全文获取类型
收费全文 | 259篇 |
免费 | 13篇 |
国内免费 | 68篇 |
专业分类
化学 | 265篇 |
力学 | 11篇 |
综合类 | 4篇 |
数学 | 7篇 |
物理学 | 53篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2022年 | 12篇 |
2021年 | 8篇 |
2020年 | 11篇 |
2019年 | 12篇 |
2018年 | 7篇 |
2017年 | 11篇 |
2016年 | 12篇 |
2015年 | 17篇 |
2014年 | 12篇 |
2013年 | 23篇 |
2012年 | 25篇 |
2011年 | 17篇 |
2010年 | 21篇 |
2009年 | 18篇 |
2008年 | 17篇 |
2007年 | 14篇 |
2006年 | 18篇 |
2005年 | 12篇 |
2004年 | 12篇 |
2003年 | 4篇 |
2002年 | 5篇 |
2001年 | 2篇 |
2000年 | 7篇 |
1999年 | 9篇 |
1998年 | 13篇 |
1997年 | 10篇 |
1996年 | 3篇 |
1995年 | 1篇 |
1990年 | 3篇 |
1986年 | 1篇 |
排序方式: 共有340条查询结果,搜索用时 46 毫秒
121.
高重复频率飞秒脉冲激光辐照钼酸镝玻璃表面后,通过显微拉曼测试,发现在辐照区域内形成了含有MoO4四面体结构的β′-Dy2(MoO4)3晶体和含有MoO6八面体结构的α-MoO3晶体。通过电子能谱(EDS)测量辐照前后样品中钼(Mo)元素的含量,发现在辐照中心位置形成α-MoO3晶体相的区域内出现了明显的Mo元素缺失现象,表明了在高温场作用下,微爆现象引起了材料中心密度的降低。此外,随着辐照时间的增加辐照中心位置还出现了由Dy2(MoO4)3相向MoO3晶体α相的相变。这说明随着激光作用程度的加剧,中心区域Mo元素浓度降低,使得钼氧结构由MoO4四面体向MoO6八面体转变,导致在Mo元素浓度较低的区域更容易形成八面体结构的α-MoO3。 相似文献
122.
实验用红光记录紫光敏化,研究了几种不同掺杂浓度和氧化还原状态的近化学配比铌酸锂晶体的双色全息记录特性,如其饱和衍射效率和记录灵敏度的变化规律。实验结果表明,晶体的饱和衍射效率随透射光强与紫外光强比值的增加先增加后减小,而记录灵敏度在不断减小。Mn含量相同时,Tb含量越高的晶体饱和衍射效率越高,而记录灵敏度越低。Tb含量相同时,含Mn比不含Mn的晶体的饱和衍射效率低,但记录灵敏度更高。还原晶体的饱和衍射效率和记录灵敏度均比氧化晶体高。记录光与敏化光的比值、掺杂浓度和氧化还原状态对晶体的全息特性产生影响。通过适当调整上述参数之间的关系,可对材料的全息记录特性进行优化。 相似文献
123.
124.
125.
126.
ICP—AES法测定玫瑰花、金银花中多种微量元素 总被引:1,自引:0,他引:1
研究了用微波消解ICP—AES对玫瑰花、金银花中Cu、Zn、Fe、Mn、Na、Ca6种元素进行测定的方法,优化了ICP—AES的工作参数,考察了消解液的种类及用量对测定结果的影响,选择玫瑰花的消解液为V(HNO,)+V(HClO4):5+3,金银花的消解液为V(HNO,)+V(HClO4)=10+3。结果表明,6种元素的检出限在0.005~0.021μg/mL之间,相对标准偏差(RSD)均小于8%,回收率为95.6%~103.9%,该法用于玫瑰花、金银花中元素的测定,结果令人满意。金银花、玫瑰花中含有丰富的微量元素,对人体健康十分有益。 相似文献
127.
