全文获取类型
收费全文 | 466篇 |
免费 | 82篇 |
国内免费 | 122篇 |
专业分类
化学 | 343篇 |
晶体学 | 3篇 |
力学 | 49篇 |
综合类 | 14篇 |
数学 | 67篇 |
物理学 | 194篇 |
出版年
2023年 | 3篇 |
2022年 | 8篇 |
2021年 | 3篇 |
2020年 | 10篇 |
2019年 | 13篇 |
2018年 | 12篇 |
2017年 | 10篇 |
2016年 | 19篇 |
2015年 | 15篇 |
2014年 | 14篇 |
2013年 | 29篇 |
2012年 | 25篇 |
2011年 | 33篇 |
2010年 | 35篇 |
2009年 | 21篇 |
2008年 | 39篇 |
2007年 | 34篇 |
2006年 | 30篇 |
2005年 | 30篇 |
2004年 | 28篇 |
2003年 | 14篇 |
2002年 | 18篇 |
2001年 | 23篇 |
2000年 | 19篇 |
1999年 | 24篇 |
1998年 | 10篇 |
1997年 | 10篇 |
1996年 | 13篇 |
1995年 | 12篇 |
1994年 | 13篇 |
1993年 | 6篇 |
1992年 | 7篇 |
1991年 | 5篇 |
1990年 | 9篇 |
1989年 | 13篇 |
1988年 | 7篇 |
1987年 | 9篇 |
1986年 | 2篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1975年 | 3篇 |
1884年 | 2篇 |
1875年 | 1篇 |
1874年 | 1篇 |
1872年 | 2篇 |
1871年 | 1篇 |
排序方式: 共有670条查询结果,搜索用时 15 毫秒
61.
We propose an image watermarking scheme based on the phase retrieval algorithm in gyrator domain. The watermark is converted into a noise-like image by Arnold transform. The scrambled image is regarded as the amplitude of gyrator spectrum. The Gerchberg-Saxton algorithm is employed to obtain the unknown phase function in gyrator pair, in which the host image is the amplitude of input function. The phase information and the parameters of the two transforms serve as the key of watermarking algorithm. The numerical simulation has demonstrated the performance of the proposed algorithm. 相似文献
62.
Lie ZS Pardede M Hedwig R Suliyanti MM Kurniawan KH Munadi Lee YI Kagawa K Hattori I Tjia MO 《Analytical and bioanalytical chemistry》2008,390(7):1781-1787
The applicability of spectrochemical analysis of minute amounts of powder samples was investigated using an ultraviolet Nd-YAG
laser (355 nm) and low-pressure ambient air. A large variety of chemical powder samples of different composition were employed
in the experiment. These included a mixture of copper(II) sulfate pentahydrate, zinc sulfide, and chromium(III) sulfate n-hydrate powders, baby powder, cosmetic powders, gold films, zinc supplement tablet, and muds and soils from different areas.
The powder samples were prepared by pulverizing the original samples to an average size of around 30 μm in order to trap them
in the tiny micro holes created on the surface of the quartz subtarget. It was demonstrated that in all cases studied, good
quality spectra were obtained with low background, free from undesirable contamination by the subtarget elements and featuring
ppm sensitivity. A further measurement revealed a linear calibration curve with zero intercept. These results clearly show
the potential application of this technique for practical qualitative and quantitative spectrochemical analysis of powder
samples in various fields of study and investigation. 相似文献
63.
Lie M Barnholt Klepper K Nilsen O Fjellvåg H Kjekshus A 《Dalton transactions (Cambridge, England : 2003)》2008,(2):253-259
Thin films of iron cobalt oxides with spinel-type structure are made by the atomic layer deposition (ALD) technique using Fe(thd)3 (Hthd = 2,2,6,6-tetramethylheptane-3,5-dione), Co(thd)2, and ozone as precursors. Pulse parameters for ALD-type growth are established and such growth can be achieved at deposition temperatures between 185 and 310 degrees C. Films have been deposited on amorphous soda-lime glass and single-crystalline substrates of Si(100), MgO(100), and alpha-Al2O3(001) which all provide crystalline films, but with various orientations and crystallite sizes. Application of an external magnetic field during the film growth does not influence film growth characteristics (growth rate, crystallinity, topography etc.). Magnetization data are reported for phase-pure films of spinel-type structure with composition Fe2CoO4. 相似文献
64.
