全文获取类型
收费全文 | 1155篇 |
免费 | 202篇 |
国内免费 | 53篇 |
专业分类
化学 | 1353篇 |
晶体学 | 6篇 |
力学 | 1篇 |
综合类 | 4篇 |
物理学 | 46篇 |
出版年
2024年 | 1篇 |
2023年 | 9篇 |
2022年 | 19篇 |
2021年 | 32篇 |
2020年 | 55篇 |
2019年 | 44篇 |
2018年 | 34篇 |
2017年 | 31篇 |
2016年 | 65篇 |
2015年 | 64篇 |
2014年 | 75篇 |
2013年 | 87篇 |
2012年 | 82篇 |
2011年 | 66篇 |
2010年 | 49篇 |
2009年 | 53篇 |
2008年 | 69篇 |
2007年 | 81篇 |
2006年 | 59篇 |
2005年 | 60篇 |
2004年 | 60篇 |
2003年 | 53篇 |
2002年 | 30篇 |
2001年 | 38篇 |
2000年 | 20篇 |
1999年 | 33篇 |
1998年 | 11篇 |
1997年 | 39篇 |
1996年 | 13篇 |
1995年 | 14篇 |
1994年 | 6篇 |
1993年 | 11篇 |
1992年 | 8篇 |
1991年 | 9篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1980年 | 2篇 |
1979年 | 5篇 |
1978年 | 1篇 |
1976年 | 3篇 |
1974年 | 1篇 |
排序方式: 共有1410条查询结果,搜索用时 32 毫秒
51.
Lisa A. Bischoff Jarno Riefer Raphael Wirthensohn Tobias Bischof Rüdiger Bertermann Dr. Nikolai V. Ignat'ev Prof. Dr. Maik Finze 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(60):13615-13620
Salts of the tetrakis(pentafluoroethyl)aluminate anion [Al(C2F5)4]− were obtained from AlCl3 and LiC2F5. They were isolated with different counter-cations and characterized by NMR and vibrational spectroscopy and mass spectrometry. Degradation of the [Al(C2F5)4]− ion was found to proceed via 1,2-fluorine shifts and stepwise loss of CF(CF3) under formation of [(C2F5)4−nAlFn]− (n=1–4) as assessed by NMR spectroscopy and mass spectrometry and supported by results of DFT calculations. In addition, the [(C2F5)AlF3]− ion was structurally characterized. 相似文献
52.
以离子液体1-乙基-3-甲基咪唑对甲苯磺酸盐([EMIm]TS)为背景电解质,采用双端进样方式,实现了毛细管电泳-间接紫外检测法同时分析测定葡萄酒中无机阳离子(K+、Ca2+、Na+、Mg2+和Li+)和阴离子(Cl-、SO42-和ClO3-)。[EMIm]TS作为电泳缓冲溶液的同时,其阳离子和阴离子分别作为样品中阳离子和阴离子组分的间接紫外检测的背景电解质。在最佳分析条件下,可在6.5 min内完成8种无机离子的同时分离检测,其线性范围为0.005~0.7 g/L,相关系数为0.963~0.995,检出限(S/N=3)为1.2~12.5 mg/L。该方法成功测定了3种不同品牌的市售葡萄酒中8种无机离子。在3个加标水平下,8种无机离子的回收率为90.1%~110.5%,相对标准偏差(RSD)≤ 4.8%。结果表明,该方法可应用于葡萄酒中无机阴、阳离子的同时分离检测,且方法简单、快速且结果可靠。 相似文献
53.
Zouaoui Setifi Mehdi Boutebdja Fatima Setifi Hocine Merazig Christopher Glidewell 《Acta Crystallographica. Section C, Structural Chemistry》2014,70(7):702-706
In the title compound, catena‐poly[bis[(2,2′‐bipyridine‐κ2N,N′)(1,1,3,3‐tetracyano‐2‐ethoxypropenido‐κN)copper(II)]‐μ4‐hexanedioato‐κ6O1,O1′:O1:O6,O6′:O6], [Cu2(C9H5N4O)2(C6H8O4)(C10H8N2)2]n, the adipate (hexanedioate) dianion lies across a centre of inversion in the space group P. The CuII centre adopts a distorted form of axially elongated (4+2) coordination, and the CuII and adipate components form a one‐dimensional coordination polymer from which the 2,2′‐bipyridine and 1,1,3,3‐tetracyano‐2‐ethoxypropenide components are pendent, and where each adipate dianion is bonded to four different CuII centres. The coordination polymer chains are linked into a three‐dimensional framework structure by a combination of C—H...N and C—H...O hydrogen bonds, augmented by a π–π stacking interaction. 相似文献
54.
