全文获取类型
收费全文 | 1882篇 |
免费 | 52篇 |
国内免费 | 11篇 |
专业分类
化学 | 1158篇 |
晶体学 | 25篇 |
力学 | 54篇 |
数学 | 331篇 |
物理学 | 377篇 |
出版年
2023年 | 9篇 |
2022年 | 39篇 |
2021年 | 46篇 |
2020年 | 27篇 |
2019年 | 40篇 |
2018年 | 22篇 |
2017年 | 21篇 |
2016年 | 65篇 |
2015年 | 58篇 |
2014年 | 58篇 |
2013年 | 89篇 |
2012年 | 126篇 |
2011年 | 125篇 |
2010年 | 74篇 |
2009年 | 72篇 |
2008年 | 103篇 |
2007年 | 125篇 |
2006年 | 98篇 |
2005年 | 106篇 |
2004年 | 98篇 |
2003年 | 75篇 |
2002年 | 70篇 |
2001年 | 17篇 |
2000年 | 24篇 |
1999年 | 25篇 |
1998年 | 16篇 |
1997年 | 15篇 |
1996年 | 27篇 |
1995年 | 17篇 |
1994年 | 11篇 |
1993年 | 17篇 |
1992年 | 16篇 |
1991年 | 11篇 |
1990年 | 8篇 |
1989年 | 7篇 |
1988年 | 16篇 |
1987年 | 10篇 |
1986年 | 5篇 |
1985年 | 14篇 |
1984年 | 15篇 |
1983年 | 19篇 |
1982年 | 17篇 |
1981年 | 14篇 |
1980年 | 11篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1975年 | 4篇 |
1973年 | 5篇 |
1966年 | 3篇 |
1960年 | 5篇 |
排序方式: 共有1945条查询结果,搜索用时 0 毫秒
61.
Mauro C.C. Ribeiro 《Journal of Non》2009,355(31-33):1659-1662
Molecular dynamics (MD) simulations of LiCl·6H2O showed that the diffusion coefficient D, and also the structural relaxation time <τ>, follow a power law at high temperatures, D?1 ∝ (T ? To)?μ, with the same experimental parameters for viscosity (To = 207 K, μ = 2.08). Decoupling between D and <τ> occurs at Tx ~ 1.1To. High frequency acoustic excitations for the LiCl·6H2O model were obtained by the calculation of time correlation functions of mass current fluctuations. The temperature dependence of the instantaneous shear modulus, G∞(T), was considered in the shoving model for supercooled liquids [J.C. Dyre, T. Christensen, N.B. Olsen, J. Non-Cryst. Solids 352 (2006) 4635] resulting in a linear relationship log (D?1) vs. G∞/T. 相似文献
62.
Eva Lucaccini Matteo Briganti Dr. Mauro Perfetti Dr. Laure Vendier Dr. Jean‐Pierre Costes Dr. Federico Totti Prof. Dr. Roberta Sessoli Prof. Dr. Lorenzo Sorace 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(16):5552-5562
The magnetic behaviour of a Dy(LH)3 complex (LH? is the anion of 2‐hydroxy‐N′‐[(E)‐(2‐hydroxy‐3‐methoxyphenyl)methylidene]benzhydrazide) was analysed in depth from both theoretical and experimental points of view. Cantilever torque magnetometry indicated that the complex has Ising‐type anisotropy, and provided two possible directions for the easy axis of anisotropy due to the presence of two magnetically non‐equivalent molecules in the crystal. Ab initio calculations confirmed the strong Ising‐type anisotropy and disentangled the two possible orientations. The computed results obtained by using ab initio calculations were then used to rationalise the composite dynamic behaviour observed for both pure DyIII phase and YIII diluted phase, which showed two different relaxation channels in zero and non‐zero static magnetic fields. In particular, we showed that the relaxation behaviour at the higher temperature range can be correctly reproduced by using a master matrix approach, which suggests that Orbach relaxation is occurring through a second excited doublet. 相似文献
63.
