全文获取类型
收费全文 | 393篇 |
免费 | 11篇 |
专业分类
化学 | 206篇 |
晶体学 | 1篇 |
力学 | 11篇 |
数学 | 47篇 |
物理学 | 109篇 |
无线电 | 30篇 |
出版年
2022年 | 4篇 |
2021年 | 11篇 |
2020年 | 7篇 |
2019年 | 6篇 |
2018年 | 9篇 |
2017年 | 3篇 |
2016年 | 14篇 |
2015年 | 9篇 |
2014年 | 11篇 |
2013年 | 29篇 |
2012年 | 24篇 |
2011年 | 14篇 |
2010年 | 13篇 |
2009年 | 24篇 |
2008年 | 32篇 |
2007年 | 27篇 |
2006年 | 16篇 |
2005年 | 18篇 |
2004年 | 9篇 |
2003年 | 11篇 |
2002年 | 11篇 |
2001年 | 10篇 |
2000年 | 4篇 |
1999年 | 4篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 6篇 |
1995年 | 4篇 |
1994年 | 7篇 |
1993年 | 6篇 |
1992年 | 7篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1986年 | 1篇 |
1985年 | 6篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1976年 | 4篇 |
1973年 | 1篇 |
1932年 | 1篇 |
排序方式: 共有404条查询结果,搜索用时 15 毫秒
101.
Single vibronic level dispersed fluorescence spectra of jet-cooled HGeCl and DGeCl have been recorded by laser excitation of selected bands of the A 1A"-X 1A' electronic transition. Twenty-six ground state vibrational levels of HGeCl and 42 of DGeCl were measured, assigned, and fitted to standard anharmonicity expressions, which allowed all the harmonic frequencies to be determined for both isotopomers. A normal coordinate least squares analysis obtained by fitting the harmonic frequencies yielded reliable values for five of the six force constants. The ground state effective rotational constants and force field data were combined to calculate average (rz) and approximate equilibrium (re z) structures, with re z(GeH)=1.586(1) A, re z(GeCl)=2.171(2) A, and the bond angle fixed at our CCSD(T)/aug-cc-pVTZ ab initio value of 93.9 degrees . Comparisons show that the derived bond lengths are consistent with those of the appropriate diatomic molecules in their ground electronic states and the bond angle is similar to that of germylene (GeH2). A Franck-Condon simulation of the vibrational intensities in the 0(0) (0) band emission spectrum of HGeCl using ab initio force field data shows good agreement with experiment, lending credence to the vibrational analysis of the observed spectra. 相似文献
102.
Victor S. M. Braga Taiza P. Mancilha Ricardo J. Cassella Wagner F. Pacheco 《Journal of fluorescence》2013,23(1):49-55
Statins are a class of drugs mostly used for treating hyperlipidemia, and rosuvastatin is the newest drug in the market belonging to this class. In this present work, a method was developed based on the molecular fluorescence technique, with the objective to quantify rosuvastatin in urine samples. For this purpose, the study of several parameters was made to achieve the maximum analytical signal (under reaction with sulfuric acid during 40 min). Also, a previous step to avoid matrix interference was carried out (liquid–liquid extraction). The limit of detection (LOD) and the limit of quantification (LOQ) were 0.38 and 1.28 mg L?1, respectively. Linear relationship between rosuvastatin concentration and it’s fluorescence intensity was found until 5.0 mg L?1. The proposed method was tested in several samples spiked with rosuvastatin and recovery was found in the range of 90?±?10 %. 相似文献
103.
Wendell P. de Oliveira Marcelo A. Savi Pedro Manuel C. L. Pacheco 《Archive of Applied Mechanics (Ingenieur Archiv)》2013,83(7):1013-1037
Heat treatment processes are usually employed to control the mechanical properties of steels and quenching is one of the most common treatments. This article deals with the modeling and simulation of quenching in steel cylinders using a multi-phase constitutive model. Finite element method is employed for spatial discretization. Numerical simulations are carried out by considering an iterative process associated with the operator split technique. Initially, a verification procedure is of concern establishing a comparison between numerical and experimental data, presenting a good agreement. Afterward, notched steel cylinders are treated evaluating the influence of notches in quenched pieces. Temperature, phase transformations and stresses are monitored during the quenching in order to give a general idea of the thermomechanical behavior of the process. 相似文献
104.
