全文获取类型
收费全文 | 367篇 |
免费 | 0篇 |
国内免费 | 221篇 |
专业分类
化学 | 565篇 |
力学 | 5篇 |
数学 | 3篇 |
物理学 | 15篇 |
出版年
2018年 | 2篇 |
2015年 | 1篇 |
2014年 | 2篇 |
2012年 | 8篇 |
2011年 | 7篇 |
2010年 | 4篇 |
2009年 | 112篇 |
2008年 | 149篇 |
2007年 | 37篇 |
2006年 | 87篇 |
2005年 | 86篇 |
2004年 | 26篇 |
2003年 | 14篇 |
2002年 | 9篇 |
2001年 | 5篇 |
2000年 | 11篇 |
1999年 | 16篇 |
1998年 | 1篇 |
1997年 | 5篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有588条查询结果,搜索用时 15 毫秒
551.
Wirtz M Schumann CA Schellenträger M Gäb S Vom Brocke J Podeschwa MA Altenbach HJ Oscier D Schmitz OJ 《Electrophoresis》2005,26(13):2599-2607
Reactive oxygen molecules are formed in vivo as by-products of normal aerobic metabolism. All organisms dependent on oxygen are inevitably exposed to these species so that DNA damage can occur in both genomic and mitochondrial DNA (mtDNA). In order to determine endogenous DNA damage we have developed an analytical method that involves the isolation and hydrolysis of genomic DNA or mtDNA, the labeling of modified and unmodified nucleotides and micellar electrokinetic chromatography with laser-induced fluorescence detection. With this method we have found etheno-adenine, thymine glycol, uracil, hypoxanthine, and 5-methylcytosine. These were identified by the addition of internal standards to the genomic or mtDNA. There are a large number of other signals in the electropherograms of mtDNA that we have never found in genomic DNA analysis because they are at lower concentration in the genome. In the DNA of untreated patients with chronic lymphocytic leukemia (CLL), uracil and high levels of etheno-adenine were found, which can be explained by antioxidant enzyme alterations and oxidative stress in the CLL lymphocytes. 相似文献
552.
1 INTRODUCTIONThemaintargetinmacrocyclicdesignistosynthesizemacrocycleswhichareabletodiscriminateamongthedifferentmetalcations.Manyfactorsinfluencingtheselectivitiesofmacrocyclesforcationshavebeendeterminedsuchassubstituenteffect,donoratomictypesand… 相似文献
553.
以3-叠氮-1,2,4-三唑为配体,PA–(苦味酸根)或HTNR–(2,4,6-三硝基间苯二酚脱去一个羟基的质子后形成的离子)为外阴离子,制备得到了两种新的配合物:[Zn(AZT)4(H2O)2](PA)2∙4H2O和[Zn(AZT)2(H2O)4](HTNR)2∙4H2O。[Zn(AZT)4(H2O)2](PA)2∙ 4H2O的X射线晶体数据表明,中心Zn2+离子与来自4个AZT分子的N原子和2个H2O分子的O原子配位;而对于[Zn(AZT)2(H2O)4](HTNR)2∙4H2O来说,6个配位原子来自2个AZT分子的N原子和4个H2O分子的O原子。在两种配合物中,AZT配体分子的配位点都是三唑环上的4位N原子。H2O分子对于分子间氢键的形成起到了重要的作用,在分子间氢键的作用下形成了配合物的晶体结构。在[Zn(AZT)4(H2O)2](PA)2∙4H2O的晶体结构中,还存在错位面对面π-π堆积作用,它对于晶体结构的形成和稳定性也起到了重要作用。TG-DTG和DSC分析结果显示,[Zn(AZT)2(H2O)4](HTNR)2∙4H2O的热分解过程不如[Zn(AZT)4(H2O)2](PA)2∙4H2O剧烈,原因在于前者分子中含有较多配位水分子和较少AZT配体分子。感度测试结果表明,[Zn(AZT)4(H2O)2](PA)2∙4H2O有一定的火焰感度,而[Zn(AZT)2(H2O)4](HTNR)2∙4H2O却对热不敏感;两种化合物在撞击和摩擦作用下都表现钝感。 相似文献
554.
555.