Zufeng Guo Zhiqiang Cheng Jingxin Wang Wukun Liu Hanjing Peng Yuefan Wang A. V. Subba Rao Ruo‐jing Li Xue Ying Preethi Korangath Maria V. Liberti Yingjun Li Yongmei Xie Sam Y. Hong Cordelia Schiene‐Fischer Gunter Fischer Jason W. Locasale Saraswati Sukumar Heng Zhu Jun O. Liu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(48):17318-17322
Glucose transporters play an essential role in cancer cell proliferation and survival and have been pursued as promising cancer drug targets. Using microarrays of a library of new macrocycles known as rapafucins, which were inspired by the natural product rapamycin, we screened for new inhibitors of GLUT1. We identified multiple hits from the rapafucin 3D microarray and confirmed one hit as a bona fide GLUT1 ligand, which we named rapaglutin A (RgA). We demonstrate that RgA is a potent inhibitor of GLUT1 as well as GLUT3 and GLUT4, with an IC50 value of low nanomolar for GLUT1. RgA was found to inhibit glucose uptake, leading to a decrease in cellular ATP synthesis, activation of AMP‐dependent kinase, inhibition of mTOR signaling, and induction of cell‐cycle arrest and apoptosis in cancer cells. Moreover, RgA was capable of inhibiting tumor xenografts in vivo without obvious side effects. RgA could thus be a new chemical tool to study GLUT function and a promising lead for developing anticancer drugs. 相似文献
128.
Summary: Linear and branched alkanes are oligomers of polyethylene. Alkanes with higher molar masses are called waxes. These substances are widely used as fuels, oils, lubricants, etc. and for these reasons many groups have tried to analyse, separate and characterise alkanes by various methods, including liquid chromatography. Alkanes may be separated according to their size in solution by SEC. In addition to chromatographic systems separating in the SEC mode, various sorbent-solvent systems have been published, where alkanes have been separated one from another by adsorption and/or precipitation mechanism. The mobile phase is either a non-polar solvent or a polar solvent or a mixture of a solvent and a non-solvent for alkanes. Even near critical conditions, which have several advantages for applications of HPLC in polymer analysis, have been identified for alkanes. Moreover, selective separations of branched alkanes according to their structure have been published. In the majority of these published studies, solvents with low boiling points have been used as the mobile phases, which do not allow dissolution of crystalline polyolefins at atmospheric pressure. However, taking into account experiences with the separation of alkanes, new HPLC systems for the separation of polyolefins may be developed. This is a major challenge and first results are presented in this contribution. 相似文献
129.
摩擦片的摩擦磨损性能严重影响盘式制动器的使用寿命和客车行驶的安全性.以灰铸铁HT250圆盘为对偶件,利用销盘式摩擦磨损试验机,在不同温度下对树脂基复合材料摩擦片的摩擦系数和磨损率进行研究,同时应用JSM-651010LA型扫描电子显微镜、HGP-7500型光电直读光谱仪和HXD-1000TMSC型显微硬度测试仪对摩擦磨损表面进行观察和测量,表征其摩擦表面的微观形貌和测定微观硬度,进而推断其磨损机理.结果表明:在不同温度下,平均摩擦系数和磨损率均随着温度的升高先增加后降低;随着温度升高,摩擦层的面积和其微观硬度的变化和平均摩擦系数、磨损率的变化规律基本相同;在高温摩擦磨损过程中,黏着磨损占主导作用,同时伴随着切削磨损. 相似文献
130.
Yongmei Pan Shanjia Xu 《International Journal of Infrared and Millimeter Waves》2008,29(12):1163-1171
A new leaky-wave antenna structure is carefully investigated in the paper, which is based on a grounded Left-Handed material
(LHM) slab periodically loaded with metal strips. A rigorous formulation similar to the spectral domain method for planar
circuits is deduced to analyze the radiation characteristics of the antenna. Theoretical analysis results reveal that at specific
frequency region or with proper geometrical parameters chosen, the present structure supports simultaneously two leaky modes
corresponding to the forward and backward radiations. The principle of the antenna is due to the peculiar propagation properties
of the unperturbed LHM grounded slab waveguide, which is totally different from the phenomenon of double or even more space
harmonic mode radiations in normal periodic structures. Extensive numerical results of the leakage characteristics are given
to establish useful guidelines for the design of the new type leaky wave antenna. 相似文献