全文获取类型
收费全文 | 2808篇 |
免费 | 114篇 |
国内免费 | 14篇 |
专业分类
化学 | 2099篇 |
晶体学 | 18篇 |
力学 | 46篇 |
数学 | 215篇 |
物理学 | 558篇 |
出版年
2023年 | 25篇 |
2022年 | 49篇 |
2021年 | 74篇 |
2020年 | 55篇 |
2019年 | 68篇 |
2018年 | 36篇 |
2017年 | 48篇 |
2016年 | 94篇 |
2015年 | 88篇 |
2014年 | 99篇 |
2013年 | 158篇 |
2012年 | 176篇 |
2011年 | 214篇 |
2010年 | 113篇 |
2009年 | 106篇 |
2008年 | 157篇 |
2007年 | 169篇 |
2006年 | 133篇 |
2005年 | 116篇 |
2004年 | 95篇 |
2003年 | 75篇 |
2002年 | 93篇 |
2001年 | 47篇 |
2000年 | 68篇 |
1999年 | 31篇 |
1998年 | 42篇 |
1997年 | 25篇 |
1996年 | 26篇 |
1995年 | 35篇 |
1994年 | 31篇 |
1993年 | 33篇 |
1992年 | 28篇 |
1991年 | 36篇 |
1990年 | 32篇 |
1989年 | 21篇 |
1988年 | 24篇 |
1987年 | 19篇 |
1986年 | 20篇 |
1985年 | 26篇 |
1984年 | 26篇 |
1983年 | 17篇 |
1982年 | 16篇 |
1981年 | 17篇 |
1980年 | 10篇 |
1979年 | 6篇 |
1978年 | 7篇 |
1977年 | 11篇 |
1976年 | 7篇 |
1975年 | 7篇 |
1974年 | 6篇 |
排序方式: 共有2936条查询结果,搜索用时 0 毫秒
101.
102.
Ibon Alkorta Fernando Blanco Pere M. Deyà José Elguero Carolina Estarellas Antonio Frontera David Quiñonero 《Theoretical chemistry accounts》2010,126(1-2):1-14
This review covers two aspects concerning cooperativity in multiple weak bonds: a summary of literature results and a theoretical study of a complete series of model complexes. All the 15 combination of five weak bonds were explored: hydrogen bonds, hydric bonds, dihydrogen bonds, halogen bonds and ion–π interactions. Since in several cases there were no examples reported, a systematic exploration has been carried out on simple models at the MP2/aug-cc-pVTZ level. The results thus obtained have been analyzed using the atoms in molecules methodology. 相似文献
103.
Laurent A. Baumes Dr. Mireia Buaki Sogo Pedro Montes‐Navajas Dr. Avelino Corma Prof. Dr. Hermenegildo Garcia Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(15):4489-4495
γ‐Hydroxybutyric acid (GHB), a colourless, odourless and tasteless chemical, has become one of the most dangerous illicit drugs of abuse today. At low doses, this drug is a central nervous system depressant that reduces anxiety and produces euphoria and relaxation, sedating the recipient. There is an urgent need for simple, easy‐to‐use sensors for GHB in solution. Here, we present a colorimetric sensor array based on supramolecular host–guest complexes of fluorescent dyes with organic capsules (cucurbiturils) for the detection of GHB. 相似文献
104.
105.
Carolina M. Rodrigues Odair P. Ferreira Oswaldo L. Alves 《Journal of nanoparticle research》2010,12(7):2355-2361
In this work is reported the synthesis of nanotubes and nanoribbons from mixed oxides (Ti1−x Zr x O2·nH2O), employing hydrothermal treatment in a highly alkaline medium. The morphology and crystal structure of the products obtained via hydrothermal treatment depend on the value of x. For example, for x equal to 0 and 0.50 were observed the presence of nanotubes (diameter around 9 nm) and nanoribbons (diameter around 200 nm), respectively. However, for x values above 0.50, there was no morphological change. Regarding the crystalline structure of these samples, for x equal to 0 was observed the sodium titanate phase; already for x values up to 0.50, we observed the presence of two crystalline phases: sodium titanate and tetragonal ZrO2. For x values above 0.50, only tetragonal ZrO2 was observed. Furthermore, only the product obtained from x equal to 0.15 was observed the presence of three-dimensional flower-like arrangements. The results obtained by the characterization techniques showed the segregation of zirconium after hydrothermal treatment of precursors with x less or equal to 0.50. Thus, we describe the important role that Ti/Zr molar ratio of the precursor plays on the morphology and crystalline phase of the products formed by hydrothermal treatment. 相似文献
106.
