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41.
Pavel S. Kulyabin Georgy P. Goryunov Dmitry Y. Mladentsev Dr. Dmitry V. Uborsky Prof. Dr. Alexander Z. Voskoboynikov Dr. Jo Ann M. Canich Dr. John R. Hagadorn 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(44):10478-10489
Heteroarylamido hafnium post-metallocenes with [C,N,N] ligands were functionalized by the insertion of small electrophilic unsaturated molecules into the CAr−Hf bond of the ligand, which gave rise to various 1,1- and 1,2-insertion complexes with the modified ligands of previously unknown [O,N,N], [N,N,N], [O,N,N,N], and [N,N,N,N] types. It was found that C1 symmetry of the starting complexes, in some cases, results in the formation of two diastereoisomers after 1,1- or 1,2-insertion. Most of the obtained novel complexes were shown to form active catalysts for olefin polymerization in the presence of MAO (methylaluminoxane). Thus, a new approach to the feasible and easy “late stage” modification of the precatalyst structure has been suggested; it can be performed immediately prior to the polymerization tests without isolation and even in a high-throughput manner. 相似文献
42.
Sourav Kar Subhash Bairagi Gaurav Joshi Prof. Dr. Eluvathingal D. Jemmis Prof. Dr. Sundargopal Ghosh 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(63):15634-15637
Despite the synthesis and structural characterization of closo-hydroborate dianions, [BnHn]2− (n=6–12) more than 50 years ago, some ambiguity remains about the structure of [B8H8]2−. Although the solid-state structure of [B8H8]2− was established by single-crystal X-ray studies in 1969, fast rearrangements in solution at accessible temperatures prevented its detailed characterization. We therefore stabilized a derivative of [B8H8]2− by using Cp2MBH3 and structurally characterized two new octaborane analogues, [(Cp2MBH3)2B8H6] (Cp=η5-C5H5; M=Zr ( 1-Zr ) and Hf ( 1-Hf )), so that the dynamics of the B8 skeleton were arrested. The solid-state structures of both 1-Zr and 1-Hf comprise a dodecahedron core protected by {Cp2MBH3} moieties on both sides of the cluster. Spectroscopic characterization (11B NMR) validates the intactness of the B8 dodecahedron core in solution as well. Theoretical calculations establish that the two exo-{Cp2MBH3} fragments provide structural and electronic structural stability to the B8 core and its intact dodecahedral dianionic nature. Furthermore, we propose isodesmic equations for the formation of higher analogues of the Bn core (n>8) guarded by different group 4 transition metals. Our analysis suggests that, as we move to higher polyhedra (n>10), the formation becomes unfavourable irrespective of metal. 相似文献
43.
44.
为了研究阻变存储器导电细丝的形成位置和分布规律, 使用X射线光电子能谱研究了Ti/HfO2/Pt阻变存储器件单元中Hf 4f的空间分布, 得到了阻变层的微结构信息. 通过I-V测试, 得到该器件单元具有典型的阻变特性; 通过针对Hf 4f的不同深度测试, 发现处于低阻态时, 随着深度的增加, Hf4+化学组分单调地减小; 而处于高阻态和未施加电压前, 该组分呈现波动分布; 通过Hf4+在高阻态和低阻态下组分含量以及电子能损失谱分析, 得到高阻态下Hf4+组分的平均含量要高于低阻态; 另外, 高阻态和低阻态下的O 1s谱随深度的演变也验证了Hf4+的变化规律. 根据实验结果, 提出了局域分布的氧空位聚簇可能是造成这一现象的原因. 空位簇间的链接和断裂决定了导电细丝的形成和消失. 由于导电细丝容易在氧空位缺陷聚簇的地方首先形成, 这一研究为导电细丝的发生位置提供了参考. 相似文献
45.