基于均苯三甲酸与对羟基吡啶的超分子水凝胶 总被引:1,自引:0,他引:1
以均苯三甲酸和对羟基吡啶为原料, 采用简便方法合成了一种新的凝胶因子, 并采用1H NMR、IR和元素分析确认其结构. 红外光谱中2849和1894 cm-1处出峰证明羧基与吡啶基间形成了氢键. 在凝胶化过程中, 凝胶因子可自组装形成纤维状网络结构. 随着凝胶因子浓度的增加, 纤维搭接逐渐致密, 凝胶网络密度逐渐增大, 可冻结水含量逐渐增加. 因此, 通过改变凝胶因子浓度可有效控制凝胶的结构及性能. 该凝胶因子在较低浓度下形成的超分子水凝胶在100 ℃下也能够稳定存在. 相似文献
556.
557.
Tăbăcaru A Pettinari C Masciocchi N Galli S Marchetti F Angjellari M 《Inorganic chemistry》2011,50(22):11506-11513
Solvothermal reactions of the flexible, pyrazole-based 1,4-bis((3,5-dimethyl-1H-pyrazol-4-yl)methyl)benzene ligand (H(2)BDMPX) with late transition metal ions allowed the isolation of the four coordination compounds M(x)(BDMPX) (x = 1 for M = Zn, 1; Co, 2; Cd, 3; x = 2 for M = Cu, 4). The investigation of the thermal behavior assessed the high thermal robustness of these materials, which are stable in air at least up to 300 °C, with the Cd(II) derivative starting to decompose only around 500 °C. As retrieved by ab initio X-ray powder diffraction, the isomorphous compounds 1-3 possess a dense 3-D network featuring rhombic motifs hinged about rigid and parallel chains of tetrahedral MN(4) chromophores. As demonstrated by thermodiffractometric measurements, temperature increase triggers framework flexibility. The latter is at work also when N(2) adsorption is assayed at 77 K: 1 and 2 show permanent porosity, with BET and Langmuir specific surface areas of 515, 667 m(2)/g and 209, 384 m(2)/g, respectively. 1 and 2 thus represent an intriguing example of "porosity without pores", their pro-porous nature being explained in terms of the flexibility of the rhombic motifs, stimulated by the gas probe and facilitated by the nature of the ligand. 相似文献
558.
We have investigated the phase behavior of the R(F)(7)(EO)(8) surfactant in water as well as the effect of the solubilization of various fluorocarbons in this system. Results show that the cloud point (CP) curve is shifted to high temperatures upon addition of fluorocarbons, following the sequence 1-bromo-perfluorooctane (PFOB) < perfluorodecalin (PFD) < perfluorooctane (PFO). The values of the phase inversion temperature (PIT) associated with these systems increase in the same order: PFOB approximately 65 degrees C, PFD approximately 82 degrees C, and PFO > 90 degrees C. Starting from these systems, we have prepared mesoporous and hierarchical porous materials. The formation of the ordered mesoporous materials has been related to the CP curve. Indeed, our results show that mesoporous materials with a high degree of ordering are obtained from systems whose CP curve is shifted toward high temperatures. We have also correlated the formation of the hierarchical porous silica to the PIT. It appears that the design of macro-mesoporous materials is favored with systems that exhibit a high value of the PIT. 相似文献
559.
1 INTRODUCTION It has been reported that botrytis cinerea, a plant pathogenic fungus, can produce abscisic acid ((2- cis,4-trans)-5-(1-hydroxy-2,6,6-trimethyl-4-oxo-2- cyclohexen-1-yl)-3-methyl-2,4-pentadienoic acid 1)[1] and 1?,4?-trans-diol of abscisic acid 2 that is a pre- cursor of 1[2]. Abscisic acid is an important plant hormone that can inhibit the germination of seeds[3]. Meanwhile, the derivatives of 2, 1?,4?-trans-diol of abscisic acid ester 3 and 4?-methoxy derivative 4, are oil… 相似文献
560.
LI Hao-Honga CHEN Zhi-Rong ② WANG Canga REN Yong-Ganga LI Jun-Qiana b HUANG Chang-Canga ZHAO Bina a 《结构化学》2005,24(11):1318-1323
1 INTRODUCTION The importance of metal ions in nucleic acid and other biologic processes has stimulated considerable research interest in the area of metal interactions with nuclei acid constituents[1, 2] due to the discovery that some platinum compounds, especially cis-Pt (NH3)2- Cl2, exhibit carcinostatic properties[3]. This has led to an increased research activity in the chemistry and structures of platinum complexes containing novel or- ganic ligands. And crystal engineering has its… 相似文献