全文获取类型
收费全文 | 467篇 |
免费 | 89篇 |
国内免费 | 70篇 |
专业分类
化学 | 365篇 |
晶体学 | 12篇 |
力学 | 14篇 |
综合类 | 6篇 |
数学 | 34篇 |
物理学 | 195篇 |
出版年
2024年 | 5篇 |
2023年 | 20篇 |
2022年 | 38篇 |
2021年 | 41篇 |
2020年 | 31篇 |
2019年 | 38篇 |
2018年 | 16篇 |
2017年 | 19篇 |
2016年 | 31篇 |
2015年 | 17篇 |
2014年 | 24篇 |
2013年 | 43篇 |
2012年 | 28篇 |
2011年 | 28篇 |
2010年 | 27篇 |
2009年 | 33篇 |
2008年 | 25篇 |
2007年 | 29篇 |
2006年 | 23篇 |
2005年 | 24篇 |
2004年 | 10篇 |
2003年 | 8篇 |
2002年 | 10篇 |
2001年 | 5篇 |
2000年 | 5篇 |
1999年 | 4篇 |
1998年 | 4篇 |
1996年 | 9篇 |
1995年 | 4篇 |
1994年 | 5篇 |
1993年 | 5篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1982年 | 1篇 |
1981年 | 2篇 |
排序方式: 共有626条查询结果,搜索用时 15 毫秒
101.
显微荧光光谱已经成为流体包裹体系统测试分析中较为成熟的一项技术,可用于区分不同类型的原油与油包裹体,从而为研究含油气盆地的油气成藏历史提供重要依据。不同来源的原油在运聚的过程中可能会发生不同程度的混合作用,为了有效识别这一类地质过程,基于不同比例的原油配比混合实验,研究原油混合后的显微荧光光谱的具体变化特征。结果表明: 原油混源使得显微荧光光谱参数λmax,QF-535和CIE-XY发生了非线性变化,具体表现为混源后原油的荧光光谱参数均介于两个端元油之间,混源油中某一端元油的比例越大,其荧光光谱参数越靠近这一端元油。在CIE-XY色品图中主要表现为非线性渐变的荧光颜色特征。光谱谱形的改变主要表现为谱形由“单峰型”变为“双峰型”和“三峰型”,同时主峰波长和次峰波长保留了两个端元油的信息;QF-535与混源比例可建立曲线用来定量计算两端元油的相对贡献度。综合上述荧光光谱参数和谱形的变化特征,利用原油和油包裹体的显微荧光分析,识别出东海盆地西湖凹陷A气田有三种不同类型原油充注,中间还发生了一次原油混源作用,即蓝绿色荧光原油和黄色荧光原油发生了混合,定量计算其混源程度为介于47%~55%。 相似文献
102.
为了利用微尺度热效应的热致飞高控制(TFC)磁头技术实现磁头飞行高度的精确控制,分析了工作状态下TFC滑块在多物理场综合作用下所呈现出来的传热特性及其主要影响因素,考虑了磁头磁盘间超薄气膜的稀薄效应,建立滑块导热、空气轴承表面传热、气膜流动等模型,利用有限元法,对磁头热变形作用机理及热传导特性对滑块动力学特性影响进行了仿真研究,结果表明,建立的传热模型及对雷诺方程的修正适用于求解磁头磁盘界面气膜传热问题和磁头滑块的动力学问题;影响滑块热力学性能的因素主要可以归结为加热器高度、热生成率以及材料的传热系数;空气轴承力及工作表面热变形的双重作用决定了滑块飞行高度的改变.仿真结果为磁头滑块加热器的设计及空气轴承动力学特性分析提供了依据. 相似文献
103.
In the present paper, we consider the oscillation of a class of self‐adjoint fourth order differential equation. Some oscillation and non‐oscillation criteria on a perturbation equation of Euler differential equation are given. In particular, we find the exact value of a constant in some oscillation criteria, which has answered the open problem presented by Do?lý in 2004. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
104.
