全文获取类型
收费全文 | 6463篇 |
免费 | 2245篇 |
国内免费 | 4180篇 |
专业分类
化学 | 6133篇 |
晶体学 | 301篇 |
力学 | 753篇 |
综合类 | 182篇 |
数学 | 206篇 |
物理学 | 5313篇 |
出版年
2024年 | 83篇 |
2023年 | 261篇 |
2022年 | 262篇 |
2021年 | 303篇 |
2020年 | 236篇 |
2019年 | 318篇 |
2018年 | 212篇 |
2017年 | 324篇 |
2016年 | 330篇 |
2015年 | 413篇 |
2014年 | 707篇 |
2013年 | 599篇 |
2012年 | 529篇 |
2011年 | 588篇 |
2010年 | 557篇 |
2009年 | 534篇 |
2008年 | 582篇 |
2007年 | 544篇 |
2006年 | 524篇 |
2005年 | 522篇 |
2004年 | 529篇 |
2003年 | 474篇 |
2002年 | 389篇 |
2001年 | 427篇 |
2000年 | 293篇 |
1999年 | 263篇 |
1998年 | 283篇 |
1997年 | 239篇 |
1996年 | 239篇 |
1995年 | 234篇 |
1994年 | 190篇 |
1993年 | 175篇 |
1992年 | 191篇 |
1991年 | 156篇 |
1990年 | 130篇 |
1989年 | 125篇 |
1988年 | 42篇 |
1987年 | 23篇 |
1986年 | 16篇 |
1985年 | 19篇 |
1984年 | 6篇 |
1983年 | 9篇 |
1982年 | 6篇 |
1980年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
We investigate the potential profiles and elemental distribution of barriers in Co/ZrAlOx/Co magnetic tunnel junctions (MTJs) using electron holography (EH) and scanning transmission electron microscopy. The MTJ barriers are introduced by oxidizing a bilayer consisting with a uniform 0.45-nm Al layer and a wedge-shaped Zr layer (0-2 nm). From the scanning transmission electron microscopy, AlOx and ZrOx layers are mixed together, indicating that compact AlOx layer cannot be formed in such a bilayer structure of barriers. The Eli results reveal that there are no sharp interfaces between the barrier and magnetic electrodes, which may be responsible for a smaller tunnelling magnetoresistance compared with the MTJs of Co/AlOx/Co. 相似文献
22.
23.
The adsorption of asymmetrical triblock copolymers from a non-selective solvent on solid surface has been studied by using Scheutjens-Fleer mean-field theory and Monte Carlo simulation method on lattice model. The main aim of this paper is to provide detailed computer simulation data, taking A8-kB20Ak as a key example, to study the influence of the structure of copolymer on adsorption behavior and make a comparison between MC and SF results. The simulated results show that the size distribution of various configurations and density-profile are dependent on molecular structure and adsorption energy. The molecular structure will lead to diversity of adsorption behavior. This discrepancy between different structures would be enlarged for the surface coverage and adsorption amount with increasing of the adsorption energy. The surface coverage and the adsorption amount as well as the bound fraction will become larger as symmetry of the molecular structure becomes gradually worse. The adsorption layer becomes thicker with increasing of symmetry of the molecule when adsorption energy is smaller but it becomes thinner when adsorption energy is higher. It is shown that SF theory can reproduce the adsorption behavior of asymmetrical triblock copolymers. However, systematic discrepancy between the theory and simulation still exists.The approximations inherited in the mean-filed theory such as random mixing and the allowance of direct back folding may be responsible for those deviations. 相似文献
24.
用XRD,ESR和TPD等技术研究冲击波处理的结晶MgO后发现,MgO的晶格发生畸变,微应力值ε1/2D显著增大,有大量缺陷产生并形成F心,晶体的平均晶粒减小,且表现出各向异性,从而引起了催化剂表面碱中心强度增大,数目变化,在对乙烷氧化脱氢反应中表现出较高的活性和对乙烯的选择性,初步讨论了可能的结构模型和催化机理。 相似文献
26.
27.
Thermal Rate Constants of the N(^4S)+O2(X^3∑g^-) → NO(X^2Ⅱ) +O(^3P) Reaction on the ^2A′ Potential Energy Surface 下载免费PDF全文
A quasiclassical trajectory study with the sixth-order explicit symplectic algorithm for the N(^4S)+O2(X^3∑g^-) → NO(X^2Ⅱ) +O(^3P) reaction has been reported by employing a new ground potential energy surface. We have discussed the influence of the relative translational energy, the vibrational and rotational levels of O2 molecules on the total reaction cross section. Thermal rate constants at temperatures 300, 600, and 1000 K determined in this work for the reaction are 4.4 × 10^7, 1.8 × 10^10, and 3.1 × 10^11 cm^3mol^-1s^-1, respectively. It is found that they are in better agreement with the experimental data than previous theoretical values. 相似文献
28.
磁控溅射技术制备ZnO透光薄膜 总被引:1,自引:0,他引:1
采用RF磁控溅射方法,在玻璃衬底上制备了择优取向的ZnO薄膜;通过台阶仪、X射线衍射技术、原子力显微镜和分光光度计分别测量了不同溅射功率条件下淀积的ZnO薄膜厚度(淀积速率)、结晶质量、表面形貌与粗糙度、透光光谱,报道了该薄膜结晶质量、薄膜粗糙度与其在可见光区透光率的关系. 相似文献
29.
Jouni PARKKONEN Vesa RUUSKA 《数学学报(英文版)》2007,23(1):89-94
A conjecture of Ehrenpreis states that any two compact Riemann surfaces of genus at least two have finite degree unbranched holomorphic covers that are arbitrarily close to each other in moduli space. Here we prove a weaker result where certain branched covers associated with arithmetic Riemann surfaces are allowed, and investigate the connection of our result with the original conjecture. 相似文献
30.