全文获取类型
收费全文 | 1148篇 |
免费 | 36篇 |
专业分类
化学 | 772篇 |
晶体学 | 8篇 |
力学 | 34篇 |
数学 | 145篇 |
物理学 | 225篇 |
出版年
2023年 | 6篇 |
2022年 | 19篇 |
2021年 | 38篇 |
2020年 | 29篇 |
2019年 | 29篇 |
2018年 | 17篇 |
2017年 | 19篇 |
2016年 | 39篇 |
2015年 | 35篇 |
2014年 | 29篇 |
2013年 | 77篇 |
2012年 | 68篇 |
2011年 | 85篇 |
2010年 | 63篇 |
2009年 | 56篇 |
2008年 | 82篇 |
2007年 | 61篇 |
2006年 | 55篇 |
2005年 | 63篇 |
2004年 | 57篇 |
2003年 | 23篇 |
2002年 | 24篇 |
2001年 | 23篇 |
2000年 | 25篇 |
1999年 | 17篇 |
1998年 | 5篇 |
1997年 | 10篇 |
1996年 | 15篇 |
1995年 | 7篇 |
1994年 | 10篇 |
1993年 | 5篇 |
1992年 | 5篇 |
1991年 | 3篇 |
1990年 | 9篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 6篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1981年 | 9篇 |
1980年 | 4篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 5篇 |
1975年 | 3篇 |
1973年 | 6篇 |
1972年 | 3篇 |
排序方式: 共有1184条查询结果,搜索用时 15 毫秒
51.
J.C.S. Rocha B.V. Costa P.Z. Coura S.A. Leonel R.A. Dias 《Journal of magnetism and magnetic materials》2012
In this work we report a numerical Monte Carlo study of the behavior of a magnetic nano-disk put over an antiferromagnetic substrate. Three approaches were considered for describe the substrate: (1) A stacked antiferromagnetic configuration, (2) an Ising like arrangement and (3) Heisenberg like spins. For the Heisenberg case we still have considered an easy-plane and an easy-axis symmetry of the substrate. The hysteresis loop for the nano-disk is obtained by considering the three cases. The signature of the vortex in the nano-disk appears as small jumps in the hysteresis curve. Exchange bias effects are observed since the substrate has an easy axis symmetry. 相似文献
52.
53.
54.
55.
J.M. Dudley C. Finot G. Millot J. Garnier G. Genty D. Agafontsev F. Dias 《The European physical journal. Special topics》2010,185(1):125-133
In this contribution we describe and discuss a series of challenges and questions relating to understanding extreme wave phenomena
in optics. Many aspects of these questions are being studied in the framework of the MANUREVA project: a multidisciplinary
consortium aiming to carry out mathematical, numerical and experimental studies in this field. The central motivation of this
work is the 2007 results from optical physics [D. Solli et al., Nature 450, 1054 (2007)] that showed how a fibre-optical system can generate large amplitude extreme wave events with similar statistical
properties to the infamous hydrodynamic rogue waves on the surface of the ocean. We review our recent work in this area, and
discuss how this observation may open the possibility for an optical system to be used to directly study both the dynamics
and statistics of extreme-value processes, a potential advance comparable to the introduction of optical systems to study
chaos in the 1970s. 相似文献
56.
57.
