全文获取类型
收费全文 | 373篇 |
免费 | 15篇 |
专业分类
化学 | 252篇 |
晶体学 | 2篇 |
力学 | 25篇 |
数学 | 59篇 |
物理学 | 50篇 |
出版年
2023年 | 1篇 |
2022年 | 8篇 |
2021年 | 6篇 |
2020年 | 6篇 |
2019年 | 6篇 |
2018年 | 2篇 |
2017年 | 6篇 |
2016年 | 14篇 |
2015年 | 13篇 |
2014年 | 14篇 |
2013年 | 21篇 |
2012年 | 29篇 |
2011年 | 21篇 |
2010年 | 14篇 |
2009年 | 11篇 |
2008年 | 26篇 |
2007年 | 22篇 |
2006年 | 15篇 |
2005年 | 17篇 |
2004年 | 14篇 |
2003年 | 9篇 |
2002年 | 10篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1999年 | 2篇 |
1998年 | 5篇 |
1997年 | 8篇 |
1996年 | 6篇 |
1995年 | 1篇 |
1994年 | 4篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 9篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 8篇 |
1984年 | 8篇 |
1983年 | 4篇 |
1981年 | 1篇 |
1980年 | 5篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1975年 | 2篇 |
1973年 | 3篇 |
1965年 | 1篇 |
1912年 | 1篇 |
排序方式: 共有388条查询结果,搜索用时 31 毫秒
41.
Fernando De Andrés Mohammed Zougagh Gregorio Castañeda Angel Ríos 《Analytical and bioanalytical chemistry》2010,397(1):223-231
A rapid and simple method for separation and detection of six heterocyclic aromatic amines (2-amino-1-methyl-6-phenylimidazo
[4,5-b]-pyridine, 2-amino-1-methyl-imidazo [4,5-f]-quinoline, 2-amino-3,8-dimethyl-imidazo [4,5-f]-quinoxaline, 2-amino-3,7,8-trimethyl-imidazo [4,5-f]-quinoxaline, 2-amino-3,4,8-trimethyl-imidazo [4,5-f]-quinoxaline, and 2-amino-3,4-dimethyl-imidazo [4,5-f]-quinoline) in human urine samples is proposed to reflect daily intake and recent HAAs exposure. This method comprises previous
clean-up and preconcentration of the analytes on Strata-X reversed phase extraction cartridges followed by capillary liquid
chromatography (CLC) and evaporative light-scattering detection (ELSD). A mobile phase of acetonitrile and ammonium acetate
35 mM at pH 5.15 through a gradient of composition and a flow rate of 15 μL min−1 resulted in good separations of the analytes. Temperature and gas pressure were optimized for detection. The CLC-ELSD allows
the separation and quantification of HAAs with good resolution, precision, and sensitivity. The usefulness of the proposed
method was demonstrated by the analysis of synthetic and natural human urine samples spiked with different concentration levels
of heterocyclic amines. 相似文献
42.
We study a lattice QCD mixed action with overlap valence quarks on two flavours of Wilson maximally twisted mass sea quarks. Employing three different matching conditions to relate both actions to each other, we investigate the continuum limit by using three values of the lattice spacing ranging from a≈0.05 fm to 0.08 fm. A particular emphasis is put on the effect on physical observables of the topological zero modes appearing in the valence overlap operator. We estimate the region of parameter space where the contribution from these zero modes is sufficiently small such that their effects can be safely controlled and a restoration of unitarity of the mixed action in the continuum limit is reached. 相似文献
43.
44.
45.
46.
In this paper we review a recently introduced method for solving the Hamilton-Jacobi equations by the method of Separation of Variables. This method is based on the notion of pencil of Poisson brackets and on the bihamiltonian approach to integrable systems. We discuss how separability conditions can be intrinsically characterized within such a geometrical set-up, the definition of the separation coordinates being encompassed in the bihamiltonian structure itself. We finally discuss these constructions studying in details a particular example, based on a generalization of the classical Toda Lattice. 相似文献
47.
48.
Marcia Cristina Branciforti Vitor Sencadas Senentxu Lanceros‐Mendez Rinaldo Gregorio Jr. 《Journal of Polymer Science.Polymer Physics》2007,45(19):2793-2801
Oriented β‐phase films were obtained by utilizing two different techniques: conventional uniaxial drawing at 80 °C of predominantly α‐phase films, and by drawing almost exclusively β‐phase films obtained by crystallization at 60 °C from dimethylformamide (DMF) solution with subsequent pressing. Wide angle X‐ray diffraction (WAXD) and pole figure plots showed that with the conventional drawing technique films oriented at a ratio (R) of 5 still contained about 20% of phase α, a crystallinity degree of 40% and β‐phase crystallographic c ‐axis orientation factor of 0.655. Drawing at 90 °C and with R = 4 of originally β‐phase films results in exclusively β‐phase films with crystallinity degree of 45% and orientation factor of 0.885. Crystalline phase, crystallinity degree, and crystallographic c‐axis orientation factor of both phases were also determined for α‐phase oriented films obtained by drawing α‐phase films at 140 °C. For films drawn at 140 °C the α to β phase transition drops to about 22%. Reduction in crystallinity degree with increasing R is more pronounced at draw temperature of 140 °C compared with 80 °C. Moreover, for both phases the c ‐axis orientation parallel to the draw direction is higher at draw temperature of 140 °C than at 80 °C. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2793–2801, 2007 相似文献
49.
We consider in this paper random flights in ℝ
d
performed by a particle changing direction of motion at Poisson times. Directions are uniformly distributed on hyperspheres
S
1
d
. We obtain the conditional characteristic function of the position of the particle after n changes of direction. From this characteristic function we extract the conditional distributions in terms of (n+1)−fold integrals of products of Bessel functions. These integrals can be worked out in simple terms for spaces of dimension
d=2 and d=4. In these two cases also the unconditional distribution is determined in explicit form. Some distributions connected with
random flights in ℝ3 are discussed and in some special cases are analyzed in full detail. We point out that a strict connection between these
types of motions with infinite directions and the equation of damped waves holds only for d=2.
Related motions with random velocity in spaces of lower dimension are analyzed and their distributions derived. 相似文献
50.
E Bolzacchini P Di Gennaro G Di Gregorio B Rindone P Falagiani G Mistrello I Sondergaard 《Journal of chromatography. A》1991,542(2):337-344
High-performance ion-exchange chromatography and immunoaffinity chromatography suggest that Par jI, the principal allergenic component of Parietaria judaica pollen, is a very unstable molecule, which tends to fragment in solution. Several fragments were obtained from Par jI and some of them show positivity toward the anti-Par jI monoclonal antibody, suggesting that they retain the entire structure of the allergenic determinant. These fragments could be the target for sequence and conformation studies. 相似文献