全文获取类型
收费全文 | 655篇 |
免费 | 25篇 |
国内免费 | 2篇 |
专业分类
化学 | 536篇 |
晶体学 | 5篇 |
力学 | 11篇 |
数学 | 72篇 |
物理学 | 58篇 |
出版年
2023年 | 6篇 |
2022年 | 21篇 |
2021年 | 18篇 |
2020年 | 22篇 |
2019年 | 10篇 |
2018年 | 10篇 |
2017年 | 14篇 |
2016年 | 20篇 |
2015年 | 20篇 |
2014年 | 17篇 |
2013年 | 38篇 |
2012年 | 49篇 |
2011年 | 46篇 |
2010年 | 24篇 |
2009年 | 21篇 |
2008年 | 28篇 |
2007年 | 42篇 |
2006年 | 34篇 |
2005年 | 25篇 |
2004年 | 16篇 |
2003年 | 20篇 |
2002年 | 17篇 |
2001年 | 9篇 |
1999年 | 4篇 |
1997年 | 3篇 |
1996年 | 9篇 |
1995年 | 2篇 |
1994年 | 4篇 |
1993年 | 3篇 |
1991年 | 4篇 |
1990年 | 6篇 |
1989年 | 5篇 |
1987年 | 2篇 |
1985年 | 6篇 |
1984年 | 7篇 |
1983年 | 3篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1978年 | 3篇 |
1975年 | 4篇 |
1974年 | 2篇 |
1973年 | 5篇 |
1967年 | 2篇 |
1957年 | 4篇 |
1956年 | 26篇 |
1955年 | 18篇 |
1937年 | 2篇 |
1934年 | 2篇 |
1927年 | 2篇 |
1921年 | 3篇 |
排序方式: 共有682条查询结果,搜索用时 31 毫秒
141.
Rosa Martha Prez Gutirrez Julio Tllez Gmez Raúl Borja Urby Jos G Contreras Soto Hctor Romo Parra 《Molecules (Basel, Switzerland)》2022,27(17)
The absence of a treatment efficient in the control of type 2 diabetes mellitus requires more functional products to assist treatment. Luteolin (LU) and diosmin (DIO) have been known as bioactive molecules with potential for the treatment of diabetes. This work aimed to establish the role that a combination of LU and DIO in selenium nanoparticles (SeNPs) played in streptozotocin (STZ)- induced diabetes mice. Green synthesis of Se NPs was performed by mixing luteolin and diosmin with the solution of Na2SeO3 under continuous stirring conditions resulting in the flavonoids conjugated with SeNPs. The existence of flavonoids on the surface of SeNPs was confirmed by UV-Vis spectra, Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) images, and DLS graphs via Zetasizer. The average diameter of GA/LU/DIO-SeNPs was 47.84 nm with a PDI of −0.208, a zeta potential value of −17.6, a Se content of 21.5% with an encapsulation efficiency of flavonoids of 86.1%, and can be stabilized by gum Arabic for approximately 175 days without any aggregation and precipitation observed at this time. Furthermore, The C57BL/6 mice were treated with STZ induced-diabetes and were exposed to LU/DIO, SeNPs, and GA/LU/DIO-SeNPs for six weeks. The treatment by nanospheres (GA/LU/DIO-SeNPs) in the mice with diabetes for a period of 6 weeks restored their blood glucose, lipid profile, glycogen, glycosylated hemoglobin, and insulin levels. At the same time, there were significant changes in body weight, food intake, and water intake compared with the STZ- untreated induced diabetic mice. Moreover, the GA/LU/DIO-SeNPs showed good antioxidant activity examined by catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx) in liver and kidney and can prevent the damage in the liver evaluated by aspartate aminotransferase (AST), alanine aminotransferase (ALT), and alkaline phosphatase (ALP) activities. The nanospheres exhibited a significant anti-diabetic activity with a synergistic effect between the selenium and flavonoids. This investigation provides novel SeNPs nanospheres prepared by a high-efficiency strategy for incorporating luteolin and diosmin to improve the efficiency in type 2 diabetes. 相似文献
142.
Efrn V. García-Bez Itzia I. Padilla-Martínez Alejandro Cruz Martha C. Rosales-Hernndez 《Molecules (Basel, Switzerland)》2022,27(19)
Benzimidazole is an important heterocyclic fragment, present in many biologically active compounds with a great variety of therapeutic purposes. Most of the benzimidazole activities are explained through the existence of 1,3-tautomeric equilibrium. As the binding affinity of each tautomer to a protein target depends on an established bioactive conformation, the effect of tautomers on the ligand protein binding mechanism is determinant. In this work, we searched and analyzed a series of reported 13C-NMR spectra of benzazoles and benzazolidine-2-thiones with the purpose of estimating their tautomeric equilibrium. Herein, several approaches to determine this problem are presented, which makes it a good initial introduction to the non-expert reader. This chemical shift difference and C4/C7 signals of benzimidazolidine-2-thione and 1-methyl-2-thiomethylbenzimidazole as references were used in this work to quantitatively calculate, in solution, the pyrrole–pyridine tautomeric ratio in equilibrium. The analysis will help researchers to correctly assign the chemical shifts of benzimidazoles and to calculate their intracyclic or exocyclic tautomeric ratio as well as mesomeric proportion in benzimidazoles. 相似文献
143.
