全文获取类型
收费全文 | 54841篇 |
免费 | 4933篇 |
国内免费 | 4056篇 |
专业分类
化学 | 33073篇 |
晶体学 | 722篇 |
力学 | 1428篇 |
综合类 | 718篇 |
数学 | 7327篇 |
物理学 | 20562篇 |
出版年
2023年 | 481篇 |
2022年 | 744篇 |
2021年 | 1754篇 |
2020年 | 1528篇 |
2019年 | 1530篇 |
2018年 | 1279篇 |
2017年 | 1454篇 |
2016年 | 1987篇 |
2015年 | 1948篇 |
2014年 | 2380篇 |
2013年 | 4242篇 |
2012年 | 3280篇 |
2011年 | 3677篇 |
2010年 | 3006篇 |
2009年 | 3629篇 |
2008年 | 3479篇 |
2007年 | 3780篇 |
2006年 | 2834篇 |
2005年 | 2007篇 |
2004年 | 1893篇 |
2003年 | 1782篇 |
2002年 | 1706篇 |
2001年 | 1383篇 |
2000年 | 1073篇 |
1999年 | 849篇 |
1998年 | 839篇 |
1997年 | 611篇 |
1996年 | 652篇 |
1995年 | 602篇 |
1994年 | 588篇 |
1993年 | 578篇 |
1992年 | 563篇 |
1991年 | 364篇 |
1990年 | 321篇 |
1989年 | 251篇 |
1988年 | 293篇 |
1987年 | 239篇 |
1986年 | 255篇 |
1985年 | 355篇 |
1984年 | 275篇 |
1983年 | 158篇 |
1982年 | 322篇 |
1981年 | 492篇 |
1980年 | 442篇 |
1979年 | 492篇 |
1978年 | 389篇 |
1977年 | 289篇 |
1976年 | 245篇 |
1974年 | 83篇 |
1973年 | 162篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
Unraveling σ and π Effects on Magnetic Anisotropy in cis‐NiA4B2 Complexes: Magnetization,HF‐HFEPR Studies,First‐Principles Calculations,and Orbital Modeling
下载免费PDF全文
Dr. Gaëlle Charron Dr. Elena Malkin Dr. Guillaume Rogez Dr. Luke J. Batchelor Dr. Sandra Mazerat Dr. Régis Guillot Dr. Nathalie Guihéry Dr. Anne‐Laure Barra Dr. Talal Mallah Dr. Hélène Bolvin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(47):16850-16862
By using complementary experimental techniques and first‐principles theoretical calculations, magnetic anisotropy in a series of five hexacoordinated nickel(II) complexes possessing a symmetry close to C2v, has been investigated. Four complexes have the general formula [Ni(bpy)X2]n+ (bpy=2,2′‐bipyridine; X2=bpy ( 1 ), (NCS?)2 ( 2 ), C2O42? ( 3 ), NO3? ( 4 )). In the fifth complex, [Ni(HIM2‐py)2(NO3)]+ ( 5 ; HIM2‐py=2‐(2‐pyridyl)‐4,4,5,5‐tetramethyl‐4,5‐dihydro‐1H‐imidazolyl‐1‐hydroxy), which was reported previously, the two bpy bidentate ligands were replaced by HIM2‐py. Analysis of the high‐field, high‐frequency electronic paramagnetic resonance (HF‐HFEPR) spectra and magnetization data leads to the determination of the spin Hamiltonian parameters. The D parameter, corresponding to the axial magnetic anisotropy, was negative (Ising type) for the five compounds and ranged from ?1 to ?10 cm?1. First‐principles SO‐CASPT2 calculations have been performed to estimate these parameters and rationalize the experimental values. From calculations, the easy axis of magnetization is in two different directions for complexes 2 and 3 , on one hand, and 4 and 5 , on the other hand. A new method is proposed to calculate the g tensor for systems with S=1. The spin Hamiltonian parameters (D (axial), E (rhombic), and gi) are rationalized in terms of ordering of the 3 d orbitals. According to this orbital model, it can be shown that 1) the large magnetic anisotropy of 4 and 5 arises from splitting of the eg‐like orbitals and is due to the difference in the σ‐donor strength of NO3? and bpy or HIM2‐py, whereas the difference in anisotropy between the two compounds is due to splitting of the t2g‐like orbitals; and 2) the anisotropy of complexes 1 – 3 arises from the small splitting of the t2g‐like orbitals. The direction of the anisotropy axis can be rationalized by the proposed orbital model. 相似文献
92.