Latifa Latrous Jeanine Tortajada Violette Haldys Emmanuelle Léon Catarina Correia Jean‐Yves Salpin 《Journal of mass spectrometry : JMS》2013,48(7):795-806
Gas‐phase interactions of organotins with glycine have been studied by combining mass spectrometry experiments and quantum calculations. Positive‐ion electrospray spectra show that the interaction of di‐ and tri‐organotins with glycine results in the formation of [(R)2Sn(Gly)‐H]+and [(R)3Sn(Gly)]+ ions, respectively. Di‐organotin complexes appear much more reactive than those involving tri‐organotins. (MS/MS) spectra of the [(R)3Sn(Gly)]+ ions are indeed simple and only show elimination of intact glycine, generating the [(R)3Sn]+ carbocation. On the other hand, MS/MS spectra of [(R)2Sn(Gly)‐H]+complexes are characterized by numerous fragmentation processes. Six of them, associated with elimination of H2O, CO, H2O + CO and formation of [(R)2SnOH]+ (?57 u),[(R)2SnNH2]+( ?58 u) and [(R)2SnH]+ (?73 u), are systematically observed. Use of labeled glycines notably concludes that the hydrogen atoms eliminated in water and H2O + CO are labile hydrogens. A similar conclusion can be made for hydrogens of [(R2)SnOH]+and [(R2)SnNH2]+ions. Interestingly, formation [(R)2SnH]+ ions is characterized by a migration of one the α hydrogen of glycine onto the metallic center. Finally, several dissociation routes are observed and are characteristic of a given organic substituent. Calculations indicated that the interaction between organotins and glycine is mostly electrostatic. For [(R)2Sn(Gly)‐H]+complexes, a preferable bidentate interaction of the type η2‐O,NH2 is observed, similar to that encountered for other metal ions. [(R)3Sn]+ ions strongly stabilize the zwitterionic form of glycine, which is practically degenerate with respect to neutral glycine. In addition, the interconversion between both forms is almost barrierless. Suitable mechanisms are proposed in order to account for the most relevant fragmentation processes. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
58.
Anderson Hollerbach Klier Ricardo José Alvea Maria Auxiliadora Fontes Prado José Dias de Bouza Filho Norma Beatriz D'accorso 《合成通讯》2013,43(23):4361-4374
The synthesis of 5-[6′-deoxy-(1′,2′:3′,4′-di-O-isopropylidene-α-D-galactopyranos-6′-yl)]tetrazole and its reaction with acetic anhydride and 1,2:3,4-di-O-isopropylidene-6-O-(4-toluenesulfonyl)-α-D-galactopyranose are described. 相似文献
59.
Claudio L. Donnici Elaine Henriques Teixeira Pereira Júlio C. Dias Lopes Liliana Marzorati Blanka Wladislaw 《合成通讯》2013,43(3):342-350
The study on reactivity of several α-substituted α-sulfonyl malonates toward 1,4-diazabicyclo[2.2.2]octane (DABCO) and Bu3N is described. The reactivity with DABCO revealed the possible competition between decarbalkoxylation and unexpected desulfonylation, depending on the α-substituent, because of sterical hindrance around the electrophilic centers (SO2 and CO2R). The derivatives with crowded α-substituents suffer selective desulfonylation, and a novel and efficient desulfonylation method can be proposed. The dependence of the reactivity of α-sulfonyl malonates on the sterical hindrance around the electrophilic centers is confirmed by conformational analysis (Macromodel/MM2? and Mopac/MP3). The carbanionic mechanism is proved because the corresponding protonated, deuterated, and sulfenylated products were obtained by addition of the corresponding electrophilic agents. Bu3N showed itself to be a novel selective decarbalkoxylation agent for any α-substituted α-sulfonyl malonate. 相似文献
60.
André Luís Branco de Barros Saulo Fernandes de Andrade José Dias de Souza Filho Valbert Nascimento Cardoso Ricardo José Alves 《Journal of Radioanalytical and Nuclear Chemistry》2013,298(1):605-609
Glycodendrimers are neoglycoconjugates that can be considered as bioisosters of glycoproteins, since they can mimic the multivalent interactions of lectin-carbohydrate. The ability of glycodendrimers to present multivalent interactions with lectins as compared to a monovalent ligand is referred to as “cluster effect”. It is expected that, because of the cluster effect, glycodendrimers would result in a better association with lectins than mono-carbohydrate anchored systems. Radioisotopes are useful to evaluate biodistribution of molecules. This study is important to obtain information about molecule–receptor interactions. Indeed, such study can provide an exquisite tool to evaluate the affinity of certain molecules to specific areas in the body, leading to the development of new radiopharmaceuticals and/or drug delivery systems. Herein, we describe a d-galactose coated low molecular weight PAMAM G0 dendrimer that was successfully radiolabeled with technetium-99m. Biodistribution studies and scintigraphic images were performed in healthy mice. It was observed high liver uptake which was significantly reduced in blocking studies, indicating hepatic specificity. Therefore, low molecular weight glycodendrimer can be considered as useful platform for selective targeting of drugs to the liver and to assess hepatic function. 相似文献