全文获取类型
收费全文 | 5024篇 |
免费 | 875篇 |
国内免费 | 1116篇 |
专业分类
化学 | 4191篇 |
晶体学 | 62篇 |
力学 | 332篇 |
综合类 | 81篇 |
数学 | 558篇 |
物理学 | 1791篇 |
出版年
2024年 | 18篇 |
2023年 | 92篇 |
2022年 | 170篇 |
2021年 | 206篇 |
2020年 | 196篇 |
2019年 | 224篇 |
2018年 | 169篇 |
2017年 | 180篇 |
2016年 | 244篇 |
2015年 | 261篇 |
2014年 | 279篇 |
2013年 | 392篇 |
2012年 | 428篇 |
2011年 | 471篇 |
2010年 | 356篇 |
2009年 | 333篇 |
2008年 | 373篇 |
2007年 | 317篇 |
2006年 | 288篇 |
2005年 | 266篇 |
2004年 | 183篇 |
2003年 | 171篇 |
2002年 | 239篇 |
2001年 | 208篇 |
2000年 | 153篇 |
1999年 | 138篇 |
1998年 | 110篇 |
1997年 | 86篇 |
1996年 | 51篇 |
1995年 | 58篇 |
1994年 | 67篇 |
1993年 | 49篇 |
1992年 | 55篇 |
1991年 | 55篇 |
1990年 | 29篇 |
1989年 | 20篇 |
1988年 | 17篇 |
1987年 | 11篇 |
1986年 | 10篇 |
1985年 | 12篇 |
1984年 | 7篇 |
1983年 | 10篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1957年 | 1篇 |
1943年 | 1篇 |
排序方式: 共有7015条查询结果,搜索用时 15 毫秒
961.
A significant growth of research on adaptive liquid lens is achieved over the past decades, and the field is still attracting increasing attentions, focusing on the transition from the current stage to the commercialized stage. The challenges faced are not limited to fabrication, material, small tuning range in focal lengths, additional control systems, limitations in special actuation methods and so on. In addition, the use of external driving parts or systems induce extra problem on bulky appearance, high cost, low reliability etc. Therefore, adaptive liquid lens will be an interesting research focus in both microfluidics and optofluidics science. This review attempts to summarize and focus on the droplet profile deformation under different driving mechanisms in tunable liquid microlens as well as the application in cameras, cell phone and so on. The driving techniques are generally categorized in terms of mechanisms and driving sources. 相似文献
962.
以聚L-谷氨酸苄酯(PBLG)为原料, 通过溶剂浇铸与粒子沥滤法分别构建PBLG单层致密和PBLG单层多孔膜, 利用乙醇胺对薄膜表面改性, 构筑双层引导骨再生膜. 研究了不同胺解改性时间对PBLG-s-PHEG双层膜亲水性和力学性能的影响, 结果表明, 随着PBLG分子量的增大, 薄膜的力学性能增强而降解速率减缓. 延长胺解改性时间可提高薄膜亲水性和体内外降解速率. 细胞实验结果表明, 双层薄膜的致密结构能够有效阻隔成纤维细胞的侵入, 多孔结构能够支持细胞贴壁黏附和铺展. 体外生物活性评价结果表明, 表面改性的PBLG基材料可用于体内骨缺损修复. 本文所构建的双层引导骨再生膜在体外具有良好的力学性能和降解性能, 与组织具有一定的贴合性, 同时可有效阻碍成纤维细胞侵入, 具有潜在应用价值. 相似文献
963.
Wu Bo Zhao Yuanyang Liu Qinfeng Zhou Changlin Zhang Xi Lei Jingxin 《Journal of Thermal Analysis and Calorimetry》2019,137(4):1225-1232
Journal of Thermal Analysis and Calorimetry - Utilization of renewable biomass to prepare phase change material (PCM) that can reversibly store renewable thermal energy is of great interest. Castor... 相似文献
964.
965.
