全文获取类型
收费全文 | 329篇 |
免费 | 39篇 |
国内免费 | 34篇 |
专业分类
化学 | 220篇 |
力学 | 1篇 |
数学 | 1篇 |
物理学 | 180篇 |
出版年
2024年 | 3篇 |
2023年 | 16篇 |
2022年 | 5篇 |
2021年 | 9篇 |
2020年 | 6篇 |
2019年 | 6篇 |
2018年 | 5篇 |
2017年 | 11篇 |
2016年 | 13篇 |
2015年 | 14篇 |
2014年 | 20篇 |
2013年 | 23篇 |
2012年 | 25篇 |
2011年 | 18篇 |
2010年 | 18篇 |
2009年 | 19篇 |
2008年 | 16篇 |
2007年 | 21篇 |
2006年 | 20篇 |
2005年 | 16篇 |
2004年 | 23篇 |
2003年 | 10篇 |
2002年 | 11篇 |
2001年 | 13篇 |
2000年 | 7篇 |
1999年 | 5篇 |
1998年 | 5篇 |
1997年 | 5篇 |
1996年 | 7篇 |
1995年 | 8篇 |
1994年 | 5篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1976年 | 1篇 |
1967年 | 2篇 |
排序方式: 共有402条查询结果,搜索用时 31 毫秒
111.
Hua Wei Ruiqiang Yang An Li Erik R. Christensen Karl J. Rockne 《Journal of chromatography. A》2010,1217(17):2964-2972
The gas chromatographic (GC) retention times of 180 polybrominated diphenyl ethers (PBDEs) were obtained under different operational conditions on two types of commonly used capillary columns, Restek Rtx-1614 and J&W DB-5MS, of different dimensions. The relative retention times (RRTs) for PBDEs were calculated by normalizing the retention times of individual congeners to the sum of those of BDEs 47 and 183. In clear contrast to polychlorinated biphenyls (PCBs), the elution of PBDEs has few cross-homolog overlaps, and this observation is discussed in terms of molecular conformation with regard to co-planarity. Within a homolog, ortho substitution in PBDEs tends to decrease GC retention, and such an effect is stronger for higher homologs. With the RRT database established in this work, a simple approach is evaluated for the identification of all mono to hepta PBDEs from the RRTs of 39 congeners under various GC conditions to facilitate the identification of unknown PBDE peaks for which chemical standards are not available. 相似文献
112.
A combination of CBr4–Ph3P, a non-metal method, enables us to carry out aerobic photo-oxidation of alcohols and aromatic methyl groups to the corresponding carboxylic acids under irradiation of vis from a general-purpose fluorescent lamp. Aliphatic primary- and secondary alcohols, benzyl alcohols, and methyl groups at the aromatic nucleus generally afforded the carboxylic acids directly in good to high yield. 相似文献
113.
K. Dehnicke 《Angewandte Chemie (International ed. in English)》1967,6(3):240-246
Until recently, the explosive nature of halogen azides made these compounds unsuitable for preparative uses and greatly impeded investigation of their physical properties. Reactions of ClN3 and BrN3 with metal halides, metal carbonyls, and organometallic compounds to from metal azide halides, nitride halides, carbonyl azide halides, and alkylmetal azides were reported only very recently. The stability relationships of the halogen azides are discussed. 相似文献
114.
Toshikazu Sakaguchi Masashi Shiotsuki Fumio Sanda Toshio Masuda 《Journal of membrane science》2006,280(1-2):720-726
Novel diphenylacetylenes with both trimethylsilyl groups and other substituents (R2C6H3CCC6H4-p-SiMe3, R = m,p-Cl,Cl, m,m-Cl,Cl, m,p-Br,Br, m,m-Br,Br, m,p-Me,Me, m,m-Me,Me, 1a–f, respectively) were polymerized with TaCl5–n-Bu4Sn to produce solvent-soluble polymers (2a–f). Most polymers (2a–e) had high molecular weight over 1 × 106, and gave free-standing membranes by the solution casting method. Desilylation of these Si-containing polymer membranes was carried out with trifluoroacetic acid (TFA), which afforded solvent-insoluble desilylated polymer membranes (3a–e). According to thermogravimetric analysis (TGA), both Si-containing and desilylated polymers showed high thermal stability (T0 ≥ 420 °C). The fractional free volume (FFV) of both Si-containing and desilylated polymer membranes (2a–d, 3a–d) were fairly large (ca. 0.27–0.32), while the FFVs of membranes (2e, 3e) were rather small (0.28 and 0.24). The oxygen permeability coefficients (PO2) of 2a was as high as 5400 barrers, which is the largest among all the poly(diphenylacetylene) derivatives. Polymers 2b–d also exhibited high oxygen permeability, and their desilylated ones 3b–d retained similar high oxygen permeability. On the other hand, the PO2 values of 2e and 3e were 1200 and 530 barrers, respectively, which are smaller than those of the halogen-containing polymers (2a–d and 3a–d). 相似文献
115.
