全文获取类型
收费全文 | 1060篇 |
免费 | 36篇 |
国内免费 | 153篇 |
专业分类
化学 | 1059篇 |
力学 | 3篇 |
综合类 | 33篇 |
数学 | 12篇 |
物理学 | 142篇 |
出版年
2023年 | 26篇 |
2022年 | 48篇 |
2021年 | 53篇 |
2020年 | 32篇 |
2019年 | 26篇 |
2018年 | 25篇 |
2017年 | 21篇 |
2016年 | 27篇 |
2015年 | 39篇 |
2014年 | 33篇 |
2013年 | 35篇 |
2012年 | 57篇 |
2011年 | 55篇 |
2010年 | 40篇 |
2009年 | 50篇 |
2008年 | 81篇 |
2007年 | 69篇 |
2006年 | 51篇 |
2005年 | 54篇 |
2004年 | 50篇 |
2003年 | 42篇 |
2002年 | 53篇 |
2001年 | 31篇 |
2000年 | 35篇 |
1999年 | 20篇 |
1998年 | 33篇 |
1997年 | 25篇 |
1996年 | 18篇 |
1995年 | 16篇 |
1994年 | 14篇 |
1993年 | 10篇 |
1992年 | 10篇 |
1991年 | 17篇 |
1990年 | 10篇 |
1989年 | 8篇 |
1988年 | 11篇 |
1987年 | 5篇 |
1986年 | 2篇 |
1985年 | 5篇 |
1984年 | 1篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有1249条查询结果,搜索用时 15 毫秒
31.
《Analytical letters》2012,45(4):721-734
Selective hydrolysis of the protein to peptides, their resolution by chromatography and determination of the amino-acid sequence in individual peptides is one method applied to studies of their modifications and mutations in pathological conditions. The purpose of this work is the determination of the green and black tea effect on peptides and their amino acid contents in integral erythrocyte membrane proteins in ethanol intoxicated rats. It was shown that ethanol intoxication causes a decrease in peptides and their amino acid contents in comparison with the control group. The ingestion of green (black) tea with ethanol partially prevents these ethanol-induced changes. 相似文献
32.
傅里叶变换近红外光谱法同时定量分析水溶液中乙醇、果糖和葡萄糖 总被引:6,自引:0,他引:6
利用乙醇、果糖和葡萄糖在波数为14000-7500cm^-1范围内的吸收值,在近红外谱区用偏最小二乘法(PLS)对体系进行建模,并通过内部和外部样品校验确认最佳数据预处理方法。结果表明,乙醇在0.05-0.25L/L,果糖在0.01-0.05g/mL及葡萄糖在0.005-0.009g/mL的范围内外部校验模型较好的分别是在PLS中所用的一阶偏导(平滑点数是5)、二阶偏导(平滑点数是5)和直线消除法的数据预处理方法所建立的模型,其外部校验预测结果的相对误差在2%左右。此方法具有可同时测定不同样品,简便快速及成本低等优点。 相似文献
33.
Silva Daniel Pereira Pessoa Adalberto Roberto Inês-Conceição Vitolo Michele 《Applied biochemistry and biotechnology》2001,91(1-9):605-613
A batch culture of Saccharomyces cerevisiae for the production of hexokinase was carried out in a 5-L fermentor containing 3 L of culture medium, which was in oculated
with cell suspension (about 0.7 g/L), and left ferm entingat 35°C and pH 4.0. The aeration and agitation were adjusted to
attain k
La values of 15, 60, 135, and 230 h−1. The highest hexokinase productivity (754.6 U/[L h]) and substrate-cell conversion yield (0.21 g/g) occurred for a k
La of 60 h−1. Moreover, the formation of hexokinase and cell growth are coupled events, which is in accordance with the constitutive character
of this enzyme. Hexokinase formation for k
La>60 h−1 was not enhanced probably owing to saturation of the respiratory pathway by oxygen. 相似文献
34.
Multipulse feed strategy for glycerol fed-batch fermentation 总被引:4,自引:0,他引:4
Dongming Xie Dehua Liu Haoli Zhu Tianzhong Liu 《Applied biochemistry and biotechnology》2001,95(2):103-112
During glycerol fed-batch fermentation, the process could be divided into multiple equal subintervals, and the feed operation
was performed in pulse form at the start of each subinterval. Based on the macrokinetic models, the multipulse feed strategy
for both glucose and corn steep slurry was determined by a general nonlinear optimization approach to maximize the final glycerol
productivity and still control the residual glucose at a low concentration. The experimental results in a 600-mL Airlift Loop
Reactor showed that the tested data with this strategy agreed well with the corresponding model prediction, and that the feed
mode with nonlinear optimization could improve the glycerol productivity significantly compared with those determined just
by limited experimental optimization in previous studies. 相似文献
35.
