also this highly selective endoglucanase is able to catalyze hydrolysis of glucosidic bonds adjacent to mono-substituted
anhydroglucose units (AGUs). Furthermore, the results also indicate that substituents on the nearby AGUs will affect the hydrolysis. 相似文献
74.
Kimmo Eriksson Jonas Sjöstrand Pontus Strimling 《International Journal of Game Theory》2008,36(3-4):421-440
A fundamental fact in two-sided matching is that if a market allows several stable outcomes, then one is optimal for all men in the sense that no man would prefer another stable outcome. We study a related phenomenon of asymmetric equilibria in a dynamic market where agents enter and search for a mate for at most n rounds before exiting again. Assuming independent preferences, we find that this game has multiple equilibria, some of which are highly asymmetric between sexes. We also investigate how the set of equilibria depends on a sex difference in the outside option of not being mated at all. 相似文献
75.
Anisa Elhamili Magnus Wetterhall Angel Puerta Douglas Westerlund Jonas Bergquist 《Journal of chromatography. A》2009,1216(17):3613-3620
The effect of adding alkali salts to protein samples for capillary electrophoretic (CE) analysis of intact proteins was studied. A high degree of peak stacking, even for large proteins, was found to occur when alkali salts were added to the sample. The addition of salt to the protein sample promotes a strong improvement in the peak efficiency of individual proteins giving up to 2.1 × 106 apparent plates/m. The concentration of salt required in the sample to reach optimal peak efficiency show dependency on both the molecular weight and molar concentration of the protein. However, adding salt will, at a sufficiently high concentration, cause a mixture of proteins to co-migrate to one very sharp peak. The observed sample stacking effect was obtained with a number of different surface modified silica capillaries indicating a general phenomenon and not surface coating specific. 相似文献
76.
Lina Skardžiūtė Karolis Kazlauskas Jelena Dodonova Jonas Bucevičius Sigitas Tumkevičius Saulius Juršėnas 《Tetrahedron》2013
Pyrrolo[2,3-d]pyrimidine derivatives possessing different sterically-hindered end-groups at position 7 of the heterocycle were studied and compared with respect to nanoaggregate formation ability by the reprecipitation method in aqueous solutions. The emergence of nanoaggregates with an increasing water fraction in THF/water mixture was traced by observing sudden changes in spectral and transient fluorescence dynamics accompanied by fluorescence efficiency turn-on. The aggregation induced emission with a maximal 20-fold emission efficiency enhancement was obtained. Tuning of the nanoaggregates sizes from about 50 nm to 600 nm by increasing the THF/water ratio was revealed by electron microscopy. Almost perfect spherical shapes of the nanoaggregates and their structureless fluorescence bands similar to those of their neat amorphous films suggested an amorphous-like nature of the pyrrolo[2,3-d]pyrimidine-based nanoparticles. 相似文献
77.
Jonas T. Hartwig 《Journal of Pure and Applied Algebra》2008,212(4):863-883
We derive necessary and sufficient conditions for an ambiskew polynomial ring to have a Hopf algebra structure of a certain type. This construction generalizes many known Hopf algebras, for example U(sl2), Uq(sl2) and the enveloping algebra of the three-dimensional Heisenberg Lie algebra. In a torsion-free case we describe the finite-dimensional simple modules, in particular their dimensions, and prove a Clebsch-Gordan decomposition theorem for the tensor product of two simple modules. We construct a Casimir type operator and prove that any finite-dimensional weight module is semisimple. 相似文献
78.
79.
80.