A novel ligand with double sulfinyl groups, bis(benzylsulfinyl)methane, was synthesized by a new method and its two lanthanide
(III) complexes were synthesized and characterized by element analysis, molar conductivity, coordination titration analysis,
IR, TG-DSC, 1HNMR and UV spectra. The results indicated that the composition of these complexes was REL2.5(ClO4)3·3H2O (RE = Tb (III), Dy (III), L = C6H5CH2SOCH2SOCH2C6H5). The FT-IR results revealed that the perchlorate group was bonded with the lanthanide ion by the oxygen atoms, and the coordination
was bidentate. The fluorescent spectra illustrated that both the Tb (III) and Dy (III) complexes displayed characteristic
fluorescence in solid state, especially for the Tb (III) complex, the peak of 5D4 → 7 F5 of the Tb (III) ion in 544 nm was stronger than that of others. It indicated that the Tb (III) complex could emit purer green
fluorescence. By analysis fluorescence and phosphorescence spectra, it was found that the ligand had the advantage to absorb
energy and transfer it to the Tb (III) and Dy (III) ions. The phosphorescence spectra and fluorescence lifetimes of the complexes
were also measured. 相似文献
105.
Lycoris species have been known since long ago as a multi-utility ethnomedicinal herbal in China. It has been reported to exhibit a number of properties such as anticancer, neuroprotective, and antibacterial activities. In the present study, the anticancer efficacy of dichloromethane extracts of Lycoris aurea (DELA), was evaluated both in vivo and in vitro using murine sarcoma 180 cells. To evaluate the effects of DELA on apoptotic cell death, flow cytometry and Western blotting were performed. DELA demonstrated promising inhibition effects on sarcoma 180 cells in vitro and a 53.49% inhibitory rate on cancer cells in vivo. DELA treatment increased thymus indices and spleen indices in vivo, indicating that it reduced tumours, but did not damage the main immune organs. The DELA-evoked increase in apoptotic cell death was accompanied by occurrence of cleaved caspase-3 and decreases in the ratio of Bcl-2/Bax. Further purification and LCMS analysis showed DELA contained homolycorine, 2α-hydroxyoduline, oduline, hippeastrine, 2α-hydroxy-6-O- methyloduline, and 2α-methoxy-6-O-methyloduline. These results indicate that DELA exerted its anticancer effects, at least in part, by inducing cancer cell apoptosis and thus can be considered as a potential candidate agent for treatment of cancer. 相似文献
106.
Na Ye Xiangtao Xu Fuying LiMengmeng Ning Zhiqing LiuYuqing Cao Ying Leng Ao Zhang 《Tetrahedron letters》2012,53(35):4738-4742
RuCl3/NaIO4-initiated oxidation of oxiranemethanols was investigated, and two products, oxirane-2-carboxylic acid and (5′-oxotetrahydrofuran-3-yl)acetic acid, were obtained in variant ratios. The product structures were determined and a tentative mechanism involving oxidation-rearrangement-oxidation process was proposed. Glucokinase enzymatic assay revealed that oxiranecarboxamides 4a-c retained moderate GK activation potency with amide 4a showing an EC50 value of 584 nM and a high activation fold of 3.14. However, (5′-oxotetrahydrofuran-3-yl)acetamide 11a is inactive. This study not only provided an alternative protocol to access (5′-oxotetrahydrofuran-3-yl)acetic acid analogs, but also yielded nanomolar GA activators (esp. 4a) for further structure-activity relationship study. 相似文献
107.
108.
以基碳酸酰氯作衍生化试剂 ,采用高效液相色谱拆分 1,1′ 联萘 2 ,2′ 二酚光学异构体。当采用LichrosorbSi 6 0 (4mm× 30 0mm ,5 μm)柱 ,紫外 2 75nm检测 ,正己烷 乙醇 (98.5 1.5 ,V V)为流动相 ,1,1′ 联萘 2 ,2′ 二酚单基碳酸酯的分离因子和分离度分别为 1.36 8、3.0 5 1;用正己烷 乙醚 (98.5 1.5 ,V V)为流动相 ,1,1′ 联萘 2 ,2′ 二酚双基碳酸酯的分离因子和分离度分别为 1.0 5 5、1.347。这一方法可简便、快速地测定联萘二酚单基碳酸酯拆分样品的光学纯度 相似文献
109.
110.
吡唑啉衍生物具有高的蓝色荧光,并且具有高量子效率,很易于用作发光材料中电子传输层。依据Schellhammer经验中化学结构与荧光性关系,在吡唑啉的1-位引入了苯并噻唑基,3-位引入苯基衍生物,使其具有荧光性,5-位引入呋喃基作为助色团,可使荧光波长红移,增加荧光性。文章设计并合成了六种5-位引入呋喃基苯并噻唑吡唑啉类荧光化合物,通过红外光谱、荧光光谱、1HNMR、元素分析对合成的化合物进行了表征,表明这类化合物具有良好的荧光性,其最大发射波长在440~460 nm之间,经过分析得知其荧光强度的大小与衍生物中不同的取代基有关。 相似文献