全文获取类型
收费全文 | 308篇 |
免费 | 35篇 |
国内免费 | 23篇 |
专业分类
化学 | 195篇 |
晶体学 | 3篇 |
力学 | 14篇 |
综合类 | 5篇 |
数学 | 48篇 |
物理学 | 101篇 |
出版年
2023年 | 24篇 |
2022年 | 5篇 |
2021年 | 4篇 |
2020年 | 10篇 |
2019年 | 4篇 |
2018年 | 9篇 |
2017年 | 13篇 |
2016年 | 12篇 |
2015年 | 8篇 |
2014年 | 14篇 |
2013年 | 34篇 |
2012年 | 17篇 |
2011年 | 26篇 |
2010年 | 15篇 |
2009年 | 18篇 |
2008年 | 20篇 |
2007年 | 16篇 |
2006年 | 17篇 |
2005年 | 18篇 |
2004年 | 10篇 |
2003年 | 17篇 |
2002年 | 8篇 |
2001年 | 4篇 |
2000年 | 6篇 |
1999年 | 4篇 |
1998年 | 2篇 |
1997年 | 6篇 |
1996年 | 2篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 5篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1983年 | 1篇 |
1981年 | 2篇 |
1979年 | 1篇 |
排序方式: 共有366条查询结果,搜索用时 15 毫秒
91.
92.
93.
几种标准蛋白质的毛细管区带电泳的分离及其迁移行为 总被引:1,自引:0,他引:1
本文采用毛细管区带电泳分离了几种标准蛋白,研究了不同的清洗方式,不同PH的缓冲溶液等对迁移行为及分离的影响,并同时考察了迁移时间和相对迁移时间与操作电压的关系。 相似文献
94.
The caffeine content of foods and beverages varies considerably, interfering with our ability to obtain valid interpretations in many human studies with regard to the mechanism of action(s) of caffeine and/or its metabolites. The rate of metabolism of caffeine and other xanthine drugs also varies greatly from one individual to another. Therefore, it is extremely important to develop accurate, reliable analytical methods to quantify caffeine and its metabolites in simple and complex matrixes. A simple method is described for the separation and characterization of caffeine and its major metabolites employing capillary electrophoresis (CE) coupled to ultraviolet-absorption and mass spectrometry (MS) detection. After optimization of the electrophoresis separation conditions, a reliable separation of caffeine and 11 of its major metabolites was achieved in 50 mM ammonium carbonate buffer, pH 11.0. The volatile aqueous electrolyte system used with a normal electroosmotic flow polarity also provided an optimal separation condition for the characterization of the analytes by MS. The CE method achieved baseline resolution for all 12 compounds in less than 30 min. The CE-MS method is suitable for use as a routine procedure for the rapid separation and characterization of caffeine and its metabolites. The usefulness of this method was demonstrated by the extraction, separation, and identification of caffeine and its 11 metabolites from normal urine samples. The urine specimens were first acidified to obtain optimum binding efficiency to the sorbents of the off-line, solid-phase extraction procedure employed here, and an acidified eluent solvent was employed for the desorption step to maximize the recovery of the bound analytes. 相似文献
95.
M.O. Boussoum 《Polymer Degradation and Stability》2006,91(3):579-584
Commercial sunflower oil was epoxidised and used as organic co-stabiliser for rigid and plasticised poly(vinyl chloride) (PVC) containing Zn and Ca stearates as primary stabilisers and stearic acid as lubricant. For applications in the packaging of foodstuffs, migration testing must be performed. The detection and the quantification of contaminants migrating from the polymer into the food simulants are essential for the safety assessment of food contact plastic packaging materials. For that purpose, two food simulants were used: olive oil and 15% (v/v) aqueous ethanol. These represent fatty and moist food and beverages, respectively. The test conditions were 12 days at 40 °C. Circular samples of rigid PVC and PVC plasticised with dioctyl phthalate were immersed in a known volume of food simulant. A circular sample and 10 ml of food simulant were taken off every day to be analysed. Each sample was wiped and weighed. The rate of variation of the mass was determined as a function of time. The evolution of the peroxide index of olive oil with time was analysed. The specific migrations of the present additives were investigated by using two analytical methods (atomic absorption spectrometry and Fourier transform infrared spectroscopy). The influence of various parameters such as the nature of food simulant, the presence or the absence of the plasticiser, the agitation and time of contact was considered. 相似文献
96.
150×3 mm I.D. columns, packed with 1-μm non-porous spherical silica particles, were used to separate soluble synthetic polymers by hydrodynamic chromatography. The columns exhibited a plate height of about 1.4 μm allowing very fast and efficient separations of polymers in the molecular mass range 103−2·106 g/mol. The migration behaviour of polymers could be well described by a simple theoretical model. The applicability of packed bed HDC for the fast separation of polymers was illustrated with separations of polystyrene and poly(methyl methacrylate) mixtures. 相似文献
97.
98.
Summary A series of small peptides containing varying degree of charge and size was used to study the effects of physicochemical properties on migration in free-solution capillary electrophoresis (FSCE). A semiempirical relationship between migration time under acidic conditions and the square root of molecular weight divided by the quantity of the number of the positively ionizable groups has been established. The ionization of the carboxyl terminal group in the polypeptides is negligible under acidic conditions. The relationship developed from this work has been used for the prediction of migration parameters in free solution capillary electrophoresis. 相似文献
99.
We introduce the notion of a weighted δ-vector of a lattice polytope. Although the definition is motivated by motivic integration, we study weighted δ-vectors from a combinatorial perspective. We present a version of Ehrhart Reciprocity and prove a change of variables formula. We deduce a new geometric interpretation of the coefficients of the Ehrhart δ-vector. More specifically, they are sums of dimensions of orbifold cohomology groups of a toric stack. 相似文献
100.
We show that the left-greedy algorithm is a better algorithm than the right-greedy
algorithm for sorting permutations using t stacks in series when t > 1. We also supply a method
for constructing some permutations that can be sorted by t stacks in series and from this get a
lower bound on the number of permutations of length n that are sortable by t stacks in series.
Finally we show that the left-greedy algorithm is neither optimal nor defines a closed class of
permutations for t > 2.AMS Subject Classification: 05A05, 68R05, 68W01. 相似文献