N,N,N-Trimethylchitosan chloride with different degrees of quaternization has been synthesized and characterized by (1)H NMR spectroscopy. The particle size ranges from 150 to 600 nm, which is dependent on the N/P ratio and is less influenced by the degree of quaternization. The majority of the particles have a spherical morphology. The zeta potential of the particles increases with the N/P ratio and the quaternization degree of TMC. Short-term contact experiments show good biocompatibility of TMC, but long-term contact experiments reveal its high toxicity. This study suggests that TMC is a promising gene carrier, but further modification is still required to improve its cytocompatibility. 相似文献
65.
66.
On the one hand, for a general Calabi–Yau complete intersection X, we establish a decomposition, up to rational equivalence, of the small diagonal in X×X×X, from which we deduce that any decomposable 0-cycle of degree 0 is in fact rationally equivalent to 0, up to torsion. On the other hand, we find a similar decomposition of the smallest diagonal in a higher power of a hypersurface, which provides us an analogous result on the multiplicative structure of its Chow ring. 相似文献
67.
建立幂级数和函数相关的代数方程,给出形如sum from n=o to ∞ anxn(其中an为以n为变元的多项式)的幂级数求和函数的一种方法. 相似文献
68.
尾缘凹陷轴流风轮内流特性分析与降噪研究 总被引:1,自引:0,他引:1
为减少空调室外机用低压轴流风轮叶片的颤振,改善音质,降低噪音和电机功率。本文设计了尾缘凹陷新型三叶轴流风轮,同时除对前缘局部加厚处理外,对叶片其他区域整体减薄。文中采用Navier-Stokes方程对新风轮和原风轮的内流及气动特性进行了三维数值模拟,同时对两者的流量压力曲线和噪音频谱进行了实验研究。研究表明:对轴流风轮叶片尾缘进行凹陷设计,对前缘以外的区域减薄设计,能够减轻风轮重量,降低电机负荷同时减弱转子尾迹;对叶轮前缘进行局部加厚处理可以减小叶尖颤振,降低叶片旋转频率峰值噪音,从整体上降低噪音,改善音质。 相似文献
69.
胶原-磺化羧甲基壳聚糖/硅橡胶皮肤再生材料的制备及其对小型猪烫伤创面全层皮肤缺损的修复研究 总被引:3,自引:0,他引:3
制备了一种胶原-磺化羧甲基壳聚糖/硅橡胶皮肤再生材料,并以小型猪为模型,考察了其对烫伤全层皮肤缺损的修复性能.首先合成了磺化羧甲基壳聚糖,并对其结构进行了表征.制备了胶原-磺化羧甲基壳聚糖多孔支架,采用扫描电子显微镜(SEM)研究了磺化羧甲基壳聚糖含量对支架微结构的影响.随着磺化羧甲基壳聚糖含量的增大,胶原-磺化羧甲基壳聚糖支架从纤维结构向片状结构转化,且支架的孔径相对变大.采用体外成纤维细胞培养实验证明胶原-磺化羧甲基壳聚糖支架无明显细胞毒性.进一步将胶原-磺化羧甲基壳聚糖支架与硅橡胶膜复合,构建具有双层结构的皮肤再生材料.以小型猪为模型,评价了其对深度烫伤创面的修复性能.大体观察和组织学分析结果显示,胶原-磺化羧甲基壳聚糖/硅橡胶皮肤再生材料具有更快的血管化性能,且经该材料处理的创面能有效支持薄自体皮片的移植成活,实现深度烫伤创面的全层修复. 相似文献
70.