全文获取类型
收费全文 | 2609篇 |
免费 | 93篇 |
国内免费 | 19篇 |
专业分类
化学 | 1815篇 |
晶体学 | 20篇 |
力学 | 57篇 |
数学 | 473篇 |
物理学 | 356篇 |
出版年
2023年 | 23篇 |
2022年 | 61篇 |
2021年 | 96篇 |
2020年 | 56篇 |
2019年 | 57篇 |
2018年 | 56篇 |
2017年 | 44篇 |
2016年 | 98篇 |
2015年 | 83篇 |
2014年 | 101篇 |
2013年 | 164篇 |
2012年 | 162篇 |
2011年 | 227篇 |
2010年 | 142篇 |
2009年 | 117篇 |
2008年 | 161篇 |
2007年 | 168篇 |
2006年 | 128篇 |
2005年 | 117篇 |
2004年 | 110篇 |
2003年 | 80篇 |
2002年 | 77篇 |
2001年 | 29篇 |
2000年 | 24篇 |
1999年 | 24篇 |
1998年 | 16篇 |
1997年 | 19篇 |
1996年 | 21篇 |
1995年 | 18篇 |
1994年 | 23篇 |
1993年 | 20篇 |
1992年 | 14篇 |
1991年 | 13篇 |
1990年 | 14篇 |
1989年 | 11篇 |
1988年 | 9篇 |
1987年 | 10篇 |
1986年 | 9篇 |
1985年 | 13篇 |
1984年 | 11篇 |
1983年 | 14篇 |
1982年 | 19篇 |
1981年 | 12篇 |
1980年 | 4篇 |
1979年 | 6篇 |
1978年 | 9篇 |
1976年 | 3篇 |
1975年 | 5篇 |
1974年 | 5篇 |
1912年 | 2篇 |
排序方式: 共有2721条查询结果,搜索用时 15 毫秒
131.
Eduardo Rosado Paloma Delgado-Fernndez Blanca de las Rivas Rosario Muoz Francisco Javier Moreno Nieves Corzo Cesar Mateo 《Molecules (Basel, Switzerland)》2022,27(4)
The synthesis of β-galactosyl xylitol derivatives using immobilized LacA β-galactosidase from Lactobacillus plantarum WCFS1 is presented. These compounds have the potential to replace traditional sugars by their properties as sweetener and taking the advantages of a low digestibility. The enzyme was immobilized on different supports, obtaining immobilized preparations with different activity and stability. The immobilization on agarose-IDA-Zn-CHO in the presence of galactose allowed for the conserving of 78% of the offered activity. This preparation was 3.8 times more stable than soluble. Since the enzyme has polyhistidine tags, this support allowed the immobilization, purification and stabilization in one step. The immobilized preparation was used in synthesis obtaining two main products and a total of around 68 g/L of β-galactosyl xylitol derivatives and improving the synthesis/hydrolysis ratio by around 30% compared to that of the soluble enzyme. The catalyst was recycled 10 times, preserving an activity higher than 50%. The in vitro intestinal digestibility of the main β-galactosyl xylitol derivatives was lower than that of lactose, being around 6 and 15% for the galacto-xylitol derivatives compared to 55% of lactose after 120 min of digestion. The optimal amount immobilized constitutes a very useful tool to synthetize β-galactosyl xylitol derivatives since it can be used as a catalyst with high yield and being recycled for at least 10 more cycles. 相似文献
132.
Dayanne Cristiane Mozaner Bordin Marcela Nogueira Rabelo Alves Eduardo Geraldo de Campos Bruno Spinosa De Martinis 《Journal of separation science》2016,39(6):1168-1172
Disposable pipette tips extraction consists of a solid‐phase extraction in which the sorbent is poorly dispersed in a pipette tip, which allows a quick and dynamic contact between the aspirated analyte from the sample and the solid phase. It is a technique used particularly in food and forensic analysis, since it requires a small amount of sample and solvent. This article highlights the principles, advantages and disadvantages of the disposable pipette tips extraction method and reviews recent applications. 相似文献
133.
134.
