全文获取类型
收费全文 | 363篇 |
免费 | 11篇 |
国内免费 | 4篇 |
专业分类
化学 | 198篇 |
晶体学 | 10篇 |
力学 | 18篇 |
数学 | 50篇 |
物理学 | 102篇 |
出版年
2023年 | 3篇 |
2022年 | 3篇 |
2021年 | 10篇 |
2020年 | 9篇 |
2019年 | 10篇 |
2018年 | 5篇 |
2017年 | 3篇 |
2016年 | 11篇 |
2015年 | 12篇 |
2014年 | 8篇 |
2013年 | 20篇 |
2012年 | 17篇 |
2011年 | 32篇 |
2010年 | 11篇 |
2009年 | 19篇 |
2008年 | 28篇 |
2007年 | 26篇 |
2006年 | 14篇 |
2005年 | 25篇 |
2004年 | 10篇 |
2003年 | 15篇 |
2002年 | 9篇 |
2001年 | 8篇 |
2000年 | 15篇 |
1999年 | 4篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1996年 | 5篇 |
1995年 | 5篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1992年 | 8篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1962年 | 1篇 |
排序方式: 共有378条查询结果,搜索用时 15 毫秒
151.
We report the observation of a Plateau instability in a thin filament of solid gel with a very small elastic modulus. A longitudinal undulation of the surface of the cylinder reduces its area thereby triggering capillary instability, but is counterbalanced by elastic forces following the deformation. This competition leads to a nontrivial instability threshold for a solid cylinder. The ratio of surface tension to elastic modulus defines a characteristic length scale. The onset of linear instability is when the radius of the cylinder is one-sixth of this length scale, in agreement with theory presented here. 相似文献
152.
José R. Mora Alexis Maldonado Rosa M. Domínguez Gabriel Chuchani 《Journal of Physical Organic Chemistry》2010,23(9):845-852
The rates of gas‐phase elimination of several β‐substituted diethyl acetals have been determined in a static system and seasoned with allyl bromide. The reactions, inhibited with toluene, are homogeneous, unimolecular, and follow first‐order law kinetics. These elimination processes involve two parallel reactions. The first parallel reaction yields ethanol and the corresponding ethyl vinyl ether. The latter product is an unstable intermediate and further decomposes to ethylene and the corresponding substituted aldehyde. The second parallel reaction gives ethane and the corresponding ethyl ester. The kinetics has been measured over the temperature range of 370–441 °C and pressure range of 23–160 torr. The rate coefficients are given by the following Arrhenius equations: The differences in the rates of ethanol formation may be attributed to electronic transmission of the β‐substituent. The comparative kinetic and thermodynamic parameters of the parallel reactions suggest two different concerted polar four‐membered cyclic transition state types of mechanisms. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
153.
Muñoz de la Peña A Mora Diez N Bohoyo Gil D Cano Carranza E 《Journal of fluorescence》2009,19(2):345-352
A second-order multivariate calibration approach, based on a combination of PARAFAC with time-resolved room temperature phosphorescence
(RTP), has been applied to resolve a binary mixture of Phenanthrene and 1,10-Phenanthroline, as model compounds. The RTP signals
were obtained in aqueous β-cyclodextrin solutions, in the presence of several heavy atom containing compounds. No deoxygenation
was necessary to obtain the phosphorescence signals, which adds simplicity to the method. The resolution of the model compounds
was possible in base to the differences in the delay-time of the RTP signals of the investigated analytes, opening a new approach
for second-order data generation and subsequent second order multivariate calibration. 相似文献
154.
Lino Reyes J. Raul Alvarez‐Idaboy Nelaine Mora‐Diez 《Journal of Physical Organic Chemistry》2009,22(7):643-649
This paper reports the first complete theoretical study of substituent effects on the mechanism of the Baeyer– Villiger (BV) reaction in non‐polar solvents taking into account the lowest‐energy mechanism that has been proposed for this rearrangement which is non‐ionic and fully concerted. The BV reaction of p‐substituted acetophenones, p‐XC6H4COCH3 (X = NO2, CN, H, CH3, OCH3), with performic (PFA) and trifluoroperacetic (TFPAA) acids, catalyzed by formic (FA) and trifluoroacetic (TFAA) acids, respectively, using the MPWB1K functional and the 6‐311G(d,p) and 6‐311++G(d,p) basis sets, are studied. Solvent effects are taken into account by means of the PCM continuum model using dichloromethane as solvent. Electron‐donating substituents on the aryl group have a relatively small activation effect on the first step, but a pronounced activation effect on the second to the point of being able to change the rate‐determining step (RDS) of the reaction, as observed in the case of p‐methoxyacetophenone with TFPAA acids. After analyzing the changes in Gibbs free energy of activation, geometrical parameters, and charge distributions of the transition states (TSs), explanations are provided for the two distinct effects that substituents on the ketone have on the kinetics of the addition and migration steps of the BV oxidation. The effect of the acid/peracid pair used is also discussed. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
155.
