全文获取类型
收费全文 | 1239篇 |
免费 | 28篇 |
国内免费 | 2篇 |
专业分类
化学 | 880篇 |
晶体学 | 18篇 |
力学 | 20篇 |
数学 | 98篇 |
物理学 | 253篇 |
出版年
2023年 | 8篇 |
2022年 | 29篇 |
2021年 | 36篇 |
2020年 | 30篇 |
2019年 | 31篇 |
2018年 | 27篇 |
2017年 | 20篇 |
2016年 | 37篇 |
2015年 | 36篇 |
2014年 | 39篇 |
2013年 | 81篇 |
2012年 | 84篇 |
2011年 | 105篇 |
2010年 | 75篇 |
2009年 | 95篇 |
2008年 | 100篇 |
2007年 | 80篇 |
2006年 | 56篇 |
2005年 | 45篇 |
2004年 | 35篇 |
2003年 | 32篇 |
2002年 | 30篇 |
2001年 | 20篇 |
2000年 | 18篇 |
1999年 | 19篇 |
1998年 | 13篇 |
1997年 | 11篇 |
1996年 | 11篇 |
1995年 | 3篇 |
1994年 | 6篇 |
1993年 | 4篇 |
1992年 | 6篇 |
1991年 | 4篇 |
1990年 | 7篇 |
1989年 | 2篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1983年 | 6篇 |
1981年 | 6篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1971年 | 1篇 |
1965年 | 1篇 |
1961年 | 1篇 |
排序方式: 共有1269条查询结果,搜索用时 171 毫秒
81.
Paola D. D. S. Maia Diego dos Santos Baio Hayandra F. Nanini Victor Paulo F. da Silva Lissa Bantim Frambach Iuri Matheus Cabral Beatriz Pêgo Beatriz E. Ribeiro Mauro Srgio Gonalves Pavo Vania M. F. Paschoalin Heitor S. P. de Souza Anna Paola T. R. Pierucci 《Molecules (Basel, Switzerland)》2022,27(4)
Phenolic compounds (PCs) present in foods are associated with a decreased risk of developing inflammatory diseases. The aim of this study was to extract and characterize PCs from craft beer powder and evaluate their potential benefits in an experimental model of inflammatory bowel disease (IBD). PCs were extracted and quantified from pure beer samples. BALB/c mice received either the beer phenolic extract (BPE) or beer powder fortified with phenolic extract (BPFPE) of PCs daily for 20 days by gavage. Colon samples were collected for histopathological and immunohistochemical analyses. Dextran sodium sulfate (DSS)-induced mice lost more weight, had reduced colon length, and developed more inflammatory changes compared with DSS-induced mice treated with either BPE or BPFPE. In addition, in DSS-induced mice, the densities of CD4- and CD11b-positive cells, apoptotic rates, and activation of NF-κB and p-ERK1/2 MAPK intracellular signaling pathways were higher in those treated with BPE and BPFPE than in those not treated. Pretreatment with the phenolic extract and BPFPE remarkably attenuated DSS-induced colitis. The protective effect of PCs supports further investigation and development of therapies for human IBD. 相似文献
82.
Ana L. R. Silva Vnia M. S. Costa Maria D. M. C. Ribeiro da Silva 《Molecules (Basel, Switzerland)》2022,27(1)
The determination of the reliable thermodynamic properties of 2-benzoxazolinone derivatives is the main goal of this work. Some correlations are established between the energetic properties determined and the structural characteristics of the title compounds, and the reactivity of this class of compounds is also evaluated. Static-bomb combustion calorimetry and high-temperature Calvet microcalorimetry were used to determine, respectively, the standard molar enthalpies of formation in the solid state and the standard molar enthalpies of sublimation, both at T = 298.15 K. Using the results obtained for each compound, the respective gas-phase standard molar enthalpy of formation was derived. High-level quantum chemical calculations were performed to estimate the same property and the results evidence good accordance. Moreover, the gas-phase relative thermodynamic stability of 2-benzoxazolinone derivatives was also evaluated using the respective gas-phase standard molar Gibbs energy of formation. In addition, the relationship between the energetic and structural characteristics of the benzoxazolinones is presented, evidencing the enthalpic increments associated with the presence of a methyl and a nitro groups in the molecule, and this effect is compared with similar ones in other structurally related compounds. 相似文献
83.