Cholesterylbutyrate (Chol-but) was chosen as a prodrug of butyric acid. Butyrate is not often used in vivo because its half-life is very short and therefore too large amounts of the drug would be necessary for its efficacy. In the last few years butyric acid's anti-inflammatory properties and its inhibitory activity towards histone deacetylases have been widely studied, mainly in vitro. Solid Lipid Nanoparticles (SLNs), whose lipid matrix is Chol-but, were prepared to evaluate the delivery system of Chol-but as a prodrug and to test its efficacy in vitro and in vivo. Chol-but SLNs were prepared using the microemulsion method; their average diameter is on the order of 100-150 nm and their shape is spherical. The antineoplastic effects of Chol-but SLNs were assessed in vitro on different cancer cell lines and in vivo on a rat intracerebral glioma model. The anti-inflammatory activity was evaluated on adhesion of polymorphonuclear cells to vascular endothelial cells. In the review we will present data on Chol-but SLNs in vitro and in vivo experiments, discussing the possible utilisation of nanoparticles for the delivery of prodrugs for neoplastic and chronic inflammatory diseases. 相似文献
64.
Mauro Vaccaro Gaetano Mangiapia Antonella Accardo Diego Tesauro Eliana Gianolio Henrich Frielinghaus Giancarlo Morelli Luigi Paduano 《Colloid and polymer science》2008,286(14-15):1643-1652
Two novel amphiphilic unimers containing an aliphatic hydrophobic chain (PDA) with two C≡C triple bonds and hydrophilic heads presenting the chelating agent DTPAGlu and the CCK8 bioactive peptide, respectively, have been prepared by solid phase synthesis. Aggregates obtained by mixing together PDA-DTPAGlu, or its Gd(III) complex, and PDA-L2-CCK8 in 70/30 molar ratio before and after a polymerization process carried out by UV irradiation have been structurally characterized by means of small angle neutron scattering. The relaxivity properties of aggregates containing Gadolinium complexes have also been investigated. Elongated mixed micelles have been observed, in which the relaxivity value r 1p for each Gadolinium complex, measured at 20 MHz and 298 K, is around 12 mM–1 s–1. 相似文献
65.
Filippi A Speranza M Paladini A De Carolis R Guidoni AG Laganà A Satta M 《Journal of mass spectrometry : JMS》2006,41(1):98-102
Diastereomeric clusters of general formula [MAB(2)](+) and [MA(2)B](+) (M = Li(I), Na(I), Ag(I), Ni(II)-H, or Cu(II)-H; A = (R)-(-)- and (S)-(+)-(1-aminopropyl)phosphonic acid; B = (1R)-(-)- and (1S)-(+)-(1-aminohexyl)phosphonic acid) have been readily generated in the electrospray ionization (ESI) source of a triple-quadrupole mass spectrometer and their collision-induced dissociation (CID) investigated. CID of diastereomeric complexes, e.g. [MA(S)(B(S))(2)](+) and [MA(R)(B(S))(2)](+), leads to fragmentation patterns characterized by R(homo) = [MA(S)B(S)](+)/[M(B(S))(2)](+) and R(hetero) = [MA(R)B(S)](+)/[M(B(S))(2)](+) abundance ratios, which depend upon the relative stability of the diastereomeric [MA(S)B(S)](+) and [MA(R)B(S)](+) complexes in the gas phase. The chiral resolution factor R(chiral) = R(homo)/R(hetero) is found to depend not only on the nature of the M ion but also on that of the fragmenting species, whether [MAB(2)](+) or [MA(2)B](+). The origin of this behavior is discussed. 相似文献
66.
Barone V Casarin M Forrer D Pavone M Sambi M Vittadini A 《Journal of computational chemistry》2009,30(6):934-939
A semiempirical addition of dispersive forces to conventional density functionals (DFT-D) has been implemented into a pseudopotential plane-wave code. Test calculations on the benzene dimer reproduced the results obtained by using localized basis set, provided that the latter are corrected for the basis set superposition error. By applying the DFT-D/plane-wave approach a substantial agreement with experiments is found for the structure and energetics of polyethylene and graphite, two typical solids that are badly described by standard local and semilocal density functionals. 相似文献
67.