93.
Inside Back Cover: Weak Ligand‐Field Effect from Ancillary Ligands on Enhancing Single‐Ion Magnet Performance (Chem. Eur. J. 36/2016) 下载免费PDF全文
94.
Aromaticity Relocation in Perylene Derivatives upon Two‐Electron Oxidation To Form Anthracene and Phenanthrene 下载免费PDF全文
Akinobu Matsumoto Dr. Mitsuharu Suzuki Dr. Hironobu Hayashi Dr. Daiki Kuzuhara Dr. Junpei Yuasa Prof. Dr. Tsuyoshi Kawai Prof. Dr. Naoki Aratani Prof. Dr. Hiroko Yamada 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(41):14462-14466
We prepared perylene dications 1 2+ and 2 2+ by using “capped” perylene derivatives, and for the first time, successfully obtained single crystals of a perylene dication 1 2+ that enabled us to perform its structural analysis. We realized that the substituted aryl groups on perylene control the positions of positive charges, thus the remaining electronic system satisfies Clar's sextet rule toward the highest number of localized sextets. Experimental and theoretical evidence proved that Clar's aromatic π‐sextet rule could be applied even for the dicationic perylenes in a very simple way. 相似文献
95.
Synthesis and physical properties of highly branched perfluorinated polymers from AB and AB2 monomers 下载免费PDF全文
Matthew J. Quast Aaron D. Argall Cassandra J. Hager Anja Mueller 《Journal of polymer science. Part A, Polymer chemistry》2015,53(16):1880-1894
Highly branched perfluorinated aromatic polyether copolymers were prepared from the polycondensation of the AB2 monomer, 3,5‐bis[(pentafluorobenzyl)oxy]benzyl alcohol with a variety of fluoroaryl and alkyl bromide AB comonomers. The structures and comonomer distribution of the resulting polymers were characterized in detail. 1H NMR data from kinetic trials illustrated that perfluoroaryl AB comonomer distribution correlated to AB comonomer sterics. 19F NMR data revealed that fluorinated AB monomers and 3‐bromo‐1‐propanol AB monomers were distributed within the AB2 polymer backbone, while longer alkyl bromide AB monomers, 6‐bromo‐1‐hexanol, were mostly distributed along hyperbranched polymer chain ends. In general, as AB comonomer incorporation increased for nonsterically hindered copolymers, thermal decomposition onset increased and glass transition temperatures decreased. The combined data demonstrated the effect of comonomer distribution and sterics on physical properties of AB2‐based polymer systems. The resulting materials were used to cast thin polymer films for measurement of contact angle, which were shown to be directly related to comonomer content. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1880–1894 相似文献
96.
采用高压烧结技术制备了稀土元素Tb掺杂的n型Bi2Te2.7Se0.3基纳米晶块体热电材料.将高压烧结成型的样品于633 K真空退火36 h.研究了Tb掺杂量对样品的晶体结构和热电性能的影响.结果表明,高压烧结制备的样品为纳米结构, Tb掺杂使样品的晶胞体积变大,功率因子增大,热导率降低,从而使ZT值提高.Tb掺杂量为x=0.004是最优的掺杂量,该掺杂量的高压烧结样品经退火处理后,于373 K时ZT值达到最大为0.99,并且在323-473 K范围内, ZT值均大于0.8,这对用于温差发电领域具有重要意义. 相似文献
97.
