全文获取类型
收费全文 | 126篇 |
免费 | 20篇 |
国内免费 | 31篇 |
专业分类
化学 | 84篇 |
晶体学 | 2篇 |
力学 | 1篇 |
综合类 | 1篇 |
数学 | 28篇 |
物理学 | 61篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 5篇 |
2021年 | 7篇 |
2020年 | 10篇 |
2019年 | 13篇 |
2018年 | 6篇 |
2017年 | 8篇 |
2016年 | 6篇 |
2015年 | 13篇 |
2014年 | 13篇 |
2013年 | 11篇 |
2012年 | 17篇 |
2011年 | 11篇 |
2010年 | 10篇 |
2009年 | 3篇 |
2008年 | 2篇 |
2007年 | 12篇 |
2006年 | 8篇 |
2004年 | 3篇 |
2003年 | 3篇 |
2002年 | 2篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1992年 | 1篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 2篇 |
排序方式: 共有177条查询结果,搜索用时 15 毫秒
131.
为了研究三峡水库库尾水域中浮游藻类的群落结构、组成、分布及其在水库水位定期涨落影响及变化规律,尤其是浮游藻类对库区水质状况的影响机理,选择了三峡水库回水区末端,即重庆朝天门至下游太洪岗约50 km水域的6个代表性的断面,在库区水位由最高蓄水水位稍落的开始阶段,即水华的敏感期2012年3月、4月、5月,采集各个断面水体中的水样,获得了三峡水库末端回水区域浮游藻类的种类、组成及其分布特征的初步信息,并将其与同时段水体的水质参数和溶解有机质(DOM)的三维荧光光谱(EEM)特性的进行了相关性拟合研究。研究结果表明,三峡水库水华敏感期,其回水末端优势藻有属蓝藻门的蓝纤维藻、属绿藻门的小球藻、属硅藻门的直链藻和舟形藻,藻密度分别在0.40~0.56×106,1.9~0.8×106,0.36~0.25×106,0.42~0.15×106 cells·L-1;此外在少数断面鱼腥藻、席藻、刚毛藻、羽纹藻和卵形藻,优势藻密度的变化规律与DOM中类蛋白质荧光峰强度、呈显著相关。为便捷检测水华提供有益参考。 相似文献
132.
制备了衍生于双氰基二苯代乙烯的双光子荧光锌离子探针, 该探针以4-(2-吡啶甲基)哌嗪为锌离子受体, 当络合锌离子时, 探针的荧光强度增强了72.5倍和580 GM的双光子吸收截面. 该探针无细胞毒性且在体内环境中无pH敏感性, 其解离常数 =(0.52±0.01) μmol/L. 性能测试结果表明, 该探针能选择性地检测活细胞中的游离锌离子, 耐时长达约1500 s, 且能探测活体组织80~150 μm深处的锌离子, 不受其它金属离子与生物膜的干扰. 相似文献
133.
《International Journal of Plasticity》2000,16(10-11):1345-1369
A general 3-D multivariant model for shape memory alloy constitutive behavior is further developed in this paper. The model is based on the habit planes and transformation directions for variants of martensite and uses a thermodynamic and micromechanics approach to develop the governing equations for thermomechanical response. The model accounts for the self-accomodating group structure exhibited during martensitic plate formation and utilizes this concept in its calculation of the interaction energy between variants. In this paper, we expand the multivariant model to consider the impact of inclusion shape on model predictions. A direction selection scheme is proposed for penny shaped inclusions and is based on the fact that several habit plane variants tend to cluster about one of the {011} or {001} poles. We also explore in detail the crystallographic basis of material response and the impact of specific crystallographic changes on the macroscopic single crystal constitutive response. Differences between type I and type II twinning are examined and it is shown that choice of the proper twinning type is essential to capture experimental data. The grouping structure is examined and several different options published for a NiTi alloy are implemented and results compared. Several concepts, i.e. artificial merging, exclusive and non-exclusive grouping, are raised to assist exploration of NiTi grouping possibilities. The anisotropy of the single crystal material response is illustrated and implications on higher level modeling are discussed. It is noted that properly representing the details of the crystallographic microstructure is crucial to obtaining accurate macroscopic stress–strain predictions. 相似文献
134.
建立了X射线荧光光谱法测定镓酸钠溶液中的镓和钒含量的方法,通过塑料样品杯和麦拉膜封装液体样品,测定中添加仪器自带Zn、Cr两种影响元素排除干扰,减少X射线荧光光谱仪对样品测定结果的偏差,即可得出镓和钒在样品中的含量。结果表明,方法的相对标准偏差(RSD)小于3%,加标回收率为93.33%~102.1%,可实现金属镓生产过程中的物料成分快速检测。 相似文献
135.
136.
《Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy》1988,44(7):695-698
Resonance CARS spectra of 9,9′-bianthryl in the twisted intramolecular charge-transfer (TICT), locally excited (LE)-S1 and T1 states were obtained in solution at room temperature. Observed Raman frequencies were compared with those of the S0 state, the values of anthracene in the S1, T1 and radical ion states. The results show those vibrational modes of bianthryl not only in the S0 state but also in the LE-S1, TICT and T1 states more or less consist of those of anthracene moieties. The inter-moiety CC stretching vibrational mode was not observed in the excited states. 相似文献
137.
通过乳酸衍生物和3-溴-4-羟基苯甲酸的组合得到对映体3-溴-4-(((1R)-1-羧基乙基)氧基)苯甲酸(R-H2bba)和3-溴-4-(((1S)-1-羧基乙基)氧基)苯甲酸(S-H2bba)。以其为手性合成子在水热条件下分别与1,3-二(吡啶-4-基)丙烷(1,3-dpp)和Ni2+反应,构建了对映手性配位聚合物{[Ni(R-bba)(1,3-dpp)(H2O)0.5]·1.5H2O}n(HU12-R)和{[Ni(S-bba)(1,3-dpp)(H2O)0.5]·1.5H2O}n(HU12-S)。结构分析揭示HU12-R和HU12-S是具有dia网络特征的三维螺旋骨架。在骨架中,阴离子配体R-bba2-和S-bba2-分别与Ni2+中心连接在一起围绕2,螺旋轴得到一对小的对映螺... 相似文献
138.
139.
《Superlattices and Microstructures》1998,23(1):173-176
Current transport properties of thin Ag–SiO2granular films were studied. In spite of very simple device structures (i.e., just sandwiching the granular film with Al electrodes), clear Coulomb blockade and Coulomb staircase structures were observed in the current–voltage (I–V) characteristics. The observedI–Vcharacteristics were qualitatively explained by a double-barrier and a triple-barrier tunnel-junction model. 相似文献
140.