Gas-phase behaviour of negative ions produced from thiazidic diuretics under electrospray conditions
Garcia P Popot MA Fournier F Bonnaire Y Tabet JC 《Journal of mass spectrometry : JMS》2002,37(9):940-953
A systematic mass spectrometric study of 10 thiazidic diuretics and related compounds was undertaken by mass spectrometry (MS) with electrospray ionization in the negative ion mode. Collisional dissociation 'in-source' (CID-MS) and in a low-pressure collision cell (CID-MS/MS) were compared in both excitation regions. Spectra obtained by CID-MS and by CID-MS/MS were matched. Using the two methods, loss of HCl and consecutive dissociations from 2HCl losses were exhibited from compounds such as methyclothiazide and trichlormethiazide but not from other thiazidic diuretics that contain chlorine substituents in the aromatic moiety. However, deprotonated dichlorphenamide gave rise to loss of HCl by CID-MS and CID-MS/MS. For other diuretics such as hydroflumethiazide and hydrochlorothiazide, the loss of HCN and [HCN + SO(2)] was relevant. Reaction mechanisms were checked by means of deuterium-hydrogen exchange, which showed that deprotonation took place regioselectively on the heterocyclic moiety. The cleavage pathways require molecular isomerization forming ion-dipole complexes prior to decompositions, allowing long-distance proton transfer for neutral elimination. Identifications of the most specific fragmentations presented in this paper were applied to the screening and unambiguous identification of diuretics for horse doping control. 相似文献
107.
Cristina García‐Simón Marc Garcia‐Borràs Dr. Laura Gómez Dr. Isaac Garcia‐Bosch Dr. Sílvia Osuna Prof. Marcel Swart Dr. Josep M. Luis Prof. Concepció Rovira Prof. Manuel Almeida Dr. Inhar Imaz Prof. Daniel Maspoch Dr. Miquel Costas Dr. Xavi Ribas 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(4):1445-1456
The metal‐directed supramolecular synthetic approach has paved the way for the development of functional nanosized molecules. In this work, we report the preparation of the new nanocapsule 3? (CF3SO3)8 with a A4B2 tetragonal prismatic geometry, where A corresponds to the dipalladium hexaazamacrocyclic complex Pd‐1 , and B corresponds to the tetraanionic form of palladium 5,10,15,20‐tetrakis(4‐carboxyphenyl)porphyrin ( 2 ). The large void space of the inner cavity and the supramolecular affinity for guest molecules towards porphyrin‐based hosts converts this nanoscale molecular 3D structure into a good candidate for host–guest chemistry. The interaction between this nanocage and different guest molecules has been studied by means of NMR, UV/Vis, ESI‐MS, and DOSY experiments, from which highly selective molecular recognition has been found for anionic, planar‐shaped π guests with association constants (Ka) higher than 109 M ?1, in front of non‐interacting aromatic neutral or cationic substrates. DFT theoretical calculations provided insights to further understand this strong interaction. Nanocage 3? (CF3SO3)8 can not only strongly host one single molecule of M(dithiolene)2 complexes (M=Au, Pt, Pd, and Ni), but also can finely tune their optical and redox properties. The very simple synthesis of both the supramolecular cage and the building blocks represents a step forward for the development of polyfunctional supramolecular nanovessels, which offer multiple applications as sensors or nanoreactors. 相似文献
108.
