全文获取类型
收费全文 | 378篇 |
免费 | 11篇 |
国内免费 | 3篇 |
专业分类
化学 | 228篇 |
晶体学 | 2篇 |
力学 | 15篇 |
数学 | 80篇 |
物理学 | 67篇 |
出版年
2023年 | 5篇 |
2022年 | 2篇 |
2021年 | 14篇 |
2020年 | 3篇 |
2019年 | 8篇 |
2018年 | 7篇 |
2017年 | 4篇 |
2016年 | 10篇 |
2015年 | 11篇 |
2014年 | 15篇 |
2013年 | 29篇 |
2012年 | 20篇 |
2011年 | 25篇 |
2010年 | 10篇 |
2009年 | 21篇 |
2008年 | 24篇 |
2007年 | 26篇 |
2006年 | 20篇 |
2005年 | 17篇 |
2004年 | 15篇 |
2003年 | 10篇 |
2002年 | 8篇 |
2001年 | 7篇 |
2000年 | 7篇 |
1999年 | 4篇 |
1998年 | 4篇 |
1997年 | 3篇 |
1996年 | 5篇 |
1995年 | 2篇 |
1994年 | 4篇 |
1992年 | 1篇 |
1991年 | 3篇 |
1990年 | 5篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1972年 | 1篇 |
1971年 | 2篇 |
1962年 | 2篇 |
1956年 | 1篇 |
排序方式: 共有392条查询结果,搜索用时 31 毫秒
111.
Bromination of quercetin with N-bromosuccinimide in neutral aqueous methanol occurs surprisingly in the electron-deficient A-ring only. Deprotonation of the acidic 7-OH is a major driver of this regioselective reaction. The increase of electron density makes in fact the quercetin anion suitable for an electrophilic attack by bromine at positions 8 and 6. Several pieces of evidence (NMR spectra and H/D exchange) are presented to substantiate the mechanism advanced. Bromoquinones/quinomethides produced in excess of N-bromosuccinimide are responsible for the formation of a stable ‘violet chromogen’. 相似文献
112.
Ottorino Chillemi Benedetto Gui Lorenzo Rocco 《International Journal of Game Theory》2017,46(3):737-760
A large population of fixed-type agents engage in exclusive pairwise relationships in a decentralized setting. At the onset, agents randomly meet in pairs under private information of individual time-invariant types. They play a voluntary contribution game. At the end of the first period, members of each pair either stay together in the second period, in which case reported information is common knowledge, or quit and meet randomly new partners, under private information of individual types. Thus, either long-term or short-term relationships may arise. We show that there are values of the parameters such that information extracted in the first period has a positive effect on social efficiency. We give an interpretation of our results in terms of advantageous delegation of decisions to uninformed agents. Finally, we consider several extensions of the model in which our results still hold. 相似文献
113.
Claudio De Rosa Finizia AuriemmaOdda Ruiz de Ballesteros Rocco Di GirolamoMartina Pepe Oreste TaralloAnna Malafronte 《European Polymer Journal》2013
A study of the thermodynamic stability and the related polymorphic transformations induced by thermal treatments of the mesomorphic form that crystallizes in stereodefective metallocene isotactic polypropylene (iPP) is presented. We show that the mesomorphic form of the more isotactic samples is stable at room temperature, whereas the mesomorphic form crystallizing in the more stereoirregular sample is unstable and crystallizes at room temperature in the crystalline α form. In any case, the mesomorphic form transforms during heating or by annealing at temperatures higher than 60–80 °C always in the α form, regardless of the stereoregularity, even in the case of stereoirregular samples generally crystallizing from the melt in the γ form. These data confirm the proposed model of structure of the mesomorphic form as small aggregates of chains in three-fold helical conformation packed with lateral correlations similar to the α form of iPP. 相似文献
114.
G. Moruzzi F. Strumia C. Bonetti B. Carli F. Mencaraglia M. Carlotti G. Di Lonardo A. Trombetti 《Journal of Molecular Spectroscopy》1984,105(1):24-52
The experimental Fourier spectrum of CH3OH has been investigated between 8 and 40 cm?1. Good agreement was found between the experimental measurements and the results of the computational routines available up to now when low J values (J ? 10) are involved. At higher J, the line assignments are possible by means of Taylor expansions of the energy levels. A catalog of almost 1500 lines, two-thirds of which have been assigned, is presented. 相似文献
115.
