全文获取类型
收费全文 | 689篇 |
免费 | 40篇 |
国内免费 | 3篇 |
专业分类
化学 | 488篇 |
晶体学 | 4篇 |
力学 | 9篇 |
数学 | 99篇 |
物理学 | 132篇 |
出版年
2023年 | 4篇 |
2022年 | 5篇 |
2021年 | 12篇 |
2020年 | 8篇 |
2019年 | 15篇 |
2018年 | 5篇 |
2017年 | 16篇 |
2016年 | 28篇 |
2015年 | 21篇 |
2014年 | 25篇 |
2013年 | 45篇 |
2012年 | 42篇 |
2011年 | 43篇 |
2010年 | 35篇 |
2009年 | 39篇 |
2008年 | 36篇 |
2007年 | 36篇 |
2006年 | 36篇 |
2005年 | 32篇 |
2004年 | 32篇 |
2003年 | 22篇 |
2002年 | 20篇 |
2001年 | 24篇 |
2000年 | 29篇 |
1999年 | 21篇 |
1998年 | 11篇 |
1997年 | 10篇 |
1996年 | 16篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 6篇 |
1984年 | 8篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1976年 | 2篇 |
排序方式: 共有732条查询结果,搜索用时 15 毫秒
121.
Pedro Carmona Arantxa Rodríguez-Casado Marina Molina 《Analytical and bioanalytical chemistry》2009,393(4):1289-1295
We describe the improvement of a novel approach to investigating hydrogen/deuterium (H/D) exchange kinetics in biomolecules
using transmission infrared spectroscopy. The method makes use of a Fourier transform infrared spectrometer coupled with a
microdialysis flow cell to determine exchange rates of labile hydrogens. With this cell system, the monitoring of exchange
reactions has been studied here as a function of some cell characteristics such as: (a) dialysis membrane surface contacting
both the H2O and D2O compartments; (b) molecular cutoff of dialysis membrane; and (c) distance between the cell-filling holes. The best improvement
has been obtained by increasing the dialysis membrane surface followed by increase of molecular cutoff. However, not significant
differences were found using various distances between filling holes. The fastest exchange rate which can be measured with
the cell system used here is found to be k = 0.41 ± 0.02 min−1, that is, about threefold greater than the one got in a previous work. This microdialysis flow cell has been used here for
the study of H/D exchange in nucleic acids with subsequent structural analysis by 2D correlation spectroscopy. 相似文献
122.
This work assumes that the small area quantities of interest follow a Fay–Herriot model with spatially correlated random area
effects. Under this model, parametric and nonparametric bootstrap procedures are proposed for estimating the mean squared
error of the empirical best linear unbiased predictor (EBLUP). A simulation study based on the Italian Agriculture Census
2000 compares bootstrap and analytical estimates of the MSE and studies their robustness to non-normality. Results indicate
lower bias for the non-parametric bootstrap under specific departures from normality.
相似文献
123.
Manuel F. Pérez Polo Manuel Pérez Molina Javier Gil Chica 《Chaos, solitons, and fractals》2009,39(3):1356-1370
This paper explores chaotic behaviour and control of micro-electro-mechanical systems (MEMS), which consist of thousands of small read/write probe tips that access gigabytes of data stored in a non-volatile magnetic surface. The model of the system is formed by two masses connected by a nonlinear spring and a viscous damping. The paper shows that, by means of an adequate feedback law, the masses can behave as two coupled Duffing’s oscillators, which may reach chaotic behaviour when harmonic forces are applied. The chaotic motion is destroyed by applying the following control strategies: (i) static output feedback control law with constant forces and (ii) geometric nonlinear control. The aim is to drive the masses to a set point even with harmonic base excitation, by using chaotic dynamics and nonlinear control. The paper shows that it is possible to obtain a positioning time around a few ms with sub-nanometre accuracy, velocities, accelerations and forces, as it appears in the design of present MEMS devices. Numerical simulations are used to verify the mathematical discussions. 相似文献
124.
Ramos-Tejada MM Ontiveros-Ortega A Giménez-Martín E Espinosa-Jiménez M Molina Díaz A 《Journal of colloid and interface science》2006,297(1):317-321
Data are presented on the kinetics, electrokinetics, and surface free energy in the process of adsorption of polyethyleneimine (PEI) as a pretreatment of Leacril, later dyed with the reactive dye Remazol Brilliant Blue R (RBBR). The electrokinetic potential of Leacril is negative, due probably to the presence of sulfonate and sulfate end-group onto Leacril fibers. The zeta potential of Leacril decreases in absolute value as a function of NaCl concentration in solution, probably because of compression of the electrical double layer. The zeta potential of Leacril as a function of the concentration of PEI in solution increases because of the adsorption of PEI ions through chemical reaction between the sulfonate end-groups of Leacril and the amine groups of PEI. The adsorption kinetics shows that an increase in the concentration of PEI, brings about an increase in the amount of RBBR adsorbed onto the fiber. This may be an indication of the chemical reaction between the reactive groups of the polyelectrolyte and dye molecules. The behavior of the surface free energy of the systems involved confirms these conclusions. 相似文献
125.
We discuss the formation of self-trapped localized states near the edge of a semi-infinite array of nonlinear optical waveguides. We study a crossover from nonlinear surface states to discrete solitons by analyzing the families of odd and even modes centered at finite distances from the surface and reveal the physical mechanism of the nonlinearity-induced stabilization of surface modes. 相似文献
126.