Marc Garcia‐Borràs Dr. Josep M. Luis Prof. Dr. Marcel Swart Prof. Dr. Miquel Solà 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(14):4468-4479
One of the most important reactions in fullerene chemistry is the Diels–Alder (DA) reaction. In two previous experimental studies, the DA cycloaddition reactions of cyclopentadiene (Cp) and 1,2,3,4,5‐pentamethylcyclopentadiene (Cp*) with La@C2v‐C82 were investigated. The attack of Cp was proposed to occur on bond 19 , whereas that of Cp* was confirmed by X‐ray analysis to be over bond o . Moreover, the stabilities of the Cp and Cp* adducts were found to be significantly different, that is, the decomposition of La@C2v‐C82Cp was one order of magnitude faster than that of La@C2v‐C82Cp*. Herein, we computationally analyze these DA cycloadditions with two main goals: First, to compute the thermodynamics and kinetics of the cycloadditions of Cp and Cp* to different bonds of La@C2v‐C82 to assess and compare the regioselectivity of these two reactions. Second, to understand the origin of the different thermal stabilities of the La@C82Cp and La@C82Cp* adducts. Our results show that the regioselectivity of the two DA cycloadditions is the same, with preferred attack on bond o . This result corrects the previous assumption of the regioselectivity of the Cp attack that was made based only on the shape of the La@C82 singly occupied molecular orbital. In addition, we show that the higher stability of the La@C82Cp* adduct is not due to the electronic effects of the methyl groups on the Cp ring, as previously suggested, but to higher long‐range dispersion interactions in the Cp* case, which enhance the stabilization of the reactant complex, transition state, and products with respect to the separated reactants. This stabilization for the La@C82Cp* case decreases the Gibbs reaction energy, thus allowing competition between the direct and retro reactions and making dissociation more difficult. 相似文献
109.
Dr. Aloysius Siriwardena Kiran Kumar Pulukuri Pancham S. Kandiyal Dr. Saumya Roy Dr. Omprakash Bande Dr. Subhash Ghosh Dr. José Manuel Garcia Fernández Dr. Fernando Ariel Martin Dr. Jean‐Marc Ghigo Dr. Christophe Beloin Dr. Keigo Ito Dr. Robert J. Woods Dr. Ravi Sankar Ampapathi Dr. Tushar Kanti Chakraborty 《Angewandte Chemie (International ed. in English)》2013,52(39):10221-10226
110.
Kadish KM Wang LL Thuriere A Giribabu L Garcia R Van Caemelbecke E Bear JL 《Inorganic chemistry》2003,42(25):8309-8319
Three Ru2(5+) diruthenium complexes, (4,0) Ru2(2-CH3ap)4Cl, (3,1) Ru2(2-Fap)4Cl, and (3,1) Ru2(2,4,6-F3ap)4Cl where ap is the 2-anilinopyridinate anion, were examined as to their electrochemical and spectroelectrochemical properties in five different nonaqueous solvents (CH2Cl2, THF, PhCN, DMF, and DMSO). Each compound undergoes a single one-electron metal-centered oxidation in THF, DMF, and DMSO and two one-electron metal-centered oxidations in CH2Cl2 and PhCN. The three diruthenium complexes also undergo two reductions in each solvent except for CH2Cl2, and these electrode processes are assigned as Ru2(5+/4+) and Ru2(4+/3+). Each neutral, singly reduced, and singly oxidized species was characterized by UV-vis thin-layer spectroelectrochemistry, and the data are discussed in terms of the most probable electronic configuration of the compound in solution. The three neutral complexes contain three unpaired electrons as indicated by magnetic susceptibility measurements using the Evans method (3.91-3.95 muB), and the electronic configuration is assigned as sigma2pi4delta2pi(*2)delta, independent of the solvent. The three singly oxidized compounds have two unpaired electrons in CD2Cl2, DMSO-d6, or CD3CN (2.65-3.03 muB), and the electronic configuration is here assigned as sigma2pi4delta2pi(*2). The singly reduced compound also has two unpaired electrons (2.70-2.80 muB) in all three solvents, consistent with the electronic configuration sigma2pi4delta2pi(*2)delta(*2) or sigma2pi4delta2pi(*3)delta*. Finally, the overall effect of solvent on the number of observed redox processes is discussed in terms of solvent binding, and several formation constants were calculated. 相似文献