全文获取类型
收费全文 | 345篇 |
免费 | 8篇 |
专业分类
化学 | 206篇 |
晶体学 | 5篇 |
力学 | 9篇 |
数学 | 41篇 |
物理学 | 92篇 |
出版年
2022年 | 8篇 |
2021年 | 7篇 |
2020年 | 10篇 |
2019年 | 11篇 |
2018年 | 6篇 |
2017年 | 5篇 |
2016年 | 15篇 |
2015年 | 8篇 |
2014年 | 8篇 |
2013年 | 14篇 |
2012年 | 27篇 |
2011年 | 25篇 |
2010年 | 21篇 |
2009年 | 14篇 |
2008年 | 19篇 |
2007年 | 19篇 |
2006年 | 20篇 |
2005年 | 9篇 |
2004年 | 10篇 |
2003年 | 7篇 |
2002年 | 9篇 |
2001年 | 5篇 |
2000年 | 6篇 |
1999年 | 4篇 |
1998年 | 1篇 |
1997年 | 9篇 |
1996年 | 2篇 |
1995年 | 5篇 |
1994年 | 5篇 |
1993年 | 3篇 |
1992年 | 7篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1976年 | 2篇 |
排序方式: 共有353条查询结果,搜索用时 812 毫秒
51.
It has been recently reported that a granular mixture in which grains differ in their restitution coefficients presents segregation:
the more inelastic particles sink to the bottom. When other segregation mechanisms as buoyancy and the Brazil nut effect are
present, the inelasticity induced segregation can compete with them. First, a detailed analysis, based on numerical simulations
of two dimensional systems, of the competition between buoyancy and the inelasticity induced segregation is presented, finding
that there is a transition line in the parameter space that determines which mechanism is dominant. In the case of neutrally
buoyant particles having different sizes the inelasticity induced segregation can compete with the Brazil nut effect (BNE).
Reverse Brazil nut effect (RBNE) could be obtained at large inelasticities of the intruder. At intermediate values, BNE and
RBNE coexist and large inelastic particles are found both near the bottom and at the top of the system. 相似文献
52.
53.
Chirleanny M. Mendes Marília A. Brito Tatiana S. Porto Ana L. F. Porto Ranilson S. Bezerra Luiz B. CarvalhoJr. Ana M. A. Caneiro-Leão Maria G. Carneiro-da-Cunha 《Chemical Papers》2009,63(6):662-669
Intestine proteases of Nile tilapia (Oreochromis niloticus) were partially purified by heat treatment (purification factor of 3.5, enzyme activity remained almost constant) to reach the maximum activity and stability within an alkaline pH range of 7.2–11.0. The optimum temperature and stability over a 120 min period were found to be at 55°C and at 35–45°C, respectively. The proteases’ activity was not affected by a 1 vol. % saponin surfactant, inactivated by 0.01 g mL?1 sodium dodecylsulphate after 120 min, and it remained stable for 30 min in a 5 vol. % and 10 vol. % hydrogen peroxide solutions. The proteases were slightly activated by Ca2+, Mg2+, and K+ and the substrate most effectively hydrolysed was casein (40.0 U mg?1). A 24 full factorial design used to evaluated the influence of independent variables showed that the enzyme extract, detergent concentration and the incubation time had a significant influence on the enzymatic activity. The best conditions to be used concerning detergent additive were found with 0.3 mg mL?1 of protein and 3.0 mg mL?1 of detergent for 30 min in the presence of Astrus® detergent. 相似文献
54.
Ferreira MC Gameiro J Nagib PR Brito VN Vasconcellos Eda C Verinaud L 《Photochemistry and photobiology》2009,85(1):227-233
The effect of HeNe laser on the extracellular matrix deposition, chemokine expression and angiogenesis in experimental paracoccidioidomycotic lesions was investigated. At days 7, 8 and 9 postinfection the wound of each animal was treated with a 632.8 nm HeNe laser at a dose of 3 J cm(-2). At day 10 postinfection, the wounds were examined by using histologic and immunohistochemical methods. Results revealed that laser-treated lesions were lesser extensive than untreated ones, and composed mainly by macrophages and lymphocytes. High IL-1beta expression was shown in the untreated group whereas in laser-treated animals the expression was scarce. On the other hand, the expression of CXCL-10 was found to be reduced in untreated animals and quite intensive and well distributed in the laser-treated ones. Also, untreated lesions presented vascular endothelial growth factor (VEGF) in a small area near the center of the lesion and high immunoreactivity for hypoxia-inducible factor-1 (HIF-1), whereas laser-treated lesions expressed VEGF surrounding blood vessels and little immunoreactivity for HIF-1. Laser-treated lesions presented much more reticular fibers and collagen deposition when compared with the untreated lesion. Our results show that laser was efficient in minimizing the local effects observed in paracoccidioidomycosis and can be an efficient tool in the treatment of this infection, accelerating the healing process. 相似文献
55.
