全文获取类型
收费全文 | 217篇 |
免费 | 3篇 |
国内免费 | 2篇 |
专业分类
化学 | 117篇 |
力学 | 5篇 |
数学 | 44篇 |
物理学 | 56篇 |
出版年
2022年 | 3篇 |
2021年 | 8篇 |
2020年 | 3篇 |
2019年 | 3篇 |
2018年 | 7篇 |
2017年 | 5篇 |
2016年 | 13篇 |
2015年 | 2篇 |
2014年 | 3篇 |
2013年 | 14篇 |
2012年 | 17篇 |
2011年 | 8篇 |
2010年 | 8篇 |
2009年 | 14篇 |
2008年 | 12篇 |
2007年 | 14篇 |
2006年 | 8篇 |
2005年 | 6篇 |
2004年 | 11篇 |
2003年 | 5篇 |
2002年 | 5篇 |
2001年 | 9篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 1篇 |
1994年 | 4篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1987年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1978年 | 1篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 4篇 |
1972年 | 1篇 |
1958年 | 1篇 |
排序方式: 共有222条查询结果,搜索用时 15 毫秒
81.
Viviane S. M. Campos Chang C. Y. Dorea 《Annals of the Institute of Statistical Mathematics》2005,57(3):443-453
Let {X
n
}
n
≥0 be a Markov chain with stationary distributionf(x)ν(dx), ν being a σ-finite measure onE⊂R
d
. Under strict stationarity and mixing conditions we obtain the consistency and asymptotic normality for a general class of
kernel estimates off(·). When the assumption of stationarity is dropped these results are extended to geometrically ergodic chains.
Partially supported by CAPES.
Partially supported by CNPq, PROCAD/CAPES, PRONEX/FAPDF and FINATEC/UnB. 相似文献
82.
Pratik K. Sen Nasimul Gani Jayanta K. Midya Biswajit Pal 《Transition Metal Chemistry》2008,33(2):229-236
The kinetics of reduction of tetrachloroaurate(III) by glycine has been spectrophotometrically studied in NaOAc–AcOH buffer
in the pH range 3.73–4.77. The reaction is first order with respect to both Au(III) and glycine. Both H+ and Cl− ions have inhibiting effects on the reaction rate. The rate decreases with a decrease in the dielectric constant of the medium.
AuCl4− and AuCl3(OH)− are presumed to be the predominant oxidizing species under the conditions of the experiment. The reaction of gold(III) and
zwitterionic species of glycine proceeds with the intermediate formation of gold(I) and iminic cation and the latter subsequently
hydrolyses in a fast step to produce formaldehyde and ammonium ion. Formaldehyde was identified as the only organic product
by 1H NMR spectroscopy. 相似文献
83.
84.
Andreia Ascenso Filipe Vultos Diogo Ferrinho Ana Salgado Samuel Guerra Filho Viviane Ferrari Sandra Sim?es Helena Cabral Marques 《Journal of inclusion phenomena and macrocyclic chemistry》2012,73(1-4):459-465
The aim of this work was to study the release, permeation and skin retention profiles of 0.05% tretinoin hydrogel formulations in which tretinoin was in free form or complexed with dimethyl-beta-cyclodextrin in a stoichiometry of 1:4. Theoretically, this complexation will mainly allow to: overcome drug’s low water solubility and low stability; enhance the drug permeation by promoting skin absorption and alleviate drug inducing local irritation. In vitro release, permeation and skin retention tests were performed in both formulations in order to compare the main advantages of this complexation. The influence of the thermodynamic activity on the drug release profile was also investigated. This study proved that tretinoin inclusion complexes formulation with excess of cyclodextrins had better release profile than the free tretinoin formulation. It was concluded that in this study, thermodynamic activity was not the driving force for the release rate improvement observed with cyclodextrins. Probably, this improvement was due to the increased availability of tretinoin near the membrane surface. In fact, the percentage of total drug that had been retained in the skin was 0.41?±?0.08% for complexed tretinoin gel and 0.17?±?0.04% for the free tretinoin gel. 相似文献
85.
