全文获取类型
收费全文 | 242篇 |
免费 | 121篇 |
国内免费 | 81篇 |
专业分类
化学 | 181篇 |
晶体学 | 7篇 |
力学 | 10篇 |
综合类 | 2篇 |
数学 | 79篇 |
物理学 | 165篇 |
出版年
2023年 | 1篇 |
2022年 | 5篇 |
2021年 | 6篇 |
2020年 | 7篇 |
2019年 | 12篇 |
2018年 | 13篇 |
2017年 | 12篇 |
2016年 | 13篇 |
2015年 | 8篇 |
2014年 | 17篇 |
2013年 | 17篇 |
2012年 | 24篇 |
2011年 | 34篇 |
2010年 | 20篇 |
2009年 | 19篇 |
2008年 | 24篇 |
2007年 | 18篇 |
2006年 | 11篇 |
2005年 | 22篇 |
2004年 | 5篇 |
2003年 | 5篇 |
2002年 | 8篇 |
2001年 | 15篇 |
2000年 | 19篇 |
1999年 | 11篇 |
1998年 | 8篇 |
1997年 | 9篇 |
1996年 | 7篇 |
1995年 | 10篇 |
1994年 | 9篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 6篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 8篇 |
1985年 | 2篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有444条查询结果,搜索用时 31 毫秒
31.
在水溶液中反应制得无色透明的标题化合物单晶 ,单晶X -射线结构分析表明 ,属单斜晶系 ,空间群P2 1,晶胞参数 :a=1.15 47(2 )nm ,b =1.430 9(3)nm ,c =1.5 495 (3)nm ,β =10 5 .41(3)° ,V =2 .46 81(9)nm3,Z =2 ,Dc=4.6 39Mg/m3,对 5 45 4个独立衍射点 (I>2δ(I) )进行全矩阵最小二乘法修正后 ,可靠性因子R =0 .0 487 相似文献
32.
YAN HuiJuan LI ShanShan YAN CunJi CHEN Qing & WAN LiJun Beijing National Laboratory for Molecular Sciences 《中国科学B辑(英文版)》2009,(5)
The adsorption and adlayer structures of tetrathiofulvalene (TTF), tetracyanoquinodimethane (TCNQ) and TTF-TCNQ on Au(111) have been systematically investigated by in situ electrochemical scanning tunneling microscopy (ECSTM) and cyclic voltammetry in 0.1 mol?L?1 HClO4. All the three molecules were found to form well-ordered adlayers in the double-layer potential region of Au(111). For TTF and TCNQ adlayers, (6×3) and (4×7) structures have been observed, respectively. A structural transition was observed on... 相似文献
33.
34.
LU Yang LIU Xiang-guo YU Ying QU He-zhi YANG Shuo NING BO WANG Xiao-ping HAO Dong-yun 《高等学校化学研究》2010,(4):583-590
<正>The development of industrial biotechnology has created an increasing demand for alkaline lipolytic enzymes with functional diversity.In this study,an alkaline soil metagenomic library was constructed to search for new lipolytic enzymes.Two novel gene encoded alkaline esterases(designated as estA and estB) were isolated by functional screening from the library.The estA gene consisted of 834 bp and coded for 277 amino acids with a molecular mass of 29998.Amino acid sequence homology analysis indicates that EstA belongs toα/βhydrolase fold family 4.4(abH4.4),with EstA being the smallest member of that family yet reported.The estB gene consisted of 1185 bp and encoded 394 amino acids with a theoretical molecular mass of 40090.Its conserved domain analysis shows that EstB belongs to the GDSL hydrolase superfamily.Both EstA and EstB exhibit only moderate identity(38%) in amino acid sequence to the known lipolytic enzyme genes in the database.The two genes were respectively expressed in Escherichia coli and the protein products were purified for functional characterization.While the expressed EstA did not exhibit the functional properties that were superior to those of other esterases previously reported,the EstB was stable at temperature up to 45℃and its maximum activity was measured to be 53.6 U/mg at pH=10.Both the enzymes have further enriched the diversity of the lipolytic enzymes database and also appear to be promising biocatalysts for potential biotechnological application. 相似文献
35.
基于静电吸引的自组装树状超分子复合物 总被引:5,自引:1,他引:4
树状分子合成和基于静电作用组装研究是目前十分活跃的研究领域[1-3].树状分子的大小、形状、拓扑形态、柔曲性、内部空腔分布和表面化学可以在分子水平上得到严格的控制,因而其具有独特的性质,被用作“纳米构筑单元”来组装特殊的超分子结构和微环境[3~5].大环共轭卟啉分子在生物体系内的电子转移过程中起着重要作用,以卟啉为核的树状分子可作为人工模拟酶的模型[6].本文首次报道以阴离子卟啉作为树状分子的核,树状阳离子为外层,基于卟啉阴离子与树状阳离子之间静电作用力来组装树状超分子复合物.合成与组装过程如下:1实验部分… 相似文献
36.
37.
Yu-Yu LIU Jie-Wei LI Yi-Fan BO Lei YANG Xiao-Fei ZHANG Ling-Hai XIE Ming-Dong YI Wei HUANG 《物理化学学报》2017,33(9):1803-1810
[4]Cyclo-9, 9-dimethyl-2, 7-fluorenylene ([4]CF) was used as a model compound to explore the steric strain effect on the structures and photoelectrical properties of materials. A series of strained cyclic polyfluorene materials, [n]CFs (n=3-8), was designed. It was found that the strain energy decreased and the energy gap increased as the number of n and ring diameter increased. The ionization potential and electronic affinity tended to increase and decrease as the strain energy decreased at the same number of [n]CFs, respectively. With a balance between hole and electron reorganization energies in the system, these compounds demonstrated great potential as ambipolar materials. It was also found that [n]CFs showed an obvious blue shift in their emission spectra wavelengths (λem2) as the strain energy decreased. Steric strain provides a powerful tool for the design of multifunctional semiconductors in organic optoelectronics. 相似文献
38.
39.
建立了水果、蔬菜、豆类和粮谷中百草枯残留的高效液相色谱-串联质谱(HPLC-MS/MS)分析方法.用水提取样品中的百草枯,弱阳离子交换(WCX)固相萃取柱(SPE)净化.采用CAPCELL PAK ST色谱柱(150 mm×2.0mm).乙腈-10 mmol/L乙酸铵水溶液(用甲酸调至pH 4.0)为流动相,以电喷雾离... 相似文献
40.
单壁碳纳米管Nafion复合膜修饰玻碳电极用于示差脉冲伏安法测定多巴胺 总被引:1,自引:0,他引:1
将单壁碳纳米管(SWCNT′s)分散在5%(质量分数)的Nafion溶液中并滴涂在玻碳电极表面,红外灯烘干后,制得了SWCNT′s/Nafion修饰电极。采用循环伏安法研究了多巴胺在修饰电极上的电化学行为。结果表明,多巴胺在该修饰电极上出现了一对氧化还原峰,其氧化峰峰电位(Epa)为0.408 V(对Ag/AgCl电极,下同),还原峰峰电位(Epc)为0.335 V,且其峰电流与裸玻碳电极比较增大50倍。据此提出了用示差脉冲伏安法测定多巴胺的方法。多巴胺的浓度在120μmol.L-1以内与对应的氧化峰电流呈线性关系,检出限(3S/N)为0.2μmol.L-1。修饰电极用于多巴胺注射液中多巴胺的测定,测定值与标示值相符,加标回收率在96.2%~101.0%之间。 相似文献