Brito e Abreu S Skinner W 《Langmuir : the ACS journal of surfaces and colloids》2012,28(19):7360-7367
Methylated quartz surfaces are extensively used in colloid science for wettability studies and the control and impact of hydrophobicity in key physicochemical processes. In this study, time-of-flight secondary ion mass spectrometry (ToF-SIMS) has been used to correlate the surface chemistry of trimethylchlorosilane-methylated quartz surfaces with the contact angle. Models have been developed for the calculation of both advancing and receding contact angles based on measurements of the ToF-SIMS signals for SiC(3)H(9)(+) (TMCS) and Si(+) (quartz). These models enable the contact angle across surfaces and, more importantly, that of individual particles to be determined on a micrometer scale. Distributions of contact angles in large ensembles of particles, therefore, can now be determined. In addition, from the ToF-SIMS analysis, the surface coverage of the methylated species can be quantitatively determined, in line with the Cassie equation. Moreover, advancing and receding contact angle maps can be calculated from ToF-SIMS images, and hence the variation in microscopic hydrophobicity (e.g., at the particle level) can be extracted directly from the images. 相似文献
56.
Joana Monterrosa José Daniel Martínez Mary Lorena Araujo Felipe Brito Giuseppe Lubes Mildred Rodríguez Lino Hernández Vito Lubes 《Journal of solution chemistry》2012,41(4):589-598
We studied speciation of the mixed-ligand complex formation equilibria of vanadium(III) with both 2,2??-bipyridine (Bipy) and the amino acids glycine (HGly), proline (HPro), ??-alanine (H??Ala), and ??-alanine (H??Ala) by means of electromotive forces measurements emf(H) using 3.0?mol?dm?3 KCl as the ionic medium at 25 °C. The experimental data were analyzed by means of the computational least-squares program LETAGROP, taking into account the hydrolysis of the vanadium(III) cation, the respective stability constants of the binary complexes, and the acid/base reactions of the ligands which were kept fixed during the analysis. In all four amino acid systems studied we observed the complexes [V2O(Bipy)(B)]3+, [V2O(Bipy)2(B)2]2+, [V(OH)(Bipy)(B)2] and [V(OH)2(Bipy)(B)], where B represents the deprotonated form of the amino acids studied in this work. The respective stability constants were determined and the species distribution diagrams as a function of pH are briefly discussed. 相似文献
57.
J. Brito F. J. Martinez J. A. Moreno J. L. Verdegay 《Fuzzy Optimization and Decision Making》2012,11(3):337-349
Problems concerning the distribution routes for frozen products need to incorporate constraints that avoid breaks in the cold chain. The decision making process under uncertain environments is a common one in real logistics problems. The purpose of this study is to apply a fuzzy approach which will provide an optimal solution to the distribution of frozen food with uncertainty in its time values. A soft computing approach is used where fuzzy constraints are included in the modeling and the solution of the problem. 相似文献
58.
59.
Lucas H. Martorano Jordana T. Brito Ana Carolina F. de Albuquerque Carlos Magno Rocha Ribeiro Rodolfo Goetze Fiorot José Walkimar de Mesquita Carneiro Fabio Luiz Paranhos Costa Alessandra L. Valverde Fernando Martins dos Santos Junior 《Magnetic resonance in chemistry : MRC》2022,60(4):434-441
Recently, structural elucidation of natural products has undergone a revolution. The combined use of different modern spectroscopic methods has allowed obtaining a complete structural assignment of natural products using small amounts of sample. However, despite the extraordinary ongoing advances in spectroscopy, the mischaracterization of natural products has been and remains a recurrent problem, especially when the substance presents several stereogenic centers. The misinterpretation of nuclear magnetic resonance (NMR) data has resulted in frequent reports addressing structural reassignment. In this context, a great effort has been devoted to developing quantum chemical calculations that simulate NMR parameters accurately, allowing to achieve a more precise spectral interpretation. In this work, we employed a protocol for theoretical calculations of 1H NMR chemical shifts and coupling constants using density functional theory (DFT), followed by the application of the DP4+ method to revisit the structure of Heliannuol L, a member of the Heliannuol class, isolated from Helianthus annuus. Our results indicate that the originally proposed structure of Heliannuol L needs a stereochemical reassignment, placing the hydroxyl bonded to C10 in the opposite side of the methyl and hydroxyl groups bonded to C7 and C8, respectively. 相似文献
60.
G. Magela e Silva L. A. C. Malbouisson A. Naves de Brito J. D. M. Vianna 《Journal of mathematical chemistry》1993,13(1):317-330
Concepts of functional analysis, namely, regular points, tangent subspaces, constraint surfaces, Lagrangian matrix restricted to the tangent subspace of a constraint surface, are presented in connection with the Hartree-Fock (HF) problem. The energy functional in LCAO approximation is considered to be a polynomial function of several variables subject to subsidiary conditions. General HF equations and instability conditions for the unrestricted Hartree-Fock (UHF) solutions are derived from this standpoint. 相似文献