Lee J. Silverberg Carlos Pacheco Debashish Sahu Peter Scholl Hany F. Sobhi Joshua T. Bachert Kaitlyn Bandholz Ryan V. Bendinsky Heather G. Bradley Baylee K. Colburn David J. Coyle Jonathon R. Dahl Megan Felty Ryan F. Fox Kyanna M. Gonzalez Jasra M. Islam Stacy E. Koperna Quentin J. Moyer Duncan J. Noble Melissa E. Ramirez Ziwei Yang 《Journal of heterocyclic chemistry》2020,57(4):1797-1805
A series of 11 novel 3-aryl-2-phenyl-2,3-dihydro-4H-1,3-benzothiazin-4-ones was prepared at room temperature by T3P-mediated cyclization of N-aryl-C-phenyl imines with thiosalicylic acid. This provides simple and ready access to N-aryl compounds in this family, which have been generally difficult to prepare. 相似文献
105.
Carroll L Pacheco MC Garcia L Gouverneur V 《Chemical communications (Cambridge, England)》2006,(39):4113-4115
Allenylsilanes reacted at room temperature in acetonitrile with Selectfluor, an electrophilic fluorinating reagent, to give secondary propargylic fluorides in moderate to good yields; mechanistically, a side-product resulting from a 1,2-silyl shift testifies to the presence of a cationic intermediate. 相似文献
106.
Yady J. Manrique Diana P. Pacheco Fleming Martínez 《Journal of solution chemistry》2008,37(2):165-181
By using the van’t Hoff and Gibbs equations, solubility data of ibuprofen (IBP) and naproxen (NAP) determined at several temperatures
in propylene glycol (PG) + water (W) cosolvent mixtures were used to evaluate the Gibbs energies, enthalpies, and entropies
of solution, mixing and solvation. The solubilities are greater in pure PG and lower in W in both cases at all studied temperatures.
These results clearly show that a cosolvent effect is present in these systems. The solvation of these drugs was greater in
W compared to PG, and it was lower in the cosolvent mixtures compared with the pure solvents. By means of an enthalpy-entropy
compensation analysis, non-linear ΔH
solno versus ΔG
solno compensation plots were obtained, with negative and positive slopes if all of the composition intervals are considered. Accordingly,
it follows that at low PG solvent fractions the dominant factor for the solubility of IBP and NAP in this cosolvent system
is the entropy, probably due to loosening of the water structure caused by the addition of the cosolvent. 相似文献
107.
Liliana Fátima Bezerra de Lira Jose Geraldo Andrade Pacheco Eduardo Homem de Siqueira Cavalcanti Maria Fernanda Pimentel 《Microchemical Journal》2010,96(1):126-34
This paper evaluates analytical methods based on near infrared (NIR) and middle infrared (MIR) spectroscopy and multivariate calibration to monitor the stability of biodiesel. There was a focus on three parameters: oxidative stability index, acid number and water content. Ethylic and methylic biodiesel from different feedstocks were used in experiments of accelerated aging, in order to take into account the wide variety of oilseeds and feedstocks available in Brazil. Partial least squares (PLS) and multiple linear regression (MLR) models were developed. Different pre-processing techniques and spectral variable/regions selection algorithms were evaluated. For MLR models, the successive projection algorithm (SPA) was employed. Interval PLS (iPLS) and selection of variables taking into account the significant regression coefficients were used for PLS models. Results showed that both near and middle infrared regions, and all variable selection methods tested were efficient for predicting these three important quality parameters of B100, the root mean squares error of prediction (RMSEP) values being comparable to the reproducibility of the corresponding standard method for each property investigated. 相似文献
108.