Chemical and structural changes preceding electrocatalysis obfuscate the nature of the active state of electrocatalysts for the oxygen evolution reaction (OER), which calls for model systems to gain systematic insight. We investigated the effect of bulk oxidation on the overpotential of ink-casted LiMn2O4 electrodes by a rotating ring-disk electrode (RRDE) setup and X-ray absorption spectroscopy (XAS) at the K shell core level of manganese ions (Mn−K edge). The cyclic voltammogram of the RRDE disk shows pronounced redox peaks in lithium hydroxide electrolytes with pH between 12 and 13.5, which we assign to bulk manganese redox based on XAS. The onset of the OER is pH-dependent on the scale of the reversible hydrogen electrode (RHE) with a Nernst slope of −40(4) mV/pH at −5 μA monitored at the RRDE ring. To connect this trend to catalyst changes, we develop a simple model for delithiation of LiMn2O4 in LiOH electrolytes, which gives the same Nernst slope of delithiation as our experimental data, i. e., 116(25) mV/pH. From this data, we construct an ERHE-pH diagram that illustrates robustness of LiMn2O4 against oxidation above pH 13.5 as also verified by XAS. We conclude that manganese oxidation is the origin of the increase of the OER overpotential at pH lower than 14 and also of the pH dependence on the RHE scale. Our work highlights that vulnerability to transition metal redox may lead to increased overpotentials, which is important for the design of stable electrocatalysts. 相似文献
966.
Based on the extended Huygens–Fresnel principle, the closed-form propagation equation of partially coherent Sinh-Gaussian (ShG) beams through the turbulent atmosphere has been derived by using the quadratic approximation of the Rytov's phase structure function. The influence of turbulence on propagation properties of partially coherent ShG beams and their beam quality in the far field are studied both analytically and numerical. The fully coherent ShG beam has been treated as a special case of the partially coherent ShG beam when the degree of spatial coherence α=∞. It is shown that in comparison with the free-space propagation the turbulence accelerates the evolution of three stages that partially coherent ShG beams undergo. The smaller α is, the less partially coherent ShG beams are affected by the turbulence. In particular, we find that the β parameter decreases as the decentered parameter δ increases, but the dependence of the Strehl ratio on δ is not monotonous. There exists an optimal δopt, the influence of turbulence on the maximum intensity of the corresponding partially coherent ShG beam with δopt is the smallest. Therefore, a suitable choice of δ may reduce the influence of turbulence on the beam quality in the far field in practice. 相似文献
967.
Low energy ion beam assisted deposition (IBAD) was employed to prepare Ag films on Mo/Si (100) substrate. It was found that Ag films deposited by sputtering method without ion beam bombardment were preferred (111) orientation. When the depositing film was simultaneously bombardment by Ar+ beam perpendicular to the film surface at ion/atom arrival ratio of 0.18, the prepared films exhibited weak (111) and (200) mixed orientations. When the direction of Ar+ beam was off-normal direction of the film surface, Ag films showed highly preferred (111) orientation. Monte Carlo method was used to calculate the sputtering yields of Ar+ ions at various incident and azimuth angles. The effects of channeling and surface free energy on the crystallographic orientation of Ag films were discussed. 相似文献
968.
969.
金属薄膜表面化学反应活性中的量子尺寸效应 总被引:1,自引:0,他引:1
本文首先简要介绍了金属薄膜的量子尺寸效应及其对表面化学性质的影响,然后对Pb/si体系量子尺寸效应的近期研究进行了综述,最后详细介绍了量子效应对表面化学反应活性的影响.扫描隧道显微镜观察表明:在Pb(111)单晶薄膜表面卜的分子吸附和氧化反应随着薄膜厚度一个原子层一个原子层变化时会出现振荡现象.通过研究薄膜中量子阱态的形成、费米能级处电子态密度的变化与薄膜的表面反应活性之间的关系,我们从实验上直接定量地证明了最子尺寸效应对表面反应活性的调控作用. 相似文献
970.
基于高分辨质谱技术的婴幼儿食品中过敏原蛋白质的高灵敏检测 总被引:2,自引:0,他引:2
基于高效液相色谱-串联质谱(LC-MS/MS)技术,选择稳定性好、灵敏度高的特征肽段,利用平行反应监测(PRM)技术,实现了多类过敏原蛋白质的高灵敏度同时检测,并成功应用于婴幼儿食品中过敏原成分的分析。对于婴幼儿食品中蛋白质的提取,与传统的丙酮沉淀法比,采用膜上原位样品预处理方法(i-FASP)可实现更高的蛋白质提取效率和抗干扰能力。所检测的过敏原蛋白质的定量限(LOQ)最小可达到0.028 mg/L,其线性范围最宽可跨越4个数量级,且线性关系良好(相关系数R~2≥0.99)。该方法为食品中过敏原蛋白质组学快速分析提供了一种可靠的分析方法。 相似文献