全文获取类型
收费全文 | 5537篇 |
免费 | 499篇 |
国内免费 | 388篇 |
专业分类
化学 | 1013篇 |
晶体学 | 59篇 |
力学 | 3462篇 |
综合类 | 74篇 |
数学 | 502篇 |
物理学 | 1314篇 |
出版年
2024年 | 3篇 |
2023年 | 29篇 |
2022年 | 81篇 |
2021年 | 226篇 |
2020年 | 158篇 |
2019年 | 93篇 |
2018年 | 114篇 |
2017年 | 155篇 |
2016年 | 209篇 |
2015年 | 159篇 |
2014年 | 202篇 |
2013年 | 328篇 |
2012年 | 200篇 |
2011年 | 271篇 |
2010年 | 220篇 |
2009年 | 270篇 |
2008年 | 287篇 |
2007年 | 333篇 |
2006年 | 339篇 |
2005年 | 287篇 |
2004年 | 285篇 |
2003年 | 244篇 |
2002年 | 182篇 |
2001年 | 205篇 |
2000年 | 213篇 |
1999年 | 176篇 |
1998年 | 143篇 |
1997年 | 135篇 |
1996年 | 128篇 |
1995年 | 112篇 |
1994年 | 88篇 |
1993年 | 91篇 |
1992年 | 81篇 |
1991年 | 75篇 |
1990年 | 48篇 |
1989年 | 40篇 |
1988年 | 43篇 |
1987年 | 42篇 |
1986年 | 30篇 |
1985年 | 21篇 |
1984年 | 18篇 |
1983年 | 10篇 |
1982年 | 20篇 |
1981年 | 17篇 |
1980年 | 2篇 |
1979年 | 5篇 |
1977年 | 2篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有6424条查询结果,搜索用时 341 毫秒
11.
The interaction between multiple incompressible air jets has been studied numerically and experimentally. The numerical predictions have been first validated using experimental data for a single jet configuration. The spreading features of five unequal jets in the configuration of one larger central jet surrounded by four smaller equi‐distant jets, have been studied, for different lateral spacing ratios of 1.5, 2.0 and 2.5 and a central jet Reynolds number of 1.24×105 (corresponding to a Mach number of 0.16). Flow of five equal jets has also been simulated, for the sake of comparison. The jet interactions commence at an axial distance of about 3–4 diameters and complete by an axial distance of about 10 diameters for the lowest spacing ratio of 1.5. For larger spacing ratios, the length required for the start and completion of jet interaction increase. Peripheral jets bend more towards the central jet and merge at a smaller distance, when their sizes are smaller than that of the central jet. The entrainment ratio for multiple jets is higher than that for a single jet. Excellent agreement is observed between the experimental data and theoretical predictions for both mean flow field and turbulent quantities, at regions away from the jet inlet. The potential core length and initial jet development, however, are not predicted very accurately due to differences in the assumed and actual velocity profiles at the jet inlet. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
12.
Sang‐Uk Kim Choonkeun Lee Saimani Sundar Wonbong Jang Seung‐Jin Yang Haksoo Han 《Journal of Polymer Science.Polymer Physics》2004,42(23):4303-4312
A series of polyimides were synthesized from 2,2‐Bis(3,4‐dicarboxyphenyl)hexafluoropropane, 2,2‐bis(3‐amino‐4‐hydroxyphenyl)‐hexafluoropropane, and 4,4′‐oxydianiline by chemical imidization. The effects of the diamine ratios on the properties of the films were evaluated through the study of their thermal, electrical, and morphological properties. All the polymers exhibited better solubility in most of the organic solvents and hence were easily processable. Polyimides with more 2,2‐bis(3‐amino‐4‐hydroxyphenyl)‐hexafluoropropane exhibited better solubility and a low refractive index, which is highly desired for microelectronic applications. The dielectric constant and birefringence were strongly dependent on the fluorine content. With an increase in the fluorine substitution, both the dielectric constant and birefringence decreased. All the polymers exhibited high thermal stability (>400 °C). The absence of crystalline melting in differential scanning calorimetry and broad wide‐angle X‐ray diffraction patterns revealed the amorphous nature of the polymers, which was due to the presence of bulky CF3 groups and hinged ether linkages of the diamine component. The residual stress values decreased with an increase in the 4,4′‐oxydianiline content, and the results were in agreement with the dielectric constant. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4303–4312, 2004 相似文献
13.