Ferragina C. Cafarelli P. De Stefanis A. Di Rocco R. Petrilli L. 《Journal of Thermal Analysis and Calorimetry》2003,71(3):1023-1034
Long chain trimethylammonium salts can be successfully used as guest molecules to produce mesoporous layered materials when
intercalated in sol-gel zirconium phosphate, an inorganic ion-exchanger. The obtained materials are very similar independently
of the chain length and the synthesis method batch (B) or direct intercalation (DI). They show a good thermal stability, and
a very high interlayer distance if compared with their precursor. By the thermal characterization it can be observed that
the surfactant is lost in two or three steps depending on its position in the host. The layered structure with the expanded
interlayer distance is maintained up to 300°C. From the IR spectra the different surfactant release models for (B) and (DI)
are confirmed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
116.
Cusack Francene Lappin-Scott Hilary Singh Surindar De Rocco Mario Costerton J. William 《Applied biochemistry and biotechnology》1990,24(1):885-898
Applied Biochemistry and Biotechnology - Microbial experiments to study enhanced oil recovery have generally been conducted using vegetative microorganisms and one-dimensional laboratory models.... 相似文献
117.
Arturo Arduini Eleonora Ghidini Andrea Pochini Rocco Ungaro Giovanni Dario Andreetti Gianluca Calestani Franco Ugozzoli 《Journal of inclusion phenomena and macrocyclic chemistry》1988,6(2):119-134
From the reaction ofp-t-butylcalix[4]arene with -chloro-N,N-diethyl acetamide a new lipophilic ether-amide ligand (2) has been obtained in high yield. Solution studies show (2) to be a very strong cation receptor for alkali cations, especially sodium and potassium. The X-ray crystal structure determination of the free ligand (2) and two potassium complexes (KI and KSCN) shows the calix[4]arene in a fixed cone structure and the cation completely encapsulated in a polar cavity of eight oxygen atoms.
Supplementary Data relating to this article are deposited with the British Library as supplementary publication No. SUP 82059 (57 pages).Presented at the Fourth International Symposium on Inclusion Phenomena and the Third International Symposium on Cyclodextrins, Lancaster, U.K., 20–25 July 1986. 相似文献
118.
“Kinetic selectivity” in the cross condensation of α,β-unsaturated aldehydes and methyl ketones are obtained using 2,4,6-trimethylphenoxymagnesium bromide (2,4,6-TMPOMgBr) in benzene as catalyst. 相似文献
119.
Quasi-classical trajectory calculations have been performed on the adiabatically allowed reactions taking place on the two lowest-lying electronic states of the LiH2+ system, using the ab initio potential energy surfaces of Martinazzo et al. (J. Chem. Phys., 2003, 119, 11 241). These reactions comprise: (i) the exoergic H2 and H2+ formation occurring through LiH+ + H and LiH + H+ collisions in the ground and in the first electronically excited state, respectively; (ii) the endoergic (ground state) LiH+ dissociation induced by collisions with H atoms; and (iii) the endoergic (excited state) Li + H2+ --> LiH + H+ reaction. The topic is of relevance for a better understanding of the lithium chemistry in the early universe. Thermal rate constants for the above reactions have been computed in the temperature range 10-5000 K and found in reasonably good agreement with estimates based on the capture model. 相似文献
120.
Castelli F Sarpietro MG Micieli D Stella B Rocco F Cattel L 《Journal of colloid and interface science》2007,316(1):43-52
Molecular interactions between gemcitabine, alone or conjugated with squalene to form the gem-squalene prodrug, with dimyristoylphosphatidylcholine have been investigated by differential scanning calorimetry and Langmuir film balance techniques to gain information about the interaction of gemcitabine and its prodrug with mammalian cell membranes and to evaluate the potential of liposomes as a delivery system for gemcitabine prodrugs. Phospholipids assembled as multilamellar vesicles or monolayers (at the air water interface) have been used as biomembrane models. Different interactions of gemcitabine, its prodrug, and squalene with the lipid were detected by dispersing the compounds in the MLV and were compared with kinetic experiments carried out to consider the ability of the examined compounds to dissolve in an aqueous medium, to migrate through it, and to be captured by multilamellar vesicles. Their ability to be released from drug-loaded liposomes and be taken up by empty vesicles mimicking biomembranes was also considered. Analysis of the differential scanning calorimetry curves reveals that gemcitabine has very little interaction with multilamellar vesicles whereas the gem-squalene prodrug strongly interacts with multilamellar vesicles. The kinetic experiments suggest that an aqueous medium does not permit the prodrug uptake by the biomembrane models, whereas it is allowed when gem-squalene is gradually released by the liposomes. The molecular area/surface pressure isotherms of the gemcitabine/lipid, gem-squalene/lipid, and pure compound monolayers, in agreement with the calorimetric results, indicate that gem-squalene interacts with the phospholipid monolayer with the squalene moiety in contact with the phospholipid chains and gemcitabine protruding in the aqueous medium. 相似文献