Dr. Nicholas H. Evans Prof. Paul D. Beer 《Angewandte Chemie (International ed. in English)》2014,53(44):11716-11754
Since the start of this millennium, remarkable progress in the binding and sensing of anions has been taking place, driven in part by discoveries in the use of hydrogen bonding, as well as the previously under‐exploited anion–π interactions and halogen bonding. However, anion supramolecular chemistry has developed substantially beyond anion recognition, and now encompasses a diverse range of disciplines. Dramatic advance has been made in the anion‐templated synthesis of macrocycles and interlocked molecular architectures, while the study of transmembrane anion transporters has flourished from almost nothing into a rapidly maturing field of research. The supramolecular chemistry of anions has also found real practical use in a variety of applications such as catalysis, ion extraction, and the use of anions as stimuli for responsive chemical systems. 相似文献
55.
Origin and Location of Electrons and Protons during the Formation of Intermetalloid Clusters [Sm@Ga3−xH3−2xBi10+x]3− (x=0, 1) 下载免费PDF全文
Dipl.‐Chem. Bastian Weinert B.Sc. Fabian Müller Dr. Klaus Harms Dr. Rodolphe Clérac Prof. Dr. Stefanie Dehnen 《Angewandte Chemie (International ed. in English)》2014,53(44):11979-11983
Reaction of [GaBi3]2? with [Sm(C5Me4H)3] yielded the first protonated ternary intermetalloid clusters [Sm@Ga3?xH3?2xBi10+x]3? ( 1 ; x=0,1). The presence of the Ga? H bonds and the transfer of electrons and protons during the formation of 1 were elucidated by a combination of experimental and quantum chemical methods, thereby rationalizing the role of the solvent ethane‐1,2‐diamine as a Brønsted acid. As an organic by‐product, we observed the previously unknown octamethylfulvene ( 2 ) upon C? C coupling of (C5Me4H)?. 相似文献
56.
Simultaneous determination of peroxydisulfate and conventional inorganic anions by ion chromatography with the column‐switching technique 下载免费PDF全文
Zhongping Huang Chengzhu Ni Fengli Wang Zuoyi Zhu Qamar Subhani Muhua Wang Yan Zhu 《Journal of separation science》2014,37(3):198-203
The application of ion chromatography with the column‐switching technique for the simultaneous analysis of peroxydisulfate and conventional inorganic anions in a single run is described. With this method, conventional inorganic anions were separated by consecutive elution through both the guard column and separation column, but peroxydisulfate that only passed through the guard column had a good peak shape and short retention time. A series of standard solutions consisting of target anions of various concentrations from 0.01 to 75 mg/L were analyzed, with a correlation coefficient (r) ≥ 0.9990. The limits of detection were in the range of 0.49–9.84 μg/L based on the S/N of 3 and a 25 μL injection volume. RSDs for retention time, peak area, and peak height were all <1.77%. A spiking study was performed with satisfactory recoveries between 97.6 and 103.4% for all anions. The quantitative determination of peroxydisulfate and conventional inorganic anions in surface waters was accomplished within 18 min by this column‐switching technique. 相似文献
57.
Andong Zhang Wei Jiang Zhaohui Wang 《Angewandte Chemie (International ed. in English)》2020,59(2):752-757
The first example of a two‐state (neutral and reduced), stable electron‐accepting material and its radical anion is presented. FV‐PDI, generated from cyclocarbonylation and then a carbonyl coupling reaction, shows a largely degenerate LUMO of ?4.38 eV based on the delocalization of π‐electrons across the whole molecular skeleton through a fulvalene bridge. The stability and electron affinity allow spontaneous electron transfer to afford a stable radical anion. Spectroscopic characterization and structural elucidation showed that the radical anion [FV‐PDI].? has remarkable stability and near‐infrared absorptions extending to 1200 nm. Single‐crystal X‐ray diffraction analyses revealed significant changes in the molecular shape and packing arrangement of the formed radical anion. The central C?C bond linking the two PDI halves is lengthened from approximately 1.33 to 1.43 Å, and the alternating arrangement of positively and negatively charged units favor the stable charge‐transfer complex. 相似文献
58.