Halogen Exchange at Re3-Clusters: A New Synthetic Route to Binary and Ternary Rhenium(III) Bromides. Crystal Structures of Cs2[Re3Br11] and Cs3[Re3Br3Cl9] The substitution of “inner” ligands in transition metal clusters in aqueous HX solutions is hitherto unknown. For the first time the substitution of bridging and terminal chloride for bromide ions was observed at rhenium clusters, [Re3(μ-Cli,b)3(Cl)(Cli,t)(3?x)(H2Oi,t)x](3?x)? (x = 0–3), via the reaction of “ReCl3 · 2 H2O” in hot hydrobromic acid solution under an inert gas atmosphere. This establishes a new synthetic route to ternary Re(III) bromides as well as to ReBr3. However, ternary Re(IV) bromides, A2ReBr6 (A = Rb, Cs), are dominating in the presence of oxygen, rhenium(III) bromides are only by-products. Dark brown rods of Cs2[Re3Br11] are obtained from argon saturated, hot hydrobromic acid solutions of “ReCl3 · 2 H2O” and CsBr. The crystal structure (orthorhombic, Pnma (Nr. 62); a = 955.51(5); b = 1 610.29(10); c = 1 372.70(9); Z = 4; Vm = 318.0(2) cm3mol?1; R = 0.084, Rw = 0.058) consists of defect clusters [Re3BrBrBr□i,t]2? in which one in plane, terminal position is not occupied. The substitution of “inner” ligands has been observed in the case of chloride for bromide only, the Bri,b and Ii,b ligands in ReBr3 and ReI3, respectively, are not substituted in hydrochloric acid even at temperatures as high as 100°C. Bordeaux red square pyramids of CsReBrCl3 = Cs3[Re3(μ-Bri,b)3ClCl] are obtained from hot hydrochloric acid solutions of ReBr3 · 2/3 H2O upon evaporation. CsReBrCl3 (orthorhombic, C2cm (Nr. 40); a = 1 419.0(1); b = 1 419.2(1); c = 1 080.30(8) pm; Z = 4; Vm = 327.6(3) cm3mol?1; R = 0.033, Rw = 0.028) is isostructural to the corresponding chloride CsReCl4. 相似文献
116.
Toshifumi Takeuchi Yuji Minato Masayoshi Takase Hideyuki Shinmori 《Tetrahedron letters》2005,46(52):9025-9027
Molecular recognition materials bearing halogen bonding-based binding sites were synthesized by a non-covalent imprinting technique using a 2,3,5,6-tetrafluoro-4-iodostyrene (TFIS) as the functional monomer. The binding sites were generated by co-polymerizing TFIS, styrene and divinylbenzene in the presence of the template molecule (4-dimethylaminopyridine—DMAP). The imprinted polymer preferentially adsorbed aminopyridine derivatives, suggesting that halogen bonding may play a role in the selective recognition of analytes by the synthesized synthetic receptor. 相似文献
117.
George Asimellis Aggelos Giannoudakos Michael Kompitsas 《Spectrochimica Acta Part B: Atomic Spectroscopy》2006,61(12):1270-1278
Investigation via Laser-Induced Breakdown Spectroscopy of a near-infrared bromine emission line (827.2 nm) with an UltraViolet ablation laser and a gated detector is reported. The effects of ambient pressure and gas species (air, O2, N2 and He) on the atomic emission line strength and spectral profile were systematically investigated. Substantially improved signal strength and reduced background radiation are demonstrated near 100 mbar ambient pressure with all gases. Optimal results were achieved when helium was used. Asymmetric broadening and shift of the 827.2 nm bromine line, attributed to pressure-dependent Stark effect has been revealed. This effect is prominent when air, oxygen or nitrogen are present and is much less manifested when helium is used. Possible interpretations of this effect are presented. 相似文献
118.
用合肥800 MeV同步辐射光源标定氘灯的光谱辐射亮度 总被引:1,自引:0,他引:1
利用合肥800 MeV电子存储环同步辐射(HESYR)作为紫外真空紫外光谱辐射测量的绝对标准,标定了传递标准氘灯光源的光谱辐亮度。采用德国国家物理技术研究院(PTB)的数据处理及不确定度分析方法,得到了两支氘灯在115~300nm波段的光谱辐亮度数据,其相对定标不确定度为12.1%。详细分析了相关参量对定标不确定度的贡献,指出辐射计量系统偏振特征量的不确定度贡献最大。在164~300 nm波段,德国德国国家物理技术研究院在BESSYⅡ同步辐射装置上标定的绝对光谱辐亮度值与本实验在中国合肥同步辐射装置上标定的绝对光谱辐亮度值之间一致性优于±20%,在给定的不确定度范围内两光谱辐射标准定标结果一致。 相似文献
119.
120.