Giovana de Fátima Menegotto Paulo César Borges Eduardo Mauro do Nascimento Carlos Maurício Lepienski Elaine Cristina Azevedo 《Brazilian Journal of Physics》2011,41(4-6):223-228
The influence of hydrogen loading temperature on the mechanical strength of optical fibers is investigated. Fibers subjected to high-pressure hydrogen loading at different temperatures were submitted to bend tests, and the results compared with those for pristine fibers. The Weibull probability distribution function was used to analyze the data of the mechanical bending strength of the fibers. Fiber strength is reduced by the presence of hydrogen, and this decrease is greater for higher hydrogen loading temperatures. The mechanical properties of the polymers used to coat fibers are affected by the hydrogen loading process and also by the increase in temperature. However, there is no evidence of cracks formation that might allow water to penetrate to the surface of the glass. Observation using scanning electron microscopy revealed that the morphology of fractures in nonhydrogen-loaded fibers have distinct fracture characteristics to that of fibers that are hydrogen loaded at 90°C and 120°C. 相似文献
135.
Thiago F. Tormin Leandro G. Silva Eduardo M. Richter Rodrigo A.A. Muñoz 《Talanta》2010,82(4):1599-1055
The direct amperometric determination of tert-butylhydroquinone (TBHQ) in biodiesel at an unmodified glassy carbon electrode is reported. A biodiesel aliquot was added into an electrochemical cell containing a 75% (v/v) ethanol-water solution under stirring (with final concentration of 50 mmol L−1 HClO4). The amperometric method involved the continuous application of three sequential potential pulses to the working electrode (700 mV for 300 ms, 0 mV for 100 ms and −50 mV for 1 s). TBHQ was continuously monitored at the first (direct oxidation) and optionally at the second (reduction) potential pulse while the third potential pulse was applied for cleaning of the electrode surface. For comparison, the samples were also analyzed by high-performance liquid-chromatography and a good agreement between the results was verified. Recovery values for spiked samples were between 90% and 95% and the reproducibility of the proposed method was around 5% (n = 5). The proposed method can be easily adapted for on-site analysis. 相似文献
136.
Leitão Jorge C. Parente Lopes João M. Viana Altmann Eduardo G. 《The European Physical Journal B - Condensed Matter and Complex Systems》2017,90(10):1-10
The European Physical Journal B - A way to make financial models effective is by letting them to represent the so called “fat tails”, i.e., extreme changes in stock prices that are... 相似文献
137.
Optimal conditions for chlorotris(triphenylphosphine)rhodium(I) (Wilkinson's catalyst) catalyzed selective saturation of a double bond in the presence of a nitro function are developed. Aryl iodide and benzyl ether are also tolerated under these hydrogenation conditions. 相似文献
138.
We simulate neutral evolution of proteins imposing conservation of the thermodynamic stability of the native state in the framework of an effective model of folding thermodynamics. This procedure generates evolutionary trajectories in sequence space which share two universal features for all of the examined proteins. First, the number of neutral mutations fluctuates broadly from one sequence to another, leading to a non-Poissonian substitution process. Second, the number of neutral mutations displays strong correlations along the trajectory, thus causing the breakdown of self-averaging of the resulting evolutionary substitution process. 相似文献
139.
Turing computability with neural nets 总被引:1,自引:0,他引:1
This paper shows the existence of a finite neural network, made up of sigmoidal neurons, which simulates a universal Turing machine. It is composed of less than 105 synchronously evolving processors, interconnected linearly. High-order connections are not required. 相似文献
140.
Luis F. Urrutia Eduardo Hernández 《International Journal of Theoretical Physics》1984,23(12):1105-1127
A calculation of the quantum mechanical propagator for a general time-dependent one-dimensional damped, forced harmonic oscillator based on a direct application of the Schwinger action principle is presented. Contact with an earlier general method of calculation is made and in particular two previously found results are recovered from our general expression. The apparent dependence of one of them upon some unphysical parameters is clarified. The method presented here can be applied to any system described by a quadratic Hamiltonian and is an immediate extension of the calculation for the propagator of a simple harmonic oscillator with constant frequency. 相似文献