全文获取类型
收费全文 | 4959篇 |
免费 | 217篇 |
国内免费 | 38篇 |
专业分类
化学 | 3569篇 |
晶体学 | 16篇 |
力学 | 132篇 |
数学 | 724篇 |
物理学 | 773篇 |
出版年
2024年 | 7篇 |
2023年 | 45篇 |
2022年 | 121篇 |
2021年 | 146篇 |
2020年 | 137篇 |
2019年 | 130篇 |
2018年 | 84篇 |
2017年 | 81篇 |
2016年 | 194篇 |
2015年 | 135篇 |
2014年 | 174篇 |
2013年 | 300篇 |
2012年 | 341篇 |
2011年 | 420篇 |
2010年 | 246篇 |
2009年 | 235篇 |
2008年 | 357篇 |
2007年 | 335篇 |
2006年 | 278篇 |
2005年 | 281篇 |
2004年 | 217篇 |
2003年 | 156篇 |
2002年 | 167篇 |
2001年 | 59篇 |
2000年 | 44篇 |
1999年 | 31篇 |
1998年 | 31篇 |
1997年 | 33篇 |
1996年 | 38篇 |
1995年 | 32篇 |
1994年 | 28篇 |
1993年 | 25篇 |
1992年 | 24篇 |
1991年 | 22篇 |
1990年 | 32篇 |
1989年 | 17篇 |
1988年 | 27篇 |
1987年 | 19篇 |
1986年 | 15篇 |
1985年 | 23篇 |
1984年 | 15篇 |
1982年 | 18篇 |
1981年 | 14篇 |
1980年 | 11篇 |
1979年 | 11篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1975年 | 6篇 |
1974年 | 6篇 |
1973年 | 6篇 |
排序方式: 共有5214条查询结果,搜索用时 0 毫秒
121.
Clarissa A. Olivati Rodrigo F. Bianchi Osvaldo N. Oliveira Jr. 《Polymer Degradation and Stability》2006,91(10):2342-2346
Poly(p-phenylene vinylene) (PPV) derivatives are well known for their applications in polymer light emitting diodes (PLEDs). PPV derivatives are highly susceptible to photo-oxidation though, which is mainly caused by the scission of the vinyl double bond on the polymer backbone. In this work, we show that Langmuir-Blodgett (LB) films are less degraded than cast films of a PPV derivative (OC1OC6-PPV). Both films had similar thickness (∼50 nm) to allow for a more realistic comparison. Degradation was monitored with UV-vis and FTIR spectroscopies. The results indicated that cast films were completely degraded in ca. 400 min, while LB took longer time, i.e. about four times the values for the cast films. The differences can be attributed to the more compact morphology in the LB than in the cast films. With a compact morphology the diffusion of oxygen in the LB film is hampered and this causes a delay in the degradation process. 相似文献
122.
Jesús Gutirrez-Gutirrez Fernando M. Villar-Rosety Xabier Insausti Marta Zrraga-Rodríguez 《Entropy (Basel, Switzerland)》2022,24(5)
In the era of the Internet of Things, there are many applications where numerous devices are deployed to acquire information and send it to analyse the data and make informed decisions. In these applications, the power consumption and price of the devices are often an issue. In this work, analog coding schemes are considered, so that an ADC is not needed, allowing the size and power consumption of the devices to be reduced. In addition, linear and DFT-based transmission schemes are proposed, so that the complexity of the operations involved is lowered, thus reducing the requirements in terms of processing capacity and the price of the hardware. The proposed schemes are proved to be asymptotically optimal among the linear ones for WSS, MA, AR and ARMA sources. 相似文献
123.