Viviane Köhler Marcia Fampa Olinto Araújo 《Computational Optimization and Applications》2013,55(1):113-135
The clustering problem has an important application in software engineering, which usually deals with large software systems with complex structures. To facilitate the work of software maintainers, components of the system are divided into groups in such a way that the groups formed contain highly-interdependent modules and the independent modules are placed in different groups. The measure used to analyze the quality of the system partition is called Modularization Quality (MQ). Designers represent the software system as a graph where modules are represented by nodes and relationships between modules are represented by edges. This graph is referred in the literature as Module Dependency Graph (MDG). The Software Clustering Problem (SCP) consists in finding the partition of the MDG that maximizes the MQ. In this paper we present three new mathematical programming formulations for the SCP. Firstly, we formulate the SCP as a sum of linear fractional functions problem and then we apply two different linearization procedures to reformulate the problem as Mixed-Integer Linear Programming (MILP) problems. We discuss a preprocessing technique that reduces the size of the original problem and develop valid inequalities that have been shown to be very effective in tightening the formulations. We present numerical results that compare the formulations proposed and compare our results with the solutions obtained by the exhaustive algorithm supported by the freely available Bunch clustering tool, for benchmark problems. 相似文献
86.
We hereby report the first preparation of the 3,4-dihydrofuro[3,2-d]pyrimidin-2(1H)-one skeleton formed by two controlled Curtius rearrangements of the corresponding acyl azides, prepared from 2-(2-methoxy-2-oxoethyl)furan-3-carboxylate via the hydrazide. Rearrangement of the acyl azides followed by trapping by nucleophiles and intramolecular trapping provided the target compounds. 相似文献
87.
Gláucia M.M. Guedes Rosimeire S. Albuquerque Rafela S. Soares-Maciel Maria A. Freitas Viviane A. Silva Edeltrudes O. Lima Micheline A. Lima Emidio V.L. Cunha Henrique D.M. Coutinho 《Arabian Journal of Chemistry》2019,12(7):1576-1580
Globally there are a larger number of strains of microorganisms resistant to multiple drugs mainly due to misuse and indiscriminate, resulting in increased morbidity, costs inherent benefits of health care, as well as mortality rates for infections. As a result of this a large number of researches have been conducted emphasizing the antimicrobial properties of plant products. In this study, the ethanol extract and hexane fraction of Dalbergia ecastophyllum (L.) Taub. (Leguminosae) have been used to evaluate the antibacterial and antifungal activity and for modulating the resistance of antimicrobials against bacterial strains of Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa and Candida albicans and fungal strains of Candida krusei, Candida tropicalis. The antibacterial and modulatory activity was determined by microdilution. Inhibition of the growth of bacteria and fungi tested extract was ?1024. The activity was enhanced when aminoglycosides were associated with sub-inhibitory concentrations of the ethanol extract and hexane fraction of Dalbergia ecastophyllum. Therefore, it is suggested that the ethanol extract and hexane fraction of Dalbergia ecastophyllum (L.) Taub. (Leguminosae) can be used as a source of natural products with a view to changing the resistance of these microorganisms to antimicrobials. 相似文献
88.
In this work we propose a computational model to investigate the proliferation of cancerous cell by using complex networks. In our model the network represents the structure of available space in the cancer propagation. The computational scheme considers a cancerous cell randomly included in the complex network. When the system evolves the cells can assume three states: proliferative, non-proliferative, and necrotic. Our results were compared with experimental data obtained from three human lung carcinoma cell lines. The computational simulations show that the cancerous cells have a Gompertzian growth. Also, our model simulates the formation of necrosis, increase of density, and resources diffusion to regions of lower nutrient concentration. We obtain that the cancer growth is very similar in random and small-world networks. On the other hand, the topological structure of the small-world network is more affected. The scale-free network has the largest rates of cancer growth due to hub formation. Finally, our results indicate that for different average degrees the rate of cancer growth is related to the available space in the network. 相似文献
89.
Tormena CF Vilcachagua JD Karcher V Rittner R Contreras RH 《Magnetic resonance in chemistry : MRC》2007,45(7):590-594
Theoretical and experimental 2JHH coupling constants for six-membered rings containing oxygen or sulfur atoms were studied to investigate whether the 2JHH coupling constant can be used for stereoelectronic studies in heterocyclohexanes, instead of 1JCH, because it is well known that experimental measurements of 2JHH coupling constants at low temperature are much easier to determine than the corresponding 1JCH couplings. For all compounds studied here, the 2JHH coupling constants are affected by sigma*C-H antibonding occupancy together with bond angle effects. For cyclohexane and oxygen-containing compounds, the influence on the geminal coupling for Hax-C2-Heq and for X1-C2-X3 (X=O and C), bond angles are more pronounced than for the sulfur derivatives. 相似文献
90.