Mauro M De Paoli G Otter M Donghi D D'Alfonso G De Cola L 《Dalton transactions (Cambridge, England : 2003)》2011,40(45):12106-12116
We describe a new class of water soluble metallosurfactant molecules based on luminescent neutral iridium(III) complexes. The compounds possess an alkyl chain terminated with a negatively charged group, a sulphate. Due to their amphiphilic nature they assemble in aggregates in water and their photophysical properties, as well as the morphological characterization of the assemblies are presented. In particular, UV-Vis absorption, steady-state and time-resolved emission spectroscopy, dynamic light scattering and scanning electron microscopy techniques have been employed towards the analysis of the assemblies in different media. Comparison with the single components shows that the aggregates have very different photophysical properties. Importantly, the change in colour upon self-assembly is a remarkable feature which could be used for the design of probes which can change properties in different environments. 相似文献
68.
Ryan T. Chester Roland de Marco Mauro Mocerino Brian W. Skelton Allan H. White 《Supramolecular chemistry》2013,25(6):479-485
The tetra-isopropyl ethers of calix[4]arene and p-t-butylcalix[4]arene have been isolated in the cone conformation, and structurally characterised as chloroform solvates. Thermogravimetric analysis demonstrated that the parent isopropylcalix[4]arene solvate is significantly more stable than the p-t-butylcalix[4]arene analogue, retaining the solvent up to a temperature of 125°C. It was found that the calix[4]arene ether sublimes at atmospheric pressure, and solvent-free crystals appropriate for structure determination were produced at reduced pressure. The p-t-butylcalix[4]arene ether was also isolated without solvent in the lattice, but in this case the calixarene was crystallised from acetone, as sublimation did not produce crystals of sufficient quality. 相似文献
69.
Enrico Dalcanale Giancarlo Antonioli Mauro Ricco Herbert Groothues Friedrich Kremer 《Liquid crystals》2013,40(9):1161-1169
The dynamic and conformational behaviour of four mesogenic resorcinarenes exhibiting columnar mesophases have been studied by a combination of broadband dielectric spectroscopy and deuterium solid state NMR. Broadband dielectric spectroscopy provided evidence for two relaxation processes present both in the mesophase and in the isotropic liquid. The high frequency process II, common to all mesogens, has been assigned to the libration of the carbonyl groups of the ester junctions between the core and the side chains. The low frequency process I, present in conformationally mobile mesogens 1 and 2, has been attributed to the ring inversion process of the macrocyclic core associated with dipole inversion along the columnar axis. Deuterium solid state NMR performed on 4, the deuteriated analogue of 1, confirmed the molecular dynamics attribution for process I, assigning the ring inversion to the interconversion of the two equivalent crown conformations. 相似文献
70.
Dr. Matteo P. Placidi Prof. Dr. Mauro Botta Dr. Ferenc K. Kálmán Dr. Gisela E. Hagberg Dr. Zsolt Baranyai Andreas Krenzer Alexandria K. Rogerson Prof. Dr. Imre Tóth Prof. Dr. Nikos K. Logothetis Priv.‐Doz. Dr. Goran Angelovski 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(35):11644-11660
A series of low molecular weight lanthanide complexes were developed that have high 1H longitudinal relaxivities (r1) and the potential to be used as dual frequency 1H and 19F MR probes. Their behavior was investigated in more detail through relaxometry, pH‐potentiometry, luminescence, and multinuclear NMR spectroscopy. Fitting of the 1H NMRD and 17O NMR profiles demonstrated a very short water residence lifetime (<10 ns) and an appreciable second sphere effect. At lower field strengths (20 MHz), two of the complexes displayed a peak in r1 (21.7 and 16.3 mM ?1 s?1) caused by an agglomeration, that can be disrupted through the addition of phosphate anions. NMR spectroscopy revealed that at least two species are present in solution interconverting through an intramolecular binding process. Two complexes provided a suitable signal in 19F NMR spectroscopy and through the selection of optimized imaging parameters, phantom images were obtained in a MRI scanner at concentrations as low as 1 mM . The developed probes could be visualized through both 1H and 19F MRI, showing their capability to function as dual frequency MRI contrast agents. 相似文献