Luis Miguel Anaya-Esparza Zuamí Villagrn-de la Mora Olga Vzquez-Paulino Felipe Ascencio Anglica Villarruel-Lpez 《Molecules (Basel, Switzerland)》2021,26(17)
Currently, the high added-value compounds contained in plant by-products and wastes offer a wide spectrum of opportunities for their reuse and valorization, contributing to the circular economy. The bell pepper (Capsicum annum L.) is an exotic vegetable with high nutritional value that, after processing, leaves wastes (peel, seeds, and leaves) that represent desirable raw material for obtaining phytochemical compounds. This review summarizes and discusses the relevant information on the phytochemical profile of bell peppers and their related biological properties as an alternative to revalorize losses and wastes from bell peppers for their application in the food and pharmaceutical industries. Bell pepper fruits, seeds, and leaves contain bioactive compounds (phenols, flavonoids, carotenoids, tocopherol, and pectic polysaccharides) that exhibit antioxidant, antibacterial, antifungal, immunosuppressive and immunostimulant properties, and antidiabetic, antitumoral and neuroprotective activities, and have a potential use as functional food additives. In this context, the revalorization of food waste is positioned as a technological and innovative research area with beneficial effects for the population, the economy, and the environment. Further studies are required to guarantee the safety use of these compounds and to understand their mechanisms of action. 相似文献
156.
This paper proves that every zero of any n th , n ≥ 2, partial sum of the Riemann zeta function provides a vector space of basic solutions of the functional equation ${f(x) + f(2x) + \cdots + f(nx) = 0, x \in \mathbb{R}}$ . The continuity of the solutions depends on the sign of the real part of each zero. 相似文献
157.
Lourenço Beirão da Veiga David Mora Rodolfo Rodríguez 《Numerical Methods for Partial Differential Equations》2013,29(1):40-63
This article deals with the approximation of the bending of a clamped plate, modeled by Reissner‐Mindlin equations. It is known that standard finite element methods applied to this model lead to wrong results when the thickness t is small. Here, we propose a mixed formulation based on the Hellinger‐Reissner principle which is written in terms of the bending moments, the shear stress, the rotations and the transverse displacement. To prove that the resulting variational formulation is well posed, we use the Babu?ka‐Brezzi theory with appropriate t ‐dependent norms. The problem is discretized by standard mixed finite elements without the need of any reduction operator. Error estimates are proved. These estimates have an optimal dependence on the mesh size h and a mild dependence on the plate thickness t. This allows us to conclude that the method is locking‐free. The proposed method yields direct approximation of the bending moments and the shear stress. A local postprocessing leading to H1 ‐type approximations of transverse displacement and rotations is introduced. Moreover, we propose a hybridization procedure, which leads to solving a significantly smaller positive definite system. Finally, we report numerical experiments which allow us to assess the performance of the method. © 2012 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2013 相似文献
158.
Transition to Fulde-Ferrel-Larkin-Ovchinnikov phases near the tricritical point: an analytical study
R. Combescot C. Mora 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(4):397-406
We explore analytically the nature of the transition to the Fulde-Ferrel-Larkin-Ovchinnikov superfluid phases in the vicinity
of the tricritical point, where these phases begin to appear. We make use of an expansion of the free energy up to an overall
sixth order, both in order parameter amplitude and in wavevector. We first explore the minimization of this free energy within
a subspace, made of arbitrary superpositions of plane waves with wavevectors of different orientations but same modulus. We
show that the standard second order FFLO phase transition is unstable and that a first order transition occurs at higher temperature.
Within this subspace we prove that it is favorable to have a real order parameter and that, among these states, those with
the smallest number of plane waves are preferred. This leads to an order parameter with a cos(
.
) dependence, in agreement with preceding work. Finally we show that the order parameter at the transition is only very slightly
modified by higher harmonics contributions when the constraint of working within the above subspace is released.
Received 20 February 2002 / Received in final form 4 June 2002 Published online 13 August 2002 相似文献
159.
G. Ciccarella M. Dalla Mora A. Germani 《Journal of Optimization Theory and Applications》1995,84(3):495-507
This paper presents a nonlinear output feedback which asymptotically linearizes the class of nonlinear, continuous-time, affine in the control systems having relative degree equal to the state space dimension. Moreover, we show that any set of eigenvalues can be assigned for the asymptotic closed-loop linear system. The controller is based on a nonlinear observer, presented in a previous paper, and on the linearizing state feedback proposed by Isidori and computed in the estimated state. The main result obtained is equivalent to the separation theorem in the linear case.This work was supported by the Italian Ministry for University and Scientific and Technological Research. 相似文献
160.
S. Biade J. C. Mazière L. Mora R. Santus C. Mazière M. Auclair P. Morlière L. Dubertret 《Photochemistry and photobiology》1993,57(2):371-375
A 24 h preculture of HT29–18human colonic adenocarcinoma cells with the sterol synthesis inhibitor lovastatin at concentrations of 0.1-0.5 μM markedly increased the photocytotoxic effect of photofrin II delivered to cells by low density lipoproteins. Under the same conditions, LDL binding and photofrin II (PII) uptake by HT29 cells increased about 1.8-fold and 1.5-fold, respectively. These results suggest that hydroxymethylglutaryl-coenzyme A reductase inhibitors could be useful for potentiating the photodynamic therapy of tumors by PII. 相似文献