全文获取类型
收费全文 | 281篇 |
免费 | 5篇 |
国内免费 | 1篇 |
专业分类
化学 | 152篇 |
力学 | 4篇 |
数学 | 30篇 |
物理学 | 101篇 |
出版年
2021年 | 7篇 |
2020年 | 4篇 |
2019年 | 4篇 |
2018年 | 4篇 |
2017年 | 3篇 |
2016年 | 6篇 |
2015年 | 9篇 |
2014年 | 7篇 |
2013年 | 13篇 |
2012年 | 13篇 |
2011年 | 20篇 |
2010年 | 17篇 |
2009年 | 18篇 |
2008年 | 14篇 |
2007年 | 12篇 |
2006年 | 16篇 |
2005年 | 16篇 |
2004年 | 13篇 |
2003年 | 9篇 |
2002年 | 10篇 |
2001年 | 3篇 |
2000年 | 5篇 |
1999年 | 7篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 5篇 |
1995年 | 2篇 |
1994年 | 9篇 |
1993年 | 4篇 |
1992年 | 10篇 |
1991年 | 5篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1980年 | 1篇 |
排序方式: 共有287条查询结果,搜索用时 15 毫秒
161.
162.
The soil properties can be strongly affected by wildfires, causing direct effects on ecosystem productivity and sustainability.
These effects depend, among other things, on the soil type and on the temperature reached during the fire. The variations
of thermal properties of several Galizian soils heated in an oven in laboratory conditions at different temperatures (200–500 °C)
during 15 min have been examined in this study. The measured properties are heat of combustion of soil organic matter, ignition
temperature, specific heat and mass loss, determined using DSC 2920 TA Instruments and a TGA 7 Perkin Elmer under dry air
gas flow. In agreement with other authors, this study establishes three temperature intervals with different effects on the
soil: up to 200 °C, low intensity heating, with no significant changes in thermal properties; between 200 and 350 °C, medium
intensity heating, with losses of organic matter up to 50%; and high intensity heating to temperature higher than 350 °C,
with harmful effects on the soil organic matter. On the other hand and taking into account that the sampled soils had been
affected by forest fires, the variations of thermal soil properties with the laboratory heating temperatures allowed for an
estimation of the temperature reached by the soil in the real fire. 相似文献
163.
Andreia Ascenso Aida Duarte Alexandra Silva Ana Salgado Helena Cabral Marques 《Journal of inclusion phenomena and macrocyclic chemistry》2011,69(3-4):339-343
The aim of this work was to develop and characterize a 0.05% tretinoin hydrogel formulations in which tretinoin is free or complexed with dimethyl-beta-cyclodextrin in order to compare the main advantages of its complexation. Theoretically, the complexation will mainly allow to: overcome drug low solubility in water and low stability; enhance the drug release by promoting skin absorption and alleviate of drug inducing local irritation. The hydrogels prepared were both microbiological and physically stable during 30 days. However, the chemical stability was less encouraging. The complexed tretinoin gel had also a higher releasing profile than the free tretinoin gel. This study has demonstrated that it is possible to obtain a microbiological and physically stable gel formulation with good releasing profile. 相似文献
164.
Icaro Salgado Perovani Carolina Oliveira Serpellone Anderson Rodrigo Moraes de Oliveira 《Electrophoresis》2021,42(17-18):1726-1743
Enantioresolution processes are vital tools for investigating the enantioselectivities of chiral compounds. An analyst resolves to optimize enantioresolution conditions once they are determined. Generally, optimization is conducted by a one-factor-at-a-time (OFAT) approach. Although this approach may determine an adequate condition for the method, it does not often allow the estimation of the real optimum condition. Experimental designs are conducive for the optimization of enantioresolution methods via capillary electromigration techniques (CETs). They can efficiently extract information from the behavior of a method and enable the estimation of the real optimum condition. Furthermore, the application of the analytical quality by design (AQbD) approach to the development of CET-based enantioselective methods is a trend. This article (i) offers an overview of the application of experimental designs to the development of enantioselective methods from 2015 to mid-2020, (ii) reveals the experimental designs that are presently employed in CET-based enantioresolutions, and (iii) offers a critical point of view on how the different experimental designs can aid the optimization of enantioresolution processes by considering the method parameters. 相似文献
165.
G. Salgado 《代数通讯》2013,41(6):2261-2268
Triple products in n whose related algebra is n itself or n are classified up to isomorphism. This classification is obtained using the intimate relation between triple products and Lie (super)algebra structures. 相似文献
166.
Alfredo Bermúdez Carlos Reales Rodolfo Rodríguez Pilar Salgado 《Numerical Methods for Partial Differential Equations》2012,28(3):984-1012
The aim of this article is to analyze a transient axisymmetric electromagnetic model involving velocity terms in the Ohm's law. To this end, we introduce a time‐dependent weak formulation leading to a degenerate parabolic problem and establish its well posedness.We propose a finite‐element method for space discretization and prove well posedness and error estimates. Then, we combine it with a backward Euler time discretization and prove stability and error estimates. Finally, numerical results assessing the performance of the method are reported. © 2011 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2011 相似文献
167.
In this paper we investigate the efficacy of applying the coupled field back-propagation algorithm as a post-compensation method for nonlinearity mitigation in a coherently detected fibre optic long-haul system using multi-band orthogonal frequency division multiplexed signals. Specifically, we analyze the impact of varying the band-spacing and the number of bands. We find that its efficacy is higher for largely spaced bands and a small number of bands. Additionally, we propose a method to include the Four Wave Mixing compensating term within the coupled field method to provide simplified means of multichannel compensation. We conclude that this method is more efficient in improving the performance especially for small band spacings. The coupled field method proves to be an interesting choice for the implementation of receiver-based real-time digital signal processing. 相似文献
168.
169.
We present a derivation of the medium-induced gluon radiation spectrum beyond the current limitation of soft gluon emission. Making use of the path integral approach to describe the propagation of high-energy particles inside a medium, we study the limiting case of a hard gluon emission. Analytical and numerical results are presented and discussed within the multiple soft scattering approximation. An ansatz interpolating between soft and hard gluon emissions is provided. The Landau–Pomeranchuk–Migdal effect is observed in the expected kinematic region. 相似文献
170.
Terence Davis Matthew C Dix Michal J Rokicki Amy JC Brook Caroline S Widdowson David Kipling Mark C Bagley 《Chemistry Central journal》2011,5(1):1-5
To develop more potent small molecules with enhanced free radical scavenger properties, a series of N-substituted isatin derivatives was synthesized, and the cytoprotective effect on the apoptosis of PC12 cells induced by H2O2 was screened. All these compounds were found to be active, and N-ethyl isatin was found with the most potent activity of 69.7% protective effect on PC12 cells. Structure-activity relationship analyses showed the bioactivity of N-alkyl isatins decline as the increasing of the chain of the alkyl group, furthermore odd-even effect was found in the activity, which is interesting for further investigation. 相似文献