本文应用分子场理论,研究暴露于水蒸气中的亲水性两性离子聚合物(HP)刷的构象与结构.理论模型考虑HP-水(P-W)氢键和水-水(W-W)氢键效应,以及HP单体之间的偶极-偶极相互作用.研究发现,P-W与W-W氢键决定着HP的水合性,P-W氢键形成,会诱导HP刷溶胀.我们通过考察HP单体间的偶极-偶极相互作用发现,随着偶极-偶极相互作用增强,HP链在垂直培基表面沿着链方向,形成了结节状结构.这是由于HP单体之间的偶极-偶极静电吸引作用导致单体间汇聚结节,这种结节在刷内产生了较强的排斥体积作用,因此,这种HP刷具有抗污性能.在较高的接枝密度环境下,由于HP链间单体之间的偶极-偶极静电吸引作用,会形成链间单体-单体的结节,在刷内形成结节网络状凝胶结构,这种结构的出现,会使得HP刷呈现极强的抗污性.另外,当体系中水蒸气浓度增加、水合相互作用增强时,增加的P-W氢键将平衡HP单体之间的偶极-偶极相互作用,使得结节解开,聚合物链伸展.我们的理论结果符合实验观测,由此表明,P-W氢键效应,以及HP单体之间的偶极-偶极相互作用决定着HP刷的构象转变和结构特性,刷内出现的两性离子聚合物链内单体间的结节和链间单体结节状凝胶结构,是两性离子聚合物刷呈现较强抗污性的本质特性. 相似文献
98.
Anh N. Hong Diana Luong Mohammed Alghamdi Wei-Cheng Liao Weiyi Zhang Emily Kusumoputro Yichong Chen Prof. P. Alex Greaney Prof. Yongtao Cui Prof. Jing Shi Prof. Xianhui Bu Prof. Boniface P. T. Fokwa Prof. Pingyun Feng 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(52):e202201576
Two new rod-packing metal–organic frameworks (RPMOF) are constructed by regulating the in situ formation of the capping agent. In CPM-s7, carboxylate linkers extend 1D manganese-oxide chains in four additional directions, forming 3D RPMOF. The substitution of Mn2+ with a stronger Lewis acidic Co2+, leads to an acceleration of the hydrolysis-prone sulfonate linker, resulting in presence of sulfate ions to reduce two out of the four carboxylate-extending directions, and thus forming a new 2D rod-packing CPM-s8. Density functional theory calculations and magnetization measurements reveal ferrimagnetic ordering of CPM-s8, signifying the potential of exploring 2D RPMOF for effective low-dimensional magnetic materials. 相似文献
99.
Ya-Shan Huang Yuan Xue Prof. Alvaro Muñoz-Castro Prof. Dr. Ivan A. Popov Prof. Dr. Zhong-Ming Sun 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(62):e202202192
During the past two decades, single-atom-centered medium-sized germanium clusters [M@Gen] (M=transition metals, n>12) have been extensively explored, both from theoretical perspectives and experimental gas-phase syntheses. However, the actual structural arrangements of the Ge13 and Ge14 endohedral cages are still ambiguous and have long remained an unresolved problem for experimental implementation. In this work, we successfully synthesize 13-/14-vertex Ge clusters [Nb@Ge13]3− ( 1 ) and [Nb@Ge14]3− ( 2 ), which are structurally characterized and exhibit unprecedented topologies, neither classical deltahedra nor 3-connected polyhedral structures. Theoretical analysis indicates that the major stabilization of the Ge backbones arises due to the substantial interaction of Ge 4p-AOs with the endohedral Nb 4d-AOs through three/four-center two-electron bonds with an enhanced electron density accumulated over the shortest Nb−Ge13 contact in 1 . Low occupancies of the direct two-center two-electron (2c–2e) Nb−Ge and Ge−Ge σ bonds point to a considerable degree of electron delocalization over the Ge cages revealing their electron deficiency. 相似文献
100.
Elarbi Chatir Dr. Martial Boggio-Pasqua Prof. Frederique Loiseau Dr. Christian Philouze Prof. Guy Royal Dr. Saioa Cobo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(7):e202103755
A phenanthrene unit has been functionalized by several methylthiophene units in order to bring it a photochromic behavior. These compounds were characterized by NMR, absorption and emission spectroscopies, theoretical calculations as well as cyclic voltammetry. The association of a phenanthrene group with a photochromic center could open the door to a new generation of organic field-effect transistors. 相似文献