全文获取类型
收费全文 | 3301篇 |
免费 | 616篇 |
国内免费 | 559篇 |
专业分类
化学 | 2453篇 |
晶体学 | 34篇 |
力学 | 231篇 |
综合类 | 46篇 |
数学 | 328篇 |
物理学 | 1384篇 |
出版年
2024年 | 7篇 |
2023年 | 58篇 |
2022年 | 81篇 |
2021年 | 100篇 |
2020年 | 139篇 |
2019年 | 108篇 |
2018年 | 114篇 |
2017年 | 120篇 |
2016年 | 155篇 |
2015年 | 139篇 |
2014年 | 202篇 |
2013年 | 256篇 |
2012年 | 251篇 |
2011年 | 335篇 |
2010年 | 246篇 |
2009年 | 228篇 |
2008年 | 252篇 |
2007年 | 223篇 |
2006年 | 189篇 |
2005年 | 135篇 |
2004年 | 107篇 |
2003年 | 86篇 |
2002年 | 88篇 |
2001年 | 75篇 |
2000年 | 63篇 |
1999年 | 75篇 |
1998年 | 68篇 |
1997年 | 52篇 |
1996年 | 56篇 |
1995年 | 51篇 |
1994年 | 54篇 |
1993年 | 52篇 |
1992年 | 47篇 |
1991年 | 37篇 |
1990年 | 40篇 |
1989年 | 33篇 |
1988年 | 24篇 |
1987年 | 31篇 |
1986年 | 22篇 |
1985年 | 13篇 |
1984年 | 8篇 |
1983年 | 10篇 |
1982年 | 12篇 |
1981年 | 5篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1957年 | 4篇 |
排序方式: 共有4476条查询结果,搜索用时 125 毫秒
21.
22.
Crystal-Orientation Dependent Evolution of Edge Dislocations from a Void in Single Crystal Cu 下载免费PDF全文
The micro-void growth by dislocation emission under tensile loading is explored with focus on the influence of crystal orientations. Based on the elastic theory, a dislocation emission criterion is formulated. It is predicted that the preferential location of dislocation nucleation and its threshold stress are dependent on the crystal orientation. Large-scale molecular dynamics (MD) simulations are also performed for single crystal copper to illustrate the dislocation evolution pattern associated with a nano-void growth. The results are in line with those given by the theoretical prediction. As revealed by MD simulations, the characteristics of void growth at micro-scale depend greatly on the crystal-orientation. 相似文献
23.
The IR finite one-loop box scalar integral with massless internal lines has been recalculated. The result is very compact,
simple and valid for arbitrary values of the relevant kinematic variables. It is given in terms of only two dilogarithms and
a few logarithms, all of very simple arguments.
Received: 31 January 2002 / Published online: 26 April 2002 相似文献
24.
25.
26.
取代对苯二酚醚化物的合成研究 总被引:2,自引:0,他引:2
本文从取代的对苯三酚3出发、利用Williamson醚化反应合成了一系列它的醚化产物4a-4H,给出了它们的核磁共振数据(氢谱和碳谱)。讨论了影响醚化反应的一些因素,比较了不同烷化剂发生醚化反应的活泼性。 相似文献
27.
By means of a new force sensor based on optical beam deflection (OBD), the mechanical effects of laser-matter interaction underwater at different incident laser energy are investigated in detail. The experimental results show that a target underwater is impacted in turn by laser-plasma ablation force and high-speed liquid-jet impulse induced by bubbles collapse in the vicinity of a solid boundary. Furthermore, the amplitudes of the two forces increase monotonously with laser energy. According to the ablation force detected by the experiment and the theoretical relationship between laser intensity and ablation pressure, the value of liquid-jet impact against a solid boundary can be easily obtained. In addition, based on the model of a collapsing bubble, some characteristic parameters, such as the liquid-jet impact velocity, the maximum bubble radius, the bubble energy can also be obtained at different laser energy, which are valuable in the corresponding research fields. 相似文献
28.
The generation of ultrasound in film–substrate system by a laser line source is studied in the case of ablation mechanism, which can be realized by adding a liquid layer at the excitation point. The time domain displacement can be yielded by the numerical jointed inversed Laplace–Fourier transformation technique. The typical surface acoustic waves (SAW) of two layer structures, slow film on fast substrate and fast film on slow substrate, are obtained and the effect of the propagation distance and the thickness of the film on the SAW are given. 相似文献
29.
A. Elfving G. V. Hansson W. -X. Ni 《Physica E: Low-dimensional Systems and Nanostructures》2003,16(3-4):528
The aim of this work is to develop a Si/SiGe HBT-type phototransistor with several Ge dot layers incorporated in the collector, in order to obtain improved light detectivity at 1.3–1.55 μm. The MBE grown HBT detectors are of n–p–n type and based on a multilayer structure containing 10 Ge-dot layers (8 ML in each layer, separated by 60 nm Si spacer) in the base-collector junction. The transistors were processed for normal incidence or with waveguide geometry where the light is coupled through the edge of the sample. The measured breakdown voltage, BVceo, was about 6 V. Compared to a p–i–n reference photodiode with the same dot layer structure, photoconductivity measurements show that the responsivity is improved by a factor of 60 for normal incidence at 1.3 μm. When the light is coupled through the edge of the device, the detectivity is even further enhanced. The measured photo-responsivity is more than 100 and 5 mA/W at 1.3 and 1.55 μm, respectively. 相似文献
30.
用共沉淀法制备了Mg2 + 掺杂的In2 O3 纳米粉 ,研究了镁掺杂对In2 O3 电导和气敏性能的影响 .结果表明 :MgO和In2 O3 间可形成有限固溶体In2 -xMgxO3 (0≤x≤ 0 .40 ) ;MgIn× 电离的空穴对材料导带电子的湮灭 ,使掺镁纳米粉的电导变得很小 ;n(Mg2 + )∶n(In3 + ) =1∶2共沉淀物于 90 0℃下热处理 4h ,用所得的纳米粉制作的传感器在 32 0~ 370℃下 ,对 45 μmol/LC2 H5OH的灵敏度达 10 2 .5 ,为相同浓度干扰气体Petrol的 12倍多 . 相似文献