全文获取类型
收费全文 | 1442篇 |
免费 | 47篇 |
国内免费 | 4篇 |
专业分类
化学 | 999篇 |
晶体学 | 4篇 |
力学 | 42篇 |
数学 | 267篇 |
物理学 | 181篇 |
出版年
2023年 | 11篇 |
2022年 | 8篇 |
2021年 | 37篇 |
2020年 | 41篇 |
2019年 | 28篇 |
2018年 | 26篇 |
2017年 | 23篇 |
2016年 | 39篇 |
2015年 | 36篇 |
2014年 | 43篇 |
2013年 | 63篇 |
2012年 | 79篇 |
2011年 | 85篇 |
2010年 | 60篇 |
2009年 | 55篇 |
2008年 | 49篇 |
2007年 | 84篇 |
2006年 | 82篇 |
2005年 | 58篇 |
2004年 | 46篇 |
2003年 | 48篇 |
2002年 | 49篇 |
2001年 | 35篇 |
2000年 | 17篇 |
1999年 | 11篇 |
1998年 | 12篇 |
1997年 | 9篇 |
1996年 | 17篇 |
1995年 | 12篇 |
1994年 | 16篇 |
1993年 | 7篇 |
1992年 | 15篇 |
1991年 | 9篇 |
1990年 | 8篇 |
1989年 | 7篇 |
1986年 | 6篇 |
1984年 | 9篇 |
1983年 | 9篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1977年 | 13篇 |
1971年 | 7篇 |
1968年 | 5篇 |
1957年 | 6篇 |
1956年 | 6篇 |
1930年 | 5篇 |
1922年 | 6篇 |
1899年 | 5篇 |
1894年 | 5篇 |
1888年 | 5篇 |
排序方式: 共有1493条查询结果,搜索用时 14 毫秒
1.
2.
Enantiomeric Cyclic Peptides with Different Caco‐2 Permeability Suggest Carrier‐Mediated Transport
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
B. Sc. Eduard Puig Prof. Dr. Beat Ernst Prof. Dr. Horst Kessler 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(22):8023-8027
Recently, oral absorption of cyclic hexapeptides was improved by N‐methylation of their backbone amides. However, the number and position of N‐methylations or of solvent exposed NHs did not correlate to intestinal permeability, measured in a Caco‐2 model. In this study, we investigate enantiomeric pairs of three polar and two lipophilic peptides to demonstrate the participation of carrier‐mediated transporters. As expected, all the enantiomeric peptides exhibited identical lipophilicity (logD7.4) and passive transcellular permeability determined by the parallel artificial membrane permeability assay (PAMPA). However, the enantiomeric polar peptides exhibited different Caco‐2 permeability (Papp) in both directions a–b and b–a. The same trend was observed for one of the lipophilic peptide, whereas the second lipophilic enantiomer pair showed identical Caco‐2 permeability (within the errors). These findings provide the first evidence for the involvement of carrier‐mediated transport for peptides, especially for those of polar nature. 相似文献
3.
Eduard Feireisl Antonín Novotný Hana Petzeltov 《Mathematical Methods in the Applied Sciences》2002,25(12):1045-1073
We prove a general compactness result for the solution set of the compressible Navier–Stokes equations with respect to the variation of the underlying spatial domain. Among various corollaries, we then prove a general existence theorem for the system in question with no restrictions on smoothness of the spatial domain. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
4.
This paper solves the problem of the duration of the total eclipseof a satellite of a body, provided that (a) the body is sphericalin shape and the mass distribution inside the body is sphericallysymmetrical; (b) the satellite is a very small object; (c) thesatellite's orbit around a body is circular and the satellitecan pass through the centre of its shadow; (d) a source of lightis the source of the conical body's shadow (umbra) and it doesnot change its apparent position in the sky; (e) there are noperturbations on the satellite's orbit. The solution presentedrepresents the general discussion of the problem based on utilizationof some parts of the theory of contraction mappings. 相似文献
5.
Eduard Prugovečki 《Foundations of Physics》1991,21(1):93-124
The issue of the intrinsic nonlocality of quantum mechanics raised by J. S. Bell is examined from the point of view of the recently developed method of geometro-stochastic quantization and its applications to general relativistic quantum theory. This analysis reveals that a distinction should be made between the topological concept of locality used in formulating relativistic causality and a type of geometric locality based on the concept of fiber bundle, which can be used in extending the strong equivalence principle to the quantum domain. Both play an essential role in formulating a notion of geometro-stochastic propagation based on quantum diffusions, which throws new light on the EPR paradox, on the origin of the arrow of time, and on other fundamental issues in quantum cosmology and the theory of measurement. 相似文献
6.
7.
M. N. Vidyakin Yu. N. Lazareva Yu. P. Yampolskii A. Yu. Alentiev D. Yu. Likhachev A. L. Rusanov O. V. Kozlova 《Polymer Science Series A》2006,48(6):596-600
The correlation between chemical structure and gas transport properties is considered for a new class of membrane materials based on structurally similar polyphenylquinoxalines that are characterized by different numbers of flexible-O-ether bonds in the repeating unit and different chain rigidities. Permeability, diffusion, and solubility coefficients have been estimated for the gases H2, He, O2, N2, CO, CO2, and CH4; separation factors for various gas pairs have been determined. For the materials with a similar level of cohesive energy density, which characterizes interchain interactions, permeability decreases with a decrease in chain rigidity, whereas selectivity of gas separation increases. 相似文献
8.
9.
Exact relations for the dependence of the positions of extrema of the aggregation work on the aggregation number axis on the surfactant monomer concentration are found for a dilute micellar solution. Relations for the half-widths of the vicinities of the extrema of the aggregation work are determined also. These half-widths are determined by the condition that, within the boundaries of their values, the aggregation work deviates from its extreme values by a thermal unit. The relations derived are illustrated by calculations based on the droplet and quasi-droplet models of spherical aggregates of nonionic surfactant. Some important applications of the obtained results to the theory of relaxation in micellar solutions are considered. 相似文献
10.
O. V. Okatova N. N. Ul’yanova E. G. Bulycheva L. B. Elshina A. L. Rusanov P. N. Lavrenko 《Polymer Science Series A》2007,49(6):716-721
The molecular properties of a number of new poly(naphthylimides) derived from naphthalene-1,4,5,8-tetracarboxylic dianhydride and bis(naphthalic anhydrides) have been studied. On the basis of hydrodynamic studies of the polymers at various stages of their thermal degradation in 96% H2SO4 and thermogravimetric measurements, the hydrolytic stability and thermooxidative resistance of the polymers have been compared. A correlation between the experimental data and the chemical structure of molecular chains has been established. 相似文献