Persson A Garde A Jönsson AS Jonsson G Zacchi G 《Applied biochemistry and biotechnology》2001,94(3):197-211
The conversion of sodium lactate to lactic acid with water-splitting electrodialysis was investigated. One way of reducing
the power consumption is to add a conductive layer to the acid compartment. Doing this reduced the power consumption by almost
50% in a two-compartment cell, whereas the electric current efficiency was not affected at all. Three different solutions
were treated in the electrodialysis unit: a model solution with 70 g/L of sodium lactate and a fermentation broth that had
been prefiltered two different ways. The fermentation broth was either filtered in an open ultrafiltration membrane (cut-off
of 100,000 Dalton) in order to remove the microorganisms or first filtered in the open ultrafiltration membrane and then in
an ultrafiltration membrane with a cut-off of 2000 Dalton to remove most of the proteins. The concentration of sodium lactate
in the fermentation broth was 70 g/L, as well. Organic molecules present in the broth (peptides and similar organic material)
fouled the membranes and, therefore, increased power consumption. Power consumption increased more when permeate from the
more open ultrafiltration membrane was treated in the electrodialysis unit than when permeate from the membrane with the lower
cut-off was treated, since there was a higher amount of foulants in the former permeate. However, the electrodialysis membranes
could be cleaned efficiently with a 0.1 M sodium hydroxide solution. 相似文献
36.
Atala Daniel I. P. Costa Aline C. Maciel Rubens Maugeri Francisco 《Applied biochemistry and biotechnology》2001,91(1-9):353-365
A model of ethanol fermentation considering the effect of temperature was developed and validated. Experiments were performed
in a temperature range from 28 to 40°C in continuous mode with total cell recycling using a tangential microfiltration system.
The developed model considered substrate, product and biomass inhibition, as well as an active cell phase (viable) and an
inactive (dead) phase. The kinetic parameters were described as functions of temperature. 相似文献
37.
38.
A new method of indirect determination of ascorbic acid with ammonium sulfate and ethanol by extraction and flotation of copper in the presence of thiocyanate has been studied in this paper. The study shows that a small amount of Cu(II) is reduced to Cu(I) by ascorbic acid, then Cu(I) precipitates with SCN?. In the course of phase separation of ethanol from water, the precipitated CuSCN is extracted and stays in the interface of ethanol and water. A good linear relationship is observed between the extraction yield of Cu(II) and the amount of ascorbic acid. The detection limit for ascorbic acid is 1 10?5 M. Every parameter has been optimized and the reaction mechanism has been studied. The method is simple, rapid (5 min) and suffers from few interferences of common anions and cations. It has been successfully applied for the determination of ascorbic acid in pharmaceuticals and fruits. 相似文献
39.
Sara Chumillas Carlos Busó-Rogero José Solla-Gullón Francisco J. Vidal-Iglesias Enrique Herrero Juan M. Feliu 《Electrochemistry communications》2011,13(11):1194-1197
Formic acid and ethanol oxidations on spherical platinum nanoparticles dispersed on carbon with different loadings have been studied. The increasing loading of the catalyst leads to a lower diffusion flux of reactants in the internal parts of the catalyst layer, resulting in a lower apparent activity. In some cases, as in ethanol oxidation, it may also affect the diffusion of the products. As a practical consequence, the structure of the supporting layer and the catalyst loading should be optimized so that the maximum catalyst utilization is obtained. Finally, these diffusion effects may mask some important catalytic activity increase of the nanoparticles. In the case of formic acid, a significant increase in the activity is obtained for very small nanoparticles. 相似文献
40.
2,3-丁二醇及其衍生物作为重要的液体燃料和化工原料,具有广阔的工业应用前景。高效、经济的2,3-丁二醇生物制备方法,对我国低碳经济和循环经济的建设具有重要的促进作用。针对近三年间生物法制备2,3-丁二醇领域的最新研究成果,本文综述了当前国内外学者在该领域研究的热点,即关键基因和酶的鉴定、新菌种的开发和代谢工程改造、同步糖化和共培养等发酵条件的优化、耦合工艺等分离纯化技术改进等。使用非致病的高产单一2,3-丁二醇手性异构体的代谢工程菌株,作为细胞炼制工厂,利用廉价的非粮原料作底物,采用经济、简单、环保的分离纯化方式,是2,3-丁二醇产业化发展的可靠保障。 相似文献