朱锡雄 《宁波大学学报(理工版)》1993,(1)
以连续体的各力学守恒定律和熵函数为基础,给出了完备的变形体内参量热力学的表述框架。讨论了将热力学状态参量分划为外参量和内参量的必要性和依据,论证了热力学内参量和非弹性变形的关系以及将各种类型的非弹性应变列为内参量的数学条件。给出了考虑非弹性变形的内参量热力学基本方程,讨论了熵平衡和熵产生的关系方程和行为特性。引入两种定义的变形体自由能函数的表述方程,给出了各相应的状态方程组。 相似文献
14.
With the use of an analytical approach developed, the influence of distribution of a tangential load on the stress concentration
in uniaxially tensioned flat specimens of high-strength unidirectional composites near the grips of a testing machine is evaluated.
In view of singularity of the analytical solution derived at the points of discontinuity of boundary conditions, for estimating
the stress concentration, it is suggested to employ the averaged value of longitudinal stresses, which is calculated by means
of an improper integral across the thickness of a near-surface layer.
__________
Translated from Mekhanika Kompozitnykh Materialov, Vol. 42, No. 6, pp. 787–796, November–December, 2006. 相似文献
15.
Tatsuo Nakagawa Satoshi Fukura Munenori Nakai Kazumasa Sugiyama Ryohei Kokawa Hiroyuki Kagi 《Optical Review》2006,13(4):269-275
We constructed a scanning near-field optical microscope (SNOM) on a commercially available atomic force microscopy (AFM) apparatus
(SPM-9500J2; Shimadzu Corp.) to measure the stress distribution in ceramic composite materials. Features of our SNOM system
are: (1) a compact SNOM head substituted for the original AFM head; (2) a wide scanning range (125 × 125 μm2) inherited from the original scanner; (3) use of conventional shear-force regulation; (4) an optical system for the illumination-collection
(I-C) mode; (5) excitation by a 488 nm line of an Ar-ion laser, and (6) light detection by photon counting or a polychromator
equipped with an electronically cooled charge coupled device (CCD). This SNOM system was used to measure the surface structure
and stress distribution of an Al2O3/ZrO2 eutectic composite. We simultaneously measured topographic images and fluorescence spectra of an Al2O3/ZrO2 eutectic composite. We estimated its peak intensity, peak position, and peak width from the fluorescence spectrum during
scanning, which respectively correspond to the abundance of Al2O3, stress in the grain, and the anisotropy of that stress. Mapping images showed that the stress and its anisotropy were weaker
in the center of the Al2O3 grain than its boundary between Al2O3 and ZrO2. That observation suggests that Al2O3 underwent intense anisotropic stress induced by volume expansion in the phase transition of ZrO2 from the cubic phase to the monoclinic phase during preparation. 相似文献
16.
A method is developed for a stress analysis in an infinite elastic body containing two neighboring periodically cophasaly curved fibers located along two parallel lines. The stress distribution is studied when the body is loaded at infinity by uniformly distributed normal forces in the fiber direction. The investigation is carried out within the framework of a piecewise homogeneous body model with the use of exact three-dimensional equations of elasticity theory. Numerical results related to the stress distribution considered and the influence of interaction between the fibers on this distribution are given. 相似文献
17.
18.
19.
20.
提出了一种基于微悬臂梁传感技术研究大分子折叠/构象转变的新方法.通过分子自组装的方法将热敏性的聚N-异丙基丙烯酰胺(PNIPAM)分子链修饰到微悬臂梁的单侧表面,用光杠杆技术检测温度在20—40℃之间变化时由于微悬臂梁上的PNIPAM分子在水中的构象转变所引起的微悬臂梁变形.实验结果显示:在升温过程中,微悬臂梁的表面应力发生了变化并且导致微悬臂梁产生了弯曲变形,这个过程对应着微悬臂梁上的PNIPAM分子从无规线团构象到塌缩小球构象的构象转变.在降温过程中,微悬臂梁发生了反方向的弯曲变形,这对应着PNIPA
关键词:
构象转变
聚N-异丙基丙烯酰胺分子链
表面应力
微悬臂梁 相似文献