全文获取类型
收费全文 | 203篇 |
免费 | 67篇 |
国内免费 | 138篇 |
专业分类
化学 | 254篇 |
晶体学 | 1篇 |
力学 | 1篇 |
数学 | 13篇 |
物理学 | 139篇 |
出版年
2023年 | 6篇 |
2022年 | 11篇 |
2021年 | 8篇 |
2020年 | 8篇 |
2019年 | 6篇 |
2018年 | 6篇 |
2017年 | 17篇 |
2016年 | 11篇 |
2015年 | 18篇 |
2014年 | 22篇 |
2013年 | 44篇 |
2012年 | 27篇 |
2011年 | 33篇 |
2010年 | 33篇 |
2009年 | 17篇 |
2008年 | 30篇 |
2007年 | 19篇 |
2006年 | 25篇 |
2005年 | 11篇 |
2004年 | 11篇 |
2003年 | 8篇 |
2002年 | 7篇 |
2001年 | 4篇 |
2000年 | 10篇 |
1999年 | 5篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1995年 | 1篇 |
1994年 | 4篇 |
1986年 | 1篇 |
排序方式: 共有408条查询结果,搜索用时 15 毫秒
71.
SH Luo Y Liu J Hua XM Niu SX Jing X Zhao B Schneider J Gershenzon SH Li 《Organic letters》2012,14(16):4146-4149
The major pigment responsible for the dark brown nectar of the "bird's Coca cola tree", Leucosceptrum canum (Labiatae), was isolated and identified as a unique symmetric proline-quinone conjugate, 2,5-di-(N-(-)-prolyl)-para-benzoquinone (DPBQ). Behavioral experiments with both isolated and synthetic authentic samples indicated that DPBQ functions mainly as a color attractant to bird pollinators. 相似文献
72.
一些实验表明, 实际大气会偏离理想Kolmogorov模型. 本文基于广义Huygens-Fresnel原理和Toselli等提出的非Kolmogorov湍流模型, 推导出部分相干双曲正弦-Gauss (HSG)涡旋光束通过非Kolmogorov大气湍流的解析传输公式, 并用以对两束部分相干HSG涡旋光束相干叠加和非相干叠加形成的合成相干涡旋在非Kolmogorov大气湍流中的动态演化进行了研究. 结果表明, 合成光束平均光强的演化过程与非Kolmogorov湍流的广义指数α, 源平面上叠加涡旋光束拓扑电荷的符号, 以及叠加方式有关. 合成相干涡旋在非Kolmogorov大气湍流中传输时会出现移动、产生和湮灭. 广义指数α, 拓扑电荷符号, 以及叠加方式都会影响其演化行为. 最后, 将本文所得结果与相关文献做了比较. 相似文献
73.
进行了10—27 GPa应力范围内Zr51Ti5Ni10Cu25Al9金属玻璃的平面冲击实验以研究其高压-高应变率加载下的塑性行为.由样品自由面粒子速度剖面的分析获得了冲击加载过程的轴向应力,并通过轴向应力与静水压线的比较获得剪应力.实验结果表明,尽管存在明显的松弛效应,但Zr基金属玻璃的Hugoniot弹性极限随着冲击应力的增加而增加.然而,塑性波阵面上的剪应力则显示先硬化而后软化现象,而且软化的幅度随冲击应力的增加而增加.冲击加载下Zr基金属玻璃的上述剪应力变化特征与分子动力学模拟结果比较一致,但与压剪实验结果和一维应力冲击实验结果明显不同. 相似文献
74.
75.