Electronic Stability of Bimetallic Au2@Cu6 Nanocluster: Closed-Shell Interaction and Multicenter Bonding 下载免费PDF全文
Metallophilic interaction is a unique type of weak intermolecular interaction, where the electronic configuration of two metal atoms is closed shell. Despite its significance in multidisciplinary fields, the nature of metallophilic interaction is still not well understood. In this work, we investigated the electronic structures and bonding characteristic of bimetallic Au\begin{document}$ _{2} $\end{document} @Cu\begin{document}$ _{6} $\end{document} nanocluster through density functional theory method, which was reported in experiments recently [Angew. Chem. Int. Ed. 55 , 3611 (2016)]. In general thinking, interaction between two moieties of (CuSH)\begin{document}$ _{6} $\end{document} ring and (Au\begin{document}$ _{2} $\end{document} PH\begin{document}$ _{3} $\end{document} )\begin{document}$ _{2} $\end{document} in the Au\begin{document}$ _{2} $\end{document} @Cu\begin{document}$ _{6} $\end{document} nanocluster can be viewed as a d\begin{document}$ ^{10} $\end{document} -\begin{document}$ \sigma $\end{document} closed-shell interaction. However, chemical bonding analysis shows that there is a ten center-two electron (10c-2e) multicenter bonding between two moieties. Further comparative studies on other bimetallic nanocluster M\begin{document}$ _{2} $\end{document} @Cu\begin{document}$ _{6} $\end{document} (M = Ag, Cu, Zn, Cd, Hg) also revealed that multicenter bonding is the origin of electronic stability of the complexes besides the d\begin{document}$ ^{10} $\end{document} -\begin{document}$ \sigma $\end{document} closed-shell interaction. This will provide valuable insights into the understanding of closed-shell interactions. 相似文献
59.
采用密度泛函B3LYP(Becke, three-parameter, Lee-Yang-Parr)和HF(Hatree-Fock)方法, 从理论上探讨了1,3-双(1-苯基-1H-四唑-5-巯基)-乙酰苯腙(DAPHZ)钳形受体对卤素阴离子的识别机理,结果发现DAPHZ受体以其钳形结构中的-N-H基团与卤素阴离子间形成双侧红移氢键进行识别. 经BSSE校正后DAPHZ•••F-, DAPHZ•••Cl-和DAPHZ•••Br-体系的分子识别相互作用能ΔECP分别为-327.5,-163.5和-148.3 kJmol-1, 说明钳形DAPHZ受体对F-具有最好的识别能力. 此外, 采用自然键轨道(NBO)计算, 相关H原子化学位移计算及分子中原子(AIM)等理论分析了识别体系中红移氢键的电子结构和性质, 结果表明APHZ受体对卤素阴离子的识别能力的相对顺序为DAPHZ•••F- >> DAPHZ•••Cl- ≈ DAPHZ•••Br-. 相似文献
60.
Halotriazolium Axle Functionalised [2]Rotaxanes for Anion Recognition: Investigating the Effects of Halogen‐Bond Donor and Preorganisation 下载免费PDF全文
James M. Mercurio Richard C. Knighton Dr. James Cookson Prof. Paul D. Beer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(37):11740-11749
The anion‐templated synthesis of three novel halogen‐bonding 5‐halo‐1,2,3‐triazolium axle containing [2]rotaxanes is described, and the effects of altering the nature of the halogen‐bond donor atom together with the degree of inter‐component preorganisation on the anion‐recognition properties of the interlocked host investigated. The ability of the bromotriazolium motif to direct the halide‐anion‐templated assembly of interpenetrated [2]pseudorotaxanes was studied initially; bromide was found to be the most effective template. As a consequence, bromide anion templation was used to synthesise the first bromotriazolium axle containing [2]rotaxane, the anion‐binding properties of which, determined by 1H NMR spectroscopic titration experiments, revealed enhanced bromide and iodide recognition relative to a hydrogen‐bonding protic triazolium rotaxane analogue. Two halogen‐bonding [2]rotaxanes with bromo‐ and iodotriazolium motifs integrated into shortened axles designed to increase inter‐component preorganisation were also synthesised. Anion 1H NMR spectroscopic titration experiments demonstrated that these rotaxanes were able to bind halide anions even more strongly, with the iodotriazolium axle integrated rotaxane capable of recognising halides in aqueous solvent media. Importantly, these observations suggest that a halogen‐bonding interlocked host binding domain, in combination with increased inter‐component preorganisation, are requisite design features for a potent anion receptor. 相似文献