We examine in detail a recent work(D. Gülmez, U. G. Mei?ner and J. A. Oller, Eur. Phys. J. C,77: 460(2017)), where improvements to make ρρ scattering relativistically covariant are made. The paper has the remarkable conclusion that the J =2 state disappears with a potential which is much more attractive than for J =0,where a bound state is found. We trace this abnormal conclusion to the fact that an "on-shell" factorization of the potential is done in a region where this potential is singular and develops a large discontinuous and unphysical imaginary part. A method is developed, evaluating the loops with full ρ propagators, and we show that they do not develop singularities and do not have an imaginary part below threshold. With this result for the loops we define an effective potential, which when used with the Bethe-Salpeter equation provides a state with J =2 around the energy of the f_2(1270). In addition, the coupling of the state to ρρ is evaluated and we find that this coupling and the T matrix around the energy of the bound state are remarkably similar to those obtained with a drastic approximation used previously, in which the q~2 terms of the propagators of the exchanged ρ mesons are dropped, once the cut-off in the ρρ loop function is tuned to reproduce the bound state at the same energy. 相似文献
127.
Bernardo?Nu?ez-MoraledaEmail author Joaquin?Pizarro Elisa?Guerrero Maria?P.?Guerrero-Lebrero Andres?Yá?ez Sergio?Ignacio?Molina Pedro?Luis?Galindo 《The European Physical Journal B - Condensed Matter and Complex Systems》2014,87(11):263
In this paper, stress fields at the surface of the capping layer of self-assembled InAsP quantum wires grown on an InP (001) substrate have been determined from atomistic models using molecular dynamics and Stillinger-Weber potentials. To carry out these calculations, the quantum wire compositional distribution was extracted from previous works, where the As and P distributions were determined by electron energy loss spectroscopy and high-resolution aberration-corrected Z-contrast imaging. Preferential sites for the nucleation of wires on the surface of the capping layer were studied and compared with (i) previous simulations using finite element analysis to solve anisotropic elastic theory equations and (ii) experimentally measured locations of stacked wires. Preferential nucleation sites of stacked wires were determined by the maximum stress location at the MD model surface in good agreement with experimental results and those derived from finite element analysis. This indicates that MD simulations based on empirical potentials provide a suitable and flexible tool to study strain dependent atom processes. 相似文献
128.
A novel method, dispersive liquid-liquid microextraction combined with liquid chromatography-fluorescence detection is proposed for the determination of three beta-blockers (metoprolol, bisoprolol, and betaxolol) in ground water, river water, and bottled mineral water. Some important parameters, such as the kind and volume of extraction and dispersive solvents, extraction time, pH, and salt effect were investigated and optimized. In the method, a suitable mixture of extraction solvent (60 μL carbon tetrachloride) and dispersive solvent (1 mL acetonitrile) were injected into the aqueous samples (5.00 mL) and the cloudy solution was observed. After centrifugation, the enriched analytes in the bottom CCl(4) phase were determined by liquid chromatography with fluorescence detection. Under the optimum conditions, the enrichment factors (EFs) for metoprolol, bisoprolol, and betaxolol were 180, 190, and 182, and the limits of detection (LODs) were 1.8, 1.4, and 1.0 ng L(-1) , respectively. A good linear relationship between the peak area and the concentration of analytes was obtained in the range of 3-150 ng L(-1) . The relative standard deviations (RSDs) for the extraction of 10 ng L(-1) of beta-blockers were in the range of 4.6-5.7% (n = 5). Compared with other methods, dispersive liquid-liquid microextraction is a very simple, rapid, sensitive (low limit of detection), and economical (only 1.06 mL volume of organic solvent) method, which is in compliance with the requirements of green analytical methodologies. 相似文献
129.
Dr. Marta E. Plonska‐Brzezinska Dr. Mikołaj Lewandowski Dr. Małgorzata Błaszyk Dr. Agustin Molina‐Ontoria Prof. Dr. Tadeusz Luciński Prof. Dr. Luis Echegoyen 《Chemphyschem》2012,13(18):4134-4141
Composites of unmodified or oxidized carbon nano‐onions (CNOs/ox‐CNOs) with poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) are prepared with different compositions. By varying the ratio of PEDOT:PSS relative to CNOs, CNO/PEDOT:PSS composites with various PEDOT:PSS loadings are obtained and the corresponding film properties are studied as a function of the polymer. X‐ray photoelectron spectroscopy characterization is performed for pristine and ox‐CNO samples. The composites are characterized by scanning and transmission electron microscopy and differential scanning calorimetry studies. The electrochemical properties of the nanocomposites are determined and compared. Doping the composites with carbon nanostructures significantly increases their mechanical and electrochemical stabilities. A comparison of the results shows that CNOs dispersed in the polymer matrices increase the capacitance of the CNO/PEDOT:PSS and ox‐CNO/PEDOT:PSS composites. 相似文献
130.
We introduce a novel concept of surface bound states in the continuum, i.e., surface modes embedded into the linear spectral band of a discrete lattice. We suggest an efficient method for creating such surface modes and the local bounded potential necessary to support the embedded modes. We demonstrate that the surface embedded modes are structurally stable, and the position of their eigenvalues inside the spectral band can be tuned continuously by adding weak nonlinearity. 相似文献