Sergio G. Hernandez-Leon Jose Andre-i Sarabia Sainz Gabriela Ramos-Clamont Montfort Jos ngel Huerta-Ocampo Martha Nydia Ballesteros Ana M. Guzman-Partida María del Refugio Robles-Burgueo Luz Vazquez-Moreno 《Molecules (Basel, Switzerland)》2021,26(6)
In this work, previously synthesized and characterized core-shell silica nanoparticles (FCSNP) functionalized with immobilized molecular bait, Cibacron blue, and a porous polymeric bis-acrylamide shell were incubated with pooled urine samples from adult women or men with normal weight, overweight or obesity for the isolation of potential biomarkers. A total of 30 individuals (15 woman and 15 men) were included. FCSNP allowed the capture of a variety of low molecular weight (LMW) proteins as evidenced by mass spectrometry (MS) and the exclusion of high molecular weight (HMW) proteins (>34 kDa) as demonstrated by SDS-PAGE and 2D SDS-PAGE. A total of 36 proteins were successfully identified by MS and homology database searching against the Homo sapiens subset of the Swiss-Prot database. Identified proteins were grouped into different clusters according to their abundance patterns. Four proteins were found only in women and five only in men, whereas 27 proteins were in urine from both genders with different abundance patterns. Based on these results, this new approach represents an alternative tool for isolation and identification of urinary biomarkers. 相似文献
144.
145.
146.
Myron Miller Eugene Keating Delyle Eastwood Martha Schulz Hendrk 《Spectrochimica Acta Part B: Atomic Spectroscopy》1985,40(4):593-616
Enhancement of sensitive transition metal lines by a sodium matrix is measured in a 3-electrode d.c. plasma jet. Spiking with 0.43 M NaCI causes enhancement by factors of 1.85–2.92 in ionic lines and of 1.22–1.99 in atomic lines for eight of the structurally related analyte elements, but suppresses Zn I and Zn II emissions by about 25 %. Emission response to NaCI of lines within the same spectrum, or between different spectra of like ionization stage, can be simulated to 15 % and 20–25 %, respectively, by approximations linear in energy differences. For ionic lines these differences are the absolute value of the line excitation potential minus the energy of the ion state most readily pumped by Penning ionization by argon. For atomic lines it is the difference between emitting state excitation potential and the first ionization potential. Analyses of the experimental data strongly suggest that: (1) Na acts mainly to pertub radiative transfer rather than collisional redistribution processes; (2) population pumping of excited analyte states is largely driven by Penning ionization; (3) accelerated radiative cooling due to Na is manifested in a lowering of local kinetic temperature; (4) to a first-order of approximation, ambipolar diffusion, analyte-Na collisions of the second kind, and analyte ground state spin, do not influence emission line enhancement by easily ionized elements (EIE). Approximations are developed for predicting transition metal enhancements by arbitrary Na doping concentrations, and means are sketched for extending the method to other analyte group/EIE combinations. Practical implications of the work are noted. 相似文献
147.
Margaret W. Geiger Margaret M. Elliot Velissarios D. Karacostas Thomas J. Moricone Jesse B. Salmon Vincent L. Sideli Martha A. St . Onge 《Photochemistry and photobiology》1984,40(4):545-548
Abstract A series of ring-substituted phenyl and naphthyl azides have been prepared. Electronic absorption spectral properties and quantum yields of disappearance have been determined in aqueous solution. For phenyl azide derivatives, the wavelengths of maximum absorption vary systematically, correlating with electronic effects of the ring substituents. Quantum yield values of 0.1–0.7 are obtained and are independent of a number of experimental conditions, including concentration. There is no simple correlation of the quantum yields of azide disappearance with electronic effects, except that the naphthyl azides have higher photochemical efficiencies than the phenyl azide derivatives. A series of potential protein photolabels has been identified based on electronic absorption characteristics and photochemical efficiencies. 相似文献
148.
Anzar Khan Michael Malkoch Martha F. Montague Craig J. Hawker 《Journal of polymer science. Part A, Polymer chemistry》2008,46(18):6238-6254
Hyperbranched polymers were prepared from a variety of mono‐ and difunctional monomers and used in the development of novel UV‐imprint lithography (UV‐IL) resists. The unique physical and chemical properties of these hyperbranched materials significantly increase the range of molecular systems that could be imprinted. Traditional challenges, such as the use of monomers that have low boiling points or the use of insoluble/highly crystalline momomers, are overcome by the preparation of hyperbranched polymers that incorporate these repeat units. In addition, the low viscosity of the hyperbranched macromolecules and the large number of reactive chain ends overcome many difficulties that are traditionally associated with the use of polymeric materials as imprint resists. Hyperbranched polymers containing up to 12 mol % pendant vinyl groups, needed for secondary crosslinking during imprinting, were prepared with a wide range of repeat unit structures and successfully imprinted with features from tens of microns to ∼ 100 nm. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6238–6254, 2008 相似文献
149.
Methylation of relatively acidic (pKa<13) carbon nucleophiles occurs at neutral pH in aqueous media using suitably substituted methyl sulfonium and selenonium salt electrophiles. 相似文献
150.
Martha C. Mitchell Alon V. McCormick H. Ted Davis 《Zeitschrift für Physik B Condensed Matter》1995,97(2):353-360
The Tarazona model of molecular density functional theory is used to determine the adsorption isotherm and the density distribution of xenon atoms in zeolite NaA. We consider the alpha cage of NaA to be fully three-dimensional and we introduce a basis set for the density distribution to make the solution computationally tractable. The results of this density functional theory model are compared to previous results of grand canonical Monte Carlo simulations for the same system.We dedicate this paper to Professor Herbert Wagner, whose excellent contributions to density functional theory typify his valuable role in the advancement of statistical physics 相似文献