全文获取类型
收费全文 | 3289篇 |
免费 | 503篇 |
国内免费 | 166篇 |
专业分类
化学 | 2681篇 |
晶体学 | 29篇 |
力学 | 96篇 |
综合类 | 20篇 |
数学 | 232篇 |
物理学 | 900篇 |
出版年
2024年 | 8篇 |
2023年 | 56篇 |
2022年 | 64篇 |
2021年 | 84篇 |
2020年 | 139篇 |
2019年 | 133篇 |
2018年 | 101篇 |
2017年 | 87篇 |
2016年 | 150篇 |
2015年 | 159篇 |
2014年 | 176篇 |
2013年 | 215篇 |
2012年 | 254篇 |
2011年 | 284篇 |
2010年 | 188篇 |
2009年 | 172篇 |
2008年 | 207篇 |
2007年 | 157篇 |
2006年 | 167篇 |
2005年 | 150篇 |
2004年 | 135篇 |
2003年 | 131篇 |
2002年 | 112篇 |
2001年 | 62篇 |
2000年 | 66篇 |
1999年 | 68篇 |
1998年 | 42篇 |
1997年 | 39篇 |
1996年 | 45篇 |
1995年 | 38篇 |
1994年 | 40篇 |
1993年 | 19篇 |
1992年 | 23篇 |
1991年 | 22篇 |
1990年 | 16篇 |
1989年 | 11篇 |
1988年 | 14篇 |
1987年 | 14篇 |
1986年 | 9篇 |
1985年 | 12篇 |
1984年 | 12篇 |
1983年 | 8篇 |
1982年 | 7篇 |
1981年 | 13篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1977年 | 8篇 |
1976年 | 3篇 |
1974年 | 7篇 |
1973年 | 4篇 |
排序方式: 共有3958条查询结果,搜索用时 15 毫秒
11.
12.
The deformation surrounding Vickers indentations on InGaAsP/InP epilayers have been studied in detail. The surface topography was characterized by using atomic force microscopy (AFM). The material pile-up and sink-in regions around the indentation impression was observed for the quaternary InGaAsP/InP epilayers. The sectional analysis mode of the AFM shows the depth profile at the indented region. Microindentation studies were carried out for different atomic fraction of the quaternary InGaAsP/InP compound semiconductor alloys. The microhardness values of InGaAsP/InP epilayers were found to be in the range of 5.08 and 5.73 GPa. These results show that the hardness value of the quaternary alloy drastically increases as the composition of As was increased by 0.01 atomic fraction and when the phosphorous concentration decreases from 0.4 to 0.38. The reason may be that the increase in As concentration hardens the lattice when phosphorous concentration was less and hardness decreases when phosphorous was increased. 相似文献
13.
This study presents a compact optical configuration that can generate a multiplex dot-matrix hologram with complex interlaced images for anti-counterfeiting applications on valuable paper. Varying the orientation of the interference plane can enable the multiplex hologram to be recorded without changing the interference angle of two laser beams. With its simple asymmetric optical setup, a multiplex hologram with many interlaced images can be efficiently fabricated, increasing the cost of imitation. Experimental details of the asymmetric optical setup are also described. 相似文献
14.
15.
16.
17.
If M is an isoparametric hypersurface in a sphere S
n
with four distinct principal curvatures, then the principal curvatures κ1, . . . , κ4 can be ordered so that their multiplicities satisfy m
1 = m
2 and m
3 = m
4, and the cross-ratio r of the principal curvatures (the Lie curvature) equals −1. In this paper, we prove that if M is an irreducible connected proper Dupin hypersurface in R
n
(or S
n
) with four distinct principal curvatures with multiplicities m
1 = m
2 ≥ 1 and m
3 = m
4 = 1, and constant Lie curvature r = −1, then M is equivalent by Lie sphere transformation to an isoparametric hypersurface in a sphere. This result remains true if the
assumption of irreducibility is replaced by compactness and r is merely assumed to be constant.
相似文献
18.
In this paper, the authors present airflow field characteristics of human upper airway and soft palate movement attitude during
breathing. On the basis of the data taken from the spiral computerized tomography images of a healthy person and a patient
with Obstructive Sleep Apnea-Hypopnea Syndrome (OSAHS), three-dimensional models of upper airway cavity and soft palate are
reconstructed by the method of surface rendering. Numerical simulation is performed for airflow in the upper airway and displacement
of soft palate by fluid-structure interaction analysis. The reconstructed three-dimensional models precisely preserve the
original configuration of upper airways and soft palate. The results of the pressure and velocity distributions in the airflow
field are quantitatively determined, and the displacement of soft palate is presented. Pressure gradients of airway are lower
for the healthy person and the airflow distribution is quite uniform in the case of free breathing. However, the OSAHS patient
remarkably escalates both the pressure and velocity in the upper airway, and causes higher displacement of the soft palate.
The present study is useful in revealing pathogenesis and quantitative mutual relationship between configuration and function
of the upper airway as well as in diagnosing diseases related to anatomical structure and function of the upper airway.
The project supported by the National Natural Science Foundation of China (10672036, 10472025 and 10421002), the Natural Science
Foundation of Liaoning Province (20032109).
English text was polished by Yunming Chen. 相似文献
19.
We report viscometric data collected in a Couette rheometry on dilute, single‐solvent polystyrene (PS)/dioctyl phthalate (DOP) solutions over a variety of polymer molecular weights (5.5 × 105 ≤ Mw ≤ 3.0 × 106 Da) and system temperatures (288 K ≤ T ≤ 318 K). In view of the essential viscometric features, the current data may be classified into three categories: The first concerns all the investigated solutions at low shear rates, where the solution properties are found to agree excellently with the Zimm model predictions. The second includes all sample solutions, except for high‐molecular‐weight PS samples (Mw ≥ 2.0 × 106 Da), where excellent time–temperature superposition is observed for the steady‐state polymer viscosity at constant polymer molecular weights. No similar superposition applies at a constant temperature but varied polymer molecular weights, however. The third appears to be characteristic of dilute high‐molecular‐weight polymer solutions, for which the effects of temperature on the viscosity curve are further complicated at high shear rates. The implications concerning the relative importance of hydrodynamic interactions, segmental interactions, and chain extensibility with increasing polymer molecular weight, system temperature, and shear rate are discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 787–794, 2006 相似文献
20.