Gredson Keiff Souza Andr Gallo Luiza Hauser Novicki Heitor Rodrigues Neto Eneida de Paula Anita Jocelyne Marsaioli Luis Fernando Cabea 《Molecules (Basel, Switzerland)》2022,27(13)
The drugs delivery system in the treatment of diseases has advantages such as reduced toxicity, increased availability of the drug, etc. Therefore, studies of the supramolecular interactions between local anesthetics (LAs) butamben (BTB) or ropivacaine (RVC) complexed with 2-hydroxypropyl-β-cyclodextrin (HP-βCD) and carried in Stealth liposomal (SL) are performed. 1H-NMR nuclear magnetic resonance (DOSY and STD) were used as the main tools. The displacements observed in the 1H-NMR presented the complexion between LAs and HP-βCD. The diffusion coefficients of free BTB and RVC were 7.70 × 10−10 m2 s−1 and 4.07 × 10−10 m2 s−1, and in the complex with HP-βCD were 1.90 × 10−10 m2 s−1 and 3.64 × 10−10 m2 s−1, respectively, which indicate a strong interaction between the BTB molecule and HP-βCD (98.3% molar fraction and Ka = 72.279 L/mol). With STD-NMR, the encapsulation of the BTB/HP-βCD and RVC/HP-βCD in SL vesicles was proven. Beyond the saturation transfer to the LAs, there is the magnetization transfer to the hydrogens of HP-βCD. BTB and RVC have already been studied in normal liposome systems; however, little is known of their behavior in SL. 相似文献
124.
Raquel Muoz García Rodrigo Oliver-Simancas María Arvalo Villena Leticia Martínez-Lapuente Beln Ayestarn Lourdes Marchante-Cuevas María Consuelo Díaz-Maroto María Soledad Prez-Coello 《Molecules (Basel, Switzerland)》2022,27(9)
The objective of this study was to evaluate the effect of microwave treatment of crushed grapes on the yeast population of the must and on the development of alcoholic fermentation, as well as on the extraction of different compounds from the grapes such as polysaccharides and amino acids that can affect the organoleptic quality and stability of the wine. This study demonstrated for the first time the effect of the microwave treatment of grapes on native yeast species and their diversity, producing an increase in fermentation kinetics and a decrease in the lag phase. The microwave treatment produced a positive effect on the extraction of amino acids and polysaccharides from the grapes, resulting in significantly higher amounts of the main amino acids of the must and some major volatile compounds in the treated samples. The polysaccharides most affected by the microwave treatment were the PRAGs, the main polysaccharides liberated from grapes during the maceration. 相似文献
125.
126.
127.
Leonor Alvarado-Soto Luis Alvarez-Thon Rodrigo Ramirez-Tagle 《Journal of mathematical chemistry》2014,52(5):1182-1190
This perspective article discusses some widely-known and some less-known consequences of spin-orbit effects in inorganic chemistry, and provides a brief outline of the theoretical methods currently in use, along with a discussion of recent developments and selected applications. This is of critical importance in the interpretation of the electronic delocalization, optical and magnetic properties and Jahn–Teller effects of compounds containing heavy elements. 相似文献
128.
Ariana Borges Souza Monique Rodrigues Moreira Carly Henrique Gambeta Borges Marília Rodrigues Simão Jairo Kenupp Bastos João Paulo Barreto de Sousa Sérgio Ricardo Ambrosio Rodrigo Cassio Sola Veneziani 《Biomedical chromatography : BMC》2013,27(3):280-283
The Copaifera species (Leguminoseae) are popularly known as ‘copaíba’ or ‘copaíva’ and are grown in the states of Amazonas, Pará and Ceará in northern Brazil. The oleoresins obtained from these species have been extensively used owing to their pharmacological potential and their application in cosmetic and pharmaceutical preparations. In the present study, the development and validation of a novel, rapid and efficient RP‐HPLC methodology for the analysis of the diterpene (?)‐copalic acid (CA), pointed out as the only chemical marker of the Copaifera genus, are described. The regression equation (Y = 26,707x ? 29,498) was obtained with good linearity (r2 = 0.9993) and the limits of quantification and detection were 9.182 and 3.032 µg/mL, respectively. The precision and the accuracy of the method were adequate (lower than 4%). Finally, the validation parameters evaluated were satisfactorily met, so the developed method represents a suitable tool for application in the quality control of such natural products. Further studies aiming to develop analytical methodologies for each Copaifera species using a more representative number of chemical markers should be performed. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
129.
130.