Juan Mentado-Morales Arturo Ximello-Hernndez Javier Salinas-Luna Vera L. S. Freitas Maria D. M. C. Ribeiro da Silva 《Molecules (Basel, Switzerland)》2022,27(2)
The thermochemical study of the 1,3-bis(N-carbazolyl)benzene (NCB) and 1,4-bis(diphenylamino)benzene (DAB) involved the combination of combustion calorimetric (CC) and thermogravimetric techniques. The molar heat capacities over the temperature range of (274.15 to 332.15) K, as well as the melting temperatures and enthalpies of fusion were measured for both compounds by differential scanning calorimetry (DSC). The standard molar enthalpies of formation in the crystalline phase were calculated from the values of combustion energy, which in turn were measured using a semi-micro combustion calorimeter. From the thermogravimetric analysis (TGA), the rate of mass loss as a function of the temperature was measured, which was then correlated with Langmuir’s equation to derive the vaporization enthalpies for both compounds. From the combination of experimental thermodynamic parameters, it was possible to derive the enthalpy of formation in the gaseous state of each of the title compounds. This parameter was also estimated from computational studies using the G3MP2B3 composite method. To prove the identity of the compounds, the 1H and 13C spectra were determined by nuclear magnetic resonance (NMR), and the Raman spectra of the study compounds of this work were obtained. 相似文献
84.
Carlos M.S. Vicente Toms S. Martins Marco Leite Antnio Ribeiro Luís Reis 《先进技术聚合物》2020,31(3):501-507
This work aims to determine the influence of fused deposition modeling (FDM) printing parameters on the mechanical properties of parts fabricated on an Ultimaker2 printer with acrylonitrile butadiene styrene (ABS). The effect of several parameters such as interlayer cooling time (ILCT), nozzle diameter, infill density, raster angle and layer thickness on the ultimate tensile strength, yield strength, and elastic modulus of produced parts was evaluated. Two independent studies were conducted: a first study dedicated to the ILCT and a second study where the influence of other parameters was evaluated through a design of experiments (DoE) approach. Both studies were carried out through the execution of standard tensile tests. The statistical analysis of tensile tests results was processed with the ANOVA methodology. The obtained results indicate that a reduced ILCT improves the tensile strength of parts. It is shown that nozzle diameter and infill density are the parameters that most influence the mechanical properties of ABS, with the upper range selected values improving the studied mechanical properties. The raster angle configuration of (?45o/45o) benefits UTS and yield strength of ABS samples. Interactions of nozzle diameter on layer thickness were detected. It was observed that smaller layer thickness promotes a higher elastic modulus and UTS; however, for thinner layers (0.06‐0.10 mm), no significant differences were found on strength of samples due to potential high distortion levels. 相似文献
85.
86.
87.
José R. B. Gomes Luísa M. P. F. Amaral Manuel A. V. Ribeiro da Silva 《Journal of Physical Organic Chemistry》2008,21(5):365-371
The standard (p0 = 0.1 MPa) molar enthalpy of formation of 3,4‐dimethylbenzophenone was derived from the standard molar energy of combustion, in oxygen, at T = 298.15 K, measured by static bomb combustion calorimetry. The Calvet high temperature vacuum sublimation technique was used to measure the enthalpy of sublimation of the compound. From these experimental parameters, the standard molar enthalpy of formation of 3,4‐dimethylbenzophenone, in the gaseous phase and at T = 298.15 K, was derived as ?(17.1 ± 2.9) kJ mol?1. Density functional theory was used to investigate the gas‐phase molecular energetics of the 12 dimethylbenzophenones. Molecular geometries and vibrational frequencies were computed at the B3LYP/6‐31G(d) level of theory. The larger 6‐311+G(2d,2p) basis set was used to compute the energy of all dimethylbenzophenones and of the other compounds that were considered for the estimation of the standard molar enthalpies of formation at T = 298.15 K. The calculations show that the 2,2′‐ and 4,4′‐dimethylbenzophenones are the least and most stable isomers, respectively. Finally, the calculated enthalpy of formation of the benzophenone that was also studied experimentally, 3,4‐dimethylbenzophenone, is ?16.7 kJ mol?1, which is in excellent agreement with the experimental result. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
88.
89.
D.?Bazeia F.?A.?BritoEmail author W.?Freire R.?F.?Ribeiro 《The European Physical Journal C - Particles and Fields》2005,40(4):531-537
We investigate confinement from new global defect structures in three spatial dimensions. The global defects arise in models described by a single real scalar field, governed by special scalar potentials. They appear as electrically, magnetically or dyonically charged structures. We show that they induce confinement, when they are solutions of effective QCD-like field theories in which the vacua are regarded as color dielectric media with an antiscreening property. As expected, in three spatial dimensions the monopole-like global defects generate the Coulomb potential as part of several confining potentials.Received: 25 August 2004, Published online: 16 March 2005PACS:
11.27. + d, 12.39.-x 相似文献
90.