Ji-Zhou Kong Fei Zhou Zheng Wang Chuan-Bao Wang Mei-Ling Wang Kang-Min Chen Xue-Mei Wu Kong-Jun Zhu Jin-Hao Qiu 《Journal of Sol-Gel Science and Technology》2012,63(1):95-102
High-quality c-axis oriented Al and Er co-doped ZnO films were prepared on the quartz glasses by sol?Cgel method. In order to obtain the optimal processing parameters for the growth of the oriented film, an L16 (45) orthogonal experimental design was chosen. The experimental results show the rank of 5-factors as follows: Er at.%?>?the number of coating layer?>?annealing temperature?>?Al at.%?>?the concentration of the sol. The Al and Er co-doped film prepared using the optimal parameters exhibits the preferential orientation along the c-axis perpendicular to the substrate surface. In addition, the structural, morphological and optical properties of the films were studied by X-ray diffraction, scanning electron microscopy, and UV?Cvisible spectrophotometer, respectively. The photoluminescence spectra were also used to characterize the luminescence properties of the samples. It is found that when ZnO was co-doped with 7?% Al and 1.5?% Er, the blue emission centered at 465?nm disappears and the green emission centered at 547?nm increases with a blue shift, resulted from the rapid reducing of the interstitial Zn defect, and increasing of the oxygen defects and vacancies caused by Al3+ and Er3+ dopants. 相似文献
76.
采用荧光及紫外光谱研究了1-酮-2-(对二甲氨基苯亚甲基)-四氢萘(KDTN)与人血清白蛋白(HSA)相互作用的光谱特性。 结果表明,静态猝灭和非辐射能量转移是导致KDTN对HSA荧光猝灭的主要原因。 测得17、27和37 ℃ 3个温度下的结合常数KA分别为1.633×108、0.7998×108和0.347×108 L/mol,结合位点数n分别为1.7、1.6和1.7;据Forster偶极 偶极非辐射能量转移理论,计算得到KDTN与HSA在3个温度下的作用距离r分别为2.64、2.59和2.64 nm;能量转移效率E分别为0.5100、0.4797和0.4210。 热力学参数表明,二者主要以范德华力或氢键结合;用同步荧光技术研究了KDTN对HSA构象的影响,结果表明,KDTN的加入对HSA构象影响不大。 相似文献
77.
Binding studies of small molecules with nucleic acids can not only provide new insight into biologically important non-covalent binding mechanisms but also afford a molecular basis to understand the interaction and sequence recognition by promising drugs targeted to DNA. A series of the investigation of the binding of some natural antibiotics, metal complexes and other heterocyclic cations is valuable for the rational design of new antiviral and antitumor agents for clinical use. 相似文献
78.
It is well-known that small organic ligands can bind to the double-stranded nucleic acids by three modes, i.e.s grooving binding, intercalation, and electrostatic binding. Usually, intercalation of the ligands into the double helix involves the insertion of a planar atomatic cation into base stack of the helix, while groove binding of small molecules is pertaining to the docking of thin ribbon-like molecules in the minor groove of the helix. In both cases, electrostatic and hydrophobic interactions can afford additional stabilization for the binding. 相似文献
79.
Nanomaterials and nanotechnological devices will be certain to provide critically important applications in various fields of science and engineering due to the unique surface properties and special behavior of nanostructures typically with high ratios of surface area to volume. With a view to explore possibilities for the potential applications of some nanoscale particles, which show different behavior from that of ordinary materials, in the area of biomolecular recognition, we have tested the DNA binding properties of some ligands such as methylene green (MG), etc, in different buffer solutions of Au colloid. 相似文献
80.
常温常湿CO氧化催化剂Au/Fe2O3的制备与稳定性研究 总被引:6,自引:2,他引:4
研究了不同方法制备的Au/Fe2O3催人上常温常湿条件下CO的氧化性能。结果表明,加料顺序、焙烧温度、沉淀剂种类、金含量等因素对催化剂的稳定性均有较大影响,其中以K2CO3或Na2CO3为沉淀剂,金含量3%,焙烧温度250~350℃制得的催化剂具有较好的稳定性和抗水性,于25℃连续加篱水蒸气反应430h可保持CO完全转化,XRD结果表明,催化剂的稳定性与单质金及α-Fe2O3的粒径成反比,并与反应 相似文献