David A. Pacheco Tanaka Margot A. Llosa Tanco Junya Okazaki Yoshito Wakui Fujio Mizukami Toshishige M. Suzuki 《Journal of membrane science》2008,320(1-2):436-441
Mesoporous YSZ–γ-Al2O3 membranes were coated on α-Al2O3 (Ø2 mm) tube by dipping the α-Al2O3 support tube into mixed sol consists of nano-size YSZ and bohemite particles followed by drying and calcination at 600 °C. Addition of bohemite in YSZ sol helped a good adhesion and uniform coating of the membrane film onto α-Al2O3 support. The quality of the mesoporous YSZ–γ-Al2O3 membranes was evaluated by the gas permeability experiments. The number of defects was minimized when the γ-Al2O3 content became more than 40%. Addition of γ-Al2O3 inhibited the crystal growth of YSZ, sintering shrinkage and distortion stress. Increase of calcination temperature and time results in the increase of pore size and N2 permeance. A hydrogen perm-selective membrane was prepared by filling palladium into the nano-pores of YSZ–γ-Al2O3 layer by vacuum-assisted electroless plating. Crystal growth of palladium was observed by thermal annealing of the membrane at 600 °C for 40 h. The Pd–YSZ–γ-Al2O3 composite membrane revealed improved thermal stability allowing long-term operation at elevated temperature (>500 °C). This has been attributed to the improved fracture toughness of YSZ–γ-Al2O3 layer and matching of thermal expansion coefficient between palladium and YSZ. Although fracture of the membrane did not occur, decline of H2 flux was observed when the membrane was exposed in 600 °C. This has been attributed to the agglomeration of palladium particles by crystal growth and dense packing into the pore networks of YSZ–γ-Al2O3 by elevation of temperature. 相似文献
109.
Biosorption is a term that usually describes the removal of heavy metals from an aqueous solution through their passive binding to a biomass. Bacteria, yeast, algae and fungi are microorganisms that have been immobilized and employed as sorbents in biosorption processes. The binding characteristics of microorganisms are attributed to functional groups on the surface providing some features to the biosorption process like selectivity, specificity and easy release. These characteristics turn the biosorption into an ideal process to be introduced in solid phase extraction systems for analytical approaches. This review encompasses the research carried out since 2000, focused on the employment of biosorption processes as an analytical tool to improve instrumental analysis. Since aminoacids and peptides as synthetic analogues of natural metallothioneins, proteins present in the cell wall of microorganisms, have been also immobilized on solid supports (controlled pore glass, carbon nanotubes, silica gel polyurethane foam, etc.) and introduced into solid phase extraction systems; a survey attending this issue will be developed as well in this review. 相似文献
110.
Linares R Pacheco JR Good TA 《Journal of photochemistry and photobiology. B, Biology》2004,77(1-3):17-26
The multichain interleukin-2 receptor (IL-2R) has been proposed as a target for immunotherapy in the treatment of certain cancers including adult T-cell leukemia and cutaneous T-cell lymphoma as well as certain autoimmune diseases. The IL-2R is abnormally expressed on cells associated with each of these diseases; while normal, non-activated T-cells do not express the receptor. This report describes the selective photolysis of activated and non-activated IL-2R expressing cells using several immunoconjugates synthesized with one of two photosensitizers, hematoporphyrin (HP) or chlorin-e(6) (Ce(6)), covalently linked to IL-2 or an anti-IL-2R antibody. Destruction of IL-2R bearing cells was achieved after photosensitizer internalization and irradiation using all tested photosensitizer conjugates. Chlorin containing conjugates were more effective, by a factor of 4 or more, than HP containing conjugates. Conjugates made with IL-2 were up to 30 times more effective than conjugates that used a monoclonal antibody against the IL-2R for targeting. Activation of the cells to increase IL-2R expression decreased the internalization time required for optimal therapeutic efficacy; however, stimulation of the cell to increase IL-2 secretion greatly reduced conjugate effectiveness. This work could lead to the development of more effective strategies to treat T-cell diseases. 相似文献