本文研究HfO2掺入Al替位Hf杂质和氧空位共同掺杂对电荷俘获型存储器存储特性的影响. HfO2作为高介电常数材料由于具有缩小器件尺寸、提高器件性能等优势, 被广泛用于CTM的俘获层. 采用MS和VASP研究了HfO2俘获层中掺入Al对氧空位形成能的影响. 同时计算了两种缺陷在不同距离下的相互作用能. 计算结果表明在HfO2中掺入Al使得氧空位的形成能降低, 并且三配位氧空位的形成能比四配位氧空位的形成能降低的更多. 通过研究Al和三配位氧空位两种缺陷间不同距离的三种情况, 计算结果表明当缺陷间距为2.107 Å时, 体系的电荷俘获能最大; 量子态数最多; 布居数最小、Al–O键最长. 通过研究三种体系写入空穴后键长的变化, 得出当缺陷间距为2.107 Å时, 写入空穴后体系的Al–O键长变化最小. 以上研究结果表明, 掺入Al后可以有效提高电荷俘获型存储器的数据保持能力. 因而本文的研究为改善电荷俘获型存储器数据保持特性提供一定的理论指导. 相似文献
46.
Andreas Czulucki Dr. Gudrun Auffermann Dr. Michal Bednarski Łukasz Bochenek Maik Böhme Tomasz Cichorek Dr. Rainer Niewa Prof. Dr. Niels Oeschler Dr. Marcus Schmidt Dr. Frank Steglich Prof. Dr. Rüdiger Kniep Prof. Dr. 《Chemphyschem》2010,11(12):2639-2644
Single crystals of HfAs1.7Se0.2 are grown by chemical transport reaction and their chemical composition characterized in detail by various analytical methods. Chemical analyses and crystal structure investigations by single‐crystal X‐ray diffraction as well as powder diffraction with synchrotron radiation reveal a tetragonal PbFCl structure type with strong disorder caused by a significant arsenic deficiency (As0.9) on the 2a site and mixed occupancy of the 2c site (As0.8Se0.2). HfAs1.7Se0.2 is a diamagnetic metal which transforms into a superconducting state at Tc=0.52 K. Similar to other PbFCl‐type arsenide selenides, the title compound displays a magnetic‐field‐independent ?AT1/2 term in the low‐temperature electrical resistivity. This unusual term presumably originates from the electron scattering of structural two‐level systems. According to the experimental results, HfAs1.7Se0.2 appears to be a rare example of a nonmagnetic Kondo material. 相似文献
47.
Tomachinskaya L. A. Kolotilova Yu. Yu. Chernii V. Ya. Volkov S. V. 《Theoretical and Experimental Chemistry》2003,39(2):104-108
We have used cyclic voltammetry to study the electrochemical properties of novel bis(-diketonate)phthalocyanine complexes of Zr(IV) and Hf(IV) in dichloromethane. We found three waves for the studied complexes that can be attributed to one-electron processes MPc(L)0/1–
2, MPc(L)1+/0
2 and MPc(L)2+/1+
2. We have shown that the electrochemical behavior of the complexes depends on the nature of the substituents in axial ligands and does not depend on the nature of the metals. We have analyzed the stability of the one-electron oxidation products of the complexes relative to disproportionation. 相似文献
48.
L. Szirtes J. Megyeri L. Riess E. Kuzmann 《Journal of Thermal Analysis and Calorimetry》2001,65(3):975-981
The thermal decomposition of hafnium phosphate (both in amorphous and crystalline forms), molybdate and tungstate was investigated.
Hafnium phosphate has a layered structure, that of molybdate and of tungstate are tetragonal one. On investigating these materials
two main endothermic processes with mass loss were observed in the temperature range of 298–1023 K. These processes were identified
as crystal and structural water loss of the materials. The total mass loss of hafnium phosphate, molybdate and tungstate was
11,35 and 6.0%, respectively. In the case of mixed hafnium-titanium salts various crystal water quantities were found, depending
on the titanium content of the sample.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
49.
Arvind T. Rane 《Journal of Chemical Sciences》1980,89(4):333-336
A method is described for electrodepositing181Hf from urea-oxalate aqueous bath. The optimum conditions were determined by studying the effects of current density, time
of deposition and the cathode metals. More than 80% of181Hf is deposited on a nickel cathode in one hour. 相似文献